Kinetics and mechanism of the oxidation of aliphatic alcohols by quinolinium fluorochromate

The oxidation of some aliphatic alcohols by quinolinium fluorochromate (QFC) in dimethyl sulfoxide leads to the formation of corresponding carbonyl compounds. The reaction is first order with respect to QFC. The reaction exhibited Michaelis‐Menten type kinetics with respect to the alcohol. The reaction is catalyzed by hydrogen ions. The hydrogen‐ion dependence has the form: k_obs=a + b[H⁺]. The oxidation of [1,1‐²H₂]ethanol (MeCD₂OH) exhibits a substantial primary kinetic isotope effect. The reaction has been studied in nineteen different organic solvents. The solvent effect was analyzed using Taft's and Swain's multiparametric equations. The rate of disproportionation of the complex is susceptible to both polar and steric effects of the substituents. A suitable mechanism has been proposed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 469–475, 1999     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.     

Mechanistic and Spectral Studies of the Ruthenium(III) Catalysed Oxidation of Sulfanilic Acid by Alkaline Hexacyanoferrate(III)

Summary. The kinetics of ruthenium(III) catalysed oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium at a constant ionic strength of 2.5mol·dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 2:8 stoichiometry (SNA:HCF(III)). The reaction showed first order kinetics in [hexacyanoferrate(III)] and [ruthenium(III)] and apparent less than unit order in both sulfanilic acid and alkali concentrations. The reaction rate increases with increasing ionic strength but the relative permittivity (_T) of the medium has a negligible effect on the rate of the reaction. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between sulfanilic acid and hydroxylated species of ruthenium(III) has been proposed. The active species of HCF(III) and ruthenium(III) are understood as [Fe(CN)₆^3–] and [Ru(H₂O)₅OH]²⁺, respectively. The main products were identified by IR, NMR, and mass spectral studies. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Oxidation kinetics of tetravalent uranium monofluoride complex by nitrous acid in HNO3 medium

The kinetics of oxidation of uranium(IV) monofluoride complex by nitrous acid in nitric acid solution have been studied. The experiments were carried out at constant ionic strength of 2M (HNO₃ and NaNO₃) and temperature in the range of 18–47 °C. The rate of reaction was determined spectrophotometrically at a wavelength of 621 nm, at which the molar extinction coefficients of UF³⁺ and UF ₂ ²⁺ are the same. It was shown that reaction orders for [HNO₂] and [HNO₃] are equal to 0.12 and 0.39, respectively. The values of activation parameters H and S are determined to be 83 kJ mol^–1 and 75 J (mol·K)^–1, respectively. The rate order of the reaction studied has a weak direct dependence on [H⁺] in contrary to the strong and reverse dependence in the absence of fluoride ions. In conclusion, fluoride ions may strongly stabilize the U(IV) in nitric acid solutions.     

Polarographic oxidation of 2,5-substituted tetraphenylpyrroles

Four series of tetraphenylpyrrole derivatives were subjected to polarographic oxidation. It was found that electron-donor substituents in the p position of the phenyl ring facilitate polarographic oxidation, while electron-acceptor substituents in the p position hinder it. Correlation equations in coordinates of E_1/2 and ⁺ were found for all four series, and a correlation between the half-wave potential of polarographic oxidation and the logarithm of the rate constants for decolorization of benzene solutions of the corresponding radicals in air was detected.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1520–1522, November, 1972.     

Stability of indolyphenylmethyl cations

In order to evaluate the influence of substituents in position 5 of indole and in the para position of phenyl on the stability of 2-ethoxycarbonylindole-3-indolyphenylmethyl cations (IPMCs) we have experimentally determined by a spectrophotometric method the values of the acidity constants (pK_R+) of the IPMCs in H₂SO₄ solutions. The IPMCs were generated from 3-(-chlorobenzyl)-2-ethoxycarbonylindoles by dissolving them in sulfuric acid with a concentration of 55–93%. Two reaction series were studied. In the first, the correlation equation pK_R+ = –5.18 –10.5 was obtained for substituents in the para position of the phenyl ring. In the second series we evaluated the influence of substituents in position 5 of the indole ring: pK_R+ = –2.6 –11.3. The lower influence of substituents on the stability of the IMPCs from position 5 as compared with the para position of the phenyl ring is due to the delocalization of the charge in the heterocycle of the indole system. It was established that in sulfuric acid solutions di(2-ethoxycarbonylindol-3-yl)phenylmethanes dissociate with the formation of IMPCs and 2-ethoxycarbonylindoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 489–492, April, 1980.     

