Claims

1. A method for preparing 2-(2-pyridylmethylsulphinyl) benzimidazole having the following formula [A], which comprises undergoing an oxidation reaction of an intermediate having the following formula [B] in a solvent and in the presence of a catalyst and an oxidant to form the compound [A]: wherein R¹ in [A] and [B] is hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy, halogenated C1-C6 alkyl, or halogenated C1-C6 alkoxy; R² and R³ independently are hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy, halogenated C1-C6 alkyl, or halogenated C1-C6 alkoxy; and R⁴ is hydrogen, C1-C6 alkyl, or halogenated C1-C6 alkyl; characterized in that said catalyst is acetyl acetonate of molybdenium (II).

2. The method as claimed in claim 1, wherein said oxidant is H_2O.sub.2, tert-butylhydroperoxide, or Cumene hydroperoxide.

3. The method as claimed in claim 1, wherein said solvent is C1-C6 alcohol, chlorinated C1-C4 alkane, or ethyl acetate.

4. The method as claimed in claim 3, wherein said solvent is methanol, ethanol, iso-propanol, n-butanol, or iso-butanol.

5. The method as claimed in claim 3, wherein said solvent is dichloromethane, dichloroethane, or ethyl acetate.

6. The method as claimed in claim 1, wherein said oxidation reaction is carried out in a homogeneous phase solvent or a two-phase solvent.

7. The method as claimed in claim 6, wherein said oxidation reaction is carried out in the two-phase solvent, and an interphase transfer catalyst is added to the two-phase solvent, so that the oxidation reaction is carried out under the presence of said interphase transfer catalyst, wherein said interphase transfer catalyst is selected from the group consisting of quaternary ammonium salt, quaternary phosphate salt, polyether, and crown ether.

8. The method as claimed in claim 1, wherein said oxidation reaction is carried out in a temperature of -15~30° C.

9. The method as claimed in claim 1, wherein a weight ratio of said solvent to said intermediate [B] is 2:1 to 20:1.

10. The method as claimed in claim 1, wherein a mole ratio of said oxidant to said intermediate [B] is 1:1 to 5:1.

11. The method as claimed in claim 1, wherein a weight ratio of said catalyst to said intermediate [B] is 3% to 20%.

12. The method as claimed in claim 1, wherein said compound [A] is 2-[[3-methy-4-(2,2,2-trifluoroethoxy)pyrid-2-yl]methylsulfinyl]-1H-benzim- idazole.

13. The method as claimed in claim 1, wherein said compound [A] is 5-methoxy-2-[(4-methoxy-3,5-dimethyl-2-pyridyl) methylsulfinyl]-1H-benzimidazole.

14. The method as claimed in claim 1, wherein said compound [A] is 5-Difluoromethoxy-2-[(3,4-dimethoxy-2-pyridyl-methylsulfinyl)-1H-benzimid- azole].

15. (canceled)

16. The method as claimed in claim 7, wherein said interphase transfer catalyst is polyether.

17. The method as claimed in claim 16, wherein said, polyether is polyethylne glycol.