Abstract:
Norbornadiene and an acrylic acid ester, e.g., methyl acrylate, are catalytically codimerized in the presence of a two-component homogeneous catalytic system consisting of nickel acetylacetonate and an alkyl aluminum chloride. The resulting codimer can be used as a precursor for a missile fuel. The ester portion of the acrylic acid ester is the radical RCH 2  O-- wherein the R is an H or an alkyl containing up to 10 carbon atoms.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to applicants&#39; U.S. patent Ser. Nos. 812,206 and 812,207 filed the same date. 
     BACKGROUND OF THE INVENTION 
     The invention herein described was made in the course or under a contract thereunder with the United States Air Force Systems Command. 
     The invention relates to the catalytic codimerization of norbornadiene, hereinafter referred to as NBD, and acrylic acid ester, hereinafter referred to as AAE. Particularly, the invention relates to the preparation of a codimer using a specified catalyst system. 
     The resulting codimer can be used as a precursor for a missile fuel. The codimer can be hydrolyzed to an acid which can be decarboxylated. The resulting decarboxylated hydrocarbon can be used as a missile fuel. 
     NBD 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. The NBD can be represented by either one of the following structural formulas: ##STR1## NBD can be easily dimerized to a 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. 
     In the Journal of the American Chemical Society/97:4/Feb. 19, 1975, pages 812 &amp; ff., R. Noyori et al in an article titled &#34;Nickel (0)-Catalyzed Reaction of Quadricyclane with Electron-Deficient Olefins&#34; discloses the reaction of alkyl acrylate and NBD using bis(acrylonitrile)nickel (0). With methyl acrylate the resulting product has the following structure. ##STR2## The reaction was run at various temperatures for a substantial amount of time. Yet the yield of codimer II was very low. 
     Thus, as the aforementioned article indicates, the specific synthesis problem is to obtain codimer III (which structure is defined herein) in both a high conversion and selectivity and with a rapid reaction rate. 
     SUMMARY OF THE INVENTION 
     Rapid codimerization of NBD and AAE is obtained using a catalytic amount of a two-component homogeneous catalytic system consisting of nickel acetylacetonate, hereinafter referred to as NiA 2 , and one of three alkyl aluminum chlorides. Both the yield and selectivity as to codimer III are improved and the reaction rate is relatively rapid. Resulting codimer can be a precursor to a missile fuel. 
     DESCRIPTION 
     The catalytic codimerization of NBD and AAE via present invention can be represented by the following formula reaction; ##STR3## wherein R is an H or an alkyl containing up to 10 carbon atoms. The alkyl can be ethyl, propyl, butyl, and, up to and including decyl. As shown NBD and AAE are contacted in the presence of the catalyst system defined herein. 
     The NBD used can contain a nominal amount of similar hydrocarbons, however, which if present should not be of a type which could adversely effect the reaction. If the NBD used contains such an undesirable hydrocarbon it can be removed by known means. The foregoing also applies to the AAE used. Thus, the materials used in the invention can consist essentially of NBD and AAE. 
     In the codimerization of NBD and AAE one mole of each reacts with the other to form one mole of the NBD-AAE codimer III. However, if the NBD to AAE mole ratio is too large, NBD homodimerization can occur with its adverse effect on yields. On the other hand, if the NBD to AAE 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 AAE mole ratio is in the range between from about 0.1 to about 20 with about 0.2 to about 5 more preferred. 
     The catalytic system favoring the aforementioned codimerization reaction (A) contains two components. Both components of the system are commercially available and methods for their preparation are reported in the literature. The two are NiA 2  and an alkyl aluminum chloride selected from the group consisting of diethylaluminum chloride, ethyl aluminum dichloride and ethyl aluminum sesquichloride. The latter are hereinafter referred to as DEAC, EADC and EASC respectively. The amount of system present is a catalytic amount so that a suitable conversion to codimer III 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 NiA 2  should be catalytically sufficient to obtain the desired product. Generally the NBD to NiA 2  mole ratio can range between from about 10 to about 2000 with a preferred range between from about 20 to about 1000. 
     DEAC, EADC or EASC is the second 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 NiA 2  used. An effective mole ratio of DEAC, EADC or EASC to NiA 2  mole ratio can be between from about 1 to about 100 with from about 3 to about 50 preferred and from about 5 to about 20 more preferred. Excess DEAC, EADC or EASC also serves as a scavenger. Generally, however, when DEAC, EADC or EASC is used it is advantageous to conduct the reaction under substantially anhydrous conditions and under an inert gas blanket. 
     Selectivity refers to the amount of a particular compound formed divided by the amount of all compounds formed. From a commercial standpoint economics of an overall process determine 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 herein 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 a solvent such as toluene. 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, cycloolefins, ethers, halogenated aromatics, halogenated paraffins and halogenated cycloparaffins. Specific examples include, benzene, toluene, xylenes, cyclohexane, cyclopentene, diethylether, chlorobenzene, bromobenzene, chlorinated cyclohexane and the like. As to the amount of solvent used, excessive amounts decrease the reaction rate, and thus adversely effect the economics for a commercial operation. 
     The codimerization of NBD and AAE with the two 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. Of course if the mixture is at an extremely low temperature, then heating of the cooled mixture could be necessary. However, 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 AAE with a reasonable amount of the two-component catalyst system is not characterized by an extremely rapid exotherm. 
     Selective codimerization of the NBD and AAE occurs in a liquid phase, therefore it is not desirable to have the reaction temperature largely exceed the boiling points of the NBD and/or any solvent. Conversely, if the temperature is too low the reaction rate would be too low 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 with 1000 psi a preferred upper value. Process economics favor lower operating pressure. 
    
    
     To further illustrate the invention the following example is provided. 
     EXAMPLE 
     About 7 milligrams (0.024 millimoles) of NiA 2  hydrate were added to a glass reaction vessel along with 1 milliliter of benzene at a temperature of 24° C. The mixture was deaerated with argon and then warmed to 60° C. to dissolve the nickel compound. Then 9.8 millimoles (1 milliliter) of NBD and 0.4 milliliters (4.4 millimoles) of methyl acrylate were added to the vessel. The mixture was again deaerated and then cooled to -25° C. At the lower temperature 0.4 millimoles of DEAC (1 molar in toluene) was added to the vessel. The vessel was warmed. The maximum reaction temperature of the contents of the vessel was 70° C. After 15 hours the reaction mixture was quenched with ispropanol. 
     The resulting catalyst-free reaction mixture was analyzed by vapor phase chromatographic analysis and other tests. The analysis indicated that the reaction mixture, including unreacted reactants and solvent, contained about 5 wt.% of the codimer II and the selectivity as to the codimer II was about 98%. 
     While NiA 2  hydrate was used in the aforementioned reaction, similar results will be obtained using anhydrous NiA 2 . 
     Analogous results will be obtained when other acrylic acid esters such as ethyl, propyl, butyl and decyl acrylate are used in lieu of the aforementioned methyl acrylate.