Positive Salt Effect Research Articles

A Kinetic and Mechanistic Study of Ir (III)-Catalyzed Oxidation of Methionine by HCF (III) in an Aqueous Alkaline Medium

Introduction: The kinetic study of Ir (III) chloride-catalyzed oxidation of methionine by hexacyanoferrate (abbreviated as HCF) III ions in aqueous alkaline medium was performed spectrophotometrically at constant ionic strength of 0.5 moldm-3 and temperature of 35±0.10C. Method: The progress of the reaction was found to be first-order rate dependence kinetics with respect to [HCF (III)], [OH-], and [IrCl3]. The rate of reaction was found to decrease with an increased concentration of methionine. The ionic strength of the reaction mixture showed a positive salt effect on the reaction rate. Different activation parameters were also evaluated by studying the reaction at four different temperatures. The stoichiometry of the reaction showed Methionine: HCF (III) = 1:4. Result: The oxidation product of the reaction was found to be methionine sulphone, which was identified by an organic solvent method and IR Spectroscopy. Further, a suitable mechanism was proposed to explain all the experimental results. Conclusion: It is assumed that the reaction proceeded through complex formation between substrate (abbreviated) and iridium trichloride. A rate law was derived, which verified the results. CH3-S-(CH2)2-CH (NH2)-COO- + 4HCF (III) Ir (III), H2O CH3-SO2-(CH2)2-CH- (NH2)-COO- + 4HCF (II) result: 1.Methionine sulphone was found to be the main product of oxidation was identified using an organic solvent method and IR Spectroscopy. A suitable mechanism has been proposed to explain all the experimental results. It is assumed that reaction proceeds through complex formation between substrate (abbreviated) and iridium trichloride. A rate law has been derived which verifies the results. CH3 –S-(CH2)2-CH (NH2) – COO- + 4HCF (III) □(→┴(Ir(III),H2O) ) CH3-SO2-(CH2)2-CH (NH2)-COO- + 4HCF (II) 2. Degradation kinetic is anticipated to follow the first order kinetics at lower concentration. 3. The catalytic system can be recycled and reused without loss of activity. 4. The anticipated easy recovery of catalyst from the reaction mixture shows another positive signigficance.

Organometallic Reagents: Efficient Tools for the Synthesis of Fused Pyridinyl‐Lactones

AbstractHerein we disclose an efficient one‐pot route to a wide range of 3‐substituted fused pyridinyl‐lactones, so called aza‐phthalides. The developed strategy involves a Metal/Halogen Exchange (MHE) reaction as key step, followed by an electrophile trapping using various carbonyl derivatives and a subsequent lactonization. To promote the MHE reaction with high chemoselectivity, our investigations have particularly focused on the nature of mono‐ or bimetallic derivatives as metalation reagents including organolithiums, Grignard reagents and lithium organomagnesiate complexes, and highlighted the positive salt effect on reactional sequence. An extension to fused heteroaryl‐lactones (benzothienyl‐, benzofuranyl‐ and naphthofuranyl scaffolds) was explored.

Os(VIII) accelerated oxidation of L-leucine by hexacyanoferrate(III) in CTAB micellar medium

