Scalable, safer and greener syntheses of vinylimidazoles via reactive distillation of hydroxyethylimidazole intermediates

Abstract

1-Vinylimidazole has been extensively utilized by the polymer science community, due to its high reactivity for free radical polymerization and the variety of uses for both neutral polyvinylimidazole and cationic polyvinylimidazolium forms. While much rarer, 4-vinylimidazoles and 2-vinylimidazoles are less synthetically accessible. In comparison to conventional methods for the synthesis of vinylimidazole derivatives from energy-intensive reaction conditions utilizing hazardous, gaseous precursors, herein we demonstrate a simple and versatile two-step method applied to the synthesis of seven 1-vinylimidazoles with different substituents as well as an initial demonstration of a facile method to synthesize the rare compound 1-methyl-2-vinylimidazole. The process relies upon the synthesis of N-hydroxyethylimidazole precursors via a ring-opening reaction from substituted imidazoles with ethylene carbonate, a 'green' substance formed from CO 2 and ethylene oxide. For the synthesis of 1-methyl-2-vinylimidazole, the hydroxyethylimidazole intermediate is conveniently formed from 1,2-dimethylimidazole and paraformaldehyde. These hydroxyethylimidazoles are subsequently dehydrated to the corresponding 1-or 2-vinylimidazole forms using a base-catalyzed reactive distillation. The optimization of process conditions is discussed, and properties of the vinylimidazole derivatives were computationally studied using density functional theory calculations. This work reveals scalable synthetic methods for previously inaccessible vinylimidazole compounds which can enable the design of new polymers.