The gas phase reactivity of aliphatic polyethers towards OH radicals: Measurements and predictions

Using the flash photolysis resonance fluorescence technique, absolute rate constants were determined for the gas phase reactions of hydroxyl radicals with a series of aliphatic polyethers. At 298 K, the measured rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were: 2,2-dimethoxypropane, (3.9 ± 0.2); 2,2-diethoxypropane, (11.7 ± 1.3); 1,2-dimethoxypropane, (14.3± 1.5); 2-methoxyethylether, (17.5 ± 1.1); 2-ethoxyethlyether, (26.8 ± 2.4); 1,1-dimethoxyethane, (8.9 ± 1.0); and 1,1,3-trimethoxypropane, (16.7 ± 1.0). The temperature dependencies of the rate constants for 2,2-dimethoxypropane and 2,2-diethoxypropane, reactions (1) and (2), were studied over the temperature range 240–440 K and are expressed by the Arrhenius equations: Implications of the results are discussed in terms of reaction mechanisms and the prediction of gas phase OH radical reaction rates for aliphatic polyethers.     

On the reaction between ethylene and cyclopentene,a radical mechanism

The bimolecular reaction is shown to proceed via a simple, nonchain, radical mechanism: with the net reaction the same as (1). Rate constants are estimated for each step and for each possible competing reaction and shown to yield minor or negligible side reactions in agreement with the observations of Lalonde and Back. Estimated and observed rate constants (1) and (1′) are in excellent agreement with the assumption that k'_-1 is a typical radical disproportionation with zero activation energy. From the reported data a best value for k′₁ is where θ = 2.303RT kcal/mol.     

Kinetics and mechanism of oxidation of l‐ascorbic acid by peroxomonophosphate in aqueous acid medium

The kinetics of oxidation of l ‐ascorbic acid (H₂A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation (1) where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: (2) Such pH dependence is somewhat different from that observed in the case of metal ion oxidants. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 41–16, 2013     

The reaction of cyclohexyl radicals with carbon tetrachloride

The photolysis of azocyclohexane, carbon tetrachloride, and cyclohexane at 360 nm has been investigated over a wide temperature range. At moderate temperatures a chain reaction ensues from which the following approximate rate constants could be determined assuming 2CCl₃. → C₂Cl₆, k₅ = 10^9.7 (303–673K): The really striking feature of the results is that they show that termination in bicyclohexyl [reaction (7)] is extremely slow: The root-mean-square rule for estimating the cross-combination rate is also followed. The photolysis of carbon tetrachloride and cyclohexane at 250 nm has also been investigated. The reaction is complicated by the occurrence of two concurrent photolytic processes, the main one yielding trichloromethyl radicals and chlorine atoms, and the subsidiary one yielding dichlorocarbene and molecular chlorine. Nonetheless the results from this reaction can be interpreted in the medium temperature range 360–430K, where long chains are present, in terms of the rate constants derived from the azocyclohexane system.     

Kinetic studies and mechanism on the permanganic oxidation of L‐Glutamine in strong acid medium in the presence and absence of Silver (I)

The kinetic study and mechanism of the permanganic oxidation of L‐glutamine in sulfuric acid has been carried out both in the absence and presence of silver (I) using a spectrophotometric technique. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. The overall rate expression for the oxidation may be written as In the presence of silver (I) the rate law is The reaction appears to involve an acid catalyzed and data showed role of water molecules in the rate‐determining step is proton transfer which satisfies Bunnett's theory. A mechanism satisfying the various kinetic parameters has been proposed. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 95–102, 1999     

Kinetics and mechanism of the reaction of aqueous sulfite with N-chloroalanylalanylalanine

The rate of the reaction of aqueous sulfite with the N-chloropeptide N-chloroalanylalanylalanine has been studied as a function of pH, temperature, and ionic strength. The results of this work suggest that the mechanism of the reaction involves the interaction of the neutral chloramine with the three ionic forms of sulfite, SO, HSO, and H₂SO₃, with the rate of reaction increasing rapidly with increasing protonation. The estimated second-order rate constants for each ionic species as a function of temperature are where the activation energies are in units of cal/mol.     

The decomposition kinetics of hydrogen peroxide catalyzed by diethylenetriaminepentaacetatoiron(III) complex

The rate of reaction of (Fe(DTPA)) with H₂O₂ was investigated at various temperatures. The observed rate law is given by the expression. The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate. The results are compared with previously data for Fe EDTA complex.     

