The present invention provides a process comprising admixing a thioether with about 1.05 to about 1.6 molar equivalents of an active chlorine-containing oxidant, preferably sodium hypochlorite, and about 2.5 to about 5.0 molar equivalents of an alkali metal base; and recovering a sulfoxide that is preferably pantoprazole, lansoprazole, omeprazole, or rabeprazole. The process may further comprise contacting the sulfoxide with a source of sodium ions, preferably sodium hydroxide, to produce the sodium salt of the sulfoxide. The invention also relates to novel chlorinated derivatives of pantoprazole including 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)-chloromethyl]sulfinyl- ]-1H-benzimidazole and 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)-chlorohydroxymethyl]s- ulfinyl]-1H-benzimidazole and processes for making them. The invention also relates to processes of quantifying and identifying a compound other than pantoprazole in a mixture of pantoprazole and at least one other compound.