US3326993A - Bicycloheptadiene dimerization - Google Patents

Description

United States Patent 3,326,993 BICYCLOHEPTADIENE DIMERIZATION Bruce N. Bastian, Lafayette, and Gerhard N. Schrauzer, Orinda, Calif., assignors to Shell Oil Company, New

York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 20, 1965, Ser. No. 499,000 9 Claims. (Cl. 260-666) This invention relates to an improved method for the dimerization of bicycloheptadiene and to a novel dimer thereby produced.

Methods are known in the art for the dirnerization of bicyclo(2.2.1)hepta-2,5-diene, herein for brevity termed bicycloheptadiene, to produce polycyclicdimer derivatives. Bird et al., Chem. and Ind.; 20 (1960), disclose the reaction of bicycloheptadiene with certain metal carbonyls, e.g., iron carbonyl, to produce bicycloheptadiene dimers together with major amounts of ketone products. The bicycloheptadiene dimers of Bird et al. are ethylenically unsaturated, containing from 1 to 2 ethylenic linkages per molecule. A saturated bicycloheptadiene dimer is disclosed by Lemal et al., Tetrahedron Letters, 11, 268 (1961). Although the structure of the saturated dimer of Lemal et al. was not established with certainty, it is evident that the bicycloheptadiene moieties were joined by four separate carbon-carbon bonds as the product obtained was free from ethylenic unsaturation and was free from cyclopropane ring moieties, e.g., nortricyclene moieties. In co-pending application of Miiller et al., US. Ser. No. 457,787, filed May 21, 1965, now issued as US. Patent No. 3,282,663, there is disclosed and claimed certain compositions, useful as high energy fuels, which comprise mixtures of several unsaturated bicycloheptadiene dimers. These compositions are useful as high energy fuels, particularly as fuels for jet aircraft, because of the relatively high heat of combustion per unit volume of the dimer compositions which renders the compositions eminently suitable for applications wherein a volume savings is required. It would, however, be of advantage to provide a bicycloheptadiene dimer of an even greater heat of combustion per unit volume.

It is an object of the present invention to provide an improved method for the dimerization of bicycloheptadiene and to provide the novel saturated bioycloheptadiene dimer thereby produced. More particularly, it is an objectto provide the novel bicycloheptadien dimer heptacyclo(5.3.1.1 .1 .1 0 0 )tetradecane and .a method for the production thereof.

It has now been found that these objects are accomplished by contacting bicycloheptadiene with certain cohalt-containing carbonyl catalysts, customarily in the presence of an acidic co-catalyst, in liquid-phase solution in an inert non-polar reaction solvent. The process of the invention results in the formation of a dimer product containing major proportions of the saturated heptacyclortetradecane dimer, and in some instances results in the exclusive formation of this saturated dimer.

The novel dimer of the invention is heptacyclo (5.3.1.1 .1 .l .0 .0 )tetradecane which is depicted by the structural formula wherein the added numerals indicate one conventional method of identifying the relative locations of the carbon atoms present. Although it is apparent that the possibility 3,326,993 Patented June 20, .1967

ice

, melting point of 65.065.6 C. and is believed to be the endo-cis-endo formula.

isomer represented by the following The process of the invention comprises dimerizing ibicycloheptadiene in the presence of certain co'baltcontainmg carbonyl catalysts and inmost instances in the presence of a Lewis acid co-catalyst. Catalysts thatare suitably employed in the process of the invention are represented by the formula wherein M is zinc, cadmium or indium, m is a whole number from 0 to 1 inclusive and n is a whole number from 2 to 3 inclusive equal to the valence of the metal M, with the proviso that when m=-0, then n=2. These catalysts are dicobalt octacarbonyl and zinc, cadmium or indium tetracarbonylcobaltate. Preferred catalysts of the above formula arethose wherein m==1 and M is a metal of Group IIB of the Periodic Table of an atomic number from 30 to 48 inclusive, that is, M is zinc or cadmium. Particularly preferred as catalyst is zinc tetracarbonylcobaltate, Zn[Co(CO) The cobalt-containing carbonyl catalyst is employed in catalytic quantities. The amount of catalyst is not critical, except insofar as the ratio of catalyst to bicycloheptadiene does influence the relative proportion of the heptacyclotetradecane in the product mixture. In order to obtaina product.mixturecontaining substantial proportions of the heptacyclotetradecane product, a molar ratio of catalyst to bicycloheptadiene .of at least 1:1'000 is'preferred. There does not appear to be a critical upper limit on the relative amount of catalyst to beutilized, however molar ratios of catalyst to bicycloheptadiene,greater than about 1:10 do not appear to offer any further practical advantage that would compensate for the additional expense. Best results are obtained when molar ratios of catalyst to bicycloheptadiene of from about 1:100 to about 1120 are utilized.

