Abs. 42, 1228b (1948)], treating the resulting 2',4'-dichloro-3'-methylacetophenone derivative of formula (7) with an oxidizing agent such as nitric acid or chromic acid, and treating the resulting 2,4-dichloro-3-methylbenzoic acid of formula (8) with a halogenating agent such as thionyl chloride, phosphorus pentachloride and phosphorus tribromide, as schematically shown below. ##STR8##