The kinetics of Os(VIII) accelerated L-Leucine (L-Leu) oxidation in cetyltrimethylammonium bromide (CTAB) by hexacyanoferrate(III) [HCF(III)] was investigated by registering the decline in absorbance at 431 nm. Employing the pseudo-first-order condition, the reaction’s advancement has been examined as an indicator of [CTAB], [Os(VIII)], [OH−], [L-Leu], [HCF(III)], temperature, and ionic strength. The results show that [OH−], [CTAB], and [L-Leu] are the critical parameters with a discernible influence on reaction rate. L-Leu interacts with HCF(III) in a 1:2 ratio. The rate constant is independent of the [HCF(III)] and is merely used up to regenerate the Os(VIII) during the reaction. In the investigated concentration ranges of Os(VIII), [OH−], and [L-Leu], the reaction demonstrates first-order kinetics, but follows less than unit order at higher concentrations of L-Leu (more than 6.0 × 10−3 mole dm−3) and alkali (more than 0.4 mole dm−3). A positive salt effect is indicated by the linear rise in reaction rate with additional electrolytes. CTAB catalyzes the process substantially, and once at its peak at 7.0 × 10−4 mole dm−3, the rate remains constant as [CTAB] grows up to 8.5 × 10−4 mole dm−3. With anionic surfactant sodium dodecyl sulfate, the reaction rate was significantly reduced even in the presence of Os(VIII). Reduced repulsion between surfactant molecule’s positive charge heads brought on by the negative-charged HCF(III), OH−, and [OsO5(OH)]3− molecules may be responsible for the witnessed drop in CTAB critical micellar concentration (CMC).

Salt effects on the reactivity for ligand substitution reactions of [Ru(CN)5OH2]3− anion with two naphthalene substituted ligands (nitroso‐R‐salt and α‐nitroso‐β‐naphthol) in presence of Tetrapropylammonium bromide (Pr4NBr) and Sodium chloride (NaCl)

AbstractThe kinetics of the ligand exchange reaction between aquapentacyanoruthenate(II) [Ru(CN)5OH2]3− ion and naphthalene substituted ligands [α‐nitroso‐β‐naphthol (αNβN), and nitroso‐R‐salt (NRS)] has been studied in aqueous salt solutions of sodium chloride (NaCl) or tetrapropylammonium bromide (Pr4NBr) salt. The kinetics was monitored spectrophotometrically at 525 nm corresponding to the λmax of reddish‐brown‐colored substituted products, [Ru(CN)5(αNβN)]3− or [Ru(CN)5(NRS)]3−. Increasing the ionic strength of the reaction mixture using NaCl, exerted a negative salt effect on the rate of formation of naphthalene‐substituted products. At the same time, an increment in the concentration of Pr4NBr imparted a positive salt effect on the reaction. The observed rate constant (kobs) exhibits linear increment with respect to the concentration of NRS or αNβN while remaining invariant with variation in [Ru(CN)5OH2]3−. The computed activation parameters for NRS (∆H# = 24.55 kJ mol−1, Ea = 27.03 kJ mol−1, ∆G# = 87.83 kJ mol−1, and ∆S# = – 212.5 J K−1 mol−1) and αNβN ((∆H# = 17.33 kJ mol−1, Ea = 19.81 kJ mol−1, ∆G# = 87.87 kJ mol−1, and ∆S# = – 236.7 J K−1 mol−1) also support the proposed mechanism.

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.

Kinetic study of Ru(III) – catalyzed oxidation of L-phenylalanine by hexacyanoferrate(III) in an anionic surfactant medium

Abstract The kinetic investigation of Ru(III) promoted oxidation of L-phenylalanine (L-PheAla) by [Fe(CN)6]3− has been performed in anionic sodium dodecyl sulfate (SDS) micellar medium by recording the decrease in absorbance at 420 nm corresponding to [Fe(CN)6]3− using an UV–visible spectrophotometer. Using the pseudo-first-order condition, the course of the reaction was studied as a function of [Fe(CN)6 3−], ionic strength, [OH−], [SDS], [Ru3+], [L-PheAla] and temperature by changing one variable at a time. The results exhibit that [OH−], [SDS], and [L-PheAla] are the crucial parameters that have an appreciable influence on the reaction rate. The reaction exhibits first-order kinetics in concentration ranges of Ru(III), [Fe(CN)6]3− and at low [L-PheAla] and [OH−] concentrations. The incremental trend observed in the reaction rate with electrolyte concentration shows a positive salt effect. The reaction rate is almost 10 times faster in SDS micellar medium than in aqueous medium. [Fe(CN)6]3− has no appreciable effect on the CMC of SDS, since the polar head of SDS and [Fe(CN)6]3− are both negatively charged. The K+ obtained from K3[Fe(CN)6] and KNO3 decreases the repulsion between the negatively charged heads of the surfactant molecules, which decreases the CMC of SDS. The activation parameters also support the outer-sphere electron transfer mechanism.

