Study of adducts in the photometric determination of maleic anhydride by its reaction with 2-methylimidazole

The interaction of maleic anhydride with 2-methylimidazole in different solvents and without solvents was studied using electronic, IR, and H-1 NMR spectrometry; differential scanning calorimetry; and potentiometric titration. On the basis of experimental data and quantum-chemical calculations, it was demonstrated that molecular complexes can be formed as intermediates in the chain of consecutive reactions. It was found that, depending on the nature of anhydride, complex formation can be absent (in the case of phthalic anhydride). Because of the formation of the molecular complex between maleic anhydride and 2-methylimidazole, the nucleophilic addition of the latter at the double bond of anhydride yielding amide of the succinic acid derivative is possible.