FIELD: medicine. SUBSTANCE: preparation of the prior art antiinflammatory agent such as 2-(4-isobutylphenyl) propionic acid by carbonylation of 1-(4-isobutylphenyl)ethanol (IBPE) with carbon monoxide in an aqueous acidic medium, e. g. containing at least 10% of water based on the weight of IBPE added originally at a temperature of at least 10 deg C and at a carbon monoxide pressure of at least 500 psig (35 atm g) and in the presence of a catalyst consisting essentially of a palladium compound in which the valency of palladium is from 0 to 2 and which compound forms a complex with at least one phosphine ligand miscible with the organic phase of the reaction mixture, said palladium to ligand molar ratio being at least 2: 1 and the palladium to IBPE molar ratio being below approximately 1: 10000; in the presence of dissociated hydrogen ions from an acid which is substantially completely ionizable in a dilute aqueous solution in such an amount that the molar ratio of hydrogen ions to IBPE added to the reaction zone being at least 0.15 and the molar ratio of hydrogen ions to water being at least 0.026-1; in the presence of dissociated halogen ions in such an amount that the molar ratio of halogen ions to IBPE added to the reaction zone being at least 0.15. Hydrogen halide is recommended as a source of hydrogen and halogen ions. It is recommended to combine carbonylation with a process for preparing IBPE from isobutylenebenzene in which isobutylene is subjected to Fridel-Crafts reaction with an acebylating agent to produce 4-isobutyl acetophenone which is reduced with hydrogen in the presence of a hydrogenation catalyst or with a reducing agent containing active hydrogen to produce IBPE. EFFECT: improved properties of the antiinflammatory agent. 7 cl, 17 tbl
