17.4 g. 2,3-Diamino-1-[2-hydroxy-3-(3,4-dimethoxyphenethylamino)-propoxy]-benzene trihydrochloride are dissolved in 450 ml. chloroform and 50 ml. ethanol and mixed dropwise at ambient temperature with 3.2 ml. thiophosgene in 30 ml. chloroform. After 2 hours, the reaction mixture is treated with active charcoal and then evaporated to dryness. The residue is purified over a column of silica gel, using chloroform/methanol (8:2 v/v) as elution agent, to give 10 g. (62% of theory) of uniform product. After taking up in isopropanol and mixing with ethereal hydrochloric acid, followed by precipitation by the addition of ethyl acetate, there is obtained 4-[2-hydroxy-3-(3,4-dimethoxyphenethylamino)propoxy]-benzimidazoline-2-thione hydrochloride; m.p. 108°-110° C.
