Ethanethiol → 4-Amino-5-chloro-2-hydroxybenzoic acid

A cooled (5° C.) suspension of 60% sodium hydride/oil dispersion (20.0 g, 0.50 mole) in anhydrous dimethylformamide (300 mL) under nitrogen was treated slowly dropwise with ethyl mercaptan (18.7 g, 0.30 mole) so as to maintain a pot temperature below 15° C., then stirred at room temperature for 15 minutes, cooled (5° C.), and treated in portions with 4-amino-5-chloro-2-methoxybenzoic acid (40.33 g, 0.20 mole). The mixture was heated to 105°±5° C. for 4 hours, cooled, and concentrated in vacuo to remove most of the dimethylformamide, then plunged into water (500 mL). The aqueous solution was extracted with methylene chloride (2×150 mL), and ether (150 mL), acidified with concentrated HCl (55 mL), filtered, and the filter cake washed with water and dried in vacuo to afford 35.7 g of crude product. Crystallization from tetrahydrofuran/hexane afforded 31.3 g (83%) of white solid; mp 192° C.