NO,) into carboxylic and sulfonic acids. Reactions are second order and have small substituent effects, with p = -0.6 based on om and op substituent parameters, but rates increase markedly with increasing water content in aqueous MeCN and entropies of activation are negative. The initial step is very similar t o the oxidation of methyl aryl sulfides by HS0,which has similar solvent and substituent effects. Enthalpies of activation are much lower for oxidation of the sulfides than of the corresponding esters but entropies of activation are similar.

Rate constants of reaction of n-dodecyl [2-(hydroximino)-2-phenylethyl]dimethylammonium bromide (DHDBr) with p-nitrophenyl diphenyl phosphate in comicelles with inert surfactants, at pH such that the oximate zwitterion (DHD) is formed quantitatively, depend on the mole fraction of DHD to total surfactant. Second-order rate constants of reaction in the micellar pseudophase decrease in the following sequence of inert surfactant headgroups:  phosphine oxide ≈ sulfoxide ≈ pyrrolidinone > Me3N+ > sulfobetaine > Bu3N+ > polyoxyethylene > OSO3 -. Except for reaction in anionic comicelles these second-order rate constants vary within a factor of 5 and appear to depend on the local structure of the interface rather than on micellar charge per se. The simple relation between rate constants and nucleophile concentration given by the mole fraction of DHDBr applies reasonably well to mixtures of C16H33NMe3Br and the other inert surfactants. Reaction is relatively slow in comicelles of DHD and C12H25OSO3Na, probably due to different locations of reactants in the interfacial region. Samples of DHDBr prepared and purified by the literature method are contaminated by pyridine hydrochloride, which is removed by washing with aqueous NaBr.

No abstract

Comicelles of (Z)-dodecano-N-phenylhydroxamate ion (1b) with cationic and sulfobetaine surfactants effectively accelerate the hydrolysis of p-nitrophenyl diphenyl phosphate (pNPDPP). The surfactants are cetyl trimethyl-and tributylammonium bromide (CTABr and CTBABr respectively), and (tetradecyldimethylammonio)propanesulfonate (SB3-14). Reaction is slower in comicelles with Brij-35, 23-dodecyl ether (C12E23), and much slower in comicelles with sodium dodecyl sulfate (SDS). In all conditions, the hydroxamic acid was fully deprotonated and pNPDPP was fully micellar-bound and, on the basis of NMR data (Langmuir 1997, 13, 6439), it appears that the rate effects are due to differences in the relative locations of pNPDPP and the hydroxamate residue in the interfacial region, which are related to micellar charge. Inhibition of reaction in SB3-14 on addition of ClO4 -, and acceleration in SDS by weakly hydrophilic cations, are understandable in these terms, as are effects of n-dodecyldimethylphosphine oxide and n-decylmethyl sulfoxide on reactivity in SDS. The propiono-N-phenylhydroxamate ion (1a) is an E-Z mixture in water, which complicates comparisons of rate constants of this reaction with pNPDPP in water with those of 1b in micelles.

Reactions of OH- and F- with p-nitrophenyl diphenyl phosphate (pNPDPP) are inhibited by very dilute dodecyl (10) and (23) polyoxyethylene glycol (C12E10 and C12E23, respectively), but rate constants become independent of surfactant concentrations at concentrations above the critical micelle concentration. Low charge density anions, e.g., ClO4-, inhibit and low charge density cations, e.g., (n-C7H15)4N+, accelerate reactions, probably by controlling concentrations of nucleophiles in the palisade layer. Diphenyl phosphorofluoridate, generated by attack of F-, is not detected but is rapidly hydrolyzed to phenyl phosphorofluoridate or diphenyl phosphate ion with loss of phenol or F-. The products are different in DMSO containing modest amounts (<15 vol%) of water and no surfactant and are phenyl phosphorofluoridate and difluorophosphate ions generated by attack of F- on the initial phosphorofluoridate. These differences are consistent with the micellar palisade layer being water-rich. Although the nonionic surfactants do not intervene nucleophilically in reactions of pNPDPP, considerable amounts of ether are formed in the reaction of 2,4-dinitrochlorobenzene (DNCB), in C12E10 and C12E23 at high pH by attack of alkoxide ion with the relatively hydrophilic DNCB located close to the micellar surface. The differences in the chemistries of reactions of pNPDPP and DNCB appear to be associated largely with differences in locations of these substrates in the nonionic micelles.Key words: fluoridates, p-nitrophenyl diphenyl phosphate, 2,4-dinitrochlorobenzene, nonionic micelles, palisade layer.