A solid-state oxidation of 1,1,3,3-tetramethylguanidinium 4-methylbenzenesulfinate to 1,1,3,3-tetramethylguanidinium 4-methylbenzenesulfonate.

The organic acid-base complex 1,1,3,3-tetramethylguanidinium 4-methylbenzenesulfonate, C5H14N3(+)·C7H7O3S(-), was obtained from the corresponding 1,1,3,3-tetramethylguanidinium 4-methylbenzenesulfinate complex, C5H14N3(+)·C7H7O2S(-), by solid-state oxidation in air. Comparison of the two crystal structures reveals similar packing arrangements in the monoclinic space group P2(1)/c, with centrosymmetric 2:2 tetramers being connected by four strong N-H···O=S hydrogen bonds between the imine N atoms of two 1,1,3,3-tetramethylguanidinium bases and the O atoms of two acid molecules.