To obtain a substance which can be produced at a reasonable cost on an industrial scale and the use of which rationalizes the systhesis.

The chloride is obtained by reacting an alkali metal salt of 3-aminonapthalene-1, 5-disulfonic acid with an alkali metal hydroxide and water at a weight ratio of 1:(1-1.6):(1-1.6) at 220-230°C to give a dialkali salt of 3- hydroxy-2-methylbenzoic acid, removing insoluble components from the resultant reaction mixture, adjusting the pH of the resultant mixture by adding an acid to 11.5-13.5, reacting the resultant mixture with acetic acid anhydride at -5 to 25°C, followed by the addition of an acid to precipitate 3-acetoxy-2- methylbenzoic acid, which is then isolated to react with an inorganic acid chloride.