Mechanistic investigation of oxidation of aromatic anils by isonicotinium dichromate in acidic medium. A kinetic study

Abstract Under identical experimental conditions the kinetics of oxidation of aromatic anils to benzaldehyde and nitrosobenzene, by isonicotinium dichromate, has been studied in aqueous acetic acid medium. The low dielectric constant of the medium facilitates the reactivity. Ionic strength has no significant effect on the conversion. The added Mn(II) decreases the rate of the reaction. The added acrylonitrile has no effect on the reaction rate indicating the absence of free radical mechanism. Highly negative ΔS ^# values indicate a structured transition state. The deviation of Hammett plot is noted and a concave downward curve is obtained for the anils with substituents in the aniline moiety. The observed break in the log k _obs versus σ is attributed to the change in the transition state whereas the linear plot is observed for the substituents in the benzaldehyde moiety. A suitable mechanism has been proposed. Graphical Abstract Mechanistic investigation of oxidation of aromatic anils by isonicotinium dichromate in acidic medium. A kinetic study.      

Negative activation energies and compensation effects for the reactions of diarylaminyl radicals with phenols

The temperature dependence of the rate constants of the reaction of 4,4-disubstituted diphenylaminyl radicals (ArArN) with phenols has been studied by a laser pulse photolysis technique. The linear relationships between activation energiesE ₁ (negative in the majority of cases) and logarithms of pre-exponential factors logA ₁ have been established. These results coincide with the two-parametric correlations of logk ₁ with ⁺ constants of substituents in phenol and aminyl radicals under isothermal conditions. The reaction rate constants decrease considerably when toluene is used instead ofn-decane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2386–2390, December, 1995.The authors are sincerely grateful to Prof. E. T. Denisov for valuable critical remarks and to E. P. Marchenko for samples of substituted diphenylamines.     

A comparative kinetic and mechanistic study of glutamic acid oxidation by acid permanganate in the absence and presence of sodium dodecyl sulphate

The kinetics and mechanism of glutamic acid (GCO₂H) oxidation by acid permanganate has been carried out in the absence and presence of sodium dodecyl sulphate (SDS). The surfactant enhances the reaction rate without changing the reaction mechanism. The overall rate expression for the reduction of Mn^VII may be written:

Effect of substituents at silicon on the oxidative addition of trisubstituted silanes to [RhCl(cod)PPh3]

Summary Trisubstituted silanes, HSiR_3–n X _n (R = Me, Et, Pr or Bu; X = Cl, OEt or Ph; and n = 0–3) readily undergo oxidative addition to complex [RhCl(cod)PPh₃] (where cod = cycloocta-1,5-diene).The quantitative correlation between rate constants, k ₁, of the reaction, followed spectrophotometrically at 20 °C in benzene solutions, and the structure of tri-substituted silanes represented by stereoelectronic parameters , and E of the substituents, was established: logk ₁ = a + b + c + dE. The reaction rate is accelerated by electron-withdrawing substituents at silicon and retarded by the bulk and pd donation of nonalkyl substituents.Author to whom all correspondence should be directed.     

Reactions of hydrazobenzene and tetranitromethane with nitroxyl radicals

The values of isotropic HFS constantsa _N were obtained for nitroxyl radicals (NR) of the piperidine series in hexane and water. The interrelation between rate constants for NR reduction and oxidation reactions, isotropic HFS constantsa _N, inductive constants of the piperidine substituents, and electrochemical characteristics of NR were found. The dependence of the rate constants for the reduction of NR by hydrazobenzene (HB) and its oxidation by tetranitromethane (TNM) upon the Hammett type inductive constants _EPR, obtained using HFS constantsa _N as the basis, was analyzed. The solvent effect on the reduction and oxidation reaction rate constants, the kinetic isotopic effect of the reduction reaction for a number of NR-HB systems, and alternative reaction mechanisms are considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1079, June, 1993.     

