The mechanisms of the formation of by-products in the catalytic synthesis of C-alkylimidazoles from diamines and carboxylic acids

Article abstract of DOI:10.1007/BF00698956

The formation of 1-ethyl-2-methylimidazole (1-Et-2-MI) and 1-ethyl-2-methylimidazoline (1-Et-2-MIN), intermediates in the synthesis of 2-methylimidazole (2-MI) from ethylenediamine (EDA) and AcOH in the presence of a platinum-on-alumina catalyst, was studied.Using CH3(14)COOH the incorporation of two acetate units into 1-Et-2-MI and 1-Et-2-MIN molecules was demonstrated.The same products were also obtained on dehydrogenation of 2-methylimidazoline (2-MIN) under mild conditions (220-230 deg C).A part of the latter is transformed to N-ethyl ethylendiamine (EEDA) and EDA.These facts indicate that both 1-Et-2-MI and 1-Et-2-MIN result from hydrogenolysis of the imidazoline ring with subsequent ethylation.A reverse reaction, the C5-cyclization of EEDA, was also observed.The formation of 2-MI is favored by increasing temperature.