Butadiene oxycarbonylation

After ARCO patents issued, Stille and coworkers published on butadiene oxycarbonylation(14-16). Palladium was utilized as the oxidative carbonylation catalyst and copper(II) chloride was employed as a stoichiometric reoxidation agent for palladium. Although the desired hex-3 -enedioate is the exclusive product, commercial technology which uses stoichiometric copper is not practical. Once the copper(Il) is consumed, the monoatomic palladium spent catalyst agglomerates affording polymeric palladium which is not easily reoxidized to an active form. 

This significant difference in projected feedstock price is key to a large raw material economic advantage for butadiene oxycarbonylation technology. Recent softening of worldwide oil prices has resulted in 0.85 per gallon benzene and 0.26 per pound butadiene. Butadiene oxycarbonylation economics based on these feedstock prices are less attractive. It may be well into the year 2000 before decreased oil reserves make a synthesis gas route to adipic acid economically attractive. 

Pi-A -chloro-di- -(dimethyl hex-2 endioate) di-palladium is the preferred palladium catalyst and was used in the pilot plant studies outlined in Table II. Synthesis is easily accomplished by reaction of dimethyl hex- -endioate with palladium chloride. In actual butadiene oxycarbonylation runs catalyzed... 

Although many dehydration agents function effectively in butadiene oxycarbonylation, ketals proved to be easily regenerated and recycled. Cyclohexanone was chosen because of its more favorable equilibrium constant during regeneration(27,28)... 

It is well known that soluble copper or other transition metals will catalyze Aldol condensation reactions(29). The optimum copper(ll)/palladium(ll) molar ratio is 2.3. Normally, about 1500 ppm palladium is used in the butadiene oxycarbonylation reaction. Under typical oxycarbonylation process conditions, around. 5 mole % l, l-dimethoxycyclohexane is lost to heavies per pass. 

Adipic acid overcapacity, softening worldwide oil prices, and the increased investment necessary to establish a novel chemical process has made implementation of a world scale adipic acid plant based on butadiene oxycarbonylation technology less attractive. 

The other CO route for adipic acid manufacture involves 1,4-addition of CO and O2 to butadiene to produce an intermediate, which is subsequently hydrogenated and hydroly2ed to adipic acid (50). This is called the oxycarbonylation process. Both the BASF and the oxycarbonylation processes have been intensively investigated. 

Another alternative method to produce sebacic acid iavolves a four-step process. First, butadiene [106-99-0] is oxycarbonylated to methyl pentadienoate which is then dimerized, usiag a palladium catalyst, to give a triply unsaturated dimethyl sebacate iatermediate. This unsaturated iatermediate is hydrogenated to dimethyl sebacate which can be hydrolyzed to sebacic acid. Small amounts of branched chain isomers are removed through solvent crystallizations giving sebacic acid purities of greater than 98% (66). 

The adipic acid process we have developed involves butadiene oxidative carbonylation in the presence of methanol, a l, l-dimethoxycyclohexane dehydration agent, and a palladium(ll)/ copper(ll) redox catalyst system (Equation 1.). The reaction sequence includes an oxycarbonylation, hydrogenation and hydrolysis step(17-19). The net result is utilization of butadiene, the elements of synthesis gas, l, -dimethoxycyclohexane and air to give adipic acid, cyclohexanone and methanol. 

An attractive alternative to building a world scale adipic acid plant is to construct a specialty smaller volume oxycarbonylation plant which is capable of exclusively producing the more valuable precursors for pelargonic and sebacic acid. Oxycarbonylation process conditions can be controlled to give methyl, 4-pentadienoate which is the product from butadiene mono-carbonylation(39,40). Methyl, 4-pentadienoate can react in a subsequent step with butadiene to give an unsaturated pelargonic acid precursor in high yield(41). Methyl, 4-pentadienoate... 

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