The general procedure for the synthesis of thiomorpholine-1,1-dioxide hydrochloride from tert-butyl thiomorpholine-4-carboxylate 1,1-dioxide was as follows: tert-butyl 1,1-dioxothiomorpholine-4-carboxylate (2.03 g, 8.63 mmol) was dissolved in a hydrochloric acid-methanol (10%, 20 mL, purchased from Tokyo Kasei Kogyo Co.) and tetrahydrofuran (20 mL) in a solvent mixture. Concentrated hydrochloric acid (4.0 mL) was slowly added to the reaction system under stirring at room temperature. The reaction mixture was continued to be stirred at room temperature for 3 hours. Upon completion of the reaction, the solvent was removed by concentration under reduced pressure. Methanol (20 mL), tetrahydrofuran (20 mL), and concentrated hydrochloric acid (4.0 mL) were added to the resulting solid, followed by the addition of water (10 mL) to ensure complete dissolution of the solid. This solution was stirred at room temperature for 1 hour. The solvent was again concentrated under reduced pressure to remove the solvent. The resulting crystals were suspended in methanol, filtered, washed with methanol and dried under ventilated conditions to give thiomorpholine-1,1-dioxide hydrochloride as colorless crystals (1.49 g, 8.65 mmol, quantitative yield). The product was characterized by 1H-NMR (DMSO-d6): δ 3.54 (8H, m), 9.83 (2H, brs).
