- Alteration of electronic effect causes change in rate determining step: Oxovanadium(IV)–salen catalyzed sulfoxidation of phenylmercaptoacetic acids by hydrogen peroxide
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Sulfoxidation of a series of phenylmercaptoacetic acids (PMAA) by hydrogen peroxide catalysed by oxovanadium(IV)–salen complexes has been carried out spectrophotometrically in 100% acetonitrile medium. The formation and involvement of hydroperoxovanadium(
- Kavitha,Subramaniam
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- The “Green” Electrochemical Synthesis of Periodate
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High-grade periodate is relatively expensive, but is required for many sensitive applications such as the synthesis of active pharmaceutical ingredients. These high costs originate from using lead dioxide anodes in contemporary electrochemical methods and
- Arndt, Sebastian,Donsbach, Kai,Waldvogel, Siegfried R.,Weis, Dominik
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supporting information
p. 8036 - 8041
(2020/04/29)
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- Competitive behavior of nitrogen based axial ligands in the oxovanadium(IV)-salen catalyzed sulfoxidation of phenylmercaptoacetic acid
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The sulfoxidation of twelve phenylmercaptoacetic acids (PMAA) by H2O2 catalyzed by three oxovanadium(IV)-salen complexes, having varied substituents on PMAA and salen with regard to their position, size and inductive effect, has been performed spectrophotometrically in 100percent acetonitrile medium. Three nitrogen bases (NB), pyridine (Py), imidazole (ImH) and 1-methylimidazole (MeIm), were used as axial ligands. It has been found that the rate of sulfoxidation is not only tuned by the substituents on PMAA and salen, but it is also varied by the addition of nitrogen bases. The observed order of retardation found among the different nitrogen bases is ImH > MeIm > Py. The rate of reaction decreases with the increase in concentration of the NB axial ligands. The strongly binding ImH shows the least reactivity. Hydroperoxovanadium(V)-salen has been proposed as the sole active oxidizing species. A detailed mechanistic study reveals that the low rate constant values in the presence of the nitrogen base is due to the existence of competition of NB with H2O2 and PMAA during the formation of active species and the coordination of PMAA with active species, respectively. Both electron donating and electron withdrawing substituents on PMAA retard the sulfoxidation rate significantly. The Hammett correlation between the rate constants and substituent constants shows a non-linear concave downward curve which is explained by the existence of two different rate determining steps within the same mechanism; coordination of PMAA with the active species for electron withdrawing substituents and transfer of oxygen to PMAA for electron donating substituents. All the experimental observations are explained by proposing a suitable mechanism.
- Kavitha, C.,Subramaniam, P.
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- Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes
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The mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAA) by oxo(salen)Cr(V)+ ion in the presence of ligand oxides has been studied spectrophotometrically in acetonitrile medium. Addition of ligand oxides (LO) causes a red shift in the λmax values of oxo(salen) complexes and an increase in absorbance with the concentration of LO along with a clear isobestic point. The reaction shows first-order dependence on oxo(salen)-chromium(V)+ ion and fractional-order dependence on PSAA and ligand oxide. Michaelis-Menten kinetics without kinetic saturation was observed for the reaction. The order of reactivity among the ligand oxides is picoline N-oxide > pyridine N-oxide > triphenylphosphine oxide. The low catalytic activity of TPPO was rationalized. Both electron-withdrawing and electron-donating substituents in the phenyl ring of PSAA facilitate the reaction rate. The Hammett plots are non-linear upward type with negative ρ value for electron-donating substituents, (ρ- = -0.740 to -4.10) and positive ρ value for electron-withdrawing substituents (ρ+ = +0.057 to +0.886). Non-linear Hammett plot is explained by two possible mechanistic scenarios, electrophilic and nucleophilic attack of oxo(salen)chromium(V)+-LO adduct on PSAA as the substituent in PSAA is changed from electron-donating to electron-withdrawing. The linearity in the log k vs. Eox plot confirms single-electron transfer (SET) mechanism for PSAAs with electron-donating substituents.
