Triethylamine → 5,6-dichloro-1,3-dihydro-1-(3-hydroxypropyl)-2H-benzimidazol-2-one methanesulfonate

To a stirred mixture of 31.2 parts of 3-[(2-amino-4,5-dichlorophenyl)amino]-1-propanol hydrochloride in 200 parts of water is added dropwise, during a 15 minute-period, a solution of 10.6 parts of potassium cyanate in 50 parts of water at a temperature between 15° and 20° C. Upon completion, stirring is continued first for 20 minutes at room temperature and further for 20 hours at reflux. The reaction mixture is allowed to cool over week-end to room temperature. The precipitated product is filtered off and boiled in trichloromethane. The undissolved part is filtered off and boiled in 4-methyl-2-pentanone. After cooling, the product is filtered off and dried, yielding 14.5 parts (48%) of 5,6-dichloro-1,3-dihydro-1-(3-hydroxypropyl)-2H-benzimidazol-2-one; mp. 174.7° C. To a stirred mixture of 13.3 parts of 5,6-dichloro-1,3-dihydro-1-(3-hydroxypropyl)-2H-benzimidazol-2-one, 8 parts of N,N-diethylethanamine and 260 parts of dichloromethane are added dropwise 7.4 parts of methanesulfonyl chloride. Upon completion, stirring is continued for one hour at reflux temperature. The reaction mixture is washed with water, dried, filtred and evaporated. The solid residue is shaken with acidified water and 4-methyl-2-pentanone. The whole is filtered (the filtrate is set aside) and the filter-cake is dried, yielding a first fraction of 6.2 parts of 5.6-dichloro-1,3-dihydro-1-(3-hydroxypropyl)-2H-benzimidazol-2-one methanesulfonate. The 4-methyl-2-pentanone-phase is separated from the filtrate, dried, filtered and evaporated, yielding a second fraction of 8 parts of 5,6-dichloro-1,3-dihydro-1-(3-hydroxypropyl)-2H-benzimidazol-2-one methanesulfonate as an oily residue.