US3342814A - Adducts of metal borohydrides and organic polynitrogen compounds - Google Patents

Description

Sept. 19, 1967 J. N. HOGSETT ET ADDUCTS OF METAL BOROHYDRIDES AND ORGANIC POLYNITROGEN COMPOUNDS Filed Jan. 15. 1962 WAVENUMBER IN KAYSERS 2 Sheets-Sheet l N, N, N', N'- TETRAMETHYLETHYLENEDIAMINE DIALUMINUM BOROHYDRIDE BONVLLIWSNVELL INVENTORS JOHN N. HOGSETT ALBERT KHURI HELMUT w. SCHULZ Miami 1? PM ATTORNEY lb WAVELENGTH lN MICRONS States Patent fi 3,342,814 Patented Sept. 19, 1967 ice 3,342,814 ADDUCTS F METAL BOROI-IYDRIDES AND ORGANIC POLYNITROGEN COMPOUNDS John N. Hogsett, Charleston, Albert Khuri, South Charleston, and Helmut W. Schulz, Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York Filed Jan. 15, 1962, Ser. No. 168,005 41 Claims. (Cl. 260-242) ABSTRACT 0F THE DISCLOSURE This application is a continuation-in-part of application Ser. No. 122,350 entitled Adducts, by J. N. Hogsett, A. Kuhri, and H. W. Schulz, filed July 6, 1961, now abandoned, and assigned to the same assignee as the instant application.

This invention relates to the preparation of adducts of a metal borohydride with various organic nitrogen compounds. In various aspects, the invention relates to liquid propellant and solid propellant systems which utilize an adduct of a metal borohydride with an organic nitrogen compound a a fuel component therein.

In recent years, industry has been actively engaged in the search for fuels which are suitable for propellant systems. While various fuel compositions have been suggested and tried for such purposes, limited success has been achieved in view of the exacting requirements of the art. Among the more important characteristics of, for example, a liquid fuel can be listed (1) high specific impulse, (2) relatively high density, (3) liquid state over a wide temperature range, (4) low freezing point, (5) bypergolicity with common oxidizers, and (6) ease of handling without undue hazard. Since the above enumerated characteristics are not all consistent with one another, a balance or compromise must be made.

Metal borohydrides, such as aluminum borohydride, beryllium borohydride, and zirconium borohydride, because of their potentially high heat release, have aroused some interest in the past as a fuel in rocket systems. However, the violent chemical reactivity and thermal instability of, for example, aluminum borohydride and beryllium borohydride, have created handling and storage problems which have precluded their Serious consideration as storable rocket fuels. For instance, aluminum borohydride and beryllium borohydride inflame violently in air and react vigorously with water. Moreover, beryllium borohydride suffers from the disadvantage of being extremely toxic. The density of aluminum borohydride being 0.55 gram/rnilliliter, at 25 C., further detracts from its desirability as a rocket fuel since large tankage would be required to sustain long range rocket flights. The disadvantages which result from increased missile weight due to large fuel storage tanks are obvious. In addition, though aluminum borohydride and beryllium borohydride are generally not regarded as shock-sensitive, there is little experimental evidence on this point since these materials are so difficult to handle in the test apparatus normally employed for such determinations.

In accordance with the invention, it has been discovered that the addition of a metal borohydride, i.e., aluminum borohydride, beryllium borohydride, or zirconium borohydride, with various organic nitrogen compounds, described hereinafter, results in novel adducts, described hereinafter, which have exceptional and valuable utility in various fields of application. These novel adducts, as the fuel component in a propellant system, possess a combination of well balanced properties, especially the novel liquid adducts when employed as hypergolic fuels. The novel solid adducts can be used as energetic additives in solid propellants. The novel adducts, also, are useful as additives in fuels for conventional air-breathing engines whereby the combustion and flame-out characteristics of the hydrocarbon jet fuels are improved. The novel adducts have further utility as additive to liquid hydrocarbon rocket fuels in bipropellant rocket engines employing non-hypergolic oxidizers such as liquid oxygen or nitrogen tetroxide wherein the presence of said novel adducts improves the combustion characteristics of said propellant systems as, for example, by preventing combination instability or resonant burning.

In addition, the physical properties of the novel adducts are dramatically more desirable than the corresponding metal borohydride per se. For example, the novel adducts are more stable, and less hazardous than the parent metal borohydride. In general, the densities of the aluminum borohydride adducts and the beryllium borohydride adducts are markedly higher than the density of the corresponding metal borohydride per se.

Thermal stability determinations conducted with various novel adducts such as, for example, N,N,N,N-tetramethylmethylenediamine dialuminum borohydride show that at C., said N,N,N,N-tetramethylrnethylenediamine dialuminum borohydride decomposed to the extent of 0.78 percent by weight in six days after which decomposition stopped, whereas the literature discloses that aluminum borohydride is completely decomposed at temperatures up to about C. in five hours. Moreover, said N,N,N',N-tetramethylmethylenediamine dialuminum borohydride decomposed only to the extent of 2.8 percent by weight when heated for five hours over a temperature range which was progressively increased from about 25 C. to 228 C. Standard shock sensitivity tests conducted in the manner recommended by the Liquid Propellant Test Methods Committee 3 disclosed, for example, that none of the novel adducts tested in this manner have proved shock sensitive within the limits of the test method kg.-cm.). Also, the densities of the novel adducts are, in general, markedly higher than the density of aluminum borohydride. For instance, the density of N,N,N,N'-tetramethylmethylenediamine dialuminum borohydride is 0.724 gram/milliliter, at 25 C., as compared to 0.55 gram/milliliter, at 25 C., for aluminum borohydride.

Accordingly, one or more objects will be achieved by the practice of the invention.

Brokaw, R. S., and Pease, R. N., J. Am. Chem. 800., 74, 1590 (1952).

Ogg, R. A., and Ray, J. D., Disc. Faraday Soc 19, 239 (1955).

3 Standard Drop Weight Test, Liquid Propellant Test Meth ods No. 4, Liquid Propellan-t Information Agency, March 1960.

It is an object of the invention to provide novel adducts of various metal borohydrides with organic nitrogen compounds. Another object of the invention is directed to providing novel processes for preparing the aforementioned adducts. A further object of the invention is directed to the preparation of novel high energy fuels of well balanced properties for use in propellant systems. A still further object of the invention is directed to adducts which are useful as novel additives in conventional fuels, e.g., jet fuels for air-breathing engines, and hydrocarbon fuels for use in liquid bipropellant rocket motors, to thus improve the combustion characteristics and the hypergolicity of said fuels. Another object of the invention is to provide adducts which are useful as novel fuels for the generation of a driving fiuid for power turbines such as auxiliary power turbines in spacecraft or underwater propulsion systems utilizing, for example, sea water as an oxidizer component. Other objects of the invention are directed to the preparation of adducts having utility as reducing agents, stabilizers, color improvers, etc., which are useful in various fields of application such as in the refining of organic liquids, synthetic resins, and the like. These and other objects will become apparent to those skilled in the art from a consideration of the instant specification.

FIGURE 1 and FIGURE 2 are the infrared spectra of N,N,N,N tetramethyl-l,Z-diaminoethane monoaluminum borohydride and N,N,N',N-tetramethyl-1,2-diaminoethane dialuminum borohydride, respectively. These spectra are markedly different in a number of regions of the vibration rotation spectrum thus establishing that the aforementioned compounds have different molecular structures. The most significant spectral differences are found between about 3.9 and about 5.0a, a region recognized to be characteristic of vibrational modes which mainly involve the stretching of boron-hydrogen bonds. In this spectral region, the adduct of dialuminum borohydride has more absorption bands than the adduct of monaluminum borohydride.

The above-said infrared spectra were obtained by examining mineral oil mulls between rock salt plates using a Beckman IR4 Spectrometer equipped with sodium chloride optics. The instrument conditions employed were as follows:

Scanning speed, iminf 2 Gain, percent 3 Period 2 Slit, standard 2X Operation, double beam.

The mineral oil mulls were prepared by grinding the solid adduct, in mineral oil, with a mortar and pestle, under an anhyrous, nitrogen atmosphere.

In like manner, FIGURE 3 and FIGURE 4 are the infrared spectra of N,N,N,N'-tetramethylmethylenediamine diberyllium borohydride and N,N,N',N-tetramethylmethylenediamine dizirconium borohydride, respectively.

The broad aspect of the invention encompasses novel adducts of a metal borohydride, i.e., aluminum borohydride, beryllium borohydride, or zirconium borohydride, with an organic nitrogen compound which is composed solely of carbon, hydrogen, and nitrogen atoms, with the proviso that when said metal borohydride is aluminum borohydride, then said organic nitrogen compound cannot be R NZ wherein each R is a monovalent saturated hydrocarbon radical, i.e., alkyl and cycloalkyl, and wherein Z is hydrogen or a monovalent saturated hydrocarbon radical. The organic nitrogen compounds which are contemplated as a reagent in the preparation of the novel adducts are further characterized in that they contain at least one nitrogen atom which functions as a Lewis base. In accordance with the Werner coordination theory, these organic nitrogen compounds can be classified as ligands in that the resulting novel adducts, from a structural interpretation, can be characterized as containing at least one nitrogen to metal coordinate bond. It should be noted that if the organic nitrogen compound contains more than one nitrogen atom which can function as a Lewis base, at least one of said nitrogen atoms is coordinately bonded to metal (of the metal borohydride). In addition, the metal atom (of the metal borohydride) can be coordinately bonded to more than one nitrogen atom which function as a Lewis base. However, as indicated previously, the organic nitrogen compound must contain at least one nitrogen atom which functions as a Lewis base. It is preferred that the metal borohydride be aluminum borohydride or beryllium borohydride. Aluminum borohydride is especialy preferred. It is further preferred that the organic nitrogen compound be an organic polynitrogen compound which contains from 2 to 6 nitrogen atoms in the molecule, and preferably still, from 2 to 4 nitrogen atoms in the moleclule. It is preferred, also, that any hydrocarbon substituents which are monovalently bonded to the nitrogen atoms contain up to 12 carbon atoms, and preferably still, up to 3 carbon atoms. Methyl substituents on the nitrogen atoms are highly preferred. It is further pointed out that the word adduct(s), as used herein including the appended claims is employed in its broadest sense and encompasses within its scope complexes, coordination compounds, chelates, and the like.

In one aspect, the invention encompasses novel adducts of the aforementioned metal borohydrides with the aforementioned organic nitrogen compounds, said organic nitrogen compounds being those which contain at least one amino nitrogen atom. In another aspect, the invention encompasses novel adducts of metal borohydrides with organic polynitrogen compounds, said organic polynitrogen compounds being composed solely of carbon, hydrogen, and nitrogen atoms in which at least one of said nitrogen atoms is an amino nitrogen atom. In still another aspect, the organic polynitrogen compound is composed solely of carbon, hydrogen, and amino nitrogen atoms. In a further aspect, the organic polynitrogen compound is composed solely of carbon, hydrogen, and amino nitrogen atoms in which no nitrogen is bonded to another nitrogen atom in the molecule. In other aspects, the organic polynitrogen compound is composed solely of carbon, hydrogen, and nitrogen atoms, said nitrogen atoms being present in the form of secondary amino groups and/ or tertiary amino groups.

