CYCLIZATION AND DECARBOXYLATION IN ZWITTERIONIC MICELLES - EFFECTS OFHEAD GROUP-STRUCTURE

The spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion is strongly catalysed by micelles of zwitterionic surfactants, viz ., sulfobetaines [C(14)H(29)N(+)R(2)(CH2)(3)SO3-, R = Me, Pr and C16H3 3 N(+)Me(2)(CH2)(3)SO3-] and amine oxides (C(14)H(29)N(+)R(2)O(-), R = Me, Pr), with rates enhanced by factors of up to 1800. These micelles and those of the corresponding carboxybetaines are more effective cat alysts than those of the corresponding cationic surfactants, In all ca ses a change from Me to Pr at the head group speeds reaction by factor s of ca. 5-8 for the sulfobetaines and amine oxides and ca. 14 for the cationic surfactants. Cyclizations of the o-3-halopropyloxyphenoxide ions (halogen = Br, I), which are intramolecular S(N)2 reactions, are modestly micellar catalysed, but structural effects on the micellar ca talysis by cationic and betaine surfactants are in the same sequence, as for decarboxylation.