I have found that propylene glycol can be formed by heating glycerol to 302 F in the presence of a catalyst, which may be either an ion exchange resin or a small amount of sulfuric acid. In the process of heating Metol in glycerol, the sulfuric acid attached to the Metol was detached and served as a catalyst, and what I may have is Metol base in propylene glycol. As to what becomes of the sulfuric acid, perhaps it winds up as a sulfate of either the glycerol or the propylene glycol. Comments please.