In a particularly preferred aspect, the novel adducts of the invention can be represented by the following formula:

wherein L is an organic nitrogen compound composed solely of carbon, hydrogen, and nitrogen atoms, said organic nitrogen compound containing at least one nitrogen atom coordinately bonded to M; wherein M represents aluminum, beryllium, or zirconium; wherein x is the valence of M; and wherein n is an integer having a minimum value of one and a maximum value no greater than the number of nitrogen atoms contained in the organic nitrogen compound '(L) which function as Lewis bases; with the proviso that when M is aluminum, then L cannot be R NZ wherein each R is a monovalent saturated hydrocarbon radical, and wherein Z is hydrogen or a monovalent saturated hydrocarbon radical. Consequently, the maximum value of n will be determined by the number of nitrogen to metal coordinate bonds present in the novel adduct. This in turn will be governed by the choice of the organic nitrogen compound and, in general, by the proportions of the reagents, i.e., organic nitrogen compound and metal borohydride, which are employed in the preparation of the novel adducts. For examples, N,N,N,N'- tetramethyl-l,Z-diaminoethane has two nitrogen atoms which can function as Lewis bases. Equimolar ratios of aluminum borohydride and N,N,N,N-tetramethyl-1,2- diaminoethane will react to yield a white solid adduct. On the other hand, a ratio of two moles, or more, of alurninu-m borohydride per mole of N,N,N',N'-tetramethyl- 1,2-diaminoethane also yields a white solid adduct. Any aluminum borohydride in excess of the 2 to 1 molar ratio can be recovered as unreacted reagent. Thus, in the light of the preceding illustrations (as well as the operative examples in the specification), it is readily apparent that the number of nitrogen atoms which are capable of functioning as Lewis bases realistically governs the maximum value of the variable n in Formula I supra. It is highly preferred that L is an organic polynitrogen compound composed solely of carbon, hydrogen, and nitrogen atoms, at least one of said nitrogen atoms being coordinately bonded to aluminum, and that M is aluminum borohydride. It is preferred, also, that n be an integer having a value greater than zero and less than 5, and preferably still, greater than one and less than 4.

The following discussion will serve to exemplify the various organic nitrogen compounds which can be reacted with aluminum borohydride, beryllium borohydride, or zirconium borohydride to prepare the novel adducts. Formula II infra illustrates the diaminoalkanes.

wherein Z is a divalent saturated aliphatic hydrocarbon radical and wherein each R, individually, is hydrogen or a monovalent hydrocarbon radical, e.g., alkyl, cycloalkyl, aryl, aralkyl, alkaryl, and the like, with the proviso that when Z is methylene then at least one of the R variables is a hydrocarbon radical. In a preferred aspect, Z contains from 1 to 6 carbon atoms, and preferably still, from 1 to 4 carbon atoms, e.g., methylene, ethylene, ethylidene, propylene, propylidene, tetramethylene, etc., and each R, individually, is hydrogen or lower alkyl, e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.butyl, t-butyl, and the like. In a highly preferred aspect, one or more of the R variables is methyl. Specific diaminoalkanes include, for example, 1,2-diaminoethane; 1,2- diaminopropane; the 1,2-, 1,3-, and 1,4-diaminobutanes; the 1,2-, 1,3-, 1,4-, and 1,5-diaminopentanes; the N-methyl-, N,-N-dimethyl-, N,N,N-trimethyl-, and N,N,N,N'- tetrarnethyl-1,2-diarninomethanes; the N-rnethyl-, N,N-dimethyl-, N,N,N-trimethyl-, N,N,N,N-ltetramethyl-1,2- diaminoethanes; the N-methyl-, N,N-dimethyl-, N,N,N'- trimethyl-, and N,N,N',N tetramethyl- ,3-diaminopropanes; the Nmethyl-, N,N-dimethyl-, N,N,N-trimethyl-, and N,N,N,N-tetramethyl-1,4-diaminobutanes; the N- methyl-, N,N dimethyl-, N,N,N trimethyl-, and N,N,N',N-tetramethyl-1,5-diamino-pentanes; the N-ethyl-, N,N-diethyl, N,N,Ntriethyl-, and N,N,N,N'-tetraethyl- 1,2-dian1inoethanes; the N-ethyl-, N,N-diethyl-, N,N,N'- triethyl-, and N,N,N,N'-tetraethyl1,5-diaminopentanes; N,N-dimethyl-N,N'-diethyl-LZ-diaminoethane; N,N dimethyl-N',N'-diethyl-1, -diaminopropane; N,N-dimethyl- N,N-diethyl-lA-diaminobutane; N,N, N',N-tetraisopropyl-1,3-diaminopropane; N,N,N,N tetra-n-butyl-1,4-diaminopentane; and the like.

Formula III infra illustrates the polyalkylene polyamines.

wherein each R individually, is a divalent saturated aliphatic hydrocarbon radical which preferably contains up to 4 carbon atoms; wherein R is hydrogen or a monovalent hydrocarbon radical e.g., alkyl, cycloalkyl, aryl, aralkyl, alkaryl, and the like; preferably hydrogen or lower alkyl, and preferably still, hydrogen or methyl; wherein n is an integer which has a value from 1 to 4; and wherein each R, individually, has the same meanings 5 as set forth in Formula II supra. It is preferred that the moiety contain less than 10 carbon atoms. The polyalkylene polyamines include, by way of illustration, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, the polyethylene-polyamines, the polypropylenepolyamines, the polybutylenepolyamines, the polyethylenepolypropylenepolyamines, N,N,N',N, N" pentamethyldiethylenetriamine, N,N,N',N tetramethyldiethylenetriamine, N,N,N',N'-tetramethyltriethylenetetramine, hexamethylenetetramine, N,N,N,N',N, N"-hexamethylhexa-methylenetetramine, and the like.

Formula IV infra illustrates the 1,3,5-hexahydrotriazine compounds.

wherein each R, individually, is hydrogen or lower alkyl, preferably each R is hydrogen; wherein each E, individually, is hydrogen, alkyl, or the unit each R of said unit being hydrogen or alkyl. It is preferred that the R variables of said unit are hydrogen or lower alkyl, e.g., methyl, ethyl, n-propyl, sec.-butyl, and the like. It is highly preferred that the R variables are hydrogen or methyl. In lieu of the ,3,5-hexahydrotriazine compounds depicted structurally in Formula IV supra, the 1,2,4-hexahydrotriazine compounds and the 1,2,3-hexahy-drotriazine compounds are similarly substituted. Specific 1,3,5-hexahydrotriazines include, for instance, 1,3,5-hexahydrotriazine, the lower alkyl substituted 1,3,5-hexahydrotriazines, the N-monoamino-, the N,N'-diamino-, and the N,N',N-triamin0-1,3,5-hexahydrotriazines wherein each of the aforementioned amino substituents can be H alkyl 'NH -N or --N alkyl alkyl /H CH3 preferably -NHzN or -N Illustrative tetrazine compounds are shown, in structural form, in Formula V infra.

V R R wherein each R, individually, is hydrogen or alkyl, with the proviso that at least one R variable is always alkyl. In a preferred aspect, each R is hydrogen or lower alkyl, e.g., methyl, ethyl, isopropyl, n-butyl, and the like. It is highly preferred that all the R variables are methyl groups. Specific illustrations include 1,1-dimethyl-2-tetra- Zene, 1,1,4,4,-tetramethyl-2 tetrazene, 1,4-dimethyl-2- tetrazene, 1,4-diethyl-2-tetrazene, and the like.

Still other exemplary organic nitrogen compounds which can be reacted with aluminum borohydride, beryllium borohydride, or zirconium borohydride to prepare the novel adducts include, by way of representation, the hydrogenated 1,2,3-, 1,2,4-, and 1,3,5-triazines, e.g., the 1,2,3-, 1,2,4- and 1,3,5-dihydrotriazines; the 1,2,3-, 1,2,4-,

1 dimethyl, N,,N'

and 1',3,5tetrahydrotriazines; the 1,23 and'1,2,4-hexa'-. hydrot'riazines; the N-monoamino substituted 1,2,3-,1,2,4-,'

' l,2,4,5-tetrarnethylhexahydrotetrazine; 1,2,4,5-tetraethylhexahydrotetrazine; hydrazidicarboirnidine;; the hydro genated diazines; piperazine; Z-aminopyrrole; 2 (dimethylamino)pyrrol'e; 2,6-diaminopyridine; 2,6-di-(dimethylamino)pyridine; 2,4,5 tri (dimethylamino)pyrirnidine;' 1,2di- (-dimethylamino -tetrahydropyrazole; 1,2,3tridi- I methylamino)tetrahydrotriazole; 1,2,4 tri' (dirnethylamino)tetrahydrotriazole;. 2,4,5 tri (dimeth'ylamino') hexahydropyrimidine; N,N dimethylpiperazine; N,N'-

diaminoethylenediamine; v ethylene hydrazine N (Z-arriirioethyhhydrazinei; vinylhydrazine; N,N,N,N tetramethylhydrazine; the

monoalkyl andpolyalkylguanidines, e.g., N,N ,N',N'-tetramethylguanidine, N,N',N' -triaminoguanidine, and N methylguanidine; N,N;N',N' tetramethyl-l,4-diamino-2 butene; N,N,N-,N' tetramethyl- 1,4-diamino-2-butyne;

melamine; 2,4,6,8,9-pentazabicyclo-[3.3.1]nonane; tetra- I zole; the polyaminoalkanes,,e.g., 1,2,3-triaminoPropane,

"'LZA-triaminQbutane, 1,2,3-triaminobutane, and. the like;

the monoalkylarnines, e.g., rnethylamine, ethylamine, npropylamine, isopropylamine, n-butylamine, isobutyl amine, t-butyl'arninte, 2-ethy1hexylamine, dodecylamine, I

and the like; the monocycloalkylamines, e.g'., cyclopentyl- I amine, cyclohexylamine, and the like; the substituat'ed 'analines, e.g.,' N-methylaniline, 'N-ethylaniline, N-iso propylaniline, N,'N-dimethylaniline, N,jN-d;iethylaniline,' I N,N-di-n-propylaniline, N-cyclohexylaniline, and the like; I and heterocyclic compounds which contain a single nitrogen atom in a heterocyclic ring, e.g., piperidine, carbazole', pyrrole, 3-isopyrrole, lower alkyl substituted piperidines, and the like. Further illustrations include aniline, toluidine, xylidine, the N-lower alkyl substituted toluidines, and the like.

Further illustrative organic nitrogen compounds which can be reacted with either beryllium borohydride or zirconium borohydride to prepare the novel adducts include, the dialkylamines, e.g., dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n butylamine, diisobutylamine, di-tbutylarnine, di-Z-ethylhexylamine, didodecylamine, and the like; and the trialkylamines, e.g., trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, tri-n-butylamine, tri-t-butylamine, tri-Z-ethylhexylamine, tridodecylamine, and the like.