The cobalt-containing carbonyl catalyst is employed in conjunction with an acidic co-catalyst. The acidic materials suitably utilized .to improve the efficiency of the process, particularly the selectivity to heptacyclotetradecane product are generically characterized as Lewis acids. By the term Lewis acid is meant a material having .the ability to accept an electron pair during coordination with materials normally considered to be bases and having the ability to donate an electron pair. One class of Lewis acids is characterized as the salt of a weak base and a strong acid, the base being a metallic base wherein the metal is a member of a group of the Periodic Table other than Groups IA and HA, and the acid being a strong acid which is a non-oxidizing, mono-basic acid, preferably a hydrogen ,halide. The latter class of Lewis acids, i.e., metal salts of hydrogen halides, are covalent metal halides wherein the metal-halogen bond exhibits a substantial degree of covalent character rather than an essentially exclusively ionic character, and the covalent metal halides are on occasion referred to as Friedel-Crafts catalysts because of the ability of these covalent metal halidesto catalyze Friedel-Crafts alkylation or 'acylation processes. Particularly preferred as the Lewis acid e0 catalysts of the invention are covalent metal halides wherein the halogen has an atomic number of from to 35, that is, the halogen is fluorine, chlorine or bromine. Illustrative of covalent ametal halides suitably employed as c-o-catalyst are boron trifluoride, aluminum chloride, aluminum bromide, stannous chloride, arsenic trichloride, antimony pentafluoride, titanium tetrachloride, ferric chloride, cobalt bromide, palladium chloride, platinum chloride, cupric fluoride, zinc chloride, zinc bromide, cadmium chloride and the like. The covalent metal halides are preferably employed as such, although it is also useful to employ acidic complexes of the covalent metal halides, e.g., etherates or complexes with organic nitriles.

The catalyst and co-catalyst are typically employed in a molar ratio of catalyst to co-catalyst of from about 2:1 to about 1:15 with molar ratios of catalyst to co-catalyst of from about 1:1 to about 1:8 being preferred. A special case is observed when the catalyst employed is a compound'of the formula wherein M is zinc or cadmium. In these instances it has been found that the process is operable in the substantial absence of co-catalyst. Therefore, when a zinc or cadmium tetracarbonylcobaltate catalyst is employed, molar amounts of co-catalyst up to about 15 moles of co-catalyst per mole of the zinc or cadmium catalyst are suitable with molar amounts up to 8 moles of co-catalyst per mole of zinc or cadmium catalyst being preferred.

The dimerization is conducted in liquid-phase solution in an inert non-polar reaction solvent and solvents which are liquid at reaction temperature and pressure, which are essentially non-polar in character and are inert towards the bicycloheptadiene reactant and the dimer product are satisfactory. Preferred non-polar solvents comprise the hydrocarbons, particularly hydrocarbons free from aliphatic unsaturation including alkanes such as hexane, heptane, isooctane, decane and dodecane; cycloa'lkanes such as cyclohexane, cyclopentane, methylcyclopentane and decahydronaphthalene; and aromatic hydrocarbons including benzene, toluene, xylene, ethylbenzene and cumene.

The method of effecting dimerization is not critical. In one modification, the entire amounts of bicycloheptadiene, catalyst, co-catalyst if employed, and reaction solvent are charged to an autoclave or similar reactor and the mixture is maintained at reaction temperature and presure until reaction is complete. It is also useful to add one reaction mixture component to the others in increments, as by gradually adding the bicycloheptadiene to a mixture of the solvent and catalyst system. In yet another modification, the dimerization is conducted in a continuous manner as by contacting the bicycloheptadiene and catalyst system during passage through a tubular reactor. In any modification, the reaction is conducted at a somewhat elevated reaction temperature. Temperatures from about 40 C. to about 150 C. are generally satisfactory with the temperature range from about 50 C. to about 130 C. being preferred. Reaction pressures which are atmospheric, subatmospheric or superatmosphe-ric are suitably employed provided that the reaction mixture is maintained substantially in the liquid phase. Little advantage appears to arise from utilization of pressures which are substantially different from atmospheric and the use of substantially atmospheric pressure, e.g., from about 0.5 atmosphere to about atmospheres, is preferred.

