An improved process for the trimethylsilylation of organic compounds with at least one active hydrogen atom with hexamethyldisilazane, the improvement comprising effecting the reaction in the presence of 0.001 to 10 mole percent of a catalyst of the formula X--NH--Y I wherein X and Y are individually an electron-withdrawing group or when X is an electron-withdrawing group, Y is selected from the group consisting of hydrogen and trialkylsilyl of 1 to 6 carbon atoms or X and Y together with the nitrogen atom to which they are attached form a cyclic electron-withdrawing group and novel trimethylsilylated thiols of the formula ##STR1## wherein R is a 5-or 6-membered heterocycle having at least one nitrogen or sulfur heteroatom and optionally substituted with at least one member of the group consisting of alkyl of 1 to 6 carbon atoms, phenyl, trimethylsilyl, trimethylsilyloxycarbonylmethyl and alkylamino of 1 to 6 carbon atoms, and novel trimethylsilylated 3'-substituted cephalosporanic acid derivatives.