Abstract: Palladium salts with N-heterocyclic ligand or biphosphine ligand were used as the catalysts for the carboxylation of 1,3-butadiene with carbon monoxide in methanol to methyl 3-pentenoate, which is one of the key reactions in Altam process for production of ?-caprolactam. The combination of Pd(OAc)2 with 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine exhibited moderate catalytic activity under the optimized conditions (150 ºC, p(CO) = 6.0 MPa, 6 h), reaching 78.8% conversion of 1,3-butadiene and 92.2% selectivity for the target product (TON = 226). Using Pd(OAc)2/(oxydi-2,1-phenylene)bis(diphenylphosphine) as the catalyst remarkably increased the reaction efficiency, achieving 90.4% conversion of 1,3-butadiene and 91.6% selectivity for the product (TON = 181). At temperature above 200 ºC, 1,3-butadiene underwent dimerization to form 4-vinyl-1-cyclohexene in 96% yield.

Key words: 1,3-butadiene, palladium, N-heterocyclic ligand, carboxylation, methyl 3-pentenoate, ?-caprolactam, biphosphine ligand