Effect of cationic surfactant on Ru(III) catalyzed L‐glutamic acid oxidation by hexacyanoferrate(III)

AbstractIn CTAB micellar medium, the kinetic investigation of Ru(III) promoted oxidation of L‐glutamic acid (Glu) by [Fe(CN)6]3− was carried out by recording the decline in absorbance at 420 nm, which corresponds to [Fe(CN)6]3−. By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH−], ionic strength, [CTAB], [Ru3+], [Glu], [Fe(CN)63−], and temperature using the pseudo‐first‐order condition. The findings demonstrate that [OH−], [CTAB], and [Glu] are the key parameters that have a discernible impact on reaction rate. In the studied concentration range of Ru(III), [Fe(CN)6]3−, and at lower [Glu] and [OH−], the reaction displays first‐order kinetics. The incremental trend in reaction rate with electrolyte concentration demonstrates a positive salt effect. CTAB substantially catalyzes the process, and after reaching a maximum, the rate remains nearly constant at increased [CTAB]. The observed decline in the CMC of CTAB may be caused by the reduced repulsion between the positively charged heads of the surfactant molecules caused by the negatively charged OH−, and [Fe(CN)6]3−. The activation parameters also support the outer‐sphere electron transfer mechanism as recommended by us.

REACTION MECHANISMS BETWEEN SYNTHESIZED 2-AMINO HETEROCYCLIC DYE WITH BROMATE ION IN AQUEOUS HYDROCHLORIC ACID: A KINETIC APPROACH

Reaction mechanisms between 2-amino heterocycles dyestuff (hereafter referred to as 2AHD) using BrO3- have been studied spectrophotometrically in an acidic medium, at a temperature of 29 ± 1 oC, µ = 0.50 mol dm–3 (NaCl), [H+] = 1.00 x 10–3 mol dm–3 (HCl). The order of the reactions was one in both reactants with second order overall. The rates of redox reaction depend on acid concentrations (in the acid range used). The rate of reactions showed a positive salt effect. Ions inhibit the rate of the reaction. The results are in accordance with the rate law:

Cu(II) catalyzed oxidation of L-phenylalanine by hexacyanoferrate(III) in cationic micellar medium

The kinetics of Cu(II) accelerated oxidation of L-phenylalanine (Pheala) oxidation in cetyltrimethylammonium bromide (CTAB) by hexacyanoferrate(III) was investigated by registering the decline in absorbance at 420 nm. Employing the pseudo-first-order condition, the reaction's advancement has been examined as an indicator of[CTAB], [Cu(II)], [OH-], [Pheala], [Fe(CN)63-], temperature, and ionic strength. The results show that [CTAB] is the critical parameter with a discernible influence on reaction rate. Pheala interacts with [Fe(CN)6]3- in a 1:2 ratio, and this reaction exhibits first-order dependency with regard to [Fe(CN)63-]. In the investigated concentration ranges of Cu(II), [OH-], and [Pheala], the reaction demonstrates fractional-first-order kinetics. A positive salt effect is indicated by the linear rise in reaction rate with additional electrolytes. CTAB catalyzes the process substantially, and once at its peak, the rate remains basically constant as [CTAB] grows. Reduced repulsion between surfactant molecules' positive charge heads brought on by the negative-charged [Fe(CN)6]3-, OH-, and [Cu(OH)4]2- molecules may be responsible for the witnessed drop in CTAB CMC.

