Structural effects on surface and micellar properties of alkanediyl-alpha, omega-bis(sodium N-acyl-beta-alaninate) gemini surfactants

A study of the equilibrium surface properties (in water and in the presence of 0.01 M NaCl) of a novel series of anionic gemini surfactants, alkanediyl-alpha,omega-bis(sodium N-acyl-beta-alaninates), is described. Parameters studied include cmc (critical micelle concentration), C20 (required to reduce the surface tension of the solvent by 20 mN/m), gamma(cmc) (the surface tension at the cmc), Gamma(max) (the maximum surface excess concentration at the air/aqueous solution interface), Amin (the minimum area per surfactant molecule at the air/water interface), and the cmc/C20 ratio (a measure of the tendency to form micelles relative to adsorb at the air/water interface). The geminis with a spacer consisting of two methylene groups show premicellar self-aggregation, both in water and in 0.01 M NaCl, when the N-acyl group contains more than 12 carbon atoms; geminis with a spacer consisting of four methylene groups show no premicellar aggregation even when the N-acyl group contains 16 carbon atoms. For the acyl chain lengths where premicellar aggregation does not occur, the values of the cmc of the geminis with a two-methylene spacer are lower than those for the corresponding analogous geminis with a four-methylene spacer. The premicellar formation for the geminis with a two-methylene spacer is due to the short-chain linkage. The geminis show little or no break in their specific conductance-surfactant molar concentration plots and an increase in the pH at the cmc. This is attributed to protonation of the carboxylate group and strong Na+ release during micellization.     

Inhibition effect of {surfactant–substrate} aggregation on the rate of oxidation of reducing sugars by alkaline hexacyanoferrate(III)

The effect of cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium lauryl sulfate, NaLS), and nonionic (Brij‐35) surfactants on the rate of oxidation of some reducing sugars (xylose, glucose, and fructose) by alkaline hexacyanoferrate(III) has been studied in the temperature range from 35 to 50°C. The rate of oxidation is strongly inhibited in the presence of surfactant. The inhibition effect of surfactant on the rate of reaction has been observed below critical micelle concentration (CMC) of CTAB. In case of NaLS and Brij‐35, the inhibition effect was above CMC, at which the surfactant abruptly associates to form micelle. The kinetic data have been accounted for by the combination of surfactant molecule(s) with a substrate molecule in case of CTAB and distribution of substrate into micellar and aqueous pseudophase in case of NaLS and Brij‐35. The binding parameters (binding constants, partition coefficients, and free‐energy transfer from water to micelle) in case of NaLS and Brij‐35 have been evaluated with the help of Menger and Portnoy model reported for micellar inhibition. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 595–604, 2007     

Cu(II) promoted oxidation of L-valine by hexacyanoferrate(III) in cationic micellar medium

The kinetics of Cu(II) accelerated L-valine (Val) oxidation by hexacyanoferrate(III) in CTAB micellar medium were investigated by measuring the decline in absorbance at 420 nm. By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH⁻], ionic strength, [CTAB], [Cu(II)], [Val], [Fe(CN)₆³⁻], and temperature using the pseudo-first-order condition. The results show that [CTAB] is the critical parameter with a discernible influence on reaction rate. [Fe(CN)₆]^3- interacts with Val in a 2:1 ratio, and this reaction exhibits first-order dependency with regard to [Fe(CN)₆³⁻]. In the investigated concentration ranges of Cu(II), [OH⁻], and [Val], the reaction demonstrates fractional-first-order kinetics. The linear increase in reaction rate with added electrolyte is indicative of a positive salt effect. CTAB significantly catalyzes the process, and once at a maximum, the rate remains almost constant as [CTAB] increases. Reduced repulsion between surfactant molecules' positive charge heads brought on by the negatively charged [Fe(CN)₆]^3-, OH⁻, and [Cu(OH)₄]^2- molecules may be responsible for the observed drop in CMC of CTAB.     

