Studies on kinetics and mechanism of oxidation of D‐sorbitol and D‐mannitol by cerium(IV) in aqueous micellar sulfuric acid media

The kinetics and mechanism of cerium(IV) oxidation of hexitols, i.e. D ‐sorbitol and D ‐mannitol, in aqueous sulfuric acid media have been studied in the presence and absence of surfactants. Under the kinetic conditions, [S]_T ? [Ce(IV)]_T, where [S]_T is the total substrate (D ‐sorbitol or D ‐mannitol) concentration, the overall process shows a first‐order dependence on [Ce(IV)]_T and [S]_T. The process is acid catalyzed and inhibited by [HSO]. From the [HSO] dependence, it has been noted that the both Ce(SO₄)²⁺ and Ce(SO₄)₂ have been found kinetically active. The different rate constants in the presence and absence of surfactants have been estimated with the activation parameters. N‐cetylpyridinium chloride has been found to retard the oxidation process of hexitols, whereas sodium dodecyl sulfate has been found to accelerate the rate process. All these findings including the micellar effects have been interpreted in terms of the proposed reaction mechanism and partitioning behavior of the kinetically active different species of Ce(IV) between the aqueous and pseudomicellar phase. © 2008 Wiley Periodicals, Inc. 40: 445–453, 2008     

Effect of surfactant micelles on the kinetics of oxidation of D‐fructose by cerium(IV) in sulfuric acid medium

Kinetics of the oxidation of D ‐fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first‐order kinetics each in [cerium(IV)] and [D ‐fructose] and inverse first order in [H₂SO₄]. The Arrhenius equation is found to be valid for the reaction between 30–50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant K_s that equals to 286 mol^?1 dm³ is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na₂SO₄, NaNO₃, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18–25, 2006     

Kinetics and mechanism of ruthenium (III) catalyzed oxidation of ethanol by cerium (IV) in aqueous sulfuric acid media

The kinetics of oxidation of ethanol by cerium(IV) in presence of ruthenium(III) (in the order of 10^?7 mol dm^?3) in aqueous sulfuric acid media have been followed at different temperatures (25–40°C). The rate of disappearance of cerium(IV) in the title reaction increases sharply with increasing [C₂H₅OH] to a value independent of [C₂H₅OH] over a large range (0.2–1.0 mol dm^?3) in which the rate law conforms to: where [Ru]_T gives the total ruthenium (III) concentration. The values of 10^?3k_c and 10^?3k_d are 3.6 ± 0.1 dm³ mol^?1 s^?1 and 3.9 ± 0.2 s^?1, respectively, at 40°C, I = 3.0 mol dm^?3. The proposed mechanism involves the formation of ruthenium(III)^? substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)^? substrate complex followed by the rapid red-ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(IV) rapidly. The mechanism is consistent with the existence of the complexes Ru^III · (C₂H₅OH) and Ru^III · (C₂H₅O^?) and both are kinetically active. The overall bisulphate dependence conforms to: k_obsd = A[Ru]_T/{1 + C[HSO₄^?]} where A = 2.2 × 10⁴ dm³ mol^?1 s^?1, C = 1.3 at 40°C, [H⁺] = 0.5 mol dm^?3, and I = 3.0 mol dm^?3. The observations are consistent with the Ce(SO₄)₂ as the kinetically active species. © 1995 John Wiley & Sons, Inc.     

Aqueous polymerization of acrylamide initiated by cerium (IV)–ethylenediamine tetraacetic acid redox system

Ethylenediamine tetraacetic acid (EDTA) terminated polyacrylamide was obtained by using the EDTA–cerium(IV) ammonium nitrate [Ce(IV)] redox initiator in the aqueous polymerization of acrylamide. The polymerization behaviors as a function of the concentration of Ce(IV), EDTA, and acrylamide as well as temperature were studied. The consumption rate of cerium(IV) depends a first-order reaction on the ceric ion concentration ([Ce(IV)]). The complex formation constant (K) and disproportionation constant (k_d) of Ce(IV)–EDTA chelated complex are 1.67 × 10⁴ and 3.77 × 10^?3, respectively. The rate dependences of polymerization on monomer concentration and EDTA concentration both follow a second-order reaction in the run of initial monomer concentration ([M]_i) equal to 0.2 mol dm^?3. The number average molecular weight increases linearly with the ratio of [M]_i/[Ce(IV)]_i. The mechanism and kinetics for the polymerization was proposed. The kinetic parameters involved were determined. © 1992 John Wiley & Sons, Inc.     

Mechanistic study of cerium(IV) oxidation of antimony(III) in aqueous sulphuric acid in the presence of micro amounts of manganese(II) by stopped flow technique

The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric acid medium. A minute amount of manganese(II) (10⁻⁵ mol dm⁻³) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations. The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst are Ce(SO₄)₂, [Sb(OH)(HSO₄)]⁺ and [Mn(H₂O)₄]²⁺, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed and reaction constants involved have been determined.     