Investigation of The Chemical Reactions of 2, 4, 6-Trinitrophenol with Thiocyanate Ion in Acidic Condition: Kinetic Approach

The rate and overall observed chemical change of the redox reaction between 2, 4, 6-trinitrophenol (TNP) and thiocyanate ion (SCN–) was investigated under a constant concentration of ionic strength, [????!] and λmax = 360 nm using a spectrophotometric titration method. The research aim is to study stoichiometry, order of reaction, the influence of acid, and the effect of change in ionic concentration on the reaction speed. The stoichiometry discovered gave a 1:2 molar proportion of TNP against SCN–. The reaction is 1st - order in relation to TNP and 1st – order in relation to SCN– hence, a 2nd -order overall for the system. An acid-dependence rate constant on TNP was positive for the TNP – SCN– system. A positive salt effect was observed in the system. An increase in the concentration of added cations and anions (Mn2+, NO3− and PO43−) had no influence on the speed of the reaction. The spectroscopic and kinetic results did not show any intermediate complex emergence all through the reaction. On grounds of the experimental results attained, a presumptive mechanism in favor of an outer-sphere mechanism has been recommended.

Effect of acid and ionic strength on the kinetics of electron transfer reaction of n-(2-hydroxy-ethyl) ethylenediamine-n, n’, n’-triacetatocobaltate (ii) complex with hypochlorite ion in aqueous acidic medium

The influence of acid and ionic strength on the rate of electron transfer reaction of N-(2-hydroxy-ethyl)ethylenediamine-N,N’,N’-triacetatocobaltate(II)(hereafter, complex with Hypochlorite ion in aqueous nitric acid medium have been studied at I = 0.2 mol dm-3(NaNO3), [H+] = 1 × 10-2 mol dm-3, , T = 300 ± 1 K and λmax = 525 nm. Stoichiometric study showed 1:1 `mole ratio. The rate law derived from the kinetic study under pseudo first order condition is . The rate constant of reaction,  varies inversely with acid concentration, [H+]. The overall rate law is therefore represented as: . The reaction displayed positive salt effect which suggests the activated complex was made up of similar charged species. The reaction was catalysed by addition of formate, HCOO- and potassium, K+ ions and the Michaelis-Menten’s plot gave zero intercept indicating the absence of intermediate complex. A reaction mechanism via an outer-sphere pathway is proposed for this reaction. Â

Numerical modeling of salt effects in weak acid–weak base diodes

This work studies the effect of salt contamination in weak acid-base diodes by numerical modeling. In a positive salt effect some salt is added to the alkaline reservoir, while the negative salt effect appears as a suppression of the positive one by contaminating also the acidic side of the diode. First, the positive and negative salt effects were investigated for weak electrolytes and they were found to be similar to those in a traditional strong acid-base diode. Next, positive and negative salt effects were studied when the ions of the contaminating salt were different from that of the weak electrolytes.In the positive salt effect it was found that at a certain critical concentration of the added salt the current increases sharply in a nonlinear fashion. In a negative salt effect it was found that the diode current responds strongly even for small changes in the salt concentration on the acidic side. The sensitivity of a weak acid-base diode was found to be similar to that of a strong one, thus it can be also applied as a sensitive detector of nonhydrogen cations in an acidic medium. Furthermore, weak electrolytes provide milder conditions for the non-reactive parts of the diode, and their potential profiles can also be more suitable for ion detectors.

Kinetics and mechanism of the reduction of n-(2-hydroxyethyl)ethylenediaminetriacetatoiron(III) complex by thioglycol in bicarbonate buffer medium

The kinetics and mechanism of reduction of N-(2-hydroxyethyl) ethylenediaminetriacetatoiron (III) complex (hereafter [Fe(III)HEDTAOH2]) by thioglycol (hereafter RSH) has been studied spectrophotometrically in a bicarbonate buffer medium. The study was carried out under pseudo-first order conditions of an excess of thioglycol concentration at 28 ± 1℃, I = 0.44 mol dm-3 (KNO3) and λmax = 490 nm. The reaction is first order in [Fe(III)HEDTAOH2] and half order in [RSH] and a stoichiometric mole ratio of [Fe(III)HEDTAOH2]: RSH is 2:1. Reaction rates increased with increase in ionic strength (I) and dielectric constant (D) of the reaction medium of the reaction. The reaction displayed positive primary salt effect, which suggests the composition of activated complex are likely charged reactants ions. Test for possibility of an intermediate complex formation shows negative as Michaelis-Menten plot was linear with very negligible intercept. Based on the findings, outer-sphere mechanism is proposed for the reaction. The experimental rate law obtained is; - = k2 [Fe(III)HEDTAOH2][RSH]½  Â