Illustrative novel adducts which are encompassed within the scope of the invention include, among others,

N,N,N',N'-tetramethyl-1,Z-ethanediamine monoaluminum borohydride,

N,N,N',N'-tetramethyl-1,3-pr-opanediamine monoaluminum borohydride,

N,N,N,N'-tetramethyl-1,2-propanediamine monoaluminum borohydride,

N,N,N',N'-tetramethyl-l,4-butanediamine monoaluminum borohydride,

N,N,N',N'-tetramethyl-1,3-butanediarnine monoaluminum borohydride,

N,N,N,N'-tetramethylmethylenediamine monoaluminum borohydride,

N,N,N',N",N"-pentamethyldiethylenetriamine monoaluminum borohydride,

N,N-dimethylpiperazine monoaluminum borohydride,

1,1,4,4-tetramethy1-2-tetrazene monoaluminum borohydride,

N-methyl N- 'hexam'ethylenetetramine, monoaluminum borohydride,

1,3,5-trimethyl-s-hexahydrotriazine monoaluminum I borohydride,

' I N,N,N,N-tetramethyl -1,2-ethanediamine dialuminum borohydride,

N,N,N,N'tetramethyl-1,3-propanediamine dialuminum I borohydride, N,N,N',N'-tetramethyl-1,2-propanediarnine dialuminum borohydride, N,N,N',N'-tetramethyl-'l ,4-butanediamine diaiuminum borohydride, N,N,N,N -tetramethyl-1,3-butanediamine dialuminum borohydride,

' N,N,N,N'-tetramethylmethylenediamine dialurninum i i I borohydride, I I p N,N,N,N'ZN"-pentamethyldiethylenetriamine dialuminum borohydride, Na dirnethylpiperazine dialuminumbo'rohydride, '1,1,4,4 tetramethyl-2tetrazene dialuminum borohydride,

' l,3,5 trirnethyl-s-hexahydrotriazine dialuminumborohydride,

'N,N-dimethylmethylenediamine dialuminumboroethylenediamine aluminum borohydride,

N,N,N',N",N"-pentamethyldiethylenetriamine trialuminum borohydride,,

, 1,3,S-triamino-s=hexahydrotriazine trialuminurn borohydride,

triarninoguanidine monoaluminum borohydride,- l,2,4,5-tetramethylhexahydrotetrazine'tetraaluminum,

borohydride,

' emino-s triazine trialuminnmborohydride,

2,4,6 triamino-s-triazine d-ialuminur'n borohydride, I bis (tetramethylg-uanidine) monoaluminum borohydride,

' 1,3,S-triarnino-s-hexahydrotriazine dialurninum borohydride,

I triethylamine monoaluminum borohydride,

' butylamine monoaluminumborohydride,

aniline monoaluminumborohydride, I

piperidine monoaluminum borohydride,

N,N,N,N-tetramethylmethylenediamine diberyllium borohydride,

1,1,4,4-tetrarnethyl-Z-tetrazene diberylliu-m borohydride,

N,N,-N,N-tetramethyl-1,2-ethanediamine monoberyllium borohydride,

methylamine monoberyllium borohydride,

l,3,5-triamino-s-hexahydrotriazine triberyllium borohydride,

N,N,N,N",N"-pentamethyldiethylenetriamine triberyllium borohydride,

trimethylamine beryllium borohydride,

triethylamine beryllium borohydride,

methylamine zirconium borohydride,

dimethylamine zirconium borohydride,

trimethylamine zirconium borohydride,

l,1,4,4,-tetramethyl-2-tetrazene dizirconium borohydride,

and the like.

The novel adducts can be prepared by contacting the metal borohydride with the organic nitrogen compound under an inert, anhydrous atmosphere, e.g., hydrogen, nitrogen, argon, helium, krypton, and the like. It is essential that impurities such as oxygen, carbon dioxide, carbon monoxide, Water, and other materials which are reactive with the metal borohydride be avoided in the system in view of the highly hazardous and explosive nature of the borohydride reagent. The operative temperature can be in the range of from about 64 C., and lower, to below the boiling point of aluminum borohydride, e.g., from about 64 C. to 43 C. A preferred temperature range is from about 0 C. to about 30 C., and preferably still, from about 15 C. to about 25 C. The order of addition of the reagents does not appear to be narrowly critical. However, it is preferred that the metal borohydride be added to the organic nitrogen compound. Incremental isothermal addition of the metal borohydride to the nitrogen compound, with slow stirring, is highly preferred. If desired, the reaction mixture can be cooled to maintain the desired reaction temperature. The operative pressure can be subatmospheric, atmospheric, or moderately superatmospheric. In general, suitable results have been obtained by conducting the reaction below about 760 mm. of Hg pressure. It is preferred that the operative pressure be in the range of from about mm. of Hg to about 760 mm. of Hg. For relatively large batch production of the novel adducts, it was observed that satisfactory results were obtained by eifecting the reaction under essentially atmospheric pressure.

In view of the hazardous nature of metal borohydride, it is not preferred to have a large excess of unreacted metal borohydride present in the reaction product mixture. In the preparation of the novel liquid adducts, the preferred maximum concentration of metal borohydride is in slight excess of that quantity which is necessary to react with the organic nitrogen compound to produce the desired liquid adduct. On the other hand, when employing relatively high boiling organic nitrogen compounds to prepare the novel liquid adducts, the presence of unreacted nitrogen compound in the resulting reaction product mixture is undesirable since the resolution of said mixture, by distillation, could result in the thermal decomposition of the liquid adduct product. However, this disadvantage does not present itself when the resulting product is a solid adduct. In such cases, the solid adduct, if insoluble in the reaction product mixture, is readily recovered therefrom via filtration techniques. Should the solid adduct be soluble in the reaction product mixture, the addition of an inert, normally-liquid, organic vehicle thereto in which the solid adduct product is insoluble and the relatively high boiling organic nitrogen compound is miscible, would result in the precipitation of said solid adduct. The solid adduct then could be recovered by filtration procedures, as indicated previously. Subject to the variables illustrated above, it is desirable to employ an amount of metal borohydride which is slightly in excess of that required to react with the total amount of organic nitrogen compound to produce the desired novel liquid adduct, whereas it is desirable to employ an amount of organic nitrogen compound which is moderately in excess of that required to react with the total amount of metal borohydride to produce the desired novel solid adducts. However, it is preferred to employ essentially stoichiometric amounts of the reagents.

The reaction period will depend to a significant extent, upon various factors such as the choice of organic nitrogen compound and metal borohydride, the concentration of the reactants, the operative temperature, the operative pressure, the manner of addition of the reactants, the use of an inert, normally-liquid, organic vehicle, and other considerations. Depending upon the correlation of the variables illustrated supra, the reaction period can range from several minutes to a few days. However, highly satisfactory results have been obtained by conducting the reaction over a period of from about 0.5 hour, and lower, to about 6 hours, and higher.

If desired, the reaction can be eiiected in the presence of an inert normally-liquid, organic vehicle, i.e., a vehicle which is non-reactive with the reagents or the resulting novel adduct product. Illustrative vehicles include, for example, the normally-liquid saturated aliphatic and cycloaliphatic hydrocarbons, e.g., n-pentane, n-hexane, n-heptane, iso-octane, n-octane, cyclopentane, cyclohexane, cycloheptane, methylcyclohexane, ethylcyclopentane, and the like; the aromatic hydrocarbons, e.g., benzene, toluene, xylene, ethylbenzene, and the like; and other inert, normally-liquid, organic vehicles which would become readily apparent to one skilled in the art. The use of an inert vehicle permits the heat of reaction to be more evenly dispersed, thus minimizing the danger of inadvertently causing thermal decomposition of unreacted metal borohydride. This advantage is especially desirable when employing large quantities of reagents.

The novel adduct product can be recovered from the reaction product mixture by various procedures known to the art. For example, excess reagent and inert vehicle, if any, can be recovered from the reaction product mixture by distillation under reduced pressure, e.g., 10 to 50 mm. of Hg. The novel solid adducts also can be recovered from the reaction product mixture by filtration or crystallization techniques. Vacuum distillation is a preferred method of recovering the novel adduct product providing it can be vacuum distilled without decomposition.

The preparation of aluminum borohydride beryllium borohydride and zirconium borohydride 6 is documented in the literature.

A particularly preferred embodiment of the invention is directed to a novel process for producing novel adducts of aluminum borohydride. This novel process affords an alternative route for preparing said novel adducts in an economical manner and under far less hazardous conditions since the use of aluminum borohydrohydride per se is avoided. The novel process involves contacting the organic nitrogen compound with an excess or deficiency (but preferably a stoichiometric amount) of aluminum trihalide, e.g., aluminum trichloride, under an inert, anhydrous atmosphere, in the presence of an inert, normally-liquid, organic vehicle, to produce an adduct of aluminum trichloride and organic nitrogen compound. The resulting adduct then is reacted with an excess of alkali metal borohydride, i.e., lithium borohydride, potassium borohydride, sodium borohydride, cesium borohydride, or rubidium borohydride, under an inert, anhydrous atmosphere, in the presence of an inert, normally-liquid, organic vehicle, to give the novel adduct(s) contemplated by the invention. The reaction involving aluminum trichloride with an organic nitrogen compound can be effected at a temperature ranging from about 20 C., and lower, to below the boiling point of said nitrogen compound, whereas the reaction involving the resulting aluminum trichloride adduct with the alkali metal borohydride can be conducted at a temperature ranging from about 0 C., and lower, to about 200 C., and higher. The above said reactions can be effected under subatmospheric, atmospheric, and moderately superatmospheric pressures; the reaction is conducted for a period of time sufficient to produce the intended product, e.g., from 0.5 hour, or less, to 10 hours, or more. The order of addition of the reagents in either reaction does not appear to be critical. Illustrative inert atmospheres, e.g., helium, have been described previously as well as the various exemplary inert, normally-liquid, organic vehicles. Upon termination of the novel process, the novel adduct can be recovered from the resulting reaction product mixture by techniques and procedures which are readily apparent to one skilled in the art. For example, solid alkali metal chloride by-product and unreacted solid alkali metal borohydride can be removed via filtration, whereas the inert vehicle can be removed via distillation or solvent extraction procedures.

Another preferred embodiment of the invention is directed to the preparation of novel liquid propellant systems which utilize, as the fuel component, the liquid adducts of a metal borohydride, i.e., aluminum borohydride, beryllium borohydride, or zirconium borohydride, with an organic nitrogen compound which is composed solely of carbon, hydrogen, and nitrogen atoms, said organic nitrogen compound containing at least one nitrogen atom which is coordinately bonded to the metal of said metal borohydride. The liquid adducts which are contemplated in this embodiment include the novel liquid adducts per se, described previously, as well as the liquid adducts of aluminum borohydride with an organic nitrogen com- 4 U.S Patent No. 2,599,203. 5 Burg et al., J. Am. Chem. 800., 62, 3425 (1950). B U.S. Patent No. 2,575,760.

' pound which has the formula R N or R NH wherein each R is a monovalent saturated hydrocarbon radical. The preferred liquid adducts are the novel liquid adducts of aluminum borohydride with an organic polynitrogen compound, and the novel liquid adducts of beryllium borohydride with an organic nitrogen compound. Many of the liquid adducts are highly attractive in that they are capable of giving a high specific impulse with appropriate oxidizers when used as liquid fuels in liquid propellant systems. As is well known, the specific impulse is a measure of the pounds of thrust obtainable per pound of propellant (fuel-I-oxidizer) reacted per second. A higher specific impulse makes possible an increased range or trajectory of a vehicle driven by jet propulsion, or an increased payload, or a decreased fuel requirement, or a higher velocity at burnout.

Examples of appropriate liquid oxidizers, both storable and cryogenic include nitrogen tetroxide, the fuming nitric acids, chlorine trifluoride, hydrogen peroxide, bromine pentafiuoride, oxygen, fluorine, oxygen difluoride, perchloryl fluoride, perfluoroguanidine, and others. The ratio of oxidizer to fuel is generally chosen so as to maximize the specific impulse delivered by the given propellant system, except when said propellant system is employed in a gas generator to furnish hot compressed, driving fluid to power a turbine. When used for gas generation, it is generally advantageous to employ a fuel-rich ratio so as to limit the temperature of the combustion products in order to avoid heat damage to the turbine. Another important advantage of various liquid adducts is their ability to form hypergolic propellant systems with certain liquid oxidizers that normally do not effect hypergolic combustion with common rocket fuels. Hypergolic combustion is particularly important in spacecraft propulsion which may require intermittent combustion and variable thrust capabilities.

