ACID-CATALYZED HYDROLYSIS AND MONOLAYER PROPERTIES OF KETAL-BASED CLEAVABLE SURFACTANTS

The hydrolytic reactivities and monolayer properties of several ketal-based, cleavable surfactants were determined in 0.10 M hydrobromic acid at 50C and on a pH 7.5 buffer subphase at 25C, respectively. The hydrolyses of diastereomeric cis- (la) and frans-[(2-heptadecyl-2-methyl-l,3-dioxolan-4-yl)-methyl] trimethylammonium bromide (lb) were studied in homogeneous and mixed micellar forms. A mixture of the shorter chain analogues, cis- (2a) and frarcs-[(2-octyl-2-methyl-l,3-dioxolan-4-yl)methyl]-trimethylammonium bromide (2b), was examined in unaggregated and micellar forms. [(2,2-Dihepta-decyl-l,3-dioxolan-4-yl)methyl]trimethylammonium bromide (3) and [(2,2-dimethyl-l,3-dioxolan-4-yl)-methyl]trimethylammonium bromide (4) were studied in vesicular form and as a nonaggregating analogue, respectively. Relative to the reactivities of 4 and 2 in unaggregated form, those of micellar 1 and 2 and vesicular 3 were about 2 orders of magnitude less. The observed pseudo-first-order rate constants, kj,, for la and lb decreased on going from homogeneous to mixed micelles, and the ratio of values also changed. The ratio of values for 2a and 2b changed on going from unaggregated to mixed micellar form. The monolayer characteristics of la and lb were identical but slightly different than that of a 50:50 mixture of the two. © 1990, American Chemical Society. All rights reserved.