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

Chloride and iodide mediated oxidation of antimony(III) by cerium(IV) in aqueous sulphuric acid medium

The micro amounts of iodide (10⁻⁷) (mol dm⁻³) and chloride (10⁻²) (mol dm⁻³) mediated oxidation of antimony(III) by cerium(IV) in an aqueous sulphuric acid medium have been studied spectrophotometrically at 25 °C and μ = 3.10 mol dm⁻³. The stoichiometry is 1:2 in chloride and iodide mediated reactions. i.e. one mole of antimony(III) requires two moles of cerium(IV). In the case of chloride mediated reaction, the reaction was first order in cerium(IV) and halide concentrations, whereas in the case of iodide mediated reaction the order with respect to [cerium(IV)] was unity and with respect to iodide concentrations was more than unity (ca. 1.4). In both chloride and iodide mediated reactions the order with respect to antimony(III) concentrations was less than unity. Increase in sulphuric acid concentration increased the rate. The order with respect to H⁺ ion concentration was less than unity. Added products, cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant was understood to be , whereas that of reductant as SbCl₃ in the case of chloride and SbI²⁺ in case of iodide mediated reactions. The possible reaction mechanisms were proposed and the activation parameters were determined and discussed.     

Adsorptive Stripping Voltammetric Determination of Nanomolar Concentration of Cerium(III) at a Carbon Paste Electrode Modified by N′‐[(2‐Hydroxyphenyl)Methylidene]‐2‐Furohydrazide

The aim of this work was to obtain an adsorptive stripping voltammetric method for the Ce(III) determination at a carbon paste electrode, chemically modified with N'‐[(2‐hydroxyphenyl)methylidene]‐2‐furohydrazide (NHMF). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/NHMF complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (5.0–90 nmol dm^?3). The detection limit was found to be 0.8 nmol dm^?3 on the basis of a signal to noise ratio of 3. The precision for six determinations of 10 and 55 nmol dm^?3 Ce(III) was 5.6% and 2.1% (relative standard deviation), respectively. Application of the procedure to the determination of cerium in phosphate rock and wastewater samples gave good results.     

Kinetics and mechanism of silver(I) catalyzed oxidation of water with bismuth(V) in HClO4?HF mixture

The kinetics of the oxidation of water with bismuth(V) in presence of silver(I) has been investigated in a mixture of HClO₄ (1.0 mol dm^?3) and HF (1.5 mol dm^?3). The reaction is second order, viz., first order with respect to bismuth(V) and silver(I), each, and the second order rate constant is (6.6 ± 0.7) × 10^?3 dm³ mol^?1 s^?1. However, rate is independent of hydrogen ion concentration. A comparative analysis of these results with the results obtained for pdp, pds, and Ce(IV), reactions with silver(I) has also been made to correlate the rate constants and the redox-potentials of the oxidant couples.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov‐Zhabotinsky reaction with 2‐ketoglutaric acid

The Belousov‐Zhabotinsky (BZ) reaction of bromate ion with 2‐ketoglutaric acid (KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion exhibits sustained barely damped oscillations under aerobic conditions. In general, the reaction oscillates without an induction period. Fe(phen)₃²⁺ ion behaves differently from Ce(III) and Mn(II) ions in catalyzing this oscillating system. The gem‐diol form of KGA exhibits different behavior from that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction of KGA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was investigated. The order of relative reactivities of metal ions toward reaction with KGA is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺. Experimental results are rationalized. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 101–107, 2001     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov–Zhabotinsky reaction with ethyl hydrogen malonate

In a stirred batch reaction, Fe(phen)₃²⁺ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate‐driven oscillating reaction with ethyl hydrogen malonate [CH₂COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N₂ atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺, which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion. No good oscillations were observed for the BrO₃₋‐CH₂(COOEt)₂ reaction catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR′) with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion is also presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 52–61, 2000     

Micelle Catalyzed Oxidation of D-Mannose by Cerium (IV) in Sulfuric Acid

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40°C both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and cerium (IV), which decreased with increasing [H₂SO₄]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (IV) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was the reactive form of cerium (IV). From the kinetic data, micelle-cerium (IV) binding and rate constants in micellar medium were evaluated. The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression: -d[Ce(IV)]=k1Kc1[D-mannose][Ce(IV)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

Kinetic Study of the Bromine-Catalyzed Isomerization of Maleic Acid in Aqueous Ce(IV)-Br−-H2SO4 Medium