Another preferred embodiment of the invention is directed to the preparation of novel solid propellant formulations which utilize, as a fuel component, the solid adducts of a metal borohydride, i.e., aluminum borohydride, beryllium borohydride, or zirconium borohydride, with an organic nitrogen compound which is composed solely of carbon, hydrogen, and nitrogen atoms, said organic nitrogen compound containing at least one nitrogen atom which is coordinately bonded to the metal of said metal borohydride. The solid adducts which are contemplated in this embodiment include the novel solid adducts per se, described previously, as well as the solid adducts of aluminum borohydride with an organic nitrogen compound which has the formula R N or R NH wherein each R is a monovalent saturated hydrocarbon radical. The preferred solid adducts are the solid adducts of aluminum borohydride with an organic polynitrogen compound, and the solid adducts of beryllium borohydride with an organic nitrogen compound. Solid rocket propellants can be termed monopropellants in that a solid oxidizer and solid fuel are mixed together in a single matrix which does not require the addition of oxidizer from an external source. An important class of solid propellant systems are known as composite solid propellants which can be prepared by suspending a solid oxidizing agent in a liquid prepolymer which is capable of being cast and cured to a combustible elastomeric matrix. Composite solid propellants can be made in a great variety of compositions. Various constituents can be added to modify the characteristics of the propellant such as to improve the energetics, to improve the physical properties, to catalyze or retard the burning process, and the like. Oxidizers which can be employed include, for example, ammonium perchlorate, ammonium nitrate, nitronium perchlorate, hydrazine nitrate, hydrazine perchlorate, guanidinium perchlorate, and others. Exemplary binders include polyethylene, the butadiene-acrylic acid copolymers, the polyether polyurethanes, the fluorocarbons, and other elastomeric binders. A typical standard solid propellant composition can contain about 65 weight percent ammonium perchlorate, 15 weight percent polymeric hydrocarbon binder, and 20 weight percent aluminum powder which would produce upon combustion (at 1,000 p.s.i.) a theoretical specific impulse of about 265 pounds-second/pound. However, the actual delivered specific impulse has been somewhat less. To improve the performance of such solid propellant systems, the subject embodiment contemplates the use of the solid adducts as a high energy solid fuel additive to replace part or all of the less energetic fuel additives, such as aluminum, now commonly used. As is readily apparent to those skilled in the art, the quantity and choice of the solid adduct to be incorporated to form the novel solid propellant in order to achieve well balanced properties and optimum performance will be governed by various factors such as the compatibility with the chosen hinder, the thermal stability of the adduct, the oxidizer of choice, the nature and concentration of burning rate modifiers, and other considerations. In a preferred aspect, the solid adduct is encapsulated within a combustible material such as, for example, polyethylene, polypropylene, aluminum, polytetrafluoroethylene, polyalkyl siloxanes, and the like. The art is wellapprised of the technique of encapsulating a solid fuel component which is to be incorporated in a solid propellant.

Another preferred embodiment of the invention relates to novel compositions of liquid fuels which contain the adducts described in the two preceding embodiments in an amount sufficient to improve the combustion characteristics, ignition efiiciency, flame stability, and/ or energetics of said liquid fuel. The liquid fuels which are contemplated are useful as fuels for jet propulsion purposes which include, among others, air-breathing engines and liquid rocket engines, e.g., turbojets, ramjets, bipropellant rockets, and other combustion power plants. Although a maximum increase in specific impulse is produced by using a maximum quantity of the adduct, other practical considerations connected with the particular applications of the fuel often lead to preferred mixtures containing less than the maximum compatible quantity of said adduct. The attainment of well balanced properties in the novel liquid fuels is governed by many of the variables discussed previously, e.g., choice of liquid fuel, the choice of the adduct solubility, specific application of the novel liquid fuel, the addition of modifying components, hypergolicity, and economic factors. Illustrative liquid fuels include the aliphatic, hydroaromatic, and aromatic hydrocarbons, and mixtures thereof, for example, kerosene (RP-1, IP-4, IP-S, JP-6), n-hexane, diethylcyclohexane, petroleum ether (boiling range 3060 C.), benzene, toluene, Xylene, and the like; aliphatic, aromatic and heterocyclic amines such as isopropylamine, diethylamine, aniline, cyclohexylamine, pyridine, and the like; cyclic ethers such as dioxane, furan, tetrahydrofuran; and others.

Additional embodiments which are contemplated within the scope of the invention involve the use of the adducts described in the three preceding embodiments as color improvers, as stabilizers, as reducing agents, as antioxidants, as redox catalysts, as catalysts for olefin polymerization processes, and so forth. Contaminants such as carbonyl compounds in oxygenated organic compounds, e.g., Ox-o alcohols, are readily reduced by incorporating a small quantity of the adduct thereto. Of course, contaminated oxygenated organic compounds such as aldehydic compounds that can react with the adduct are not applicable. The amount of adduct which can be added, in general, is approximately sufficient to react with the contained contaminants. Oxidative degradation which results from traces of oxygen or oxygen-containing compounds contained in, for example, synthetic polymers, can be prevented by incorporating into said polymers an antioxidant amount of the adduct. The adducts can be employed as catalysts for the polymerization of olefins, ethylene, propylene, the butylenes, styrene, etc., preferably via the socalled low pressure techniques. The optimum catalyst con- 13 centration is readily apparent to those skilled in the art.

As is well known, the heat of formation of a compound can be defined as the enthalpy change upon forming said compound from its elements in their standard state. The heats of formation of the ligands, i.e., organic nitrogen compounds, and the metal borohydrides were calculated from standard heats of combustion which, in turn, were determined experimentally or by using the Handrick group contribution method.

It is pointed out that the terms chamber pressure and exhaust pressure, as used herein, are standardized at 1,000 p.s.i.a. and 14.7 p.s.i.a., respectively. Once these terms are specified at the above said pressures, the theoretical shifting specific impulse is a thermodynamically defined quantity that depends on the fuel composition and heat of formation, the oxidizer composition and heat of formation, and the oxidizer to fuel ratio. The specific impulses presented herein were determined by making performance calculations at selected oxidant to fuel ratios, and then plotting the results to define the maximum specific impulse and the optimum oxidant to fuel ratio. In general, the calculations were performed on an IBM 704 computer using a chemical equilibrium program prepared by Aerojet-General Corporation together with thermodynamic data for combustion species supplied with the program. In a few instance, the performance curves were extrapolated to low oxidant to fuel ratios by computing additional relative specific impulse values by the approximate NARTS hand calculation method with thermodynamic data for combustion products supplied with the method.

By the term energetics, as used herein, is meant the chemical energy release upon combustion, or, more particularly, the theoretical specific impulse.

The following examples are illustrative.

Example 1 N,N,N',N-tetramethyl-1,2-ethanediamine, 0.285 gram, 2.45 mmoles, was transferred by means of a hypodermic needle under a dry nitrogen atmosphere into a reaction flask equipped with a standard taper joint and a Teflon coated magnetic stirring bar. The reaction flask then was attached to a high vacuum system, cooled with a liquid nitrogen bath, and evacuated to at least mm. of mercury. Aluminum borohydride, 8.41 mmoles, was measured in a standard bulb and subsequently added in increments to the diamine. After each addition, the liquid nitrogen bath was removed and the reaction flask allowed to Warm to room temperature. Stirring was initiated when the solid mixture turned liquid. The pressure above the liquid, as read by a mercury manometer attached to the reaction system, gradually decreased and white solid formation was observed which indicated that a reaction was occurring. From a pressure-composition plot of the reaction, it was readily apparent that the pressure in the reaction flask was very low until the mole ratio of aluminum borohydride to diamine reached two. Beyond this ration (2:1), the pressure increased rapidly. At a 1:1 mole ratio of aluminum borohydride to diamine, no detectable vapor pressure which would be attributable to free diamine was observed. The aluminum borohydride in excess of a mole ratio of 2:1 (3.38 mmoles) was easily distilled from the reaction flask at room temperature in vacuo. Thus, 5.03 mmoles of aluminum borohydride reacted with 2.45 mmoles of 4D2 (mole ratio=2.05

The resulting product was a white, non-volatile solid. Several drops of hydrazine was added to the solid causing T G. R. Handrick, Ind. and Eng. Chem, 48, N0. 8, page 1366, August 1956.

L. J. Gordon and H. Boerlin, A Practical Approach to Computer Programming for Specific Impulse Calculations, Solid Rocket Plant, AerojetGeneral Corporation, Sacramento, Nov. 1. 1959.

D J. D. Clark. The NOD Method of Isp Calculation, Letter Report L-23, Naval Air Rocket Test Station, Lake Denmark, N..T., September 1959.

the mixture to ignite and burn with a green flame, but it did not explode. Several crystals were struck vigorously with a steel hammer. No detonation occurred suggesting that it may not be shock sensitive.

Example 2 N,N,N,N -tetramethyl-l,4 butanediamine, 0.527 gram, 3.36 mmoles, was transferred into a reaction flask as described in Example 1. The reaction flask was then attached to the high vacuum system, cooled with a liquid nitrogen bath, and evacuated to at least 10* mm. of mercury. Aluminum borohydride, 6.73 mmoles, was then measured in a standard bulb and added in about 7 equal portions to the diamine. After each portion was added, the reaction flask was slowly allowed to reach room temperature by removing the liquid nitrogen bath. After the first portion was added, the pressure in the flask gradually decreased and white solid formation was observed. At a 1:1 mole ratio of aluminum borohydride to diamine, no detectable vapor pressure which would be attributable to free diamine was observed. The resulting product was a white solid at said 1:1 ratio. As the mole ratio of aluminum borohydride to diamine exceeded one, the product remained a white solid. When the mole ratio of the reactants was 2:1, the product remained a white solid. At a 2:1 mole ratio of aluminum borohydride to diamine, no detectable vapor pressure which would be attributable to free diamine was observed.

Example 3 N,N'-dimethylpiperazine, 0.300 gram, 2.63 mmoles, was transferred in a dry nitrogen atmosphere into a 25 ml. reaction flask equipped as described in Example 1. The flask then was attached to the vacuum line, cooled with liquid nitrogen, and evacuated to at least 10 mm. of mercury. Aluminum borohydride, 5.58 mmoles, was measured in the standard bulb. Small portions of about 0.5 mmole of the borohydride were added periodically to the N,N-dimethylpiperazine. After each addition, the reaction flask was allowed to warm to room temperature, after Which the pressure gradually began to decrease. When the pressure no longer decreased, another addition of aluminum borohydride was made. White solids had formed in the reaction flask. At mole ratios of aluminum borohydride to lJ,N'-dimethylpiperazine of 1:1 and 2:1, the products were white solids. At these mole ratios, no detectable vapor pressure which would be attributable to free N,N'-dimethylpiperazine was observed. When the mole ratio of aluminum borohydride to N,N-dimethylpiperazine exceeded 2:1, the pressure increased linearly in the reaction flask. The excess aluminum borohydride was easily distilled from the reaction flask at room temperature. Calculations proved that 5.17 mmoles of aluminum borohydride reacted with 2.63 mmoles of N,N-dimethylpiperazine to form a non-volatile, white solid. The solid was allowed to stand in the atmosphere with no visible reaction having been observed. Several drops of hydrazine when added to a small amount of the 2:1 adduct caused an explosion.

Example 4 Hexamethylenetetramine, 0.154 gram, 1.10 mmoles, was added to a reaction flask and attached to the vacuum line as described in Example 1. Aluminum borohydride, 5.90 mmoles, was measured in a standard bulb and then a small amount (about 0.2 mmole) was added to the hexamethylenetetramine to make sure the reactants were compatible. No violent reaction was observed, so the rest of the aluminum borohydride was added and allowed to react, at room temperature, for 2 days. The excess aluminum borohydride, 4.72 mmoles, was then distilled from the reaction flask at room temperature leaving 1.18 mmoles having reacted with 1.10 mmoles of hexamethylenetetramine. The product was a white solid. Several drops of hydrazine when added to thewhite solid add'uct caused an explosion.

Example N,N,N',N-tetramethyl-1,3-propanediamine, 0.168 gram, 1.29 mmoles, was added to a reaction flask as described in util the mole 'ra'tiotof aluminum borohydride to diamine was greater thantwo. The pressure then increased sharp-i 1 1y. The product was liquid throughout, the experimenL At mole ratios of aluminum borohydride to diamine of 11:1 and 2:1, no detectable. vapor pressurewhich would. be;

attributable to free N,N=,N,N-tetramethyl-l,3-propane-.