Time-Dependent Modeling of Salt-Contaminated Acid-Base Diodes

The paper describes the transient behavior and modeling of the salt contaminated acid-base diode. As an example, a 0.1 M KOH-0.1 M HCl diode (used in previous investigations), where the alkaline and acidic reservoirs are connected by a hydrogel cylinder is studied. First the traditional positive salt effect and the fairly new phenomenon called negative salt effect are discussed for stationary state. In the case of positive salt effect some salt is added to the alkaline reservoir of a reverse biased electrolyte diode and as a result, close to the critical concentration of the added salt, the current increases sharply. The negative salt effect appears as a suppression of the positive one (both sides of the diode are contaminated). Afterward the time-dependent positive and negative salt effect are discussed as a step response to the salt contamination. An application of the diode would be the sensitive detection of nonhydrogen cations in an acidic medium (e.g., in ion chromatography) based on the negative salt effect, thus our first results of suitability are studied and reported as impulse response of the diode.

The oxidation of 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol by dihydroxydiperiodato nickelate(IV): A kinetic and mechanistic study

The kinetics of oxidation of 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol by dihydroxydiperiodato nickelate(IV) (DPN) had been studied spectrophotometrically in alkaline medium in the temperature range of 293.2 to 313.2 K. The reaction rate showed first order dependence on DPN, 2-(2-methoxyethoxy)-ethanol and 2-(2-ethoxyethoxy)-ethanol. It was found that the pseudo-first-order rate constant k obs increased with an increase in concentration of OH - and a decrease in concentration of IO 4 - . There was a positive salt effect and no free radicals were detected. A plausible mechanism is proposed and the rate equations derived from the mechanism can explain all the experimental observations.

Preliminary Study on the Kinetics and Mechanism of the Oxidation of Naphthol Green B by Dichromate Ion in Aqueous Hydrochloric Acid Medium

Abstract - The kinetics of the oxidation of naphthol green B (NGB3-) by Cr2O7 2- has been studied in aqueous hydrochloric acid medium at an ionic strength, I = 0.50 mol dm-3 (NaCl), H+ =1.0  10-4 mol dm-3 (HCl) and T = 25  1C. The redox reaction displayed a stoichiometry of 1:1 and obeys the rate law: -dNGB3-/dt = k2NGB3-]Cr2O7 2- . The second order rate constant increases with increase in acid concentration and in the ionic strength of reaction medium. The rates of reaction displayed a positive salt effect. Addition of acrylonitrile to a partially reacted mixture in the presence of excess methanol did not lead to gel formation. Added cations and anions inhibited the naphthol green B - Cr2O7 2- reaction. Results of the Michaelis – Menten plot gave no evidence of intermediate complex formation during the course of the reaction. Based on the results obtained, the reaction is believed to proceed through the outersphere mechanistic pathway.Keywords: Intermediate; Redox; Pseudo-octahedral; Michaelis – Menton; Outersphere

English

The present manuscript deals the kinetics of the oxidation of levulinic acid by Ce (IV) perchlorates in perchloric acid. The reaction follows a first order rate dependence on the Ce (IV) concentration but the value of k1 decreases with the increasing concentration of Ce (IV). Evidence for complex formation between Ce (IV) and levulinic acid was obtained from the Michaelies-Menten reciprocal plots. This was further confirmed spectrophotometrically where the absorption intensity in the wave length region 212 mµ-216 mµ, was intensified as com- pared to absorption spectra of Ce(IV)perchlorate under identical conditions with an increase in (H+), the rate increases and a plot between (HClO4 ) -1 and k1-1 is a straight line intercepting the ordinate. The reaction shows a positive salt effect. A suitable mechanism has been postulated and the values of activation parameters are reported. Key words-