Micellar and salt effects upon the oxidation of N,N-dimethylaniline by hexacyanoferrate(III)

The oxidation of N,N-dimethylaniline (DMA) by hexacyanoferrate (III) (Fe (CN)₆ ^3-) has been studied in aqueous and micellar solutions of N,N-dimethyl- dodecylamine N-oxide (DDAO). The rate enhancement of the reaction in the presence of micelles has been explained with the pseudo- phase model of the kinetics.The dependence of the reaction rate on the nature of the salt cation has also been discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ruthenium(VI) catalyzed oxidation of sodium salts of lactic, tartaric and glycolic acid by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(VI) catalyzed oxidation of sodium salts of lactic, tartaric and glycolic acid by hexacyanoferrate(III) in aqueous alkaline medium have been studied at constant ionic strength. The reaction shows first order dependence on ruthenium(VI) and zero order on hexacyanoferrate(III). The rate of reaction increases with increasing substrate concentration and shows Michaelis-Menten type behavior. The rate of reaction decreases with increase in hydroxide ion concentration. Oxidation proceeds via formation of a complex between substrate and ruthenium(VI). A probable mechanism is suggested.

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(VI) , (III) . (VI) (III). -. . (VI). .

     

Asymmetric synthesis of glutamic acid from sodium bis[N-salicylideneglycinato]cobaltate(III) and sodium bis[N-3-methylsalicylideneglycinato]cobaltate(III)

Conclusions The reaction of potassium -bis[N-salicylideneglycinato]cobaltate (III) and potassium -bis[N-3-methylsalicylideneglycinato]cobaltate (III) with methyl acrylate in water at pH 11.4 gives a mixture of diastereomeric complexes, and electrochemical reduction of which gives S-glutamic acid in asymmetric yields ranging from 10 to 46%, and a chemical yield that is close to 100% when based on reacted glycine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 428–430, February, 1977.     

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of As^IIIby Fe(CN)₆ ^3– has been studied spectrophotometrically in 60% AcOH–H₂O containing 4.0moldm^–3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)₆ ^3–] and [As^III]. Amongst the initially added products, Fe(CN)₆ ^4– retards the reaction and As^Vdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H₂Fe(CN)₆ ^–, is the active species of Fe(CN)₆ ^3–, while AsCl₅ ^2– in an ascending portion and AsCl₂ ⁺ in a descending portion are considered to be the active species of As^III. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.     

Kinetic, mechanistic and spectral studies for the oxidation of sulfanilic acid by alkaline hexacyanoferrate(III)

The kinetics of oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in hexacyanoferrate(III) and alkali concentrations and an order of less than unity in sulfanilic acid concentration (SAA). The rate of reaction increases with increase in alkali concentration. Increasing ionic strength increases the rate but the dielectric constant of the medium has no significant effect on the rate of the reaction. A retarding effect was observed by one of the products i.e. hexacyanoferrate(II) (HCF(II)). A mechanism involving the formation of a complex between sulfanilic acid and hexacyanoferrate(III) has been proposed. The reaction constants involved in the mechanism are evaluated. There is a good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.     

Kinetics and mechanism of oxidation of uric acid by hexacyanoferrate(III) in acetate buffers

The second order kinetics of uric acid oxidation by hexacyanoferrate(III) in acetate buffers were studied by estimating oxidant colorimetrically at 420 nm. Two moles of organic acid react with one mole of the oxidant and oxidation products are alloxan and urea. TMC 2661     

Kinetics and mechanism of oxidation of some reducing sugars by diperiodatoargentate(III) in alkaline medium

Summary The kinetics of oxidation of d-glucose, d-galactose, d-fructose, d-ribose, d-arabinose, d-xylose and 2-deoxyd-glucose by diperiodatoargentate(III) (DPA) have been investigated in alkaline medium. The order of the reaction with respect to [DPA] is unity while the order with respect to [sugar] is < 1 over the concentration range studied. The rate increases with an increase in [OH ^–] and there is a marginal decrease in the rate with an increase in [IO _inf4 ^sup– ]. No significant dependence on ionic strength was found, but the rate increases with a decreasing dielectric constant. Formic acid and the corresponding aldonic acids were detected as the products of oxidation. The participation of the open chain form of the sugar and a mechanism involving the initial formation of a complex between the enediol of the sugar and Ag^III are proposed.     

