Micellar catalysis of organic reactions. XII. Basic hydrolysis of some alkyl and aryl N-(4-Nitrophenyl)carbamates

Abstract

The basic hydrolysis of a number of alkyl and aryl N-(4-nitrophenyl)carbamates in the presence and absence of micelles of cetyltrimethylammonium bromide (ctab) are reported. In water the stable product at 26ºC was N-(4-nitrophenyl)carbamate ion (3). At higher temperatures this carbamate ion slowly decomposed to 4-nitroaniline. In ctab the decarboxylation of the N-(4-nitrophenyl)carbamate ion was strongly catalysed (× 45) and thus the observed final product even at 26ºC was 4-nitroaniline.

Kinetic studies in water and in ctab were consistent with decomposition of the methyl carbamate (la) by a B_AC2 mechanism and the 2,2,2-trifluoroethyl carbamate (lc) by an E1cB mechanism.

The extent of ionization of the substrate carbamates to nitranion (4) was enhanced in ctab as was the rate of spontaneous decomposition of the nitranion. This is in contrast to other E1cB reactions reported in the literature, for which the rate of spontaneous decomposition of the carbanion was inhibited by ctab.

For compounds reacting by the B_AC2 mechanism, the tetrahedral intermediate (2) partitioned in favour of C-OR bond breaking rather than C-N bond breaking observed previously for some N-methyl derivatives.