Hydroxy sulfonic acids in general and isethionic acid (2-hydroxy ethyl sulfonic acid) in particular can be prepared at 99+% purity and good yields by the selective oxidation of a precursor hydroxy mercaptan with hydrogen peroxide. The resulting product is pure enough to be used directly in the synthesis of sulfo-acrylic esters which are finding considerable use as stabilizers in producing vinylidene chloride copolymers used for FDA approved packaging films.