Hydrochloric Acid → p-Toluenesulfonic acid

Participants

Reaction Conditions

Reaction Steps

230.4 g of water and 172.8 g (1.706 mole) of 36% hydrochloric acid were placed in a 2-liter flask as a reactor, and cooled to 3° C. Thereto was dropwise added 276.5 g (0.315 mole) of an aqueous solution of a potassium salt of 2-amino-5-fluorothiophenol at 0 to 5° C. with stirring, followed by stirring for 1 hour. Further, 15.8 g of 50% potassium hydroxide was added dropwise to adjust the system pH to 4.95. Aging was conducted for 1 hour. Then, 56.4 g (0.296 mole) of p-toluenesulfonic acid monohydrate was added, followed by aging at 3° C. for 30 minutes. Thereto was dropwise added, at 16 to 19° C., a beforehand prepared solution of D-alanine-N-carboxyanhydride (46.8 g, purity: 78.3%, 0.318 mole) dissolved in tetrahydrofuran (73 ml). Aging was conducted at 15 to 20° C. for 18 hours. The resulting crystals were collected by filtration and dried at 60° C. to obtain 96.6 g of a p-toluenesulfonate of [2-(6-fluorobenzothiazolyl)]ethylamine (purity: 93.76%) (the yield was 78.0% relative to the potassium salt of 2 amino-5-fluorothiophenol).

Provenance & Evidence