Tautomerism in malonic ester derivatives of s-triazine

Pmr and uv spectra of tris-, bis- and monomalonic ester derivatives of s-triazine were studied in chloroform, dioxane, methanol, water, acetonitrile, dimethylsulfoxide, dimethylformamide, and cyclohexylamine. The results indicate that the enaminic structures (I, II and III) predominate in chloroform, dioxane, methanol and water. A small amount of enolate is present in acetonitrile and a larger amount of enolate is present in dimethylsulfoxide, dimethylformamide and cyclohexylamine in the case of the tris- and bismalonic ester derivatives of s-triazine. The conclusion is reached that for these latter compounds in basic solvent, a tautomeric equilibrium exists between the enaminic form and resonance-stabilized enolate ions.