Micellar effects upon the reaction of hydroxide ion with 2-phenoxyquinoxaline

Cationic micelles of alkyltrimethylammonium chloride and bromide (alkyl = n? C₁₂H₂₅, n? C₁₄H₂₉, and n? C₁₆H₃₃) catalyze and anionic micelles of sodium dodecyl sulfate inhibit the reaction of hydroxide ion with 2-phenoxyquinoxaline (1). Inert anions such as chloride, nitrate, mesylate, and n-butanosulfonate inhibit the reaction in CTABr by competing with OH^? at the micellar surface. The overall micellar effects on rate in cationic micelles and dilute electrolyte can be treated quantitatively in terms of the pseudo-phase ion-exchange model. The determined second-order rate constants in the micellar pseudo-phase are smaller than the second-order constants in water. © 1994 John Wiley & Sons, Inc.     

Micellar effect upon the reaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide in water

Summary Reaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide ion is strongly accelerated by cationic micellar systems. Kinetics both in water and in cationic micelles are consistent with a mechanism of consecuive reactions with a reversible step, and the rate constants have been determined. Results in micelles are explained in terms of thepseudo-phase ion-exchange and mass-action kinetics models, and they show that micelles speed the reaction by an authentic catalytic effect by stabilization of transition state of the reaction.     

Micellar effect on the electron transfer reaction of chromium(V) ion with organic sulfides

The rate of electron transfer from organic sulfides to [Cr^V(ehba)₂]⁻ (ehba-2-ethyl-2-hydroxy butyric acid) decreases with a decrease in the polarity of the medium. The anionic surfactant, SDS and the cationic surfactant, CTAB have different effects on the kinetics of this reaction. The micellar inhibition observed in the presence of SDS is probably due to the decrease in the polarity and the electrostatic repulsion faced by the anionic oxidant from the anionic micelle and the partition of the hydrophobic substrate between the aqueous and micellar phases. The micellar catalysis in the presence of CTAB is attributed to the increase in the concentration of both reactants in the micellar phase. This micellar catalysis is observed to offset the retarding effects of the less polar micellar medium and the unfavorable charge-charge interaction between the + charge developed on S center in the transition state and the cationic micelle. This catalysis is contrary to the enormous micellar inhibition observed with IO₄⁻, HSO₅⁻ and HCO₄⁻ oxidation of organic sulfides.     

Micellar effects upon the reactions of amino acids and their derivatives with 2,6-dinitro-4-trifluoromethylbenzene sulfonate ion

In the absence of surfactants 2,6-dinitro-4-trifluoromethylbenzene sulfonate ion (1) and 2,4-dinitrofluorobenzene (DNF) have similar reactivities towards glycinate and glycylglycinate ions, but -substituents hinder reactions with 1 but not with DNF, and hydroxide ion is relatively unreactive towards 1. Cationic micelles of cetyltrimethylammonium bromide (CTABr) strongly catalyze reactions of 1 with leucinate, phenylalaninate or -phenylglycinate, but there is little catalysis of reactions of the more hydrophilic nucleophiles glycinate, and glycylglycinate ions, glycineamide and hydroxide ion, whereas the CTABr catalysis of reactions of DNF is less sensitive to the nature of the nucleophile. Rate enhancements by CTABr of the reactions of 1 are: glycinate 6(28); glycylglycinate 6(26); leucinate 93(34); phenylalaninate 740(104); -phenylglycinate 247(65); glycineamide 1(5·5); OH⁻ 3(60). (The values for DNF are in parentheses). The concentrations of CTABr necessary for catalysis of reactions of 1 are much less than for reactions of DNF. These observations suggest that 1 interacts very strongly with CTABr micelles. Added salt decreases the CTABr catalysis and anionic micelles of sodium lauryl sulfate do not affect reactions of 1 with glycinate or glycylglycinate.     

The reaction between oxalatotetraammine-cobalt(III) ion and hydroxide ion in aqueous solution

The rate of the reaction between sodium hydroxide and oxalatotetraamminecobalt(III) ion was measured for a variety of hydroxide ion concentrations and at four temperatures. The rate law below 333 K is given by k_obs = k₀ + k₂[OH⁻]² and above 333 K is shown to be k_obs = k₀ + k₁[OH⁻]. The reaction proceeds with a single rate controlling step, which is interpreted as oxalate ring opening. This is followed by a rapid oxalate loss step.     

