Abstract:
Norbornadiene and 1,3-pentadiene are catalytically codimerized to an olefinic codimer using a three-component homogeneous catalytic system of cobaltic or cobaltous acetylacetonate, triphenylphosphine and an alkyl aluminum chloride. The codimer, after hydrogenation, has utility as a high energy missile fuel or a diluent for a higher viscous missile fuel.

Description:
BACKGROUND OF THE INVENTION 
     The invention herein described was made in the course of or under a contract thereunder with the United States Air Force Systems Command. 
    
    
     CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 819,444, filed July 27, 1977, now abandoned, which is related to U.S. application Ser. No. 819,441 filed same date by the aforementioned inventors. 
    
    
     The invention relates to the catalytic codimerization of norbornadiene and 1,3-pentadiene. Particularly the invention relates to the preparation of an olefinic codimer of norbornadiene and 1,3-pentadiene using a specified catalyst system. Hydrogenation of the olefinic codimer yields a saturated codimer having utility as a high energy fuel or a diluent for such fuels. The pentadiene is referred to hereinafter as PD. 
     High energy fuel, which is often referred to as a high density fuel, can be used in either jet or rocket propulsion. Jet propulsion includes a jet engine which can be used for a missile plane and others and includes the three basic types, i.e., ramjet, turbo-jet and pulse jet. The term rocket generally refers to a device containing its own oxygen or oxidizing agent. 
     Norbornadiene (I) is also known as bicyclo-(2.2.1)heptadiene-2,5. A method of preparation is disclosed in U.S. Pat. No. 2,875,256 issued Feb. 24, 1959. Hereinafter, norbornadiene is referred to as NBD. The latter can be represented by either one of the following structural formulas: ##STR1## NBD can be easily dimerized to an exo-exo hexacyclic dimer. Thus one problem in reacting NBD with another hydrocarbon reactant is to minimize the formation of the foregoing dimer while encouraging the formation of the desired codimer. 
     A. Greco et al, in the Journal of Organic Chemistry, Vol. 35, No. 1, January, 1970, page 271 in article titled &#34;Catalytic Norbornadiene-Butadiene and Norbornadiene-1,1-Dimethylallene Codimerization&#34; discloses using bis(cyclooctatetraene) iron or FeCl 3  (i-C 3  H 7 )MgCl as a catalyst for reacting NBD with PD. 
     SUMMARY OF THE INVENTION 
     Rapid codimerization of NBD and PD is obtained using a catalytic amount of a three-component homogeneous catalytic system consisting of cobaltic or cobaltous acetylacetonate, triphenylphosphine and one of three alkyl aluminum chlorides. The reaction rate is relatively rapid and the selectivity as to the resulting codimer of NBD and PD is good. Resulting codimer can be hydrogenated and then used as a missile fuel. 
     DESCRIPTION 
     Cobaltic acetylacetonate (Co(C 5  H 7  O 2 ) 3 ) is referred to hereinafter as CoA 3  whereas the cobaltous form (Co(C 5  H 7  O 2 ) 2 ) is referred to as CoA 2  ; collectively the two are referred to as CoA. The triphenylphosphine ((C 6  H 5 ) 3  P)) is referred to as TPP while the alkyl aluminum chloride is referred to as AAC. 
     The catalytic codimerization of NBD and PD via present invention can be represented by the following formula reaction: ##STR2## As shown NBD and PD are contacted in the presence of a catalytic amount of a catalyst system defined herein. Co-products may also be formed. 
     Olefinic codimer II is a tetracyclic hydrocarbon having the molecular formula C 12  H 16  and a C/H molar ratio of 0.750. 
     Codimer II may be hydrogenated to form α-methyltetramethylene nortricyclane (III). The hydrogenation of olefinic codimer II can be represented by the following formula reaction: ##STR3## Hydrogenated product III is also a tetracyclic hydrocarbon having the molecular formula C 12  H 18  and a C/H molar ratio of 0.667. Product III may be used as a component of a high density missile fuel. 
     The NBD used can contain a nominal amount of similar hydrocarbons, however, which if present should not be of the type which could adversely effect the reaction. If the NBD used contains undesirable hydrocarbons, they can be removed by known means. The foregoing also applies to the PD used. Thus the hydrocarbons used in the invention can consist essentially of NBD and PD. 
     In the codimerization of NBD and PD one mole of each reacts with the other to form one mole of the NBD-PD codimer II. However, if the NBD to PD mole ratio is too large homodimerization can occur with an adverse effect on codimer yields. On the other hand, if the NBD to PD mole ratio is too low then the yield per pass can be too low and hence uneconomical. Within the aforementioned limits a preferred NBD to PD mole ratio is in the range between from about 0.01 to about 10 with about 0.1 to about 2 more preferred. 
     The catalytic system favoring the aforementioned codimerization reaction (A) contains three components. All three components of the catalyst system are commercially available and methods for their preparation are reported in the literature. The three are CoA 3  or CoA 2 , TPP and AAC. The AAC can be selected from the group consisting of diethylaluminum chloride, ethyl aluminum dichloride and ethyl aluminum sesquichloride. The latter three are referred to as DEAC, EADC and EASC, respectively. The amount of any component present is a catalytic amount so that a suitable conversion to codimer II occurs and the selectivity as to it is sufficient. Material, which during the codimerization reaction could adversely affect the catalyst system, should not be present. For example, the presence of hydroxylic compounds such as water, alcohol or oxygen from air could deactivate the catalyst system. 
     The amount of NBD present compared to the CoA should be catalytically sufficient to obtain the desired product. Generally the NBD to CoA mole ratio can range between from about 10 to about 2000 with a preferred range between from about 20 to about 1000. 
     The second component of the catalyst system is TPP. The amount of this second component of the catalyst system should be catalytically sufficient to obtain the desired product. Generally the TPP to CoA mole ratio can range between from about 0.1 to about 100, with a preferred range between from about 1 to about 50. 
     DEAC, EADC or EASC is the third component of the catalyst system with DEAC preferred. The amount of the third component can vary substantially but generally it relates to the amount of CoA used. An effective DEAC, EADC or EASC to CoA mole ratio can be between from about 0.5 to about 100 with from about 1 to about 50 preferred and from about 3 to about 20 more preferred. Generally, when DEAC, EADC or EASC is used it is advantageous to conduct the reaction under substantially anhydrous conditions and under an inert gas blanket. Excess DEAC, EADC or EASC also serves as a scavenger. 
     Selectivity refers to the amount, mole or weight, of a particular compound formed divided by the amount of all compounds formed. From a commercial standpoint the economics of an overall process determines the optimal levels for both the selectivity and yield. 
     The reaction time required for an economically satisfactory selectivity and/or yield depends on a number of factors, such as catalyst to feed ratio, as well as operating conditions. Also the economics depend on capital investment versus conversion per pass and the like. The catalyst to feed ratios are discussed hereinafter while typical conditions are provided by the Example. 
     A solvent can be used in the codimerization reaction. The solvent can be inert or it can be the NBD itself. Since the reaction is mildly exothermic the solvent can serve as a heat sink. It can also assist in solubilizing the reaction components, that is the feed and the components of the catalyst, and thereby provide for a homogeneous reaction medium. Some solvent can be added to the system as a carrier for one or more of the catalyst components. For example, DEAC is often maintained in an inert solvent such as toluene rather than NBD itself. Furthermore, the solvent should not adversely react with the feed, products or catalyst, therefore, if it is not NBD, it should be inert. Also, presence of the solvent can facilitate the handling of the reaction mixture. Classes of suitable inert solvents include aromatic hydrocarbons, cycloparaffins, ethers, halogenated aromatics, halogenated paraffins and halogenated cycloparaffins. Specific examples include benzene, toluene, xylenes, cyclohexane, diethylether, chlorobenzene, bromobenzene, chlorinated cyclohexane and the like. As to the amount of solvent used, excessive amounts decrease the reaction rate, and thus adversely affect the economics for a commercial operation. 
     The codimerization of NBD and PD with the three-component catalyst system can occur at ambient temperature. Thus the temperature of the homogeneous feed catalyst system mixture need not be raised to initiate reaction A. However, if the mixture is at an extremely low temperature, then heating of the cooled mixture could be necessary. Furthermore, once reaction A is underway, some heat is generated and the temperature of the mixture increases. If the temperature increases too much then some cooling would be required. Generally, however, the codimerization of NBD and PD with a reasonable amount of the three-component catalyst system is not characterized by an extremely rapid exotherm. 
     Selective codimerization of the NBD and PD most efficiently occurs in a liquid phase and therefore it is not desirable to have the reaction exceed the boiling points of the NBD and/or any solvent. Conversely, if the temperature is too low the reaction rate will be too slow to be economically feasible. An operable temperature range is between from about 20° C. to about 100° C. with about 25° C. to about 85° C. a preferred range. The operating pressure can vary substantially, however, it can range from about atmospheric up to about 2000 psi. Process economics favor lower operating pressure, however, a moderately elevated reaction pressure may be desirable to keep the PD in solution. 
    
