PURPOSE: To provide an improved method for allowing an org. liq. to react with oxygen and to increase the efficiency of reaction of the org. liq. with oxygen (the rate of reaction, the yield of a product, etc.).

CONSTITUTION: In vapor-liq. reaction for oxidizing org. chemicals, air, oxygen or oxygen-enriched air is introduced into a liq. contg. the org. chemicals in a mechanical stirring type reactor system and shearing energy is applied to the liq. with an impeller device in the system to attain bulk mixing. Reaction temp. in the system is kept lower than reaction temp. adaptable to similar vapor-liq. mixing and vapor-liq. reaction in a nonmechanical stirring type reactor system by at least 20°C and the rate of reaction and/or the yield of the desired product is increased by such a low reaction temp. level. The desired oxidation reaction is carried out on an increased performance level by combining the low reaction temp. with the mechanical stirring type reactor system.