Anionic micelles of sodium dodecyl sulfate (SDS) inhibit periodate ion oxidations of dipropyl and dibutyl sulfide (Pr2S and Bu2S) and of 1 -methoxy-4-(methylthio)benzene (ArSMe), but there are residual reactions of micellarbound sulfides at high [SDS] because 1 0 4 -is not completely excluded from the micellar surface. Concentrations of 1 0 4 -at surfaces of SDS micelles can be estimated based on a treatment of ion-micelle Coulombic interactions, and second-order rate constants, k;, at the micellar surfaces can be calculated. These second-order rate constants are lower than those in water by factors of 2-6, but for reactions of PrzS and ArSMe in cationic micelles of cetyltrimethylammonium chloride (CTACl) rate constants in micelles are lower than those in water by factors of 2 W 1 0 3 . These differences are related to chargecharge interactions between the ionic micellar head groups and the developing positive charge on sulfur in the transition state. Rate constants of oxidation of the very hydrophilic ethanediol are unaffected by SDS.Ionic micelles typically increase rates of reactions of reactive counterions with hydrophobicsubstrates that bind to the micelles. These rate increases are due to higher local concentrations of both reactants at the micelle-water interface as compared to their stoichiometric c0ncentrations.I Ionic vesicles and oil-inwater microemulsions also speed these reactions and quantitative treatments that consider reactant distributions between bulk solvent and the association colloidal assemblies fit the rate data.I.2 Reactions of anionic nucleophiles in solutions of cationic colloids have been studied extensively, and for many of these reactions second-order rateconstants are similar in water and at the surfaces of the co1loids.l-3 Reactions of cationic electrophiles in solutions of anionic colloids can also be treated by this distribution model that considers the bulk solvent and the colloid as distinct reaction regions, Le., as pseudophases.First-order rate constants, k, for overall reactions in micelles or similar assemblies are given by where k'w and krM are first-order rate constants in the aqueous and micellar pseudophases and Ks is the substrate binding constant written in terms of the concentration of micellized surfactant, Dn,l (eq 2), where SW and SM denote substrate in the aqueous and micellar pseudophases, respectively. For bimolecular, nonsolvolytic, reactions k k and krM depend on concentrations of the second reagent and second-order rate constants in the aqueous and micellar pseudophases. Periodate and peroxymonosulfate ion are anionic electrophiles that oxidize organic ~ulfides:~*5 R,S + 10; -R,S=O + IO3-R,S + HOOSO; -R , S 4 + HSO, These anions and organic sulfides should be taken up by cationic micelles and concentrated at their surface, which should speed reaction. However, overall rate enhancements are unusually small, and with increasing [surfactant] rate constants go through maxima and with relatively high [surfactant] are much lower than in water.5 OO22-3654 I93 12O91...

Cationic micelles of cetyltrimethylammonium chloride, bromide and mesylate (CTACI, CTABr, CTAOMs) speed reactions of OH-with phosphinate and thiophosphinate esters: PhzPO.OPh (la), PhzPO.OC6H4N0z-p (lh), Ph(i-Pr)PO.OCsH4NOz-p (lc), PhzPO.SEt (2a), Ph2PO.SPh (2b), (Et0)zPO.SPh (2c) and (EtO)zPS.OCaH4NOz-p (Parathion, 3). First-order rate constants go through maxima with increasing [ surfactant 1. The rate-surfactant profiles are fitted quantitatively in terms of a kinetic model that treats the distribution of OH-between aqueous and micellar pseudo-phases in terms of coulombic and non-coulombic ion-micelle interactions. Second-order rate constants at the micellar surface are lower than in water by factors that range from 0-035 for l a to 0.7 for lc. The thiophenyl derivative (2b) is more reactive than the corresponding phenoxy derivative (la) and it is more reactive than the corresponding thioethyl derivative (2a). Parathion (3) is the least reactive substrate in both water and miceltes. R'2PO.SR (2a) R' = Ph, R = Et (2b) R' = R = P h ( 2~) R' = OEt, R = Ph