- Subramaniam,Sugirtha Devi,Anbarasan
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p. 164 - 173
(2016/06/06)
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- Importance of ground state stabilization in the oxovanadium(IV)-salophen mediated reactions of phenylsulfinylacetic acids by hydrogen peroxide – Non-linear Hammett correlation
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A systematic study on the oxidative decarboxylation of a series of phenylsulfinylacetic acids (PSAA) by hydrogen peroxide with four oxovanadium(IV)-salophen catalysts in 100% acetonitrile medium is presented. The hydroperoxovanadium(V)-salophen generated from the reaction mixture is identified as the bonafide active oxidizing species. Introduction of electron donating groups (EDG) in the oxovanadium(IV)-salophen catalyst and electron withdrawing groups (EWG) in PSAA enhances the reactivity, whereas EWG in the catalyst and EDG in PSAA have a retarding effect on the reaction. A Hammett correlation displays a non-linear downward curvature, which consists of two intersecting straight lines and the ρ value shifts from small positive to moderately high as the substituents change from EWG to EDG. The importance of the ground state stabilization of PSAA is inferred from a linear Yukawa–Tsuno plot. Based on the observed substituent effects and the spectral changes, a mechanism involving electrophilic attack of PSAA on the nucleophilic peroxo oxygen atom of the vanadium complex in the rate determining step followed by oxygen atom transfer is proposed.
- Subramaniam,Jeevi Esther Rathnakumari,Janet Sylvia Jaba Rose
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p. 496 - 503
(2016/07/21)
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- Modulation of catalytic activity by ligand oxides in the sulfoxidation of phenylmercaptoacetic acids by oxo(salen)chromium(V) complexes
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Mechanism of sulfoxidation of eleven para-substituted phenyl mercaptoacetic acids (PMAAs) by three oxo(salen)chromium(V)+PF6?complexes in the presence of different ligand oxides (LOs) such as triphenylphosphine oxide, pyridine N-oxide and 4-picoline N-oxide have been studied spectrophotometrically in 100% acetonitrile medium. Spectral and kinetic profiles establish the formation of adduct, O[dbnd]Cr(V)(salen)+-LO as the reactive intermediate in the catalytic cycle. The rate of sulfoxidation is found to be enhanced significantly by the addition of LOs and introduction of substituent in PMAA and salen complex. Both electron releasing and electron withdrawing substituents in the substrate and oxidant facilitate the rate of sulfoxidation. Correlation with Hammett constants yields a non-linear concave upward curve. Based on the experimental results and substituent effects two different mechanisms, a direct oxygen atom transfer (DOT) for PMAAs with electron withdrawing substituents and a single electron transfer for PMAAs with electron donating substituents have been postulated.
- Subramaniam,Anbarasan,Sugirtha Devi,Ramdass
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- A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non-linear Hammett
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Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron-withdrawing and electron-releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron-releasing to electron-withdrawing groups. Electron-releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron-withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron-releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright
- Subramaniam, Perumal,Janet Sylvia Jaba Rose, Jebamoney,Jeevi Esther Rathinakumari, Rajasingh
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p. 496 - 504
(2016/09/21)
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- Dynamics of cetyltrimethylammonium bromide-mediated reaction of phenylsulfinylacetic acid with Cr(VI): Treatment of pseudo-phase models
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The influence of cetyltrimethylammonium bromide, CTAB, on the oxidative decarboxylation of phenylsulfinylacetic acid, PSAA, and several meta- and para-substituted PSAAs by Cr(VI) was investigated in 95 % H2O-5 % CH3CN medium. The rate profile displayed a peculiar trend with an initial rate increase at low CTAB followed by sharp rate inhibition at higher CTAB concentrations. The initial rate acceleration could be explained by strong binding of SO42- on the positively charged micellar surface. The specific partitioning of PSAA in the micellar phase by hydrophobic interaction and the oxidizing species HCrO3+ in aqueous phase by electrostatic repulsion accounted for the rate retardation at higher CTAB concentrations. The Hammett plot with different substituted PSAAs showed excellent correlation affording negative ? value, which supports the proposed mechanism involving the intermediate formation of sulfonium cation. The obtained ? value in CTAB medium was found to be slightly lower than that in aqueous medium. Quantitative analysis of the rate data for the inhibition shown by CTAB was performed using the Menger-Portnoy and the Piszkiewicz pseudo-phase models. The binding constant for PSAA with micelles was evaluated from the Piszkiewicz cooperative model.
