The MSDS is incorrect; CAS 21799-87-1 is actually potassium 1,4-dihydroxybenzene monosulfonate. This compound is a weak developing agent and IIRC was once sold by Kodak as BD-1.
Be aware that not all ingredients may be listed in an MSDS.
My confidence in a company is diminished when I run across such errors. Moersh obviously didn't require a chemist to proofread this MSDS.