' diamine was observed. The aluminum borohydride inexcess of a 2:1 mole ratio was easily-distilled tromthe ree I action flask at room temperature. The non-volatile, clear, liquid adduct (2:1) was heated at 7 0 C. for one hour. Therewas a slightpressure' build I up during this'h'eating period,'but the pressure suddenly. decreased and the reaction product solidified, suggesting polymerization; Asmall amount of the adduct (solid), when exposed to the atmosphere, did not burnbut it re.; acted slowly'toi give ofi 'a-whitesmoke. A few drops of hydrazine reacted with the adduct causing an explosion. I

gram, 1.40 mmoles, was placed'in a reactioniiask ;in a -manner previously described in: Example: 1. Aluminum.

of 100 kg;-cm.,- could :be handled easily in a dry nitrogen atmosphere, and fumed'in air. The infrared spectrumeoj in the preceding examples. Small, measured amounts of. I aluminumborohydride were added thereto until a total of.

borohydride, O.850 mmole,:was transterredto the reaction 7 i flask at liquid nitrogen temperature (,19 6--. .C;.);. The contents of the reaction flask then were, allowed to warm slowly to room temperature. Itwas noted. that a white 1 1 solid had formed. in the reaction flask, andno. detectable vapor pressure which I would be attributable to. free. di- I 'amine'was observed. More aluminum borohydride, 2.20: I

3 'inmoles,theu was added in two equal portions, It wasthen observed that the reaction product was liquid. Excess aluminum borohydride, 0.167 mmole, was easily distilled from the reaction flask at room temperature. Hence, a total of 2.88. mmoles of aluminum borohydride reacted with 1.40 mmoles of N,N,N',N-tetramethyl-1,2-propanediamine to give a clear, non-volatile liquid product with a pressure above it of 2 mm. of mercury at 25 C. When this liquid was heated at 70 C. for one hour it became a solid, suggesting polymerization. A few drops of hydrazine added to a small portion of the adduct (solid) caused an explosion. White fumes were evolved when several crystals were allowed to stand in the atmosphere, but there was no fire or detonation.

Example 7 To 1.95 grams, 19.1 mmoles, of N,N,N',N'-tetramethylmethylcnediamine, 38.9 mmoles of aluminum borohydride was added slowly in the manner explained in the previous examples. The vapor pressure of the resulting product was about 5 mm. of mercury at 25 C. Further additions of aluminum borohydride resulted in a rapid pressure increase inside the reaction vessel which indicated that no further reaction was occuring. At mole ratios of aluminum borohydride to diamine of 1:1 and 2:1, no detectable vapor pressure which would be attributable to free N,N,N',N tetramethylmethylenediaminc was observed. The aluminum borohydride in excess of a mole ratio of 2:1 was easily distilled from the flask. The products remaining consisted mostly of a clear non-volatile liquid, a small amount of white solid, and a small amount of a distillable liquid which when isolated decomposed into diborane and a white solid.

The non-volatile liquid was separated from the solids by filtering through a sinterod glass disc. The clear liquid had a density of 0.9 g./rnl. at 25 C., a shock sensitivity showed strong. absorption: between 4-5a indicating the presence of boron-hydrogen linkages.

Example 8 m-moles, was transferred into a 25 ml.; reactionflask as described in the prccedingexamples. Aluminum borohy-v dride, 1.304'mmoles, was transferred. into the reaction flask-which was cooled to -196 C. The liquid nitrogen -.baththen was removed; the flask was allowed to: warm slowly to room tem eratu-re andthen. stirred for 10 min- Y utes.:A White-solid, formed and 0.36 mmole of a gas collected which was non condensable with liquid nitrogen.

More aluminum borohydride, 2.14 .mmoles, I was added :to the reaction flask; as described above, allowed to warm to room temperaturq-and maintained thereat for-aperiod. I

" of 30 minutes. 'T he product in the flask was a liquid. More 1 i non-condensable gas (at 196 Ca), presumably hydrogen, was collected in lthe Toc'pler pump. The total amount vofhydrogen collected was 1.25- mmoles. The additionof :more: aluminum borohydride to the reaction flask did not result inany further reaction since the excess borohydride.

I was easily distilled from the flask. 1

2 Example 9 1,3,5 trimethylhexahydrotriazine,. 0.206 gram, inmoles; was trahsterred into a reaction-flask as described i 4.82. m-moleswas reached. The mixture of the .triazine I and borohydride was allowed to stand at room tempera-' I ture for about two days; whereupon the unreacted. alu-- minum borohydride was' distilled: from-the reaction flask; 1

and measured. :At mole ratios of; aluminum borohydride. I I v t totriazine of 1:1 and 2:1, no detectable .vapor, pressure p which would bev attributable to :free. 1,3,5 -trimethylhe xa;

- hydrotriazine was observed'At these ratios, i.e., 1:1 and 2:1, the products were a white solids. The non-volatile, white solid adduct (2: 1) was very reactive with hydrazine. No visible reaction was noted when a small amount of this adduct was exposed to air to a short period.

Example 10 N,N,N',N,N pentamethyldiethylenetriamine, 0.244 gram, 1.29 mmolcs, was transferred into the reaction flask which was equipped as described in Example 1. Aluminum borohydride, 4.90 mmoles, was measured in the standard bulb and added in small increments to the triamine. The reaction flask was allowed to warm to room temperature and maintained thereat until the reaction was complete. At a mole ratio of aluminum borohydride to triamine of 1:1, the product was a white solid with a pressure above it of about 2 mm. of mercury at 26 C. At a mole ratio of aluminum borohydride to amine of 2:1, the product was also a white solid with a pressure above it of about 2 mm. of mercury at 26 C. At these mole ratios (1:1 and 2:1), no detectable vapor pressure which would be attributable to free triamine was observed. a

An exact mole ratio of 3:1 of aluminum borohydride to triamine was stirred together for several days. The pressure decreased slowly indicating that further reaction was occurring. Because the reaction was slow, more aluminum borohydride (cumulative total=4.90 mmoles) was added for the purpose of increasing the pressure, which would in turn increase the rate of the reaction. The pressure decreased slowly for about one day and then remained constant. The contents in the reaction flask were allowed to stand for a period of about 3 weeks. Thereafter, the excess aluminum borohydride, identified by its vapor pressure, was distilled slowly from the re- Example 11 in Example 1. Aluminum borohydride, 6.71 mmoles, was

measured into a standard bulb and then added to the reaction flask in seven equal portions. After each addition, the reaction flask was warmed from 196 C. to room temperature whereby the borohydride would readily react as indicated by a pressure decrease. At an exact mole ratio of 1:1, the product was a clear, non-volatile liquid. A small portion (0.0667 gram) gained 39 percent of its original weight when placed in air for 30 minutes. A drop of hydrazine added to a small amount of the adduct caused a fire which burned with a green flame. Heating 3.95 mmoles of the adduct at 70 C. for 65 hours produced 1.60 mmoles of gas in the reaction vessel. The adduct was not shock sensitive.

One mole of the 1:1 adduct was transferred into a reaction flask equipped with a magnetic stirring bar. Aluminum borohydride, 1 mmole, was added in about three equal parts to the reaction flask which was cooled to 196 C. After each addition, the contents of the flask were gradually allowed to warm to room temperature. When the mole ratio of aluminum borohydride to diamine was exactly 2: 1, the pressure within the reaction system was 9 mm. of mercury at 25.5 C.

The 2:1 liquid adduct was gradually heated to 70 C. over a period of two hours. The adduct turned into a white solid and the pressure above the solid was 48 mm. of mercury, equivalent to 0.26 mmole of gas. Therefore, the solid corresponded closely to the composition of the liquid. When the 1:1 adduct was treated in a similar manner, no solid formation occurred. Continued heating of the 2:1 adduct at 70 C. for 65 hours resulted in the evolution of 2.86 mmoles of gas.

Example 12 I Thirty-six grams of pure N,N,N',N-tetramethylmethylcnediamine was fed to a 500 ml. glass-jacketed reactor which was fitted with a thermocouple, liquid feed tank, agitator, condenser, and a nitrogen gas inlet tube. The reactor was also fitted with an outlet stopcock on the bottom to facilitate removal of the product, and the nitrogen outlet was fitted to a gas scrubber which contained 50 ml. of a tertiary amine to contain unreacted aluminum borohydride. Cooling water was applied to the jacket of the reactor and the temperature of the N,N,N',N'-tetramethylmethylenediamine was brought to 20 C. and maintained at this temperature during the feeding period. Aluminum borohydride was added dropwise to the reaction vessel until fifty grams had been added as denoted by the liquid volume of the borohydride. Addition of the first half of the aluminum borohydride was accompanied by a small amount of heat evolution; however, addition of the remaining aluminum borohydride was not exothermic and it was necessary to shut off the cooling water in order to maintain a reaction temperature of 20 C. An atmosphere of nitrogen was maintained in the reaction vessel during addition of the aluminum borohydride. After all of the aluminum borohydride had been added, the reaction was continued for a 3-hour period and then vacuum stripped for one hour at 50 mm. of mercury to remove any unreacted aluminum borohydride. The residues from the vacuum stripping operation were collected in two glass receivers maintained at liquid nitrogen temperatures. Sixty-nine grams of a liquid product 18 were recovered from the reactor which had a composition as follows as determined by elemental analyses:

Calculated C, 24.6; H, 15.6; N, 11.4; A1, 22.0; B, 26.5. Found: C, 25.1; H, 15.8; N, 11.7; A1, 22.2; B, 26.2. The physical properties of the liquid adduct are set forth in Table I infra.

TABLE I Name' N ,N,N ,N-Tetramethylmethylenediamine dialuminum borohydride (3H (3H3 Structural Formula Al(BH -NCH N-Al(BH CH3 CH3 Empirical Formula O5N2H35A12Bu Molecular Weight 245.4 Density, gm./ml. 20 0.. 0.724 Vapor Pressure, 25 C 6.0 mm. Hg Freezing Point, 0.-.. 75 l Boiling Point, C 200 Z Viscosity, centipoises, 20 C 7.19 Heat of Formation, KcaL/gm.

mole +193 2 Thermal Stability, C 3 Shock Sensitivity, kgjem 120 4 Specific Impulse, lb./sec.llb 313 5 1 Sets to glass at 75 C.

2 Theoretical calculation.

3 No decomposition for 24 hours under 1 atm. of nitrogen.

4 Limit of detection by Olin Mathieson drop weight tester.

N 6% 1,000 p.s.i. expanded to 14.7 shifting equilibrium oxidized with Example 13 Twenty-two and four tenths grams of N,N-dimethyl- 1,2-ethanediamine were reacted with 49 milliliters of aluminum borohydride in the same manner as described in Example 12 except that the reaction was conducted at 10 C. in the presence of 200 milliliters of dry benzene. The reaction was allowed to proceed overnight (15 hours), at ambient temperatures, and the benzene was then removed from the product by vacuum stripping at 6.0 mm. of Hg pressure. A viscous liquid (47.5 grams) was recovered from the reactor. This product had a vapor pressure of about 3.0 mm. of Hg at 26 C. and was only very moderately reactive with air. The product had the following composition as determined by elemental analyses:

Calculated C, 20.7; H, 15.7; N, 12.1; A1, 23.3; B, 28.0. Found: C, 18.9; H, 17.0; N, A1, 25.4; B, 27.7.

Example 14 Isooctane was arbitrarily chosen as a solvent for studying the reaction of aluminum borohydride with ethylenediamine. Use of a liquid medium enables a more rapid and safer addition of aluminum borohydride by acting as a heat sink and a dispersing-agent for the reactants.