Micellar effect of ionic surfactants in the reaction ofo-dimethylaminomethylphenol withp-nitrophenyl diphenyl phosphate

The effect of cetylpyridinium bromide (CPB) and sodium dodecyl sulphate (SDS) on the direction and the rate of the reaction ofo-dimethylaminomethylphenol (MP) withp-nitrophenyl diphenyl phosphate (1) has been studied by³¹P NMR and spectrophotometry. It was shown that the reaction of MP with1 proceeds in two steps both with and without the surfactant. The product of transesterification is formed in the first step. The second step is hydrolysis catalyzed by the aminomethyl group yielding equal amounts of diphenyl phosphate ando-dimethylaminomethyl phenyl phosphate. The reaction of MP with1 is catalyzed by CPB and inhibited by SDS. The ratio between the rates of the first and the second stages changes in the presence of surfactant. The parameters of the reaction of MP with1 inhibited by micellar SDS were calculated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 242–245, February, 1994.     

Effect of acetonitrile–water mixtures on the reaction of dinitrochlorobenzene and dinitrochlorobenzotrifluoride with hydroxide ion

The kinetics of alkaline hydrolysis of 2‐chloro‐3,5‐dinitrobenzotrifluoride 1 and 1‐chloro‐2,4‐dinitrobenzene 2 were studied in various acetonitrile–water (AN–H₂O) mixtures (10–90% w/w) at different temperatures. Thermodynamic parameters ΔH^# and ΔS^# show great variation, whereas ΔG^# appears to vary little with the solvent composition presumably due to compensating variations. The results are discussed in terms of the solvent parameters such as preferential solvation, dielectric constant, polarity/polarizability, and hydrogen bond donor and acceptor parameters. It has been found that the factors controlling the reaction rates are the desolvation of OH^?, the solvophobicity of the medium, and free water molecules in rich AN mixed solvent. The data showed that the solvatochromic parameters of (AN–H₂O) mixed solvent are destroyed in the presence of excess OH^?. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 453–463, 2010     

Kinetics of the reaction of tris(4,7-diphenyl-1,10-phenanthroline-disulphonate)iron(II) ion with hydroxide ion in water

Summary The kinetics of the hydrolysis of the tris(4,7-diphenyl-1,10-phenanthrolinedisulphonate)iron(II) ion has been studied. The results are consistent with a consecutive reaction mechanism with a reversible step, and from the analysis of the kinetic results the rate constants have been determined.     

A solvent effect upon reaction of sulphur tetrafluoride with 4-nitrobenzaldehyde

4-Nitrobenzaldehyde reacts with sulphur tetrafluoride in the absence of solvent to give a 94% yield of bis-(4-nitro- α-fluorobenzyl) ether. The reaction in benzene solution gives 4-nitrobenzylidene fluoride as the only product.     

An interesting chloride ion effect in the Heck reaction

Addition of chloride ion is found to enhance the yields of cross-couplings between aryl iodides and selected olefin acceptors.     

Reaction of the pyrazinium ion having aryl and cyano groups with hydride reagents or hydroxide ion

Reduction of 3-cyano-5-(3,4-dimethoxyphenyl)-1-methylpyrazinium ion by the hydride reagents such as sodium borohydride or Hantzsch ester gave the 1,6-dihydropyrazine derivative, and the 1,4,5,6-tetra-hydropyrazine derivative on further reduction. Addition of hydroxide ion to the pyrazinium ion gave mainly a 6-hydroxy-pseudobase, accompanied by the minor formation of a 2-hydroxy-pseudobase. Photoreaction of the pseudobase mixture gave a product from the major pseudobase but thermal transformation gave another product from the minor pseudobase.     

Micellar catalysis of the reaction of 2,4-dinitrofluorobenzene with phenoxide and thiophenoxide ions

The reactions of 2,4-dinitrofluorobenzene with phenoxide and thiophenoxide ion in water are strongly catalyzed by micelles of cetyltrimethylammonium bromide (CTABr) by factors of 230 and 1100 respectively. Nonionic micelles of Brij weakly catalyze the reaction with thiophenoxide ion. Spectral measurements show that phenoxide, and especially thiophenoxide, ions interact strongly with micelles of CTABr which also markedly change the acid dissociation of phenol under given buffer conditions.     

