Hydrochloric Acid → p-Toluenesulfonic acid

Participants

Reaction Conditions

Reaction Steps

80 ml of water and 60 g (0.592 mole) of 36% hydrochloric acid were placed in a 500-ml flask as a reactor, and cooled to 0 to 2° C. Thereto was dropwise added, at 0 to 5° C. with stirring, 96.0 g (0.112 mole) of an aqueous solution of a potassium salt of 2-amino-5-fluorothiophenol. The resulting mixture had a pH of 0.90. Further, 20.0 g (0.105 mole) of p-toluenesulfonic acid monohydrate was added. Thereto was dropwise added, at 16 to 20° C., a solution of D-alanine-N-carboxyanhydride (16.7 g, purity: 78.3%, 0.318 mole) dissolved in tetrahydrofuran (30 ml) (the solution was beforehand prepared at 16 to 20° C.). Aging was conducted at 15 to 20° C. for 4 hours. The resulting crystals were collected by filtration and dried at 60° C. to obtain 31.5 g of a p-toluenesulfonate of [2-(6-fluorobenzothiazolyl)]ethylamine (purity: 98.95%) (the yield was 75.5% relative to the potassium salt of 2-amino-5-fluorothiophenol).

Provenance & Evidence