Dry iso-octane, 5 ml., 3.45 grams, and ethylene-diamine, 0.515 gram, 8.56 mmoles, were charged to a 25' Theoretical elemental composition of N,N,N,N'-tetramethylmethylenediamine dialuminum borohydride.

Theoretical elemental composition of tN,N-dimethyl-1,2-

ethanediamine dlaluminum borohydride.

TABLE II.PRESSURE-COMPOSITION DATA FOR THE REACTION OF ALUMINUM BOROHYDRIDE WITH ETHYLENEDIAMINE IN ISO-OO- TANE AT 26 C.

The results indicate that the pressure remains relatively low and constant until the mole ratio of aluminum borohydride to ethylenediarnine exceeds one, signifying that one mole of aluminum borohyidridehas reacted with one mole of ethylenediamine thus producing a white solid. When the mole ratio of one is exceeded, there was a'relatively rapid increase in pressure which did not decrease with time. It was, therefore, concluded that no further reaction occurred. A'small amount of hydrogen, 0.60 mmole, was formed during the reaction and can be attributed to slight quantities of impurities such as moisture, or to side reactions.

Example 15 A mixture of 150 ml. of dry benzene and 23.2 grams (0.20 mole) of 1,1,4,4-tetramethyl-2-tetrazene was fed into a 500 ml. glass-jacketed reactor which was fitted with a thermocouple, aluminum borohydride feed tank, agitator, condenser, anda nitrogen gas inlet tube. The reactor was also fitted with an outlet stopcock on the bottom to facilitate removal of the product, and the nitrogen outlet was fitted with a scrubber containing 50 ml. of a tertiary amine to prevent any unreacted aluminum borohydride from contacting air. Cooling water was applied to the jacket of the reactor and the temperature of the TMT wasbrought to about 10C. and maintained at this temperature during the feeding period.

Aluminum borohydridewas added dropwise to the reaction vessel until 28.6 grams (0.4 mole) had been added. The weight was determined by measuring a known volume of the liquid borohydride. The borohydride had to be added slowly or excess fuming occurred. As a mole ratio of 1:1 was approached the evolution of gas was not evident, but as more aluminum borohydride was added there did appear to be more bubbling out ofthe amine scrubber. After all of the aluminum borohydride had been added, the reaction was allowed to proceed overnight at ambient temperatures. The product was .then collected in a filter flask under a. dry nitrogen atmosphere and the benzene and excess aluminum borohydride were collected in two traps, maintained at liquid nitrogen temperature, by vacuum stripping (5 mm. of mercury) at about C.

Forty-one grams of a very clear, liquid product was collected. The elemental analyses were:

Calculated C, 18.5%; H,14.0%. Found: C, 20.4%; H, 15.7%.

Example 16 Using the same procedure, and equipment asin Example 15, 28.6 grams (0.40 mole) of aluminum borohydride c Theoretical elemental composition of 1,1,4,4-tetramethyl-2- tetrazene dialuminum borohydride.

was added over a period of one hour to 23.2 grams (0.20 mole) of N,N,N,N'-tetramethyl-1,2-ethanediamine. A precipitate formed at first and then gradually disappeared as more aluminum borohydride was added. This observation indicates that the dialuminum borohydride adduct.

is more soluble in benzene than the mono adduct.

After the reaction was allowed to proceed at room temperature for several hours to insure completion, the benzene and any unreacted aluminum borohydride were vacuum stripped as described in, Example 15. The product was a, white solid whose elemental analyses were:

Calculated H, 15.5%; A1, 20.8%; B, 25.1%. Found: H, 15.0%; A1, 19.7%; B, 22.2%.

Example 17 The procedure used in this preparation was the same as that used in Example 12, except the reaction mixture was cooled to 20 C. by means of a glycol-water mixture.

The reaction flask was charged with 50.6 grams (0.683 mole) of N,N-dimethylmethylenediamine, and 97.8 grams (1.36 moles) of aluminum borohydride was very slowly added. When the first portions of aluminum borohydride were added, the reaction was very vigorous causing excess fuming. After about 20 grams of aluminum borohydride was added some of the solids which had formed began to turn liquid. The borohydride could be added faster from this point on, but caution still had to be exerted to prevent excessive fuming. The reactants were allowed to warm to room temperature and mix overnight after all the borohydride had been added.

The product, 136 grams, was collected in a filter flask and vacuum stripped at mm. of mercury in order to distill off any excess aluminum borohydride present. The elemental analyses of the product were:

Calculated Tl, 24.9%; H, 15.8%;. Found: Al, 25.9%; H, 13.6%.

Example 18 In the manner described in Example 14 supra, aluminum borohydride, 4.43 mmoles, was added in increments to 4.30 mmoles of tetramethylguanidine (TMG) in 5.0 ml. of iso-octane and equilibria pressures recorded. The data are summarized in Table III infra.

Theoretical elemental composition of N,-N,N, N' tetra methyl-1,2-ethanediamiue dialuminum borohydride.

0 Theoretical elemental composition of N,:N'-di1nethylmethylenediamine dialumiuum borohydride.

TABLE III.PRESSURE-COMPOSITION DATA FOR THE REACTION OF ALUMINUM BOROHYDRIDE WITH TETRAMETHYLGUANIDINE IN ISO-OCTANE AT 26 C.

From a previously determined pressure-composition analysis), collected and measured in a Toepler pump sysplot of aluminum borohydride, it was determined that 2.2 mmoles of aluminum borohydride was unreacted.

Consequently, 2.2 mmoles of the borohydride reacted occurred only after the first addition of aluminum borotem. The reaction vessel was then warmed again to room temperature -25 C. and the pressure recorded. The reaction vessel was then frozen again with liquid nitrogen,

' i a portion of the amine added, and the entire procedure repeated. The experiment is summarized in the following table.

REACTION OF UNSYMMETRICAL DIMETHYLHYDRAZINE WITH ALUMINUM BOROHYDRIDE hydride and can be attributed to a reaction with traces of moisture that were probably present.

Example 19 Using the same procedure and equipment as in Example 15, 14.3 grams (0.20 mole) of aluminum borohydride was added over a period of one hour to 23.2 grams (0.20 mole) of N,N,N',N-tetramethy1-1,2-ethanediamine.

The reaction was allowed to proceed at ambient conditions for several hours, after which the benzene was vacuum stripped as described in Example 15. A white solid product was obtained in a quantitative yield. The elemental analyses were:

calculated H, 15.0%; A1, 14.7%; N, Found: H, 15.0%; A1, 14.3%; N, 14.9%.

The infrared spectrum of this compound was made and compared to that of N,N,N',N'-tetramethyl-l,2-ethanediamine dialuminum borohydride.

Example 20 A ml. reaction flask equipped with a magnetic Teflon stirring bar was attached to the high vacuum systern with a standard taper joint. The rea'ctionflask was flamed out in order to remove the last traces of moisture.

Aluminum borohydride, 1.12 mmoles, was transferred into the reaction system. Unsymmetrical dimethylhydrazine, 1.12 mmoles, was then measured in the standard bulb and subsequently added in small portions to the reaction fiask, frozen with liquid nitrogen, containing the borohydride. After each addition, the liquid nitrogen bath was removed, the reaction flask gradually warmed to room temperature, and the reaction allowed to proceed until the pressure, as read on a manometer attached to the reaction system, remained constant. The reaction flask was then cooled with liquid nitrogen and the non-condensable gas, hydrogen (identity established by mass spectrographic Theoretical elemental composition of N,!N,'N,-N'-tetramethyl-1,2-ethanediamine m'onoaluminum borohydride.

A very small amount of vapor, 0.073 mmole, which was either excess aluminum borohydride or UDMH or both was removed causing the pressure above the produ ct(s) to be 3 mm. Thus, a summary of the data shows that UDMH will react with aluminum borohydride in a mole ratio of 1:1 to give off 2 moles of hydrogen. The products were mostly a colorless, oily liquid and a white solid. A drop of anhydrous hydrazine added to the product(s) under a dry nitrogen atmosphere resulted in vigorous bubbling and the evolution of white fumes.

Example 21 Sixteen grams of dry aluminum chloride were added to a 3-necked reaction flask, which was fitted with a microhead, stirrer, Vigreaux column, nitrogen bubbler with an outlet to several Dry Ice-acetone cold traps. The entire system was connected to a vacuum pump and manometer for reduced pressure distillation. Fifty ml. of dry benzene was fed to the reaction flask with agitation and nitrogen was admitted to the system at a slow bubble rate. N,N,N',N tetramethylmethylenediamine (4D1), 6.1 grams in .20 ml. of dry benzene, was fed dropwise to the reaction vessel which was maintained at approximately 20 C. by an ice water bath. The reaction was complete as noted by the disappearance of the solid aluminum chloride after all of the 4D1 amine had been fed to the reaction flask. A slurry of 9.4 grams of percent) lithium borohydride in benzene was prepared by homogenizing the borohydride in 75 ml. of dry benzene under a nitrogen blanket. This slurry was then fed dropwise to the reaction mixture over a period of 1 hour while maintaining a reaction temperature of from 10l5 C. by means of a cold water bath. The reaction mixture was then allowed to warm to ambient conditions over a period of 2 hours and then heated to 50 C. for a period of 2 hours. The reaction mixture then cooled to 20 C. and the salts were filtered free of the liquid product by means of a sintered glass filter stick in a dry nitrogen atmosphere.

23 The filtrate was placed back in the reaction vessel and the benzene solvent was stripped free of the product by a reduced pressuredistillation at'70 mm. Hg pressure and a kettle temperature of 14C. The vacuum stripping was discontinued. when the kettle temperature began to rise and reached 24 C. Eighteen grams of a clear liquid 118V". ing a density of 0.86 g./cc. at 20/20 were obtained as a the following composition:

Found: C, 31.1; H, 13.2; N, 99; Al, 18.8; B, 20.7; Cl,

8.9. Calculated C, 24.7; H, 15.6; N, 11.4; A1, 22.0; B, 26.5; C1, 0.0. Calculated C, 30.1; H, 13.0; N, 9.7; Al, 18.8; B, 19.9; C1, 8.6.

The elemental composition for the product closely approximates. the composition of the materialestimated. by infrared evaluationv which indicates that the desired 4D1- dialuminum b'orohydride can be synthesized in this manner.

Examples 22-32 In the following examples, the theoretical performance of various novel liquid adducts oxidized with nitrogen tetroxide is calculated. The specific impulse values (pound-second/pound) of these novel liquid propellant systems are compared with three standard liquid propellant systems (also oxidized with nitrogen tetroxide). The

data are set forth in Table IV infra.

Based on 100 percent N,N N', N'-tetramethylmethylenediamine-dialuminum borohydrlde.

Based on composition of 75 percent .N, N,-N,:N'-tetramethylmethylenediamine-dlaluminum borohydride, 15 percent N,-N,'N,N'-tetrarnethylmethylenedlamlne-dialuminum chloride, and 10 percent benzene.

TABLE IV Example, Alli", Specific Number Fuel Kcalf Impulse Mole (In) 2 22 Hydrazine +12. 05 291 23 Unsymmetrical dimcthylhyd +1272 285 (UDMH). 24 wt. percent Hydrazine plus 50 wt. 5 +29. 38 288 percent UDMHA 25 N,N,N,N'-tetramethylmethylene- +19. 3 313 diarnine dialuminum borchydride. 26 N,N,N,N-tetramethyl-1,2-ethane +13. 4 310 diarnine dialuminum borohydride. 27 N,N,N,N-tetramethyl-l,3-prc- +7.6 307 panediamiue dialuminum borohydride. 28 N,N,N,Ntetramethyl-l,2-pr0- +7.6 308 panediaminedialuminum borohydride. 29 N,N,N,N'-tetramethyl-1,4-butane- +7. 2 305 diamine dialuminum borohydride. 30 N,N, ,N-tetran1ethy1-l,3 butane- +7. 2 305 diarninc dialuminum borohy- I dride. 31 1,1,4,4-tetramethyl-2-tetrazene di- +90. 4 317 aluminum borohydride. 32 N,N,N,N-pentamethyldiethyl- +27. 2 310 enetriaminc trialuminum borohydride.

