The kinetic of degradation of 1-butyl-3-methylimidazole-2-ylidene (selected as model N-heterocyclic carbene - NHC), generated in organic solvents by cathodic reduction of the parent 1-butyl-3- methylimidazolium salts BMIm-X, was studied by a simple voltammetric analysis. The effect of NHC degradation rate on the efficiency of an organocatalyzed reaction (the synthesis of g-butyrolactone from cinnamaldehyde and trifluoromethylacetophenone) was investigated. The nature of the solvent and of the anion X have a remarkable effect on the stability of the NHC, the bis(trifluoromethylsulfonyl) imide anion being the best for a long lasting carbene (while acetonitrile seems to be the worst solvent). The role of X has been related to a competition between NHC and X , in the hydrogen bonding interaction with BMIm+. The higher the stabilization of NHC by hydrogen bond, the lower its degradation rate. These hydrogen bonding interactions, previously reported in pure BMIm-X, seem to be operative even in organic solvents containing BMIm-X at low concentrations (c < 0.1 mol L 1). The effect of the nitrogen alkyl substituents on the degradation of NHC (and thus on its efficiency as organocatalyst) is also pointed out.
Feroci, M., Chiarotto, I., D'Anna, F., Forte, G., Noto, R., Inesi, A. (2015). STABILITY AND ORGANOCATALYTIC EFFICIENCY OF N-HETEROCYCLIC CARBENES ELECTROGENERATED IN ORGANIC SOLVENTS FROM IMIDAZOLIUM IONIC LIQUIDS. ELECTROCHIMICA ACTA, 2015(153), 122-129 [10.1016/j.electacta.2014.11.135].
STABILITY AND ORGANOCATALYTIC EFFICIENCY OF N-HETEROCYCLIC CARBENES ELECTROGENERATED IN ORGANIC SOLVENTS FROM IMIDAZOLIUM IONIC LIQUIDS
D'ANNA, Francesca;NOTO, Renato;
2015-01-01
Abstract
The kinetic of degradation of 1-butyl-3-methylimidazole-2-ylidene (selected as model N-heterocyclic carbene - NHC), generated in organic solvents by cathodic reduction of the parent 1-butyl-3- methylimidazolium salts BMIm-X, was studied by a simple voltammetric analysis. The effect of NHC degradation rate on the efficiency of an organocatalyzed reaction (the synthesis of g-butyrolactone from cinnamaldehyde and trifluoromethylacetophenone) was investigated. The nature of the solvent and of the anion X have a remarkable effect on the stability of the NHC, the bis(trifluoromethylsulfonyl) imide anion being the best for a long lasting carbene (while acetonitrile seems to be the worst solvent). The role of X has been related to a competition between NHC and X , in the hydrogen bonding interaction with BMIm+. The higher the stabilization of NHC by hydrogen bond, the lower its degradation rate. These hydrogen bonding interactions, previously reported in pure BMIm-X, seem to be operative even in organic solvents containing BMIm-X at low concentrations (c < 0.1 mol L 1). The effect of the nitrogen alkyl substituents on the degradation of NHC (and thus on its efficiency as organocatalyst) is also pointed out.File | Dimensione | Formato | |
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