Hydrochloric Acid → Tetramisole Hydrochloride

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A laboratory pressure bottle is charged with 92 ml. of 37% hydrochloric acid, cooled to 0°-5° C., and a mixture consisting of 79.0 g. (0.2 mole) of dl-3-(β-hydroxyphenethyl)-2-iminothiazolidine-p-toluene sulfonate and 40.4 g. (0.69 mole) of sodium chloride is added. The mixture is cooled to 0°-5° C., and 89.2 g. of 97% sulfuric acid (0.875 mole) is added. The pressure bottle is closed, and the contents heated at 50° C. for 20 hours. The reaction mixture is cooled and added to a mixture of 200 ml. water and 250 ml. of toluene. The mixture is agitated at 20°-30° C. and 50% sodium hydroxide solution is added thereto dropwise to adjust the pH to 6. The mixture is heated to 50°-55° C., 40.0 g. of anhydrous potassium carbonate is added quickly, and the mixture is stirred at 50°-55° C. for 2 hours. At the end of this time, an additional 100 ml. of water is added, the lower aqueous layer separated, and the organic layer clarified. The clarified organic layer is treated with a solution of isopropanolic hydrogen chloride below 40° C. to the point where Congo Red test paper changes from red to blue. The reaction mixture is then cooled to 10° C., the precipitate is separated by filtration, and filter cake washed with 100 ml. of ambient temperature isopropanol. The product is air dried to constant weight to obtain 44.4 g. (92.5% yield) of dl tetramisole hydrochloride, compound VII. The product contains less than 0.1% of the styryl impurity, VIII.

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