1 Heat of formation.

Maximum theoretical performance with N 0 at 1,000 psi. expanded to 14.7 p.s.i., shifting equilibrium.

3 Standard liquid fuel for comparison.

4 Standard liquid fuel for comparison. Said liquid propellant system has been designated for theTitan ICBM.

4 Kcal./ grams.

Examples 3340 In the following examples, the theoretical performance of various novel solid adducts oxidized with ammonium perchlorate is calculated. The specific impulsevalues (pound second/pound) of these novel solid propellant systems are compared with a standard solid'propellant system (also oxidized with ammonium perchlorate). The theoretical performance calculations are based on the solid fuel plus oxidizer only (i.e., binder excluded). The data are set forthin Table V infra.

1 Weight per cent of fuel, based on total Weight of fuel plus ammonium perchlorate.

2 Heat of formation.

3 Maximum theoretical performance with NH ClO4 at 1,000 p.s.1. expanded to 14.7 psi. shifting equilibrium.

4 Standard solid fuel for comparison.

reaction flask equipped with a standard taper joint and a Teflon coated magnetic stirring bar. The reaction flask ard taper joint on a Teflon coated magnetic stiring bar. The reaction flask was then attached to a high vacuum system, cooled with a liquid nitrogen bath, and evacuated to at least 10 mm. of mercury. Aluminum borohydride, 10.45

was then attached to a high vacuum system, cooled with 5 mmoles, was measured in a standard bulb and subsequent a liquid nitrogen bath, and evacuated to at least mm. of mercury. Methylamine, 1.11 mmoles, measured as a gas, was then transferred into the reaction flask. Aluminum boro'hydride was added, in increments, to the ly added in increments to the triethylamine. After each addition the liquid nitrogen bath was removed and the reaction flask allowed to warm to room temperature while stirring was initiated. The pressure changes were observed methylamine-benzene solution. After each addition, the 10 with a mercury manometer attached to the system. When liquid nitrogen bath was removed, the reaction flask was pressure changes were no longer observed, the reactions allowed to slowly Warm to room temperature and stirring flask was cooled with liquid nitrogen and any non-conwas initiated. The pressure changes were observed with densable gas collected in a Toepler pump. The reaction a mercury manometer attached to the system. When presflask was then warmed to room temperature and the pressure changes were no longer observed, the reaction flask sure recorded. The results are summarized in Table VII was cooled with liquid nitrogen and any non-condensable infra.

TABLE VII A1(BH4)3 Mole Ratio, Total H7 Evolved,

Added, Al(BH4)a/ Pressure, Cumulative Remarks Cumulative mm mm. of Hg mmoles mmoles 3. 86 0. 156 88 Trace 5. 65 0. 756 5 Trace 8. 11 1. 09 15 Product liquid. 10. 1. 40 95 gas collected in a Toepler pump. The reaction flask was then warmed to room temperature and the pressure recorded. The results are summarized in Table VI infra.

It is readily apparent from the above data that the pressure in the reaction flask decreased until the mole ratio of aluminum borohydride to triethylamine exceeded one.

TABLE VL-PRESSURE-OOMPOSITION DATA FOR THE REACTION OF ALUMINUM BORO- HYDRIDE WITH METHYLAMINE IN BENZENE AT AMBIENT TEMPERATURES The above data indicate that at least one mole of aluminum borohydride reacted per mole of methylamine evidenced by the data showing that at mol ratios of 1:1 of reactants no aluminum borohydride was recovered, and a noticeable pressure increase was observed above this ratio. The hydrogen which was evolved during the reaction was probably due to traces of impurities such as water in the solvent or the amine. The 'vapor pressure of the white solid methylamine aluminum borohydride adduct was 3.0 mm. of Hg at 25.2 C.

Example 42 Triethylamine, 0.755 gram, 7.46 mmoles, was transferred by means of a hypodermic needle under a dry nitro- Beyond this ratio, the pressure increased rapidly. The aluminum borohydride in excess of a mole ratio of 1:1 (3.08 mmoles) was easily distilled from the reaction flask. Thus, 7.3-7 mmoles of aluminum borohydride reacted with 7.45 mmoles of triethylamine to give a clear liquid which had a vapor pressure of about 2 mm. of Hg at 24 C. Hydrolysis with water at room temperature released the theoretical quantity of hydrogen. The infrared spectrum showed strong absorption between 4-5 indicating the presence of AlBH linkages.

Example 43 Using the same procedure as in Example 42, 4.29

"mmoles of piperidine was reacted with aluminum borogen atmosphere into a reaction flask equipped with a standhydride. The data are summarized in Table V'IH in-fra.

TABLE VIIL-PRESSURE-COMPOSITION DATA FOR THE REACTION OF ALUMINUM BORO- HYD RIDE WITH PIPERIDINE AT AMBIENT TEMPERATURES AKBHm Mole Total H2 Added, Ratio, Pressure, Evolved, Remarks Cumulative A1 BH4 3I mm. of Hg Cumulative mmoles (OHmN mmoles 1. 73 0. 439 17. 5 1. 28 Product composed mostly of white solids. 3. 56 0. 829 7. 1. 28 Product turning liquid. 4. 33 1. 01 12 1. 28 Product clear liquid with small amount of white solids present.

The above data indicate that aluminum borohydride and piperidine react in a mole ratio of 1:1 because pressure decreases were recorded until this ratio was reached. Upon exceeding a 1:1 ratio, pressure increases occurred. This evolution of hydrogen occurred only during the first portion of the reaction and can be attributed to small quantities of impurities. The result and product of the reaction was a clear liquid identified by infrared as piperidine monoaluminum borohydride.

Example 44 Trimethylamine, 21.2 mmoles, and aluminum borohydride, 21.2 mmoles were condensed with liquid nitrogen into a reaction flask attached to a high vacuum system. The liquid nitrogen bath was replaced with a 80 C. bath and the reactants held at that temperature for two hours. The flask was then warmed to room temperature and stirred for 15 hours. The product was a mixture of a clear liquid and white solids. Hydrolysis of this mixture released only 74.3 percent of the theoretical hydrogen as compared to 100 percent active hydrogen released by the triethylamine aluminum borohydride adduct of Example 42. The results of this experiment indicate-two predominant products are formed in the reaction of aluminum borohydride with trimethylamine which is in contrast to the single products formed with other mononitrogen containing organic ligands, e.g., Examples 41, 42, and 43.

Example 45 A mixture of 34.4 grams of n-butylamine contained in 150 ml. of dry benzene and 23.8 grams of aluminum borohydride contained in 150 ml. of benzene were reacted in the manner described in Example 12 supra. The aluminum borohydride-benzene admixture was added slowly to the n-butylamine-benzene admixture over a period of three hours, the resulting solution being maintained at' about 5 C. The resulting solution then was allowed to react for hours at room temperature, after which period of time the resulting reaction product mixture was stripped of benzene under 5 mm. of Hg at room temperature. The resulting product, i.e., n-butylamine monoaluminum borohydride adduct was a clear liquid having a trace amount of white solids.

Elemental analysis (C H NAlB Calculated, percent: H, 16.0; N, 9.7; A1, 18.7; B, 22.5. Found, percent: H, 15.2; N, 10.3; A1, 19.3; B, 24.3.

Example 46 A mixture of 18.6 grams (0.20 mole) of aniline contained in 100 ml. of dry benzene and 14.3 grams (0.20) of aluminum borohydride contained in 150 ml. of benzene were reacted in the manner described in Example 12 supra. The aluminum borohydride-benzene admixture was added slowly to the aniline-benzene admixture over a period of three hours, the resulting solution being maintained at about 4 C. The resulting solution then was allowed to react for 15 hours at room temperature, after which period of time the resulting reaction product mixture was stripped of benzene under 5 mm. of Hg at room temperature, i.e., 25 C. The resulting product, i.e., aniline monoaluminum borohydride adduct was a white solid. Example 47 Ethylenediamine, 0.458 gram, 7.63 mmoles, was transferred by means of a hypodermic needle under a dry nitrogen atmosphere into a reaction flask containing five milliliters of dry benzene and a Teflon-coated magnetic stirring bar. The reaction flask was then attached to a high vacuum system, cooled with a liquid nitrogen bath, and evacuated to atleast 10- mm. of mercury. Aluminum borohydride, 15.4 mmoles, was measured in a standard bulb and added in increments to the ethylenediamine. After each addition, the liquid nitrogen bath was removed and the reaction flask allowed to warm to room temperature. The first addition of aluminum borohydride resulted in the evolution of a small quantity of hydrogen which probably came from traces of moisture in the solvent. No more hydrogen was released upon further addition of aluminum borohydride.

The easily volatile materials were distilled at room temperature from the reaction flask after the reactants were mixed together for about 15 hours. The resultant white, solid, relatively nonvolatile product released 91.7 percent of the theoretical hydrogen upon hydrolysis with water at room temperature based on the formation of ethylenediamine dialuminum borohydride. The infrared spectrum showed strong absorption between 4-5,u indicating the presence of boron-hydrogen linkages. Analyses gave 26.0 percent by weight Al and can be compared to the theoretical percentageof 26.6 percent Al by weight.

I Example 48 Beryllium borohydride, 0.198 gram, 5.13 mmoles, was transferred under 10 mm. of Hg from a weighing bottle into a reaction flask containing a Teflon-coated magnetic stirring, bar. N,N,N,N tetramethylmethylenediamine, 2.56 millimoles, measured as a gas, was added in increments to the beryllium borohydride which was cooled with liquid nitrogen. After each addition, the liquid nitrogen bath was removed and the reactants slowly warmed to room temperature. When all the diamine was added, the reactants were stirred for about 15 hours. The resultant product was a colorless, nonvolatile liquid, determined to be N,N,N',N-tetramethylmethylenediamine diberyllium borohydride.

The infrared spectrum of the liquid adduct, FIGURE 3, showed strong absorption between 2,4002,500 CH1."1, indicative of terminal BH There also was strong absorption at 2,180 cm. and 1,470 cmf evidence for the presence of BH Be bridge. From these infrared spectra, it can be postulated that the adduct possibly has the following structure:

Price, C., J. Chem. PhyS., 17, 1044 (1949).

29 30 Example 49 TABLE X Zirconium borohydride, 0.2481 gram (1.6471 mmoles) 4 was condensed at liquid nitrogen temperatures into a re- Density of Density 4 I F 1, 2 0. I ul action flask, under high vacuum. N,N,N',N -tetramethyl- Fue He fif ff methylenediamine (0.7959 millimole) was added, in incre- 5 merits, as a gas. Interaction of these two reactants resulted Hydrazine 1. 008 357 in the immediate formation of a reddish brown liquid resi- N N."N"F9tmmethylmtthylenediamine d b h dr d 2.78-3.50 700-850 due. The reddish brown color is believed to be due prlumcomum om y 1 e manly to unpurmes. from stopcock. grease carned Into the 1 Theoretical maximum density impulse (lend), sec.-g./cc. oxidized reactant system during reagent addition. 10 with N204 at1,000 p.s.i. expanded to 14.7 p.s.i., shifting equilibrium. The reaction product was -a liquid which had a freez- Examples 57 60 ing point between 0 C. and 10 C. It had a vapor pressure of 10 mm. of Hg at C. An infrared spectra The theoretical performance of three novel solid adwas run o the addu t, FIGURE 4, d was almost id ducts oxidized with nitronium perchlorate has been caltical to those adducts prepared with beryllium and alu- 15 culated- SPBCIfiC I P e Values (pound-second/ minum borohydride except for very slight shifts in Wave- P P thls llovel Sohd P 9P Systems are lengths in th 3-H absorption i 4 5,i pared with aluminum as a solid propellant system (also The product thus was identified as N,N,N,N'-tetra- OXidiZcd with nitronium perchlorate). The theoretical methylmethylene-diamine dizirconium borohydride. performance calculations are based on the solid fuel opti- E l 50 56 2o rnized to oxidizer concentration plus a 15.0 weight percent xamp es of a standard hydrocarbon binder. The data are set forth In the following examples, the theoretical performance in the following Table XI infra.