- Subramaniam, Perumal,Selvi, Natesan Thamil
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p. 1019 - 1034
(2015/11/27)
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- Spectral and mechanistic investigation of Oxidative Decarboxylation of Phenylsulfinylacetic Acid by Cr(VI)
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The oxidative decarboxylation of phenylsulfinylacetic acid (PSAA) by Cr(VI) in 20% acetonitrile - 80% water (v/v) medium follows overall second order kinetics, first order each with respect to [PSAA] and [Cr(VI)] at constant [H+] and ionic strength. The reaction is acid catalysed, the order with respect to [H+] is unity and the active oxidizing species is found to be HCrO3+. The reaction mechanism involves the rate determining nucleophilic attack of sulfur atom of PSAA on chromium of HCrO3+ forming a sulfonium ion intermediate. The intermediate then undergoes a,β-cleavage leading to the liberation of CO2. The product of the reaction is found to be methyl phenyl sulfone. The operation of substituent effect shows that PSAA containing electron-releasing groups in the meta- and para-positions accelerate the reaction rate while electron withdrawing groups retard the rate. An excellent correlation is found to exist between log k2 and Hammett s constants with a negative value of reaction constant. The p value decreases with increase in temperature evidencing the high reactivity and low selectivity in the case of substituted PSAAs.
- Subramaniam, Perumal,Selvi, Natesan Thamil,Devi, Soundarapandian Sugirtha
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- Mechanism of oxidation of (p-substituted phenylthio)acetic acids with N-bromophthalimide
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The kinetics of oxidation of (phenylthio)acetic acid (PTAA) by N-Bromophthalimide (NBP) in acetonitrile-water solvent mixture at 298 K in the presence of perchloric acid has been followed potentiometrically. The reaction is first-order each in NBP and PTA
- Alhaji,Uduman Mohideen,Kalaimathi
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experimental part
p. 1 - 8
(2012/02/01)
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- Mechanism of oxidation of (p-substituted phenylthio)acetic acids with N-chlorosaccharin
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The kinetics of oxidation of (phenylthio)acetic acid (PTAA) with N-chlorosaccharin (NCSA) have been studied potentiometrically in 80:20 (v/v) acetonitrile-water medium at 298 K. The reaction is first-order each with respect to PTAA and NCSA and shows a ne
- Alhaji,Mohideen, A.M. Uduman,Mary, S. Sofia Lawrence
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experimental part
p. 159 - 166
(2012/02/02)
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- Mechanistic study on the oxidation of (phenylthio)acetic acids by oxo(salen)manganese(V) complexes and the reactivity-selectivity principle
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A systematic study on the kinetics and mechanism of oxidation of several (para-substituted phenylthio)acetic acids with various substituted oxo(salen)manganese(V) complexes in acetonitrile at 20 °C is presented. The kinetic data indicate that the reaction is second-order overall, first-order each in (phenylthio)acetic acid and oxo(salen)manganese(V) complex. Rate studies with substituted (phenylthio)acetic acids give an excellent Hammett correlation with σ+/σ- constants and the ρ-values are in the range of -0.82 to -1.17 for different oxo(salen)manganese(V) complexes. The log k2 values observed in the oxidation of each (phenylthio)acetic acid by substituted oxo(salen)manganese(V) complexes correlate with 2σ, giving ρ-values from 0.26 to 0.56. A mechanism involving single electron transfer from the sulfur center of the substrate to the oxo complex in the rate-controlling step is envisaged. Kinetic data were obtained over a temperature range of 15-35 °C and the activation parameters evaluated. Correlation analyses show the presence of an inverse relationship between reactivity and selectivity in the reactions of various (phenylthio)acetic acids with a given oxo(salen)manganese(V) complex and also in various oxo(salen)manganese(V) complexes with a given (phenylthio)acetic acid. Mathematical treatment of the results shows the operation of a valid reactivity-selectivity principle in this redox system.