Phase-transfer catalytic reaction of 2,4,6-tribromophenol and dibromomethane: effect of potassium hydroxide

The reaction of 2,4,6-tribromophenol with dibromomethane in an alkaline solution of KOH/dibromomethane two-phase medium, catalyzed by tetrabutylammonium bromide (TBAB or QBr), was carried out. Both mono-substituted as well as bi-substituted products were found to have formed during or after the reaction, when dibromomethane was used both as organic solvent as well as organic-phase reactant. The active catalyst tetrabutylammonium 2,4,6-tribromophenoxide (ArOQ) was identified during the reaction, from which the organic-phase reaction was inferred to be the rate controlling step. The mass transfer of both the catalysts viz. QBr and ArOQ between the two phases was found to be fast. A peculiar phenomenon was observed while investigating the effect of KOH on the reaction rate, viz. the reaction rate does not monotonously increase or decrease with increase in the amount of KOH. This phenomenon is attributed to the activity of ArOQ, the distribution of active catalyst (ArOQ) between the two phases and the hydration of active catalyst in the organic phase, both of which are affected by the amount of KOH. An effective method is proposed to determine the two intrinsic rate constants of the organic-phase reaction, based on the reaction carried out at high KOH concentration.     

On the reaction of methoxide ion with bromoiodothiophenes

The reaction of 3-bromo-2-iodothiophene with sodium methoxide in methanol, pyridine or hexamethylphosphoric triamide and the same reaction of 4-bromo-2-iodo- and 4-bromo-3-iodo-thiophene in pyridine led to a halogen-dance, giving the same mixture of 3-bromothiophene, bromo-iodothiophenes, diiodo-bromothiophenes and triiodo-bromothiophenes. The reaction of all three isomeric bromo-iodothiophenes with sodium methoxide in methanol in the presence of cupric oxide gave 4-bromo-2-methoxythiophene.     

The reaction of the trichloromethylium ion with olefins

The reactions of [CCl₃]⁺ with ethylene, 1-hexene, cyclopentence, cyclohexene and styrene have been studied in a field-free, high-pressure ion source by time-resolved ion collection following a short ionizing pulse of electrons. Ethylene is completely unreactive, while addition of [CCl₃]⁺ to the olefinic bond of the other compounds is followed by loss of one or more HCl molecules to give unsaturated cations. Only styrene forms a stable adduct [MCCl₃]⁺ which is an arenium ion produced by addition to the aromatic ring. Rate constants for the reaction of [CCl₃]⁺ have been determined and show that whereas reaction with styrene occurs at almost every ion-molecule collision, with 1-hexene and cyclopentene only 15% of the collisions lead to reaction.     

Reduction of mononitroarenes by hydroxide ion in water catalyzed by β-cyclodextrin: enhanced reactivity of hydroxide ion

Ordinarily the reducing ability of HO⁻ in water is extremely low as a result of its stabilization by hydration. Reductions by hydroxide ion have only been observed previously in aprotic organic solvents. We find that several mononitroarenes are reduced to azoxyarenes by NaOH in water in the presence of β-cyclodextrin. HO⁻ acts as a one-electron reductant with enhanced reactivity.     

Micellar catalysis on the redox reaction of glycolic acid with chromium(VI)

Chromium(VI) oxidation of glycolic acid in the absence and presence of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) followed the same mechanism as shown by kinetic study. The reaction followed second‐order kinetics, first‐order in each reactant. The oxidation is strongly catalyzed by manganese(II) and cationic micelles of CTAB or CPB. The catalytic effect of micelles can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase. Some added inorganic salts (NaCl, NaBr, NaNO₃, and Na₂SO₄) reduce the micellar catalysis by excluding glycolic acid from the reaction site. The reactivity of glycolic acid towards chromium(VI) has been discussed and also compared with those obtained previously for the reaction between chromium(VI) and the reductants oxalic and lactic acids. On the basis of the observed results, probable mechanisms have been proposed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 377–386, 2001     

Surfactant effects on the reaction of 2‐(4‐cyanophenoxy)‐quinoxaline with hydroxide ion

A reaction of 2‐(4‐cyanophenoxy)quinoxaline 1 with hydroxide ion is accelerated by supramolecular aggregates of cetyltrialkylammonium chlorides (alkyl = Me, n‐Pr, and n‐Bu). In diluted surfactant solutions, with relatively high substrate concentration (7.0 × 10^?5 M), rate constants go through double rate maxima with increase in the surfactant concentration. The first rate maximum is ascribed to a reaction occurring in premicellar aggregates and the second to reaction in micelles. At low substrate concentration (7 × 10^?6 M), second‐order rate constants in the micellar pseudophase are dependent on the surfactant headgroup size, which is related to charge dispersion in the transition state. Nonmicellizing tri‐n‐octylmethylammonium ions (TOAMs) increase the reaction of 1 with hydroxide ion. The observed rate enhancements may be due to the formation of small, hydrophobic aggregates which bind the substrate and promote the nucleophilic substitution reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 510–515, 2006