Photochemistry of imidazolium cations. Water addition to methylimidazolium ring induced by UV radiation in aqueous solution

SARMIENTO, GABRIELA P.; ZELCER, ANDRÉS; ESPINOSA, MARIELA S.; BABAY, PAOLA A.; MIRENDA, MARTÍN

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

ELSEVIER SCIENCE SA

Lugar: Amsterdam; Año: 2016 vol. 314 p. 155 - 163

1010-6030

The UV-C induced photoaddition of water to N -alkyl- N ́-methylimidazolium cations was studied. The main products of the photoreactions exhibit chemical additions of a proton and a hydroxyl group to either positions 4 or 5 of the imidazolium ring. For the case of unsymmetrical cations, the ratio between the two positional isomer populations depends on the lengths of the alkyl chains bonded to the nitrogen atoms. The most abundant isomer is the one in which the hydroxyl group adds at the side of the ring having the longer alkyl substituent. Experiments performed in D2O solutions reveal that the additions of hydrogen and hydroxyl group take place at different carbon atoms at the imidazolium ring, in a reaction that produces equal amounts of diastereoisomers. Moreover, the formation of diastereoisomers at equal proportions suggests that the reaction proceeds in an unconcerted fashion.