- Chellamani, Arunachalam,Sengu, Paramasivan
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- Mo(VI)-catalysis of perborate oxidation of aryl sulfides in acetic acid
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Molybdenum(VI) catalyses effectively the sodium perborate oxidation of aryl sulfides to sulfoxides in glacial acetic acid. The catalysed oxidations of diphenyl sulfide and S-phenylmercaptoacetic acids are zero order with respect to the oxidant and first o
- Karunakaran, Chockalingam,Venkataramanan, Ramasamy
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p. 254 - 256
(2007/10/03)
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- Highly stereoselective asymmetric pummerer reactions that incorporate intermolecular and intramolecular nonbonded S...O interactions
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New chiral sulfoxides (RS,S)-3, (SS,S)-3, (R S,S)-4, and (SS,S)-4 and known chiral sulfoxides (R S)-5, (RS)-6, and (RS)-7 were synthesized, and the stereochemistry of the new sulfoxides (RS,S)-3 and (R S,S)-4 was determined by X-ray crystallographic analysis. In their crystallographic structures, the intramolecular nonbonded S...O close contacts were recognized. Analyses of several sulfoxide complexes including rac-11 with N,N-dimethylacetamide (DMAC) or N-methyl-2-pyrrolidone (NMP) in a MeOH solution utilizing cold-spray ionization mass spectrometry provided, for the first time, direct information for intermolecular nonbonded S...O interactions between sulfoxides and amide (or lactam) in a solution. Highly diastereoselective and enantioselective Pummerer reactions based on the concept of intermolecular and intramolecular nonbonded S...O interactions were performed by treatment of several chiral sulfoxides (RS, S)-3, (SS, S)-3, (RS, S)-4, (SS, S)-4, (R S)-5, (RS)-6, and (RS)-7 with acetic anhydride and trimethylsilyl triflate (TMSOTf) in DMAC, NMP, N,N-dimethylformamide, and N-formylpiperidine. Mechanistic studies on these facile stereoselective Pummerer reactions revealed the necessity for the amide/TMSOTf complex, such as 26 or 27, to be an efficient activation reagent for Ac2O and a trapping reagent for the released acetate ion, and that DMAC and NMP had a positive effect on this highly stereoselective chiral transfer reaction.
- Nagao, Yoshimitsu,Miyamoto, Satoshi,Miyamoto, Motoyuki,Takeshige, Hiroe,Hayashi, Kazuhiko,Sano, Shigeki,Shiro, Motoo,Yamaguchi, Kentaro,Sei, Yoshihisa
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p. 9722 - 9729
(2007/10/03)
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- HIO3 in the presence of wet SiO2: A mild and efficient reagent for selective oxidation of sulfides to sulfoxides under solvent-free conditions
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In the presence of wet SiO2, HIO3 is highly efficient for the selective oxidation of sulfides to sulfoxides. It may be applied to any type of dialkyl and alkyl aryl sulfides. It develops under solvent-free conditions, and gives high yield in the presence of different functional groups on the sulfide at room temperature.
