3,5-Dimethylpyrazole promoted sulfonation of acetic anhydride by H2SO4 to sulfoacetic acid and methanedisulfonic acid, and crystal structures of the complexes with Co2+, Zn2+, Ba2+, Pb2+ and Cs+

Sulfuric acid can sulfonate acetic anhydride (but not acetic acid) to sulfoacetic acid, and also to methanedisulfonic acid in the presence of 3,5-dimethylpyrazole. Under the experimental conditions employed, sulfonation of 3,5-dimethylpyrazole with concentrated sulfuric acid in acetic anhydride/acetic acid as solvent leads to a mixture of approximately 47 mol% 3,5-dimethylpyrazole-4-sulfonic acid, 34 mol% sulfoacetic acid and 19 mol% methanedisulfonic acid, as determined by 1H NMR spectroscopy. The Co2+, Zn2+, Ba2+ and Pb2+ complexes of the sulfoacetate ligand, as well as the Cs+ complex of the methanedisulfonate ligand were isolated upon crystallization of the compounds obtained from the reaction of the above ligand mixture with the corresponding metal oxide or carbonate in water. Single-crystal X-ray crystallography of Co(O3SCH2CO2)(H2O)3, Zn(O3SCH2CO2)(H2O)3, Ba(O3SCH2CO2)(H2O), Pb(O3SCH2CO2)(H2O) and Cs2(O3SCH2SO3) reveals a variety of new coordination modes of the two sulfonated ligands within those structures.