Sulfuric Acid → 5-(tert-Butylsulfanyl)-2-propoxybenzamide

t-Butanol (16 g.) was added to an aqueous sulphuric acid solution (200 ml.; containing 75% w/w sulphuric acid) cooled in ice-water. The mixture was stirred until all the t-butanol had dissolved, and then 2-propoxy-5-mercaptobenzamide (20 g.; prepared as described in Reference Example 2) was added in small portions with stirring during 15 minutes. After all the solid had dissolved the mixture was allowed to warm up to room temperature and kept at that temperature for 15 minutes. The solution was diluted with water (600 ml.), and the precipitated solid was filtered off and dissolved in chloroform (200 ml.). The chloroform solution was then washed with aqueous sodium hydroxide solution (2N; 40 ml.) and then with water (3 × 20 ml.), and dried over sodium sulphate. The solvent was removed in vacuo and the residue was recrystallised from aqueous ethanol, to give 5-t-butylthio-2-propoxybenzamide (15 g.), m.p. 135.5° - 137.5° C.