- Lakouraj,Tajbakhsh,Shirini,Tamami, M. V. Asady
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p. 775 - 784
(2007/10/03)
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- Kinetics and mechanism of oxidation of aromatic sulfides and arylmercaptoacetic acids by N-chlorosuccinimide
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Kinetic measurements of the oxidation of divalent organic sulfur compounds by N-chlorosuccinimide in acetonitrile-water mixture at constant [H+] show that the reaction is first order in both the oxidant and the organic sulfur compound. While th
- Thenraja, Duraisamy,Subramaniam, Perumal,Srinivasan, Chockalingam
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p. 2125 - 2129
(2007/10/03)
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- Benzyltriphenylphosphonium dichromate as a mild reagent for oxidation of thiols and sulfides
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Oxidation of thiols and sulfides under non-aqueous and aprotic conditions uses benzyltriphenylphosphonium dichromate (1, PhCH2PPh3)2 Cr2O7) which is very easily prepared by mixing an aqueous solution of benzyltriphenylphosphonium chloride with CrO3 in 3N HCl at room temperature. This reagent, a stable orange powder which may be stored for a month without loss of activity, is soluble in acetonitrile, chloroform and dichloromethane and slightly soluble in carbon tetrachloride, ether and hexane.
- Hajipour, Abdol Reza,Mallakpour, Shadpour E.
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- Formation of peracetic acid upon aging of perborate in acetic acid. Kinetics of the oxidation of S-phenylmercaptoacetic acids
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Upon aging, perborate in glacial acetic acid generates peracetic acid and thus oxidizes S-phenylmercaptoacetic acid rapidly. Perborate dissolved in ethylene glycol, however, does not show the aging effect, and the corresponding oxidation proceeds smoothly
- Karunakaran, Chockalingam,Anandhy, Kaliyaperumal,Ramachandran, Velusamy
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p. 1025 - 1029
(2007/10/03)
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- Linear free energy relationship in complex reaction: Tungsten(VI) catalyzed perborate oxidation of S-phenylmercaptoacetic acids
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Tungsten(Vl) catalyzes perborate oxidation of S-phenylmercaptoacetic acid. The catalyzed oxidation is first order with respect to the oxidant, independent of [H+], and displays Michaelis-Menten dependence on [PhSCH2COOH] and [W(VI)].
- Karunakaran,Ramachandran,Palanisamy
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p. 675 - 681
(2007/10/03)
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- KINETICS AND MECHANISM OF OXIDATION OF (ARYLTHIO)ACETIC ACIDS BY PYRIDINIUM HYDROBROMIDE PERBROMIDE
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Oxidation of several monosubstituted (phenylthio)acetic acids (PTAA) by pyridinium hydrobromide perbromide (PHPB) was studied in aqueous acetic acid.The reaction is first order with respect to PHPB.Michaelis-Menten type kinetics are observed with respect to (arylthio)acetic acid.The effect of solvent composition indicates that the transition state is more polar than the reactants.The formation constants of the intermediate substrate-PHPB complexes and the rates of their decomposition were determined at different temperatures.The rates of oxidation of para and meta-substituted (phenylthio)acetic acids were correlated with Hammett's substituent constants.The ρ value is -1.60 at 35 deg c.The rates of oxidation of ortho substituted compounds are correlated with Charton's triparametric equation.A mechanism involving the decomposition of the intermediate complex in the slow rate-determining step affording a sulphonium ion which hydrolyses in a subsequent fast step to the sulphoxide is proposed.
- Karunakaran, K.,Elango, K. P.
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p. 429 - 434
(2007/10/02)
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- Kinetics and Mechanism of the Oxidation of (Substituted Phenylthio)acetic Acids by Chloramine T
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The kinetics of oxidation of (phenylthio)acetic acid and several (para-substituted phenylthio)acetic acids by chloramine T has been studied in alkaline medium (pH 10.06).A first-order dependence in chloramine T and (phenylthio)acetic acid and a near inver
- Srinivasan, Chockalingam,Pitchumani, Kasi
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p. 289 - 292
(2007/10/02)
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