The invention provides a novel method for preparing
benzimidazole proton pump inhibitors shown in a general formula II. In the presence of [(R'1R'2R'3R'4N)p][AmBnOr] polyoxometallate catalyst shown in a general formula III, 30 percent
peroxide is used as an oxidant to ensure that
thioether shown in a general formula I is subjected to selective oxidation. (See chart) in the general formula I and the general formulas II, R1, R2 and R3 are equal to H, C1-C5
alkyl, C1-C5 alkoxyl, C1-C5 haloalkyl, C1-C5
ether alkyl, or any combination thereof, and R4 is equal to the H, the C1-C5
alkyl, the C1-C5 alkoxyl, the C1-C5 haloalkyl, or pyrrol-2-yl; and in the general formula III, R'1, R'2, R'3, and R'4 are equal to the H, the C1-C5 alkyl, or any combination of the H and the C1-C5 alkyl, A is
metal Mo and W, B is P and the H, x is an integer between 1 and 10, and n, m, p and r are between 0 and 50 or any combination thereof.