Photo-induced disproportionation of iodomalonic acid

The stoichiometry, equilibrium, and kinetics of the photo-induced disproportionation of iodomalonic acid to I^?, I₂, and tartronic acid have been studied by means of spectrophotometry and iodide selective electrode at 20.0 ± 0.2°C, pH 2.0–4.0. At pH > 2.9, only I^? and HOCH(COOH)₂ are detected as major products and the reaction reaches 100% conversion. At pH < 2.9, I₂ and malonic acid are also formed and the reaction stops at a conversion rate less than 100%. Both UV (band with a peak at 360 nm) and visible light (480 nm) have been found to be effective. Two primary photochemical processes are identified: While both reactions are sensitive to UV light, only (M2) can be affected by visible light. (M1) and (M2) are considered to initiate a chain reaction sequence in which I^· radicals oxidize iodomalonic acid. Dual effects of reaction products on the reaction rate have been observed: while iodine increases the efficiency of visible light and accelerates the reaction, malonic acid inhibits the photo-decomposition by mediating the recombination of I^· radicals to I₂. © 1995 John Wiley & Sons, Inc.     

Temperature dependence of the rate constant for the reaction OH + H2S

Absolute rate constants for the reaction of OH with H₂S have been measured over the temperature range of 239–425 K using the flash photolysis–resonance fluorescence technique. The results showed that the rate constants deviate slightly from Arrhenius behavior but can still be represented adequately by the following Arrhenius equation: Comparisons with recent literature values are presented.     

Kinetic and mechanistic study of the reactions of palladium(II) chlorocomplexes with ethylenediamine in aqueous acid medium

The complexes PdCl₄^2?, PdCl₃(H₂O)^?, and PdCl₃(Ac)^2?, in rapid equilibrium with each other under the adopted experimental conditions, react with ethylenediamine according to the experimental rate law A reaction scheme is proposed involving the reaction of enH⁺ with each of the above species, and the specific rate constants are computed. The activation parameters are given.     

Reactivity of Aquadiethylenetriamineplatinum(II) Ion with Disulfide Moiety Cystine: A Kinetic and Mechanistic Approach

Abstract

Substitution reactions of the complex [Pt(dien)H₂O]²⁺ (where dien = diethylentriamine or 1,5-diamino-3-azapentane) with sulfur-containing L-cystine have been studied in a 1.0 × 10^?1 mol dm^?3 aqueous perchlorate medium at various temperatures (298–323 K) and 4.45 ≤ pH ≤ 2.15 using UV-vis spectroscopy. The products obtained have been characterized by their infrared and ¹H NMR datasets at various pH levels and temperatures. From infrared and ¹H NMR data, products have indicated that [Pt(dien)H₂O]²⁺ reacted with L-cystine forming a Pt–S bond at low pH. At high pH, a product complex through the Pt–N bond has been formed. All rate constants have been evaluated from nonlinear double exponential plots. The activation parameters ΔH^# and ΔS^# have been determined using the Eyring equation. The products, S_Ni, and reversible rate constants have been evaluated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT      

Kinetics and mechanism of ninhydrin reaction with copper(II) complexes of glycine and α-alanine. Elucidation of the template mechanism

Ninhydrin has been found to react with Cu(glycine)⁺ and Cu(alanine)⁺ in the ratio of 1:1. The kinetic studies of the reaction were carried out at different concentrations of the reactants at 80°C (pH = 5.0). The reaction proceeds through the formation of a ternary labile complex of ninhydrin with Cu(II) complexes of glycine and alanine. The kinetics were found to follow pseudo-first-order reaction path with respect to Cu(II)-complex in presence of excess [Ninhydrin]. Formation of a ternary labile complex indicates a template reaction mechanism based on the reactions with coordinated ligands. The variation of pseudo-first-order rate constants with [ninhydrin] was found to be in good agreement with equation where B₁ and B₂ are the unknown empirical parameters. The [acetate ion] has no significant effect on the rate constants. On the basis of observed data a probable mechanism has been proposed. © 1993 John Wiley & Sons, Inc.     