In order to maintain a high degree of catalyst selectivity toward the formation of heptacyclotetradecane product, the reaction is conducted in an inert, non-basic reaction environment. Thus, it is preferred to effect dimerization in an oxygen-free, substantially anhydrous reaction environment in the substantial absence of basic materials.

Subsequent to reaction, the product mixture is separated and recovered by conventional means, as by selective extraction, fractional distillation, fractional crystallization or the like. For some applications, however, separation of individual catalyst components is not necessary as the product mixture, upon removal of solvent, is useful as such.

The product mixture comprises essentially the abovedepicted heptacyclotetradecane with varying amounts of unsaturated bicycloheptadiene dimers depending upon the precise reaction conditions employed as well as the particular ratios of reactant to catalyst and/or co-catalyst. However, the heptacyclotetradecane product is separable from any other dimer products produced and in some instances is the sole dimer product.

As previously stated, the broad class of bicycloheptadiene dimers is useful as a high energy fuel. Several criteria are useful in determining the value of a fuel in such an application, among which is the heat of combustion per unit volume of the fuel as well as the thermal stability. The above-identified copending application of Miiller et al. describes and claims certain mixtures of bicycloheptadiene dimers useful as high energy fuels. A typical mixture of dimers of the Miiller .et al. application comprises about 21.9% :by weight of dimers represented by the general formula pentacyclo(8.2.1.1 .0 0 )tetradeca-5,1 l-diene and about 76.3% by weight of .dimers of the formula hexacyclo(7.2.l.1 .1 .0 .0 )tetradec-lO-ene This mixture is characterized by a density of 1.0904 g./ ml. at 20 C. and a gross heat of combustion of 11,310 cal/ml. In contrast, the heptacyclic dimer of the present invention has a substantially greater density, 1.258 g./rn1. at 25 C., as Well as a substantially higher gross heat of combustion per unit volume, 12,932 cal./ml. In addition the heptacyclotetradecane product is characterized by a greater degree of thermal stability than either the above-identified pentacyclic or hexacyclic dimers, both of which undergo extensive pyrolysis at or below about 350 C., in contrast to the heptacyclic dimer of the invention which is thermally stable at temperatures at least as high as 445 C.

To further illustrate the improved process of the invention and the novel product thereof, the following examples are provided. It should be understood that the details thereof are not to be regarded as limitations as they may be varied as will be understood by one skilled in this art.

EXAMPLE I The zinc tetracarbonylcobaltate employed in the following examples was prepared by charging to an autoclave 12 g. of zinc dust and 400 ml. of a 10% solution of dicobalt octacar-bonyl in toluene. Carbon monoxide was introduced to give a 3000 p.s.i. pressure (20 C.) and the autoclave was heated and maintained at 200 C. and 4750 p.s.i. for 12 hours. The reactor was then cooled and vented and the yellow solution was transferred under nitrogen to a low temperature crystallizer. The yield of Zn[Co(CO) a yellow crystalline solid, was 30.95 g.

By similar procedures, In [Co(CO) and )4]2 were prepared.

EXAMPLE II To a nitrogen-filled reactor was charged 10 0 ml. of toluene, 0.81 g. of zinc tetracarbonylcobaltate and 2.28 g. of boron trifluoride etherate. The reaction mixture was swept with nitrogen and was stirred while 226 g. of bicycloheptadiene was added and the reaction mixture was heated to 70 C. After the addition was complete, the mixture was maintained at 70-80 C. for 21 hours. The product mixture was removed, washed with 5% aqueous sodium carbonate, dried over anhydrous sodium carbonate, decolorized with activated carbon and finally distilled at reduced pressure. The

heptacyclo(5.3.1.1 .1 .1 0 )tetradecane B.P. 73 C. at 1-2 mm. was obtained in a yield of 76.4% 5 based upon the bicycloheptadiene charged. The product, upon recrystallization from ethanol, had a melting point of 65.0-65.6 C. and had the following elemental analysis.

Analysis.Calc. (weight percent): C, 91.3; H, 8.7.