A kinetic and mechanistic study on the oxidation of arginine and lysine by hexacyanoferrate (III) catalysed by iridium (III) in aqueous alkaline medium

The kinetics of Ir (III) catalysed oxidation of some amino acids like arginine and lysine by hexacyanoferrate (abbreviated as HCF) (III) ions in aqueous alkaline medium at constant ionic strength 0.5 mol dm-3 and temperature 35oC has been studied spectrophotometrically. The reactions exhibit 2:1 stoichiometry and follow first order kinetics in [HCF (III)] and [alkali]. The dependence of the rate on substrate concentration has been found to be of Michaelis-Menten type. The ionic strength of the reaction mixture shows positive salt effect on the reaction rate. To calculate thermodynamic parameters, the reactions have been studied at four different temperatures between 35 to 50oC. A complex mechanism involving the complex formation between catalyst and the substrate has been proposed. Keto acids; e - guanidino-α-oxo valeric acid and 6–amino-α-oxo caproic acid have been identified chromatographically and spectroscopically as the final product of oxidation of arginine and lysine, respectively. Based on the kinetic data and product analysis a reaction mechanism is proposed. Key words: HCF (III), iridium (III), oxidation, arginine, lysine.

Kinetics and mechanism of disproportionation of Mn (VI)O 42− induced by decomposition of intramanganato-polygalacturonate methyl ester coordination polymer precursor: Medium-substituent effects on reactivity

During the oxidation of polygalacturonate methyl ester polysaccharide by MnO 4 − in highly basic medium, the formation of the green polygalacturonate methyl ester (PGME-Mn (VI)O 4 2−) and the blue (PGME-Mn (V)O 4 3−) intermediates were followed spectrophotometrically. In this paper, the kinetics of the decay of the green (PGME-Mn (VI)O 4 2−) intermediate, the second stage of the oxidation process, were followed spectrophotometrically at different concentrations of NaOH and temperatures ranging from 10 to 30 °C. The decay of the green intermediate (PGME-Mn (VI)O 4 2−) follows pseudo-first-order kinetics, d[PGME-Mn (VI)O 4 2−]/d t = k obs.[PGME-Mn (VI)O 4 2−] where k obs. = k 2[OH −]. The reaction was found to be base catalyzed. The obtained linear Michaelis–Menten kinetics proves the formation of intermediates during the decay process. A reaction mechanism involving a deprotonation pre-equilibrium step followed by a rate determining decay of the deprotonated green intermediate (PGME-Mn (VI)O 4 2−) is proposed. Moreover, the activation parameters were consistent with the assumed reaction mechanism. The positive salt effect indicates the ionic character of the transient species. The decay and formation rates increase in the following order of polysaccharides: MC-Mn (VI)O 4 2− < CMC-Mn (VI)O 4 2− ≪ PGME-Mn (VI)O 4 2−.

Negative salt effect in an acid-base diode: Simulations and experiments

The paper describes a new phenomenon discovered in the electrolytic analog of a semiconductor diode. As an example, the phenomenon is studied in the 0.1M KOH-0.1M HCl diode where the alkaline and the acidic reservoirs are connected by a hydrogel cylinder. First the traditional, so-called positive salt effect is discussed. In that case some salt is added to the alkaline reservoir of a reverse biased electrolyte diode and as a result, close to a critical concentration of the added salt the electric current increases sharply. The so-called negative salt effect appears as a suppression of the positive one. It is shown by numerical simulations, by approximate analytical formulae, and also by experiments that the high current caused by the salt contamination in the alkaline reservoir can be mostly suppressed by relatively small salt concentrations in the acidic reservoir. Thus a straightforward application of the negative salt effect would be the sensitive detection of nonhydrogen cations in an acidic medium (e.g., in ion chromatography).