Kinetics of the thermal gas-phase dimerization of hexafluoropropene

The reversible thermal gas-phase dimerization of hexafluoropropene to the four isomeric cyclobutanes has been studied by pressure change and by gas-liquid chromatographic analysis in the temperature range of 645–708 K with initial pressures of olefin from 802 to 4820 mm Hg. The reaction was accurately second order at low conversions of olefin to dimers, and at higher conversions it gave a very good fit to the rate equation for opposing second- and first-order reactions. The rate constants for the dimerization, calculated from initial rates of reaction, yielded the least-mean-squares Arrhenius equation (95% confidence limits): where k₂ is defined by Studies carried out in a packed vessel showed no evidence of heterogeneity. The rate constants found in this work are in excellent agreement with those found at lower pressures by Atkinson and Tsiamis, and the combined results give the Arrhenius equation      

Solvolysis of o‐methylbenzenediazonium tetrafluoroborate in acidic methanol‐water mixtures. Further evidence for nucleophilic attack on a solvent separated aryl cation

Rate constants for dediazoniation product formation and arenediazonium ion loss and product yields of solvolysis of o‐methylbenzenediazonium tetrafluoroborate in acidic methanol‐water mixtures at T = 35°C are reported. Observed rate constants for diazonium ion loss and product formation are the same, increasing about 45% ongoing from water to methanol, and are not affected by added electrolytes like HCl, NaCl, and CuCl₂. Only three dediazoniation products are detected, o‐cresol, o‐chlorotoluene, and o‐anisole. All data are consistent with a rate‐determining step formation of an aryl cation that reacts immediately with available nucleophiles. The selectivity of the reaction toward nucleophiles, S, which can be defined by: is low and essentially constant upon changing solvent composition, suggesting that the nucleophilic attack takes place on a solvent separated aryl cation. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 531–538, 1999     

The relaxation spectra of nickel(II) and cobalt(II) arginine complexes

The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k₁ = 2.3 × 10³(±20%), k₂ = 2.4 × 10⁴(±20%), k₃ = 3.5 × 10⁴(±40%) M^?1 sec^?1; for cobalt(II) k₁ = 1.5 × 10⁵(±20%), k₂ = 8.7 × 10⁵(±20%), k₃ = 2.0 × 10⁵(±40%) M^?1 sec^?1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.     

Thermochemical Kinetics of Nitrogen Compounds. Part 4. The gas phase unimolecular thermal decomposition of triallylamine

The gas phase thermal decomposition of triallylamine was studied in the temperature range 531 to 620 K. The major products observed in the reaction were propylene and 3-picoline. The first order rate constants for depletion of triallylamine, obtained using the internal standard technique, are found to be independent of pressure and conversion, and fit the Arrheniusrelationship The reaction appears to be homogeneous, as a 15-fold change in thc surface-to-volume ratio of the vessel left the rate constants unchanged. The Arrhenius parameters are consistent with a molecular elimination reaction involving a six-center transition state, yielding propylene and N-allyl-prop-2-enaldimine. It is proposed that the latter product undergoes a 1,5-hydrogen transfer, followed by a ring closure reaction to yield dihydropicoline, which in turn reacts forming 3-picoline via a self-initiated decomposition reaction.     

Basic elimination of HCl from chlorinated ethanes

Chloroethanes react with aqueous caustic to yield either elimination or substitution products. The reaction rates were measured for the dichloroethanes, trichloroethanes, tetrachloroethanes, and pentachloroethane between 283 and 353°K. The constants of HCl eleminations referring to the rate equation are given by all rate constants being in 1./mole·s and R in cal/mole· deg. With ethyl chloride, 1,1-dichloroethane, and 1,1,l-trichloroethane, the elimination is not observed and a slow substitution takes place. The influence of chlorine substituents on both sides of the molecule on mechanism and rate parameters is discussed.     

Photolysis of azomethane–propane mixtures. Arrhenius parameters for the hydrogen abstraction reactions of methyl with azomethane and with propane

Mixtures of up to 14% azomethane in propane have been photolyzed using mainly 366 nm radiation in the ranges of 323–453 K and 25–200 torr. Detailed measurements were made of the yields of nitrogen, methane, and ethane. Other products observed were isobutane, n-butane, ethene, and propene. A detailed mechanism is proposed and shown to account for the observed variation of product yields with experimental conditions. The quantum yield of the molecular process is found to be given by the temperature-independent equation The values of rate constants obtained are where the reactions are and it is assumed that the rate constant for the reaction is given by      

A shock-tube study of the kinetics of reaction of hydroxyl radicals with H2, CO,CH4, CF3H,C2H4, and C2H6

Concentration-time profiles have been measured for hydroxyl radicals generated by the shock-tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF₃H:H₂:CH₄:C₂H₄:C₂H₆, respectively.