Found: C, 91.3; H, 8.8.

6 in the presence of various catalysts and in the presence or absence of various Lewis acid oo-catalysts. The results of this series are shown in Table III wherein the heading M refers to any additional metal portion of the catalyst and the term mmole represents millimoles. In each case the percent by weight in the product mixture of the heptacyclic dimer was determined as well as the per-cent by weight of unreacted bicycloheptadiene.

TABLE III Time, Temp., Unreacted bi- Heptacyclic M, mole Lewis acid, mmole hr. C. cycloheptadimer,

diene, percent percent wt.

4 100 0 100 0. 1 40 6. 0 88. 5 N 4. 1 100 11. 1 50. 3 Cd, 0.5---. B1 30 (CzHsh, 0.71..-" 0. 100 0 100 Zn, 1.0..... PtC 2(CGH5C/N)z, 1.0-. 0.1 110 0 100 Cd, 0.5-... PdCl2(CsH5CN)2, 0.5.. 72 100 9.0 91. 0 None, 1.0.. B 3, 0.5 2 70 6.8 93.2 None, 0.5-. AlBr 0.5 1 60 0 00 The structure of the product was confirmed by mass spectrometric analysis and by the nuclear magnetic resonance spectrum which was consistent with the above structure. The infrared analysis showed a band at 12.53 characteristic of nortricyclene absorption and did not contain absorptions characteristic of olefinic linkages.

EXAMPLE III The procedure of Example II was employed in the dimerization of 5 ml. of bicycloheptadiene in the presence of varying amounts of zinc tetracar-bonylcobaltate as catalyst in 10 ml. of toluene as solvent. The results of this The procedure of Example II was repeated employing various ratios of boron trifluoride etherate co-catalyst to zinc tetracarbonylcobaltate catalyst. In each case the conversion of bicycloheptadiene to the heptacyclic dimer was determined as a function of the molar quantity of the zinc-containing catalyst. The results of this series are shown in Table 11 wherein the heading Ratio refers to the molar rati-o of co-catalyst to catalyst and the heading Moles Converted refers to the number of moles of bicycloheptadiene converted to the heptacyclic dimer product per mole of the catalyst present.

TABLE II Ratio Moles converted EXAMPLE V The procedure of Example II was followed to effect dimerization of bicycloheptadiene under varying conditions We claim as our invention: 1. The process of producing a heptacyclo(5.3.1.1 .1 .1 .0 .0 )tetradecane as the major bicycloheptadiene dimer product by intimately contacting bicyclo(2.2.1)hepta-25 diene with (a) from about 0.001 mole to about 0.1 mole per mole of said bicycloheptadiene of the cobalt-containing carbonyl catalyst of the formula wherein M is zinc, cadmium or indium, m is a whole number from 0 to 1 inclusive and n is a whole number from 2 to 3 inclusive equal to the valence of the metal M, with the proviso that when mi=0 then n=2, and (b) from about 0.5 mole to about 15 moles of Lewis acid co-catalyst per mole of said cobalt-containing carbonyl compound; in liquid-phase solution in inert non-polar hydrocarbon reaction solvent, at a temperature of from about 40 C. to about C., in a substantially anhydrous, non-basic reaction environment.

2. The process of claim 1 wherein the Lewis acid cocatalyst is a covalent metal halide wherein the halogen is halogen of atomic number from 9 to 35.

3. The process of claim 2 wherein m=0.

4. The process of claim 2 wherein m: 1.

5'. The process of claim 2 wherein the catalyst is M[Co(CO) wherein M is zinc or cadmium.

6. The process of claim 5 wherein the process is conducted in the substantial absence of the cocatalyst.

7. The process of claim 5 wherein the co-catalyst is boron trifluoride.

8. The process of claim 5 wherein the co-catalyst is antimony pentafluoride.

9. The compound heptacyclo(5.3.1.1 .1 .1 0 0 ")tetradecane characterized by a melting point of 65.0-65.6 C.

References Cited C. W, Bird et al., (1) Chem. & Ind., pages 20-21, 1960. C. W. Bird et al., (1) Tetrahedron Letters, No. 11, pages 373-375, 1961.

David M. Lemal et al., Tetrahedron Letters, No. 11, pages 368-372, 1961.

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Examiner.

Claims (1)

1. THE PROCESS OF PRODUCING A