Water → Omeprazole

Participants

Reaction Conditions

Reaction Steps

1.6 kg (5.0 mol) of 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)-methyl]thio]-1H-benzimidazole was dissolved in 7.51 of ethyl acetate. To the solution was added 31 ml (1.7 mol) water. To the mixture was added 856 ml (5.0 mol) of (+)-diethyl L-tartrate, 744 ml (2.5 mol) of titanium(IV) isopropoxide and 436 ml (2.5 mol) diisopropylethylamine at room temperature. The addition of 830 ml (4.5 mol) cumene hydroperoxide was then performed at 30° C. After stirring for one hour at 30° C. the reaction was complete. Chiral and achiral chromatographic analyses showed that the mixture consited of 75% sulphoxide with an enantiomeric excess (e.e.) of 80%. The mixture was cooled to 10° C. and after addition of 1.5 l of isooctane and ethyl acetate (0.5 l), the product was extracted three times with an aqueous ammonia (12%) solution with a total volume of 14 l. The combined aqueous phases were neutralised by addition of 1.5 l of concentrated acetic acid in the presence of ethyl acetate (4 l). The phases were separated and the aqueous phase was extracted with ethyl acetate (4 l). The solvent of the combined organic solutions was removed. Acetone (3.0 l) was added to precipitate the racemate of omeprazole which was filtered off. HPLC--analyses (achiral and chiral columns) of the filtrate showed that this solution consisted of 90% sulphoxide with an optical purity of 95% e.e. and thus the optical purity has been improved from 80% e.e. to 95% e.e. simply by one precipitation of racemic omeprazole. Further, a content analysis (HPLC) of the filtrate showed that the yield was 1.0 kg (58%). The (+)-enantiomer of 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl]sulphinyl]-1H-benzimidazole was not isolated in its neutral form but further processed to corresponding sodium salt.

Provenance & Evidence