Catalytic oxidation of furan and hydrofuran compounds

The characteristics of the oxidation of furfural in the hydrogen peroxide-VOSO₄-sodium acetate system and the composition of the products were studied. The principal stages of the reaction occur at pH 7. The direction of the reaction is very different from the process in an acidic medium, where -formylacrylic and maleic acids are mainly formed. The main oxidation products in the acetate buffer solution in the presence of VOSO₄ are succinic and -formylpropionic acids and 2(5H)-furanone; without the catalyst the main product is 2-furancarboxylic acid. A mechanism is proposed for the transformations of furfural in the investigated system.For Communication 1, see [1].Kubansk State Technological University, Krasnodar 350072, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 742–747, June, 1998.     

Kinetics of oxidation of 2,2,4,5,5-pentamethyl-1-hydroxy-3-imidazoline-3-oxide by decanepersulfonic acid

The kinetics was studied of the oxidation of 2,2,4,5,5-pentamethyl-1-hydroxy-3-imidazoline-3-oxide by decanepersulfonic acid in a chloroform solution. The corresponding nitroxyl radical is quantitatively formed by the reaction 2=N-OH + RSO₄H 2=NO + RSO₃H + H₂O A mechanism of the reaction was proposed and the rate constant of the limiting stage of the process was determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1265–1268, June, 1990.     

Kinetics and mechanism of the oxidation of [N-(2-hydroxy-ethyl)ethylenediamine-N,N′,N′-triacetatocobalt(II)] by vanadate ion

The kinetics of oxidation of Co^IIHEDTA {HEDTA = N-(2-hydroxyethyl)ethylenediamine-N,N,N-triacetic acid} by vanadate ion have been studied in aqueous acid in the pH range 0.75–5.4 at 43–57 °C. The reaction exhibits second-order kinetics; first-order in each of the reactants. The reaction rate is a maximum at pH = 2.1. A mechanism is proposed in which the species [Co^IIHEDTA(H₂O)]^– and VO₂ ⁺ react to form an intermediate which decompose slowly to give pentadentate Co^IIIHEDTA(H₂O) and V^IV as final products. The rate law was derived and the activation parameters calculated: H* = 26.96 kJ mol^–1 and S* = –311.08 JK^–1 mol^–1.     

Effect of acrylamide concentration on the kinetics of oxidation of tartaric acid by cerium(IV) in sulfuric-perchloric acid media

The kinetics of oxidation of tartaric acid by Ce(IV) in the absence and presence of acrylamide has been investigated spectrophotometrically in aqueous H₂SO₄–HClO₄ media at a constant ionic strength 2.0M and 25°C. Oxidation of tartaric acid in both cases was first order with respect to Ce(IV). Kinetic data showed that the reaction involves the formation of an unstable complex and an intermediate free radical. The activation parameters were calculated to be E _a =91.3±0.4 kJ-mol^–1, S=20.2±1.0 J-mol^–1-K^–1, H=88.8±0.4 kJ-mol^–1. A polymerization mechanism is discussed.     

An independent kinetic and mechanistic study of the secondary reactions in the substitution of [FeL(OH)](n−2)− (L= triethylenetetraaminehexaacetic acid) by cyanide ions

Summary The kinetics of reaction between [Fe(CN)₅OH]^3– and CN^– have been investigated spectrophotometrically at pH=11.00, I=0.25 M(NaClO₄) and temp.=25.0°C by disappearance of the absorption peak at 395 nm. The rate data for this reaction followed first order kinetics in both [Fe(CN)₅OH^3–] and [CN^–]. The second order rate constant (k_f) was found to be (3.44±0.08)×10^–3 M^–1 s^–1. The pH dependence of the reaction was also investigated in the range 9–12. The activation parameters were found to be H=36.4kJ mol^–1 and S=–168JK^–1 mol^–1.The reaction between [Fe(CN)₆]^3– and TTHA^6– (TTHA=triethylenetetraaminehexaacetic acid) has also been followed spectrophotometrically at 420 nm, pH=11.00, I=0.1M (NaClO₄) and temp.=25.0°C. This reaction also followed first order kinetics in both [Fe(CN) ₆ ^3– ] and [TTHA^6–]. The second order rate constant (k_f) was found to be (3.74±0.21)×10^–2 M^–1 s^–1. The rate of reaction was found to increase with pH in the range 9–11.5. The different reactive species of TTHA (L) are H₂L^4– HL^5– and L^6–. The rate constants for these species have been calculated and the pH profile is explained. The values of the activation parameters were found to be H= 30.9 kJmol^–1 and S=–167JK^–1 mol^–1. Electron transfer from [Fe(CN)₆]^3– to the substrate followed by decomposition of the latter is proposed. The oxidation products of TTHA have been investigated by g.l.c.     

