DECARBOXYLATION OF 6-NITROBENZISOXAZOLE-3-CARBOXYLATE ION IN DICHLOROMETHANE - THE POSSIBLE ROLE OF REVERSE MICELLES

Spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion (1) in dichloromethane with added base is catalyzed by cationic surfactants (RNMe3Br, R = n-C8H17, n-C12H25, and n-C16H33) by EtNMe3Br and n-BuNMe3Br, by R4NBr (R = Et, n-Bu, n-C8H17, and n-C12H25), and by PhCH2NR3Br (R = Et, n - Bu). The teraalkylammonium and benzylammonium bromides are better catalysts than the n-alkylammonium bromides. Reaction in Bu4NBr and CTABr (n-C16H33NMe3Br) is inhibited by water, and conductivity and 1H NMR spectrometry show that CTABr plus water form "water pool" reverse micelles. Reaction in the absence of quaternary ammonium salts is faster when the base is tetramethylguanidine rather than Et3N, probably because Et3N+H deactivates 1 by hydrogen bonding. This difference disappears in CTABr, which disrupts the hydrogen bonding. In the absence of water, reaction probably occurs in small ion clusters of quaternary ammonium bromides which are gradually transformed into less catalytically effective water pool reverse micelles on addition of water. © 1990.