The present invention is directed to a process for the catalytic oxidation of the thioether 5-methoxy-2-((4-methoxy-3,5-dimethyl-2-pyridinyl)methyl)methylthio)-1H-be- nzimidazole to its sulfoxide: 5-methoxy-2-((4-methoxy-3,5-dimethyl-2-pyridinyl)methyl)methylsulfinyl)-1- H-benzimidazole comprising: reacting the thioether with: 1) a transition metal catalyst; and, 2) an oxygen source; wherein the thioether is oxidized to a sulfoxide and wherein one of either the R and S enantiomers is formed to an enantiomeric excess.