PURPOSE: To obtain the compound of high optical purity, which is used as a synthetic intermediate for agricultural chemicals by decomposing optically active 2-chlorosulfinoxypropionic acid ester, rinsing the reaction mixture and purifying the product by distillation.

CONSTITUTION: An optically active 2-chlorosulfinoxypropionic acid ester of formula I (R is 1 to 6C alkyl) is decomposed in the presence of a base such as pyridine. After decomposition, the reaction mixture is rinsed with an adequate amount of water, separated into the organic and aqueous phases, the aqueous phase is discarded, and the remaining organic phase is purified by distillation to give the objective compound of formula II. The amount of water used is preferably 20 to 100 times the weight of the base. The objective compound of formula II is used as a synthetic intermediate of agricultural chemicals of optically active phenoxypropionic acids.