Determination of the Absolute Rate Constants of Reactions between Diphenyl Carbonyl Oxide and Alcohols by Flash Photolysis

The rate constants of the reactions of diphenyl carbonyl oxide Ph₂COO with a number of alcohols and water in acetonitrile, benzene, andn-decane solutions (295 K) were measured by flash photolysis. The rate constants vary over a range from 400 (triphenylmethanol in a MeCN solution) to 2.5 × 10⁵ l mol^–1 s^–1 (adamantanol in a benzene solution). -Methoxydiphenylmethyl hydroperoxide is the reaction product of Ph₂COO and MeOH. The absence of a kinetic isotope effect and the dependence of the logarithms of the rate constants on the first ionization potentials of alcohols are indicative of the formation of a C–O bond at the rate-limiting step of the reaction.     

Flash Photolysis of Diphenyldiazomethane in the Presence of Organic Sulfides

The flash photolysis of diphenyldiazomethane in acetonitrile, benzene, and n-decane solutions saturated with air resulted in the formation of diphenyl carbonyl oxide Ph₂COO which decayed in combination reactions. In the presence of organic sulfides, the transfer of the terminal oxygen atom of Ph₂COO to the sulfur atom was observed. The kinetics of this reaction was studied. The absolute rate constants (k ₆, dm³ mol^–1 s^–1) of the reactions of Ph₂COO with sulfides at 295 K (acetonitrile as a solvent) varied from 4.1 × 10² (Me₂S) to 8.1 × 10⁴ (Ph₂S). The solvent effect on the reaction kinetics and product composition was studied. The mechanism of the process was discussed.     

Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

Experimental Evidence for Acceleration of Reaction between Iodine Monoxide and Chlorine Monoxide at the Reactor Surface

The reaction of iodine monoxide with chlorine monoxide resulting in atom escape to the gas phase is studied at T = (303 ± 5) K and P = 2.5 Torr using a flow setup for measuring the resonance fluorescence signals of atomic iodine and chlorine. The heterogeneous reaction between chlorine monoxide and iodine monoxide occurring at the reactor surface covered with an F32-L Teflon-like compound and treated by the reaction products is characterized by the rate constant k = (4.9 ± 0.2) × 10^–11 cm³ molecule^–1 s^–1. This value is substantially higher than the rate constant for the homogeneous reaction IO^· + ClO^· (k ₁ 1 × 10^–12 cm³ molecule^–1 s^–1).     

Kinetics,mechanism, and products of the reaction of diphenylcarbonyl oxide with carboxylic acids

The kinetics of the reactions of acetic, benzoic, formic, oxalic, malic, tartaric, trifluoroacetic, and hydrochloric acids with diphenylcarbonyl oxide Ph₂COO was studied. The carbonyl oxide Ph₂COO was generated by flash photolysis of diphenyldiazomethane Ph₂CN₂ in solutions of acetonitrile and benzene at 295 K. The apparent rate constants of the reaction range from 4.6·10⁸ for (COOH)₂ in MeCN to 7.5·10⁹ L mol^–1 s^–1 for acetic acid in a benzene solution. The reaction mechanism was proposed, according to which at the first stage the carbonyl oxide is reversibly solvated by the solvent. Then the solvated carbonyl oxide reacts with the acid molecule by the mechanism of insertion at the O—H bond.     

Determination of the nature of the diperiodatocuprate(III) species in aqueous alkaline medium through a kinetic and mechanistic study on the oxidation of iodide ion

The nature of the diperiodatocuprate(III) (DPC) species present in aqueous alkaline medium has been investigated by a kinetic and mechanistic study on the oxidation of iodide by DPC. The reaction kinetics were studied over the 1.0 × 10^–3–0.1 mol dm^–3 alkali range. The reaction order with respect to DPC, as well as iodide, was found to be unity when [DPC] [I^–]. In the 1.0 × 10^–3–1.0 × 10^–2 mol dm^–3 alkali region, the rate decreased with increase in the alkali concentration and a plot of the pseudo-first order rate constant, k versus 1/[OH^–] was linear. Above 5.0 × 10^–2 mol dm^–3, a plot of k versus [OH^–] was also linear with a non-zero intercept. An increase in ionic strength of the reaction mixtures showed no effect on k at low alkali concentrations, whereas at high concentrations an increase in ionic strength leads to an increase in k. A plot of 1/k versus [periodate] was linear with an intercept in both alkali ranges. Iodine was found to accelerate the reaction at the three different alkali concentrations employed. The observed results indicated the following equilibria for DPC.[Cu(H₂IO₆)₂]^3- [Cu(H₂IO₆)]^- + H₂IO₆ ^3- [Cu(H₂IO₆)] + OH^- [Cu(HIO₆)]^- + H₂OA suitable mechanism has been proposed on the basis of these equilibria to account for the kinetic results.     