Determination of the Kinetic Significance of Elementary Steps in the Reaction of Ethylbenzene Oxidation Inhibited by para-Substituted Phenols: Choice of an Effective Antioxidant

A conceivable method (value method) for analyzing the reaction kinetics models of inhibited liquid-phase oxidation of organic compounds was considered. A procedure for the numerical calculations of the molecular structure parameters of an inhibitor and an inhibitor concentration that results in a maximum inhibition of the reaction was presented. In the kinetic model of a chain reaction of liquid-phase ethylbenzene oxidation in the presence of a para-methylphenol inhibitor, the dynamics of contributions from individual steps was calculated. This allowed us to simplify the reaction mechanism. The inhibition of the oxidation reaction due to reactions with the participation of a phenoxyl radical was found to occur under conditions of the quasi-equilibriumRO ₂ ^· +HO'RRO₂H +OC₆H₄'RThe molecular structures and initial concentrations of para-substituted phenols, which are most effective for the given reaction conditions, were determined.     

Rate Constants for the Reaction of Diphenyl Carbonyl Oxide with Phenols

The kinetics of the reaction of diphenyl carbonyl oxide Ph₂COO with o- and p-substituted phenols is studied by pulse photolysis and high-speed spectrophotometry. The rate constant strongly depends on the phenol structure and ranges from 1.3 × 10³ for ionol to 2.1 × 10⁸ l mol^–1 s^–1 for o-aminolphenol. A U-shaped curve illustrating how the logarithm of the rate constant changes with a change in the Hammett constants (⁰) of the substituents in the aromatic ring is found for the studied compounds. Possible pathways for the reaction of Ph₂COO with phenols are discussed.     

Difference spectrophotometric determination of some pharmaceutically important thioxanthene derivatives in dosage forms

A Spectrophotometric method is described for the rapid determination of four thioxanthene derivatives, namely chlorprothixene, thiothixene, flupenthixol hydrochloride and clopenthixol hydrochloride. The method is based on measuring the first derivative spectrum (D ₁) of the oxidized drug relative to a solution of the underivatized drug. At the wavelength of maximum difference in first derivative (range 285–315 nm), only the oxidation products have an appreciable difference in first derivative and the oxidizing agent has no absorbance. The oxidation products (assumed to be the thioxanthone sulphoxides) are formed rapidly at room temperature by the addition of peroxyacetic acid, prepared by the slow reaction of hydrogen peroxide and glacial acetic acid. The first derivative of the absorbance is proportional to the concentration of the drugs in solution over the ranges 2–14 g ml^–1 for chloroprothixene, 2–20 g ml^–1 for clopenthixol hydrochloride, 2–24 g ml^–1 for thiothixene and 4–40 g ml^–1 for flupenthixol hydrochloride. The method is specific for the intact drug and can be adopted in the presence of oxidative and photochemical decomposition products and tablet excipients. The recoveries ranged from 99.7 ± 1.3 to 100.2 ± 1.5%. The validity of the method was tested by analysing synthetic samples of thioxanthenes and some dosage forms containing the drugs; the results were in accordance with those given by the official methods.     

Quantitative Determination of Oxalic Acid Using Victoria Blue B Based on a Catalytic Kinetic Spectrophotometric Method

A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. The procedure is based on the effect of oxalate on the oxidation of Victoria blue B by dichromate in dilute sulfuric acid medium. The reaction is quantitatively estimated by measuring the decrease in absorbance of Victoria blue B at the maximum wavelength of 610nm after quenching the reaction with tap water. The factors effecting the sensitivity and reproducibility of the reaction were studied. The method is not interfered with by foreign species generally associated with oxalate and oxalic acid. The described method is simple, specific, inexpensive and suitable for oxalic acid concentrations of between 0.06 and 9.0µgmL^–1. It was validated with satisfactory results by determining oxalic acid content in water extracts from plant materials such as spinach and Lathyrus sativus.