US2968540A - Liquid boron containing products - Google Patents

Description

United States Patent LIQUID BORON CONTAINING PRODUCTS George F. Huff, Fox Chapel, and James D. Kliclrer, Mars, Pa., assignors to Gallery Chemical Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 24, 1957, Ser. No. 692,030

'4 Claims. (Cl. 52-.5)

This invention relates to the preparation of liquid products containing the elements boron (B), carbon (C), and hydrogen (H) where at least part of the hydrogen is active hydrogen and in particular it concerns the production of such products 'by reactions of tetraborane (B H and unstable pentaborane (B H with a lower alkyl diborane.

It is an object of the present invention to provide a process for the preparation of liquid products from the unstable boron hydrides, tetraborane and pentaborane-ll, and a lower alkyl diborane.

It is another object of the invention to provide a process according to the foregoing object that is simple and that may be readily practiced with known techniques.

We have discovered, and it is on this discovery that the invention is in large part predicated, that the unstable boron hydrides tetraborane and pentaborane-ll will react readily with a lower alkyl diborane to produce a liquid reaction product. The product obtained is characterized by stability and a higher boron content than the alkyl diborane reactant. Consequently, it is apparent that our invention provides a convenient method of converting the inherently unstable boron hydrides, tetraborane and pentaborane-ll, to a stable form that, as will appear hereinafter, is of significant utility.

The alkyldiboranes that are contemplated for use in this invention have the general formula B H ,,R where x is a number from 1 to 4 and R is a lower alkyl radical. Typical members of these alkyl diboranes include ethyl diborane, diethyl diborane, triethyl diborane, tetraethyl diborane, mono-, di-, tri-, and tetra-propyl diboranes, mono-, di-, tri-, and tetrabutyl diboranes, and so on. Mixtures of lower alkyl diboranes also can be used in our invention and constitute the preferred material for economic reasons. A particularly satisfactory mixture of alkyldiboranes that can be used is the liquid reaction product disclosed in the co-pending application of Schechter et al., Serial No. 402,805, filed January 7, 1954. That product consists essentially of mixtures of lower alkyl substituted diboranes, the alkyl radical depending primarily, of course, on the hydrocarbon used. Such liquids contain from about 70 to 98 weight percent of lower alkyldiboranes with the remainder being essentially alkylated higher boranes. The impure mixture can be used as such for we have found that the other materials present do not interfere with obtaining our desired objects. Typical liquid products produced by the Schechter et a1. process have consisted essentially of tetraethyldiboranes, whereas others have included mono-, diand triethyl-dib oranes. As noted in the Schechter et al. application, those alkyldiboranes result upon reacting diborane and an unsaturated aliphatic hydrocarbon containing up to about 6 carbon atoms such, for example, as acetylene, ethylene, propylene, butylene, butadiene, or mixtures of such hydrocarbons, using a molar ratio of hydrocarbon to diborane not exceeding about 6 to 1, and suitably on the order of 1 to 1 or 2 to 1. Where more than 6 moles of the hydrocarbon per mole of diboraue Patented Jan. 17, 1961 ICC are used, the product is an alkyl. boron, e.g., boron trialkyl, rather than a diborane derivative. That reaction can be carried out at temperatures up to about 150 C. while using atmospheric or superatmospheric pressure. The liquid reaction product as such, or a particular fraction containing an alkyldiborane and obtained, for example, by fractionation of the crude product may be used in the practice of this invention. While the mixtures of lower alkyldiboranes that are obtained in accordance with the Schechter et al. process are preferred, if desired other mixtures containing particular alkyldiboranes in any desired predetermined proportions can be prepared, as by mixing the single members, and be used in practicing our invention without departing from its scope.

Our invention is carried out by reacting tetraborane, unstable pentaborane, or mixtures of tetraborane and unstable pentaborane with at least one lower alkyl diborane. Suitably up to about 35 percent by weight, based on the weight of the alkyldiborane, of the boron hydride is used. The reaction can be carried out at ambient conditions, under refrigeration to about -40 C., or at elevated temperatures, though very high temperatures should be avoided because they will accelerate decomposition of the boron hydride reactants thereby complicating the problem of retaining the hydride. Consequently, it is desirable, though not critical, that the temperature does not exceed about C. Reaction occurs at atmospheric pressure as well as under elevated pressure or sub-atmospheric pressure. Pressure does not have a material effect on the reaction and is utilized primarily to control the reactants. Generally, Where the higher temperatures are used, We prefer to keep the mixture under autogenous pressure to avoid loss of the hydride. Accordingly, the reactants can be mixed at room temperature and atmospheric pressure and allowed to stand until sufficient reaction has occurred. Or the mixture can be formed at room temperature and atmospheric pressure in an autoclave or other closed reaction vessel and heated to expedite reaction. Also the reactants can be mixed at low temperatures, i.e. liquid nitrogen temperature (196 C.), and atmospheric pressure and then be permitted to stand whereupon the mixture reacts while heating to ambient temperature. Where a vacuum is used, it is desirable to operate below room temperature, at least for mixing purposes, to minimize handling difficulties with respect to the boron hydride used. As will be apparent to the artisan, the time of reaction is not of significance, since some yield is obtained in any finite time. Reactions in accordance with our invention have been carried out in a few minutes and others have extended for days without detriment to the desired results.