TABLE XI Ex. HP, Conc. Fuel, Specific No. Fuel Kcal./ percent by Impulse,

mole 1 wt. 2 I 3 57 Aluminum 0.0 20.0 272 58 Methylamine aluminum borohydride +4. 8 21. 0 298 59 Ethylenediamine dialuminumborohydride 27.9 18.6 291 60 Aniline aluminum borohydride 35. 6 22. 5 285 1 Heat of formation of fuel.

2 Concentration fuel, percent by weight, maximized with oxidizer.

3 Maximum theoretical performance with N 0 at 1,000 p.s.i. expanded to 14.7 p.s.i., shifting equilibrium, In: (pound/second-pound).

4 Standard liquid fuel for comparison.

of various novel liquid adducts oxidized with nitrogen tetroxide has been calculated. The specific impulse values (pound-second/ pound) of these novel propellant systems is compared with hydrazine (also oxidized with nitrogen tetroxide). The data are set forth in the following Table 2 Maximum thetretical performance with N204 at 1,000 p.s.i. expanded to 14.7 p.s.i., shifting equilibrium, In. (pound/second-pound).

3 Standard liquid fuel for comparison.

A major utility of fuel candidate, tetramethylrnethylenediamine dizirconium borohydride, consists primarily of its probable superior density compared to other highenergy fuels. To exemplify this we have listed below in Table X an extrapolated density of the fuel and its estimated density impulse as compared to hydrazine.

What is claimed is:

1. An adduct of a metal borohydride of the group consisting of aluminum borohydride, beryllium borohydride, and zirconium borohydride, with an organic polynitrogen compound which is composed solely of carbon, hydrogen, and nitrogen atoms, said organic polynitrogen compound containing at least one nitrogen atom which functions as a Lewis base, said adduct possessing at least one coordinate bond between a nitrogen atom of said compound and the metal moiety of said metal borohydride.

2. The adduct of claim 1 wherein said metal borohydride-is aluminum borohydride.

3. The adduct of claim 1 wherein said metal borohydride is beryllium borohydride.

4. The adduct of claim 1 wherein said metal borohydride is zirconium borohydride. 5. An adduct of aluminum borohydride with an organic polynitrogen compound, said organic polynitrogen compound being composed solely of carbon, hydrogen, and nitrogen atoms in which at least one of said nitrogen atoms is an amino nitrogen atom, said adduct possessing at least one coordinate bond between a nitrogen atom of said compound and the aluminum moiety of said aluminum borohydride.

6. An adduct of aluminum borohydride with an organic vpolyniti'ogen compound, said organic polynitrogen compound being composed solely of carbon, hydrogen, and amino nitrogen atoms, said adduct possessing at least one coordinate bond between a nitrogen atom of said compound and the aluminum moiety of said aluminum borohydride.

7. An adduct 01: aluminum borohydride with an organic polynitrogen compound, said organic polynitrogen compound being composed solely of carbon, hydrogen,

and amino nitrogen atoms, none of said amino nitrogen atoms being bondedto eachyother, said adduct possessing at least'one coordinate bond between a nitrogen atom of said compound and the aluminum moiety of said aluminum-borohydride.

8. An adduct of EIlIJIIllIlU-Hl'bOTOhYdl'ldfi. with an orpound being composed solely of carbon, hydrogen, and

secondary amino nitrogen atoms, said adduct possessing at least one coordinate bond between a nitrogen atom of said compound and the aluminum moiety of said aluminum borohydride.

10. An adduct of aluminum b'orohydride with an or- 32 hydrotriazine, said adduct possessing at least one coordinate bond between a nitrogen atom of said hexahydrotri-azine and the aluminum moiety of said aluminum borohydride.

21. An aluminum borohydride adduct of N,N ,N',N'-

tetramethylmethylenediamine, said adduct possessing at least one coordinate bond between a nitrogen atom of said diamine and the aluminum moiety of said aluminum borohydride.

22.'An aluminum borohydride adduct of N,N,N,N

tetramethyl-l,2,-diaminoethane, said adduct-possessing at least one coordinatebond between anitrogen atom of said diaminoethane and the aluminum'moiety of said aluminum borohydride.

23. An aluminum borohydride adduct of 1,l,4,4-tetramethyl-Z-tetrazene, said, adduct possessing at least one coordinate bond between a nitrogen atom ofsaidtetrazene and the aluminum moiety of said aluminum borohydride. 24. An aluminum bor-ohydrideadduct of N,N,N',N,

N"-pentamethyldiethylenetriarnine, said adduct possessing at least one coordinate bond between a nitrogen atom of said t-riamine and'the aluminum moiety of said aluminum ganic'polynitrogen compound, said organic polynitrogen compound being composed solely of carbon, hydrogen, and tertiary amino nitrogen atoms, said adduct possessing at least one coordinate bond between'a nitrogen atom of said compound and the aluminum moiety of said aluminum borohydride:

11. An adduct having the formula L l: 4)x]n wherein L is an organic nitrogen .compoundcomposed solely of carbon, hydrogen, and nitrogen atoms in which at least one of said nitrogen atoms functions asa Lewis base, said organic nitrogen. compound containing. at least one nitrogen atom coordinately bonded to M; wherein M is or the group consisting of aluminum, beryllium, and

zirconium; wherein x is the valence of M; and wherein n is an integer having a minimum value ofoneand, a

maximum value equal to the number of nitrogen atoms contained in L which function as Lewis bases; with the proviso that said organic nitrogen compound is not a member of the group consisting of dihydrocarbylamines and trihydrocarbylamines.

12. The adduct of claim llwherein M is aluminum. 13. The adduct of claim 11 wherein M is beryllium. 14. The adduct of claim 11 wherein M is zirconium. 15. An adduct having the formula L [A o 03111 wherein L is an organic polynit'rogen compound composed solely of carbon, hydrogen, and nitrogen atoms, at least one of said nitrogen atoms being coordinately bonded to aluminum, and wherein n is an integer having a value greater than zero and less than 5.

16. An adduct of aluminum borohydride with N,N,N, Ntetra-alkyLZ-tetrazene, said adduct possessing at least one coordinate bond between a nitrogen atom of said tetrazene and the aluminum moiety of said aluminum borohydride.

17. An adduct of aluminum borohydrid'e with a diaminoalkane, said adduct possessing at least one coordinate bond between a nitrogen atom of said diaminoalkane and the aluminum moiety of said aluminum borohydride.

18. An adduct of aluminum borohydride with a polyalkylene polyamine, said adduct possessing at least one coordinate bond between a nitrogen atom of said polyamine and thealuminum moiety of said aluminum borohydride.

' 19. An adduct of aluminum borohydride with a hydrogenated triazine, said adduct possessing at least one coordinate bond between a nitrogen atom of said triazine and the aluminum moiety of said aluminum borohydride.

20. An adduct of aluminum borohydride with a hexaborohydride.

ylmethylenedia'mine, said adduct possessing at least one coordinate bond between a nitrogen atom of said diamine. and the aluminum moiety of said aluminum borohydride.

26. An aluminum. borohydride adduct of N,N,N-triaminohexahydrotriazine, said adduct, possessing. at least one coordinate bond between anitrogen atom of said triazine and the aluminum moiety of said aluminum borohydride.

27. An aluminum borohydride adduct of ethylenediamine, said adduct. possessing .at least one coordinate bond "between a nitrogen atom of said ethylenediam-ine and the aluminum moiety of said aluminum borohydride.

28. An adduct of beryllium borohydride with a diaminoalkane, said adduct possessing at least one. coordinatebond between a nitrogen atom of said diaminoalkane and the beryllium-moiety of said beryllium borohydride.

29. An adduct of beryllium borohydride with a hydrogenated triazine, said adduct possessing at least one coordinate bond between a nitrogen atom of said triazine and the beryllium moiety of said beryllium borohydride.

30. A beryllium borohydride adduct of N,N,N',N'- tetramethylmethylenediamine, said adduct possessing at least one coordinate bond between a nitrogen atom of said diamine and the beryllium'moiety of said beryllium borohydride.

31. A Zirconium borohydride adduct of trimethylamine, said adduct possessing at least one coordinate bond between a nitrogen-atom of said trimethylamine and the zirconium moiety of said zirconium borohydride.

32. A process which comprises reacting a metal borohydride of the group consisting of aluminum borohydride, beryllium borohydride, and zirconium borohydride; with the organic nitrogen compound defined in claim 12; under an inert, anhydrous atmosphere, and recovering a metal borohydride adduct of said organic nitrogen compound, as the resulting product, from the reaction medium.

33. The process of claim 32 wherein the reaction is effected at a temperature in the range of from about 64 C. to about +43 C.

34. The process of claim 33 wherein said metal borohydride is aluminum borohydride.

35. The process of claim 34'wherein the maximum concentration of said aluminum borohydride is in slight excess of the quantity that is necessary to react with said organic nitrogen compound, and wherein theresulting product is a liquid adduct of aluminum borohydride and organic nitrogen compound.

36. The process of claim 35 wherein said aluminum borohydride is added, in increments, to said organic nitrogen compound.

37. The process of claim 34 wherein the maximum concentration of said organic nitrogen compound is in slight excess of the quantity that is necessary to react with said aluminum borohydride, and wherein the resulting product is a solid adduct of aluminum borohydride and said organic nitrogen compound.

38. The process of claim 37 wherein said aluminum 'borohydride is added, in increments, to said organic nitrogen compound.

39. The process of claim 34 wherein essentially stoichiometric amounts of aluminum borohydride and organic nitrogen compound are employed.

40. A process which comprises reacting aluminum trihalide with an organic nitrogen compound which is cornposed solely of carbon, hydrogen, and nitrogen atoms, said organic nitrogen compound containing at least one nitrogen atom which functions as a Lewis base, for a period of time suflicient to produce an adduct of aluminum trihalide and said organic nitrogen compound; subsequently reacting said adduct with an excess of alkali metal borohydride to produce an adduct of aluminum borohydride and said organic nitrogen compound, and

recovering said adduct from the resulting reaction product mixture.

41. The process of claim 40 wherein said aluminum I trihalide is aluminum trichloride.

References Cited UNITED STATES PATENTS BENJAMIN R. PADGETT, Primary Examiner.

LEON D. ROSDOL, CARL D. QUARFORTH,

Exdminers.

20 J. W. WHISLER, L. A. SEBASTIAN,

Assistant Examiners.

Claims (1)

1. AN ADDUCT OF A METAL BOROHYDRIDE OF THE GROUP CONSISTING OF ALUMINUM BOROHYDIDE, BERYLIUM BOROHYDRIDE, AND ZIRCONIUM BOROHYDRIDE, WITH AN ORGANIC POLYNITROGEN COMPOUND WHICH IS COMPOSED SOLELY OF CARBON, HYDROGEN, AND NITROGEN ATOMS, SAID ORGANIC POLYNTIROGEN COMPOUND CONTAINING AT LEAST ONE NITROGEN ATOM WHICH FUNCTIONS AS A LEWIS BASE, SAID ADDUCT POSSESSING AT LEAST ONE COORDINATE BOND BETWEEN A NITROGEN ATOM OF SAID COMPOUND AND THE METAL MOIETY OF SAID METAL BOROHYDRIDE.

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