A new class of heterocyclic betaines: 1,1-dimethyl-3-phenylpyrazolium-5-oxide

1,1-Dimethyl-3-phenylpyrazolium-5-oxide (1) was isolated as a minor product (3%) in the reaction of ethyl benzoylacetate with 1,1-dimethylhydrazine and also was obtained as the major product (58%) from the reaction of methyl p-toluenesulfonate with ethyl benzoylacetate dimethylhydrazone. The structural assignment was made on the basis of chemical reactions and spectral data and the formula is represented by a resonance structure for which there are two principal canonical forms. Reaction of 1 with methanol at room temperature afforded methyl benzoylacetate dimethylhydrazone. Ethyl benzoylacetate dimethylhydrazone was shown to exist as a tautomeric mixture containing 65% of the imine form at room temperature.