The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M (adjusted by NaClO₄), and [MA]₀=(0.5–1.0)M, the observed pseudo-first-order rate constant (k₀₃) at 25° is k₀₃=7.622×10^?5 [MA]₀/(1+0.205[MA]₀). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀=(0.025–0.150)M, the pseudo-first-order rate constant (k₀₂) at 25° is k₀₂= (4.313±0.095)x10^?2[Br^?]²+(2.060±0.119)x10^?3[Br^?]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [MA]₀=0.75 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀= (0.025–0.150)M, the pseudo-first-order rate constant (k₀₃) at 25° is k₀₃= (5.286±0.045)x10^?2[Br^?]²+(3.568±0.056)x10^?3[Br^?]. For [Ce(IV)]₀=5.0 × 10^?4 M, [Br^?]₀=0.050 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [MA]₀=(0.15–1.0)M at 25°, k₀₃=(2.108×10^?4+2.127×10^?4[MA]₀)/(1+0.205[MA]₀). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br^? reaction is much less than that of Ce(IV)—MA reaction. Maleic and fumaric acids have very different mass spectra. The mass spectrum of fumaric acid exhibits a strong metastable peak at m/e 66.5.     

Sugar‐Alcohol Complexes of Palladium(II): On the Variable Rigidity of Open‐Chain Carbohydrate Ligands

The C₄, C₅, and C₆ sugar alcohols erythritol (Eryt), D ‐threitol (D ‐Thre), D ‐arabitol (D ‐Arab), ribitol (Ribt), xylitol (Xylt), dulcitol (Dulc), and D ‐mannitol (D ‐Mann) form chelate complexes upon dissolution in Pd‐en, an aqueous solution of [Pd^II(en)(OH)₂]. Stability rules are derived from the proportion of a respective species in the solution equilibrium. Crystal‐structure analysis supports the NMR spectroscopic results for a series of binuclear compounds that contain the sugar alcohols as tetraanionic polyolato ligands: [Pd₂(en)₂(ErytH_?4)]? 10H₂O, [Pd₂(en)₂(D ‐Arab1,2;3,4H_?4)]? 7H₂O, [Pd₂(en)₂(Xylt1,2;3,4H_?4)]?4H₂O, [Pd₂(en)₂(D ‐Mann1,2;3,4H_?4)]?5H₂O, and [Pd₂(en)₂(Dulc2,3;4,5H_?4)]?6H₂O. In the case of the pentitols and hexitols, the metalated tetraanions are stabilized by intramolecular hydrogen bonds. The hydrogen bonds uniformly connect an alkoxide acceptor to the hydroxy donor group located at the δ carbon atom. As a consequence of hydrogen bonding, the open‐chain carbohydrate ligands become rigid. Crystal‐structure analysis provides information on the configurational requirements for rigidity. According to these rules, the hydrogen‐bond‐supported Dulc2,3;4,5H_?4 tetraanion provides a geometrically persistent ligating pattern. Intramolecular hydrogen bonding seems to be the most‐competitive variable to metalation of a polyol. [Pd₂(tm‐2,1:3,2‐tet)(OH)₃]OH (tm‐2,1:3,2‐tet=1,3‐bis(2′‐dimethylaminoethyl)hexahydropyrimidine) is a metallizing agent that can force full metalation even in a case as intractable as that of dulcitol. Accordingly, [Pd₄(tm‐2,1:3,2‐tet)₂‐(DulcH_?6)]Cl₂?16H₂O contains the fully deprotonated hexitol as the ligand.     

Silver(I) and Copper(II) Catalysis for Oxidation of Histidine by Cerium(IV) in Acid Medium: A Comparative Kinetic Study

The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm⁻³ and at 25°C. In both uncatalyzed and metal ions‐catalyzed paths, the reactions exhibited first‐order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first‐order dependences with respect to [His] and [H⁺]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2‐imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second‐order rate constants were evaluated.     

Aqueous polymerization of methyl methacrylate initiated by the redox system Ce(IV)–isopropyl alcohol. Kinetics and molecular weight

Polymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26–40°C, with the redox initiator system ceric ammonium nitrate–isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3–5) × 10^?3M of Ce(IV). But at lower Ce(IV) concentration (≤ 1 × 10^?3M), the order with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The rate of ceric ion disappearance was first order with respect to Ce(IV) concentration and (R_Ce)^?1 was proportional to [IPA]^?1. Both the rate of polymerization and the rate of ceric ion consumption increase with rise in temperature. The average-molecular weight can be controlled by variations in IPA, Ce(IV), and monomer concentrations, and in temperature. A kinetic scheme involving oxidation of IPA by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

Two tetrakis(benzoylacetonato)lanthanide species: synthesis,characterization and structures of tetrakis(benzoylacetonato)cerium(IV) and triethylammonium tetrakis(benzoylacetonato)lanthanate(III) tetrahydrate

Tetrakis(benzoylacetonato)cerium(IV), [Ce(bzac)₄] and triethylammonium tetrakis(benzoylacetonato)lanthanate(III) tetrahydrate, [Et₃NH][La(bzac)₄] · 4H₂O were prepared and characterized by TG and DCS measurements, IR spectroscopy, and X-ray structure analysis. The coordination polyhedron of cerium is a trigonal dodecahedron, while that of lanthanum is a distorted square antiprism. Thermal and spectroscopic measurements indicate that bonding of the ligand to metal is stronger in [Ce(bzac)₄] than in [La(bzac)₄]^?.     

