Temperature effects upon aqueous micellar-assisted decarboxylation of 6-nitrobenzisoxazole-3-carboxylate and its 5-methyl derivative.
An investigation of temperature effects upon first-order rate constants in the micellar pseudophase for decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) and its 5-methyl derivative (6-NBIC-5-Me) was carried out. Surfactants used were cationic cetyltrialkylammonium bromide with alkyl = methyl (CTABr), ethyl (CTEABr), n-propyl (CTPABr), and n-butyl (CTBABr). The investigation shows that micelles speed up reactions by decreasing enthalpies of activation. Increase in head group bulk further speeds reactions still by a small decrease in the enthalpies, for both substrates. Values of DeltaH# and DeltaS# for 6-NBIC in the various surfactants give linear isokinetic plot, with CTBABr as outlier.
Hydrolyses of Dinitroalkoxyphenyl Phosphates in Aqueous Cationic Micelles. Acceleration by Premicelles
Hydrolyses of dianionic 2,4-dinitrophenyl phosphate, substituted at position 5 by Me, OMe, n-OC14H29 (DNMePP2-, DNMeOPP2-, and DNTDOPP2- respectively) are accelerated by cationic micelles of cetyl trialkylammonium bromide (CTABr, CTPABr, and CTBABr, with alkyl = Me, n-Pr, and n-Bu, respectively). There are well-defined rate maxima in dilute surfactant, below the critical micelle concentration, for reaction of DNTDOPP2- in the sequence CTBABr > CTPABr > CTABr, because of acceleration by premicelles which is not observed with the methoxy and unsubstituted derivatives. The rate maxima disappear as these species “dissolve” in micelles at higher surfactant concentrations.
Electron microscopic observation of molecular assemblies in iridescent surfactant solutions
Abstract Aqueous solutions of octadecyldimethylamine oxide (C 18 DAO), diglycerol isostearyl ether (C 18 DGE), and tetradecyldimethylamine oxide (C 14 DAO)/hexanol/decane were observed by transmission electron microscopy. While plate-like assemblies, unilamellar vesicles, or globular microemulsions are formed in dilute solutions of C 18 DAO, C 18 DGE, or C 14 DAO/hexanol/decane, multilamellar layers, multilamellar vesicles, or multilamellar microemulsions, respectively, exist in their iridescent solutions. On the other hand, lamellar liquid crystal is formed in concentrated solutions of C 18 DAO and C 18 DGE.