Method for the synthesis of a benzimidazole compound

A process for the manufacture of 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)-methyl]-thio]-1H-benzimidazole of formula I,

• the process comprising the following reaction steps carried out in a consecutive order in a solvent system without isolation of the intermediates formed during the process:
• a) reacting (4-methoxy-3,5-dimethyl-2-pyridinyl)methyl alcohol (pyrmethyl alcohol) of formula Ia,
• with a chloro-dehydroxylating agent to obtain (4-methoxy-3,5-dimethyl-2-pyridinyl)methyl chloride (pyrmethyl chloride) of formula Ib;
• and
• b) reacting the (4-methoxy-3,5-dimethyl-2-pyridinyl)methyl chloride of formula Ib with 2-mercapto-5-methoxybenzimidazole (metmercazole) of formula Ic,
• in the presence of a base to obtain 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl]thio]-1H-benzimidazole (pyrmetazole) of formula I;
• wherein the solvent system is the same for the entire reaction sequence and comprises an organic solvent selected from the group consisting of toluene, ethyl acetate and methyl chloride and an amount of water in the range of between 0.3 and 5.5 mg water per ml of the organic solvent.