Estimation of Coupling Rate Constant of L‐Cysteine Radical Studied by Concentration‐Step Coulometry Using Porous Carbon Felt Electrode Impregnated with an Electrolyte

Controlled potential coulometry using carbon felt electrode impregnated with electrolytic solution realizes very rapid complete electrolysis and can be used to measure the faster reaction rate constant than that using conventional electrolytic cell. In this research, concentration step method was adopted to investigate coupling reaction rate of L ‐cysteine radical. The coupling reaction rate of L ‐cysteine radical becomes much larger than further electrode reaction rate of L ‐cysteine radical at high L ‐cysteine concentration, because the coupling reaction rate is proportional to the second order of L ‐cysteine radical concentration although the further electrode reaction rate is proportional to the first order of L ‐cysteine radical concentration. At a low constant potential value, apparent number of electrons (n_app) increased from 1 (L ‐cystine is produced) to 2 (L ‐cysteine sulfenic acid, RSOH, may be produced) according to decrease in concentration of L ‐cysteine to be electrolyzed. The second order rate constant of coupling reaction was estimated to be about 1200 dm³ mol^?1 s^?1 at 20 °C by curve fitting method for n_app vs. logarithm of L ‐cysteine concentration. Apparent number of electrons (n_app) consumed in the electrode oxidation of L ‐cysteine gradually increased as an applied potential increases, because the consecutive electrode reaction steps with different electrode reaction rates were involved in the electrode oxidation of L ‐cysteine. In the present method, the constant limited electrolytic current was observed at high electrode potential range, which suggests that electrode oxidation rate of L ‐cysteine is kinetically controlled.     

Kinetic Study of the Ce(III)‐, Mn(II)‐, or Ferroin‐Catalyzed Belousov‐Zhabotinsky Reaction with Allylmalonic Acid

In a stirred batch experiment and under aerobic conditions, ferroin (Fe(phen)₃²⁺) behaves differently from Ce(III) or Mn(II) ion as a catalyst for the Belousov‐Zhabotinsky (BZ) reaction with allylmalonic acid (AMA). The effects of bromate ion, AMA, metal‐ion catalyst, and sulfuric acid on the oscillating pattern were investigated. The kinetics of the reaction of AMA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was studied under aerobic or anaerobic conditions. The order of reactivity of metal ions toward reaction with AMA is Fe(phen)₃³⁺ > Mn(III) > Ce(IV) under aerobic conditions whereas it is Mn(III) > Ce(IV) > Fe(phen)₃³⁺ under anaerobic conditions. Under aerobic or anaerobic conditions, the order of reactivity of RCH(CO₂H)₂ (R = H (MA), Me (MeMA), Et (EtMA), allyl (AMA), n‐Bu (BuMA), Ph (PhMA), and Br (BrMA)) is PhMA > MA > BrMA > AMA > MeMA > EtMA > BuMA toward reaction with Ce(IV) ion and it is MA > PhMA > BrMA > MeMA > AMA > EtMA > BuMA toward reaction with Mn(III) ion. Under aerobic conditions, the order of reactivity of RCH(CO₂H)₂ toward reaction with Fe(phen)₃³⁺ ion is PhMA > BrMA > (MeMA, AMA) > (BuMA, EtMA) > MA. The experiment results are rationalized.     

A kinetic and mechanistic study on the silver (I)-catalyzed oxidation of l-alanine by cerium (IV) in sulfuric acid medium

The kinetics and mechanism of Ag(I)-catalyzed oxidation of l-alanine by cerium (IV) in sulfuric acid media have been investigated by titrimetric technique of redox in the temperature range of 298–313 K. It is found that the reaction is of first order with respect to Ce(IV) and l-alanine, and it is of a positive fractional order with respect to Ag(I). It is found that the pseudo first order ([l-alanine] ? [Ce(IV)] ? [Ag(I)]) rate constant k′ increases with the increase of[H⁺]. The major oxidation product of alanine has been identified as acetaldehyde by an ¹H NMR and IR spectroscopy. Under the experimental conditions, the kinetically active species has been found to be Ce⁴⁺. Under nitrogen atmosphere, the reaction system can initiate the polymerization of acrylonitrile, indicating generation of free radicals. On the basis of the experimental results, a suitable mechanism has been proposed. The rate constants of the rate-determining step together with the activation parameters were evaluated.