Heterocyclic thiomethylation of the 3-position of 7-aminocephalosporanic acids

A process of producing a 7-amino-3-heterocyclic thiomethyl-.DELTA..sup.3 -cephem-4-carboxylic acid represented by the formula ##STR6## wherein R.sup.1 represents a hydrogen atom or a methoxy group and R.sup.2 represents a member selected from the group consisting of a thiazolyl group, an oxazolyl group, an isothiazolyl group, a thiadiazolyl group, a triazolyl group, and a tetrazolyl group, whch are substitutable by a lower alkyl group, a carboxy lower alkyl group, a di-lower alkylamino lower alkyl group wherein lower alkyl represents 1 to 6 carbon atoms, and an amino group, or the pharmaceutically acceptable salts thereof, which comprises reacting a 7-amino cephalosporanic acid represented by the formula ##STR7## wherein R.sup.1 is defined above and the alkali metal, ammonium or organic base salts thereof and a thiol represented by the general formula

• HS--R.sup.2
• wherein R.sup.2 is defined above, in a substantially anhydrous medium consisting essentially of concentrated or fuming sulfuric acid.