MECHANISM OF SYNTHESIS OF MALEIC AND SUCCINIC ANHYDRIDES BY CARBONYLATION OF ACETYLENE IN SOLUTIONS OF PALLADIUM COMPLEXES

The mechanism of synthesis of maleic and succinic anhydrides from acet ylene and CO in the PdBr2-LiBr-organic solvent catalytic system was st udied using the procedure of advancement and discrimination of hypothe ses. The hypotheses were obtained using the data bank on elementary st eps and the Comb1 combinatorial program. The discrimination of the hyp otheses was based on the data of NMR and IR spectroscopy, studies of i sotope exchange, the role of potential organic intermediates, the kine tic isotope effect, and one-factor kinetic experiments. The most proba ble mechanism of synthesis of maleic anhydride includes insertion of a cetylene and CO into the Pd-Pd bond of the Pd-I complex, which is form ed from Pd-II at the initial step of the process. Succinic anhydride r esults from the intramolecular transformation of the hydride complex o f palladium and maleic anhydride. The palladium hydride complexes dete cted in the contact solution apparently play the crucial role in the c onjugation of oxidation, reduction, and addition type reactions.