The spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylateio n is strongly catalysed by micelles of zwitterionic surfactants, viz., sulfobetaines [C14H29N+R ,(CH,),SO, - ,R = Me, Pr and C16H33N+MeZ(CH2)3Sa0n3d- ]a mine oxides (C,,H,,N+R,O-, R = Me, Pr), with rates enhanced by factors of up to 1800. These micelles and those of the corresponding carboxybetaines are more effective catalysts than those of the corresponding cationic surfactants. In all cases a change from Me to Pr at the head group speeds reaction by factors of ca. 5-8 for the sulfobetaines and amine oxides and ca. 14 for the cationic surfactants. Cyclizations of the o-3-halopropyloxyphenoxideio ns (halogen = Br, I), which are intramolecular S,2 reactions, are modestly micellar catalysed, but structural effects on the micellar catalysis by cationic and betaine surfactants are in the same sequence, as for decarboxylation.
Cyclization and Decarboxylation in Zwitterionic Micelles. Effects of Head Group Stucture
DI PROFIO, Pietro;GERMANI, Raimondo;SAVELLI, Gianfranco;
1996
Abstract
The spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylateio n is strongly catalysed by micelles of zwitterionic surfactants, viz., sulfobetaines [C14H29N+R ,(CH,),SO, - ,R = Me, Pr and C16H33N+MeZ(CH2)3Sa0n3d- ]a mine oxides (C,,H,,N+R,O-, R = Me, Pr), with rates enhanced by factors of up to 1800. These micelles and those of the corresponding carboxybetaines are more effective catalysts than those of the corresponding cationic surfactants. In all cases a change from Me to Pr at the head group speeds reaction by factors of ca. 5-8 for the sulfobetaines and amine oxides and ca. 14 for the cationic surfactants. Cyclizations of the o-3-halopropyloxyphenoxideio ns (halogen = Br, I), which are intramolecular S,2 reactions, are modestly micellar catalysed, but structural effects on the micellar catalysis by cationic and betaine surfactants are in the same sequence, as for decarboxylation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
