FIELD: organic synthesis. SUBSTANCE: acetic acid and/or methyl acetate are prepared from methanol/methyl formate mixture using isomerization and carbonylation reactions. Carbonylation reactions proceeds simultaneously with isomerization at 150-250 C in presence of carbon monoxide, water, solvent and a catalytic system containing halogenated promoter and iridium compound. Partial pressure of carbon monoxide is maintained between 0,1•105 Pa and 25•105 Pa, amount of water being below 5% of the total weight of reaction mixture. Solvent is an aliphatic acid containing 2 to 10 carbon atoms. Process involves formation of methyl and formyl radicals at their respective molar ratio greater than unity. Number of reactants providing formyl radicals is no more than 20% of the reaction mixture. EFFECT: increased productivity of process. 21 cl, 2 ex
