Carboxylation of Isobutylene and Related Olefins with Carbon Monoxide and Water in the Presence of BF<sub>3</sub>-H<sub>2</sub>O Complex Catalysts

Abstract

Carboxylation of isobutylene (I. B.) and its oligomers (dimers∼tetramers) in the presence of BF3-H2O complex catalysts having 0.4∼1.0 BF3/H2O molar ratios was conducted in a heterogeneous liquid phase (solvent layer and catalyst layer) at 80∼140°C under CO atmosphere (50kg/cm2).Trimethylacetic acid (T. M. A. A.) was obtained as the main product together with C6, C8, C9, C13 acids and isobutylene oligomers.The rate of absorption of CO increased with the increase of BF3/H2O molar ratio of the catalyst. Carboxylic acids produced were usually distributed between solvent layer and catalyst layer, and the product distribution between both layers was greatly affected both by the BF3/H2O molar ratio of the catalyst and by reaction temperature. Total yield of carboxylic acids had the tendency to decrease with the higher reaction temperature with using catalyst of 0.5∼1.0 BF3/H2O molar ratios, but in the case of catalyst of molar ratio lower than 0.5 BF3/H2O, the yield of carboxylic acids increased along with the reaction temperature.Although the mode of addition of water to the reaction mixture did not show an appreciable effect on the total amount of carboxyl group in the products, it had an appreciable effect on the T. M. A. A. content in the acids produced.The effect of reaction time on the distribution of the products was studied too. In the early stage of the reaction, the larger part of I. B. introduced was converted into I. B. oligomers and the amount of I. B. used for the formation of carboxylic acids was comparatively small. In this stage the C9 acid content in the carboxylic acids produced predominated over that of T. M. A. A., C6 and C8, and C13 acids were also produced in appreciable amounts. However, in the latter stage of the reaction, the yield of carboxylic acids and the content of T. M. A. A. in the products increased at the expense of I. B. oligomers. The change in the composition of C9 acids in the course of the reaction was also observed.Based on the results obtained, the reaction scheme for carboxylation of isobutylene and its oligomers was discussed.