Preparation method of esomeprazole magnesium trihydrate

The invention relates to a preparation method of esomeprazole magnesium trihydrate. The preparation method of the esomeprazole magnesium trihydrate comprises the following steps: (1) synthesizing 5-methoxy-2(((4-methoxy-3,5-dimethyl-2pyridyl)-methyl)sulfenyl)-1H-benzimidazole from 2-mercapto-5-methoxybenzimidazole and 2-chloromethyl-3,5-dimethyl-4-methoxypyridine hydrochloride which serve as raw materials; (2) oxidizing the 5-methoxyl-2[[(4-methoxyl-3,5-dimethyl-2pyridyl)-methyl]sulfenyl]-1H-benzimidazole asymmetrically in the presence of a chiral ligand, a catalyst and an oxidant to generate esomeprazole, enabling the esomeprazole to react with a solution of potassium hydroxide in methanol to generate esomeprazole potassium; and (3) dissolving the esomeprazole potassium, adding an inorganic magnesium salt to carry out reaction and convert the esomeprazole potassium into crude esomeprazole magnesium, and further refining the crude esomeprazole magnesium to obtain the esomeprazole magnesium trihydrate. The preparation method of the esomeprazole is simple and controllable, the reaction condition is mild, and the product of reaction is high in yield and purity, is stable and is suitable for industrial production.