The invention will be described further by means of the following examples. It is to be understood that the details disclosed are given by way of illustration and are not to be construed as limiting the invention.

Example I 5.3 grams of tetraborane were distilled into 8.5 grams of ethyldiboranes, containing mainly diethyl diborane, in an autoclave and the mixture was heated to 58 C. for 44 hours. The resulting product was then distilled and diborane, unreacted tetraborane, and unreacted ethyl diboranes were removed. The liquid product which remained in the still pot was analyzed and found to contain 54.4% boron by weight and contained 52% of the boron originally charged to the autoclave. An infra-red spectrum of this liquid was characteristic of ethyl substituted decaboranes. The refractive index of the liquid product was n =1.5364.

The liquid products obtained in accordance with our invention are particularly useful as fuels because they exhibit high heats of combustion. The heat of combustion of the product is substantially directly proportional to its boron content. Accordingly, where a product is obtained having a higher boron content than the starting material, it is apparent that the resulting product has the higher heat of combustion and an upgrading of the starting material for fuel purposes has occurred.

Considering the foregoing facts in conjunction with Example I above, it can be observed that the resulting liquid has a significantly higher percentage of boron (54.4%) than does the starting diethyldiborane (about 25 weight percent B). Therefore, the product is a far better fuel than the diethyldiborane. Furthermore, this product was obtained by use of the unstable boron hydride, tetraborane, and constitutes an efficient utilization of the material whereby it is converted to a stable form. It should be understood that the usefulness of the resulting products is not affected by their purity. Consequently, where the volatility or similar requirements of the contemplated use permit, the product need not be resolved to remove the unreacted components. 011 the other hand, if a particular fraction is needed the product can be resolved by distillation, fractional crystallization or other conventional process.

In like manner and under substantially the same conditions, the reaction of pentaborane-ll and diethyldiborane resulted in a liquid product having a higher boron content, and therefore a higher heat of combustion, than the alkyldiborane used.

As noted above, the invention can also be practiced with a crude mixture consisting essentially of lower alkyl diboranes. The following example illustrates that embodiment of the invention.

Example II A liquid product that had been prepared by reacting acetylene and ethylene with diborane by circulating gas streams of each of the foregoing through a packed column heated to a temperature of of about 80 C. was used in this run. The hydrocarbons each were circulated at a rate of 25 mol per minute. The reaction extended for 8.2 hours. The resulting liquid reaction product was known, from routine analysis and previous experience, to consist Of C2H5B2H5, (C2H5)2B2H4, (C H B H and (C H B H It had a boron content of 26.7 mgm. a./g., expressed in milligramatoms per gram, boron, and 41.3 mgm. a./g. active hydrogen (hydrogen releasable by hydrolysis of the composition). Tetraborane, in an amount of 3.9 percent by weight and at a temperature of l96 C., was mixed with a sample of the liquid alkyldiboranes in a closed vessel and the resulting mixture was allowed to warm to room temperature. Then a sample of the mixture was analyzed and its boron content was found to have increased to 34.1 mgm. a./ g. and the active hydrogen increased to 57.0 mgm. a./ g. This product was stored for 72 hours at room temperature without any indication of decomposition.

Since it is known that tetraborane would be substantially decomposed in 72 hours at room temperature, it is evident that the tetraborane reacted in the foregoing example and was tied-up or converted to a stable form. Analysis of the product disclosed that ethyldecaborane formed, that being additional proof that reaction occurred.

As noted hereinbefore, an increase in boron content of such a liquid product is a direct measure of the improvement in the fuel value (heat of combustion) of the resulting product. The primary interest in this development is the production of these materials for fuel uses. Accordingly, a large number of experiments of a qualitative nature were conducted in order to obtain evidence of the best manner of preparing improved fuels as evidenced by obtaining products with the highest possible boron content.

Hence, a run substantially like Example II was made using 8.0 percent of tetraborane rather than the 3.9 percent of Example II. This run resulted in an increase in boron content from 26.0 mgm. a./g. to 35.4 mgm. a./g. and an increase in active hydrogen from 39.5 mgm. a./g. to 55.5 mgm. a./g.

In still another experiment with this general procedure (mixing at 196 C. and allowing to heat to room temperature) but using 27.6 percent by weight of tetraborane, the boron content was increased from 25.7 mgm. a./g. to 47.3 mgm. a./g. while active hydrogen was increased from 37.3 mgm. a./g. to 108.0 mgm. a./g. In these latter two tests .as with that of Example II, the products were stored for 72 hours at room temperature and found to be stable. Stability is, of course, direct evidence that reaction occurred. However, it also is of economic importance since it shows that the products can be stored for later use or transported from the point of production to a distant point of use satisfactorily.