UV-vis (hexanes) 266 nm (log < 4.90), 287 (4.42), 301 (4.35), 312 (4.35), 336 (4.05), 3.46 (4.21), 359 (3.54), 410 (3.07), 444 (3.15), 460 (4.20), 486 (3.82), 492 (3.86)] corresponding to that of the product mixture from the reaction of 4 with Cl2.24 l-[(Dimethylamino)methyl]azupyrene. The procedure was adapted from that of Lindsay and Hauser.26 A 0.5-mL portion (0.5 mmol of reagent) of a clear solution formed by heating (steam bath) 30 mg (1.0 mmol) of paraformaldehyde and 0.15 mL (1.1 mmol) of tetramethyldiaminomethane in 2.0 mL of acetic acid was added to 52.5 mg (0.26 mmol) of 4 suspended in 6.0 mL of acetic acid. As the mixture was warmed to 70-80 °C, 4 dissolved and the solution became green. After 2 h, the mixture was cooled, diluted with 50 mL of H20, and extracted with 3 X 20-mL portions of ether. The extracts yielded 10 mg (20%) of unchanged 4. The cooled (ice bath) aqueous solution was basified (1 N NaOH) and then extracted with ether. Removal of the solvent from the combined, dried (Na2S04) extracts gave 47 mg (70%, 86% net) of l-[(dimethylamino)methyl]azupyrene as a green solid which decomposed on standing: UV-visible (hexanes)

. Can. J. Chem. 66, 1566Chem. 66, (1988. The basic hydrolysis of diazepam and several N-alkyl nitrazepam derivatives has been studied in the presence of reactive counterion micelles of cetyltrimethylammonium hydroxide (CTAOH) and vesicles of didodecyldimethylarnmonium hydroxide (DDAOH). In both surfactants, the rate of hydrolysis of all compounds was found to be dependent on the hydroxide concentration at constant surfactant concentration and this was interpreted as evidence for initial amide hydrolysis. The hydrolysis in CTAOH was inhibited by added salts in the order Br-< NO3-< so4'-. At concentrations above 3 mM surfactant, the rate of hydrolysis of each compound was similar in CTAOH and in DDAOH. At lower concentrations of CTAOH, however, the rate of hydrolysis was significantly lower than that in DDAOH. On the basis of this evidence, it was concluded that the cmc of CTAOH was between 2-3 mM, which is in good agreement with the value of 1.8 mM obtained by Zana from conductivity measurements. For diazepam, a mechanistic change is indicated on transfer from water to either micelles or vesicles and since vesicles are considered good models of biological membranes, this suggests that conclusions concerning the bioavailability of diazepam should not be based on studies in water but rather on studies in either micelles or vesicles. puisque les vCsicules sont considCrCes comme de bons modeles des membranes biologiques, il est suggCrC que les conclusions concernant la bio-disponibilitk du diazepam ne devraient pas 6tre basCes sur des Ctudes dans l'eau mais plutbt sur des Ctudes dans des micelles ou dans des v6sicules.[Traduit par la revue]

Acidic hydrolysis of oxazepam in water involved initial azomethine cleavage at low acid concentrations (0.1-0.2 M) with initial amide hydrolysis occurring concurrently at higher acid concentrations (0.3-0.6 M). In the presence of micelles of sodium dodecyl sufate the percentage of initial amide cleavage increased. For the basic hydrolysis of oxazepam in water the rate was dependent on [ NaOH ] indicating at least some initial amide hydrolysis. At higher base concentrations the rate became independent of [ NaOH ], because of the ionization of the NH group of oxazepam, producing an unreactive nitranion. In the presence of cetyltrimethylammonium bromide, the rate of basic hydrolysis was slower than in water, due to the increased amount of ionization in the presence of micelles. Acidic hydrolysis of 2′-methyldiazepam in water was independent of [ HCl ] in the range 0.1-0.3 M, indicating initial azomethine hydrolysis. The rate was slower than for diazepam itself, indicating the existence of steric hindrance by the 2′-methyl group to water attack at C5. In basic solution, a biphasic reation was observed. The rate of the first phase was dependent on [ NaOH ], indicating the presence of initial amide hydrolysis for 2′-methyldiazepam, cf. initial azomethine hydrolysis for diazepam. At high base concentrations, a greater than first-order dependence on base concentration was observed. This was attributed to the formation of dianionic intermediates, as previously reported for the hydrolysis of similar anilides at high base concentrations.