    
     To further illustrate the invention the following example is provided, along with comparative ones. 
     EXAMPLE 
     Into a Fisher-Porter reaction vessel were added 5.8 milligrams (0.016 millimoles) of CoA 3 , 76.2 milligrams (0.29 millimoles) of TPP, 0.5 milliliters of chlorobenzene, 0.5 milliliters (4.9 millimoles) of NBD and 1.0 milliliter (10 millimoles) of PD. The combined materials were mixed and deaerated at 25° C. under nitrogen. Then to the deaerated mixture were added 0.74 millimoles of a 1.9 molar solution of DEAC in toluene. A slight exotherm occurred with the temperature reaching 65° C. after the addition of the DEAC. After a total of 30 minutes the reaction mixture was treated with isopropyl alcohol to quench the catalyst. After separation a portion of the hydrocarbon product was analyzed by vapor phase chromatographic analysis. The analysis indicated that the conversion of NBD was 99.8% and selectivity to codimer was 45.2%. About 19.2% of the PD was converted. 
     Analogous results will be obtained when CoA 2  is used in lieu of CoA 3 , and/or EASC or EADC is used in lieu of DEAC. 
     Hydrogenation of codimer II to hydrogenated product III, via reaction B, can be readily achieved by using a hydrogenation catalyst such as PtO 2 . The temperature of hydrogenation can vary widely however, generally it will be between from ambient to about 100°-200° C. The hydrogen pressure can vary substantially. 
     An attempt was unsuccessfully made to prepare codimer II using the following catalyst systems: TPP(cobaltous carbonyl)-DEAC; palladium acetylacetonate-TPP-DEAC; rhodium acetylacetonate-TPP-DEAC; and nickel acetylacetonate-TPP-DEAC.