The foregoing runs .show, along with Example II, that there is a relationship between the boron content of the final product and the quantity of boron hydride used as a reactant. In general we have found that the greater the relative quantity of hydride used, the greater will be the boron content of the resulting product.

The liquids resulting from our process have a variety of uses. As is readily apparent from the hydrogen that is released upon hydrolysis, for example dilute mineral acid hydrolysis, they constitute a convenient and portable source of hydrogen that does not require the unusual handling and storage conditions associated with gaseous hydrogen. The products also are particularly useful as fuels in view of their high heat of combustion. They can be mixed with a conventional oxidizer, such as air or oxygen, and be burned in a space heater or other means that utilizes fuels. However, they are of particular interest as a fuel in a bi-propellant system, primarily in turbo jet, ram jet and rocket engines. These fuels can be used alone or in mixtures with other fuels toward which they are chemically inert, e.g. most ordinary hyrocarbon fuels. They are considered to be exceptionally suited to these purposes in view of their high heat of combustion (20 to 50 percent greater than the best hydrocarbon fuels); they are spontaneously flammable at high temperature, have a low freezing point, a large liquidus range, and high density. In actual tests, a sample of the liquid product is introduced into the combustion section of a jet test engine, burned with compressed air, and the efficiency of the combustion and the output of the engine measured. When a sample of a product such as is obtained in Example I is burned in a test engine, it has a heat of combustion more than about 20 percent greater than the best hydrocarbon fuel. The combustion efficiency is equal to JP-4 (a standard jet fuel in use for several years past) and the thrust of engine per unit weight of fuel is substantially greater than the thrust obtained using the best hydrocarbon fuels. In comparative tests on the fuel produced by the above process and other boron-containing high energy fuels and other hydrocarbon fuels, it has been found that engine output is directly proportional to the heat of combustion per unit weight of fuel. Thus, an aircraft using a high energy boron-containing fuel can travel proportionately farther with the same load or can carry proportionately greater loads, than when burning conventional fuels.

This application is a continuation-in-part of our copending application Serial No. 429,115, filed May 11, 1954 and now abandoned.

In accordance with the provisions of the patent statutes we have explained the principle of our invention and have described what we now believe to represent its best embodiments. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. A method of increasing the boron content of a liquid consisting essentially of at least one lower alkyl diborane which comprises mixing and reaching a lower 5 6 alkyl diborane and a member selected from the group conselected from the group consisting of tetraborane, pentasisting of tetraborane, pentaborane-ll and mixtures borane-ll, and mixtures thereof, and recovering the rethereof, and recovering the resulting liquid reaction suiting liquid reaction product. product. 4. A method of: improving the heat combustion of a 2. A method of improving the heat of combustion of a 5 liquid consisting essentially of at least one lower alkyl liquid mixture consisting essentially of lower alkyl diborane which comprises mixing and reacting lower alkyl diholahes which comprises mixing and reacting Such diborane with up to about 35 weight percent of a member mixture with a member Selected from the group consist selected from the group consisting of tetraborane, pentaing of tetraborane, pentaborane-ll and mixtures thereof, borne. and mixtures th f at a temperature of up and recovering the resulting liquid Product 10 to about 100 C. and recoverin the resultin 1i uid 3. A method of improving the heat of combustion of a reach-on product. g g q liquid mixture consisting essentially of ethyldiboranes which comprises reacting such a mixture with a member No references cited.

ERNEST W. SWIDER UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No, 2,96i3,54 January 17, 1961 George F0 Huff et all,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4,, line 75 for "reaching" read reacting -==5 column 6, line 4, for "heat combustion" read we heat of combustion e Signed and sealed this 27th day of June 1961o (SEAL) Attest:

DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT oEFIcE (IERTIFICATION OF CORRECTION Patent Noe 2,96$,54O January 17, 1961 George F., Huff et ale It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below;

Column 4, line 75, for "reaching" read reacting column 6, line 4, for "heat combustion" read heat of combustion Signed and sealed this 27th day of June 19610 C SEA L) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents Patent No., 2,966,540 January 17, 1961 George F0 Huff et ale It is hereby ceroified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as corrected below'.

Column 4, line 75, for "reaching" read reacting column 6, line 4, for "heat combustion" read heat of combustion e,

Signed and sealed this 27th day of June 1961o (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. A METHOD OF INCREASING THE BORON CONTENT OF A LIQUID CONSISTING ESSENTIALLY OF AT LEAST ONE LOWER ALKYL DIBORANE WHICH COMPRISES MIXING AND REACHING A LOWER ALKYL DIBORANE AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF TETRABORANE, PENTABORANE-11 AND MIXTURES THEREOF, AND RECOVERING THE RESULTING LIQUID REACTION PRODUCT.