Method of making mercaptoalkylalkoxysilanes

In a first embodiment of a process for making mercaptoalkylalkoxysilanes, a pH adjusting agent and a sulfide containing compound are mixed in an aqueous phase to provide a pH of 4-9, a phase transfer catalyst is added to the aqueous phase, a haloalkylalkoxysilane is then added to the aqueous phase to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and the desired mercaptoalklyalkoxysilanes are separated from the water soluble byproducts. In an alternate embodiment, the haloalkylalkoxysilane, the phase transfer catalyst, and an anhydrous pH adjusting agent such as sulfur dioxide, carbon dioxide, hydrogen sulfide, phosphoric acid, boric acid, and hydrochloric acid, are mixed, then an aqueous solution of a sulfide containing compound is added to form a reaction mixture containing mercaptoalkylalkoxysilanes and water soluble byproducts, and desired mercaptoalklyalkoxysilanes are separated from water soluble byproducts.