Acid-base properties of bis(chloromethyl)phosphinic acid para-nitroanilide in aqueous micellar solutions of surface active agents

Micelles of the cation-active surface active agent (SAA), cetyltrimethylammonium bromide, decrease the pK_a of bis(chloromethyl)phosphinic acid pnitroanilide in aqueous solutions by two units, while micelles of the anionactive SAA, sodium dodecyl sulfate increase the pK_a of the same compound by 1.75 units. The presence of electrolytes in the solution lowers the influence of micelles on the acid-base properties of the anilide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 991–994, May, 1990.     

Kinetics and mechanisms of oxidation by metal ions. Part XIV(1). Osmium(VIII)-catalysed oxidation of cycloalkanones by alkaline hexacyanoferrate(III)

Transition Metal Chemistry - The OsVIII-catalysed oxidation of cyclopentanone and cyclohexanone by alkaline hexacyanoferrate(III) ions is zeroth-order with respect to $ {? F_{e}(CN)_{6}^{3-}...     

Kinetics and mechanism of the ruthenium(III) catalysed oxidation of reducing sugars by chloramine-T in alkaline medium

The kinetics of the ruthenium(III) catalysed oxidation of reducing sugars, viz. arabinose, xylose, galactose, glucose, fructose, lactose and maltose by chloramine-T have been studied in alkaline medium. The reactions exhibit a first order rate dependence with respect to: [substrate], [chloramine-T] and [OH⁻]. The rate is proportional to {k ^′ + k ^″[Ru^III]}, where k ^′ and k ^″ are rate constants for uncatalysed and catalysed path respectively. A suitable mechanism, consistent with the kinetic data, is proposed and discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ruthenium(VI)-catalysed oxidation of diols by alkaline hexacyanoferrate(III) ion. A kinetic study

The kinetics of Ru^VI-catalysed oxidation of ethane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butane-1,4-diol and 2-butoxyethanol by hexacyanoferrate(III) ion in an aqueous alkaline medium at constant ionic strength shows zeroth order dependence on hexacyanoferrate(III) and first order dependence on Ru^VI and substrate. The results suggest that a complex is formed, between Ru^VI and the diol, which slowly decomposes to a reduced form of ruthenium, which is reoxidized to Ru^VI in a fast step by alkaline hexacyanoferrate(III). A plausible reaction mechanism is proposed.     

Kinetics and mechanisms of oxidation by metal ions. Part XIII. Osmium(VIII)-catalysed oxidation of cycloalkanols by alkaline hexacyanoferrate(III)

Summary The kinetics of OsO₄-catalysed oxidation of cyclopentanol, cyclohexanol and cyclooctanol by alkaline hexacyanoferrate(III) have been studied at low [OH^–] so that the equilibrium between alcohol and alkoxide ion is not unduly shifted towards the latter. The reaction shows a first-order dependence in [OH^–]. The order of the reaction with respect to cycloalcohol is fractional, indicating the formation of an intermediate complex with Os^VIII since the order with respect to hexacyanoferrate(III) ion is zero. The order with respect to Os^VIII may be expressed by the equation k_obs=a+b[Os^VIII]. The analysis of the rate data indicates a significant degree of complex formation between [OsO₃(OH)₃]^– and ROH. It was found that the bimolecular rate constant k for the redox reaction between complex and OH^–k₁, the forward rate constant for the formation of alkoxide ion. The activation parameters of these rate constants are reported.     

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

Spectrophotometric determination of ascorbic acid with iron(III) and p-carboxyphenylfluorone in a cationic surfactant micellar medium.

A simple and highly sensitive spectrophotometric method for the determination of ascorbic acid (AA) was established by using iron(III) and p-carboxyphenylfluorone (PCPF) in a cationic surfactant micellar medium. The apparent molar absorptivity of the proposed method, which does not require an extraction procedure, was 2.05 x 10(6) dm3 mol-1 cm-1 at 655 nm. Beer's law was obeyed in the concentration range of 0.02-0.12 microgram/cm3 for AA. The procedure was successfully applied to assays of AA in pharmaceutical preparations. It is suggested that the method is based on a coupled redox-complexation reaction in which the first step is the oxidation of AA by iron(III), and the second step includes the formations of the iron(II)-PCPF (1:2) complex and the dehydroascorbic acid-iron(III)-PCPF (1:1:2) complex.