Micellar Catalyzed Reactions Research Articles

Facile chlorination of acetophenone by chloramine-T in the cationic micellar phase

The chlorination of acetophenone by chloramine-T (cat) has been catalysed by added detergents, sodium laurylsulphate (NaLS) and cetyltrimethylammonium bromide (ctab). Phenacyl chloride is the exclusive product of the reaction and the % yield of the product is greater in the cationic micellar phase indicating facile chlorination in this media (even in the absence of the mineral acid). Using Piszkiewicz’s treatment, the positive cooperativity for the micellar catalysed reactions has been calculated. At the cationic micellar phase ofctab, the interaction between ammonium ion and phenyl and methylene groups probably leads to greater stabilisation than the simple hydrophobic association encountered in the micelle interior of NaLS.

Micellar catalysed oxidative cyclisation of 1,3,5-triaryl formazan

The kinetics of Tl(III) acetate oxidation of 1,3,5-triaryl formazan has been studied in 90% aqueous HOAc, in the presence of added anionic detergent, sodium-lauryl sulphate(NaLS) and cationic detergent, cetyltrimethylammonium bromide (ctab). Both surfactants enhance the reaction rate, indicating that the reactive species involved is possibly neutral. From the substituent influence observed in the micellar phase Hammett correlations have been attempted. Higher negative ϱ values obtained in the presence of ctab, indicate that the transition state is more electron-deficient. The positive co-operativity calculated for the micellar catalysed reactions (3.0) indicates possible hydrophobic interaction between micelle and formazan.

Liquid-liquid slow and fast reactions: Micellar catalysis

The role of mass transfer in micellar catalysed liquid-liquid reactions has been considered. Analytical equations have been derived to predict the enhancement in specific rate of mass transfer for different cases in the presence of micelles. For the case of fast reactions, where the reaction occurs completely in the diffuson film, it has been shown that enhancements by an order of magnitude are possible in the specific rate of mass transfer

Micellar catalysed elimination reactions of p-substituted phenethyl bromides and related compounds in alkaline solutions

The rates of dehydrobromination of para-substituted β-phenethyl bromides (3) were determined in alkaline solutions under micellar (kψ) and non-micellar (k0) conditions by using hexadecyltrimethylammonium bromide (1) and di-methyl-(2-hydroxyethyl)octadecylammonium chloride (2) as the micellar surfactants. Large micellar effects (kψ/k0) were observed. Good Hammett relationships were obtained for both kψ and k0 with σp– constants. Fairly large isotope effects (kH/kD= 8–9) were also observed for both kψ and k0. The results suggest that the transition states are more carbanion-like under the micellar conditions compared with the non-micellar conditions. However, H–D exchange of the starting bromides with solvent water, which would indicate carbanion formation prior to elimination, was not detected.

Solute binding and catalysis by poly(vinylbenzo–18–crown–6)

AbstractPoly(vinylbenzo–18–crown–6), abbreviated as P18C6, and a polymer endowed with the cation binding crown ether ligand benzo–18–crown–6 as pendent groups, exhibits in water strong hydrophobic interactions with organic solutes such as picrates and methylorange. The binding can be modified by addition of crown ether complexable cations which superimposes an electrostatic component on the hydrophobic interaction forces. Thermodynamic parameters for the picrate binding have been determined, ΔH being –11.9 kcal/moleand ΔS = –16.8 e.u. This type of binding was utilized to catalyze reactions which are known to be sensitive to the polarity of their micro environment. The P18C6 catalyzed decarboxylation of sodium–6–nitrobenzisoxazole–3–carboxylate in water was studied in detail, and the kinetics were found to resemble that of a micellar catalyzed reaction. The hydrophobic interaction of the carboxylate with P18C6 is weak, but the binding can be greatly enhanced by addition of KCl. The rate constant of decarboxylation of the substrate in the polymer domain was found to be between 2000 to 5000 times larger than that in water, depending on the charge density on the polymer. Finally, the interaction of P18C6 with polyanions such as sodium carboxymethylcellulose is discussed. Formation of insoluble polysalt complexes can be observed in the presence of KCl and CsCl.

The problem of pH in micellar catalyzed reactions.

The problem of pH in micellar catalyzed reactions.