Antioxidant Activity of Adamantylphenols

Antioxidant properties of phenols with ortho- and para-adamantyl substituents are studied by microcalorimetry using cumene oxidation as a model reaction. The experimental rate constants for inhibition by adamantylphenols (k ₇) are comparable to the corresponding values for sterically hindered phenols, and the stoichiometric inhibition coefficient is higher than the calculated one. Adamantylphenols with adamantyl and methyl or methylene bridge groups in the ortho positions with respect to the functional group exhibit the maximal activity. The inhibition rate constant takes a maximal value of k ₇ = 3.3 × 10⁴ l mol^–1 s^–1 for 2,4-di-(adamantyl-1)-6-methylphenol and a minimal value of k ₇ = 1.4 × 10³ l mol^–1 s^–1 for 2,4,6-triadamantylphenol. The difference in the rate constants is due to steric hindrances in the reaction of a peroxy radical with the functional group of a phenol surrounded by bulky adamantyl groups.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Alkaline Hydrolysis of Nitroglycerin and Activation of Luminol Chemiluminescence

Alkaline hydrolysis of nitroglycerin (G) was studied using the chemiluminescent reaction of the hydrolysis products with 4-dimethylaminophthalhydrazide (L). The chemiluminescence kinetics follows the pseudo-unimolecular law, with the rate constant k ₁ proportional to [OH^–]. The apparent bimolecular constant k ₂ = k ₁/[OH^–] is equal to 0.021 l mol^–1 s^–1. The chemiluminescence quantum yield per one nitroglycerin molecule _G = (1.3 ± 0.3) × 10^–3 photons per one molecule ([G₀] [L]), and the reactant chemiluminescence quantum yield upon excitation by species X formed from G in the course of hydrolysis is (2.6 × 0.5) × 10^–2 photons per molecule ([G] [L₀]]). Hence, it follows that the hydrolysis of 100 nitroglycerin molecules results in about five X molecules exciting chemiluminescence. The effects of temperature, ionic strength, and composition of the solution on k ₂ were studied. Quantum-chemical calculation on the interaction of ^– ion with G molecule shows a possibility for peroxynitrite formation upon approach of the ion to the nitro group within the NO₂ plane. If the approach occurs not in the NO₂ plane, the conventional hydrolysis mechanism with substitution at nitrogen is realized.     

Rate Constant for the Reaction of the OH-Radical with CH2F2

The rate constant value of k ₁ = (6.05 ± 0.20)×10⁹ cm³ mol^–1 s^–1 (with ± 1 error) has been determined for the reaction OH + CH₂F₂ (1) by applying the discharge-flow/resonance-fluorescence method at 298 K.     

Kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) in aqueous solution

Summary The kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) ion in aqueous solution in the presence ofo-phenanthroline was studied spectrophotometrically. The first-order rate constant (k ) at 30° C [I=1 M(NaCl)] for the thermal reaction is (1.49±0.13)×10^–6 s^–1 with H =(158±7)kJ mol^–1 and S=(42±4) JK^–1 mol^–1. The initial quantum yield for the photochemical reaction at pH=7 is independent of the light intensity and is (1.49±0.33)×10^–2 mol einstein^–1.A communication on this subject was presented at the XVI Latinamerican Chemistry Congress held at Rio de Janeiro. Brasil, October 14–20, 1984.     

The kinetics of the reaction of iodine with hydrazine as studied by pulse radiolysis

Pulse radiolysis was utilized to study the iodine — hydrazine reaction in aqueous solutions of pH3 to 7, at I^– concentrations of 0.02 to 0.34M, and a constant ionic strength of 0.35M. The reaction rate was found to be proportional to [H⁺]^–1 and [I^–]^–1. Experimental results support the assumption that the rate-determining step is the reaction of I₂ with N₂H₄ with a rate constant K1.2×10⁷ M^–1s^–1.     

The Reactivity of Diphenyl Carbonyl Oxide in Reactions with Alcohols

The reactivities of ten alcohols in the reactions with diphenyl carbonyl oxide Ph₂COO is characterized by the ratio k ^OH ₃₃ /k ₃₁, where k ^OH ₃₃ and k ₃₁are the rate constants of Ph₂COO reactions with an alcohol and diphenyldiazomethane PH₂CN₂, respectively. The values of k ^OH ₃₃ /k ₃₁range between 0.6 × 10^–2for MeOH to 6.0 for iso-PrOH at 70°C in acetonitrile. The donation of electron density to the alcohol hydroxyl group favors the attack of Ph₂COO; that is, Ph₂COO reacts as an electrophile.     

Electron-transfer kinetics and mechanism of the reduction of octacyanometallates(IV) (M = Mo,W) by hydroxide ion in aqueous solution

Summary The kinetics of the reduction of octacyanometallates(IV) in alkaline aqueous medium have been studied spectrophotometrically. The experimental results are in agreement with following rate law:-d[M(CN) _inf8 ^sup3– ]/dt = k _obs[M(CN) _inf8 ^sup3– ]²[OH^–][Na⁺] where k _obs = 4.1 × 10^–2M^–3s^–1 (Mo) and 4.0 × 10^–4 M^–3 s^–1 (W). The rate data were used to calculate the thermodynamic activation parameters H and S . A mechanism of the reaction is discussed.On leave from Faculty of Chemistry, Forest Engineering Institute, Archangelsk, Russia.     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Isotope exchange reaction between NaCl-36 and triphenyltin chloride in dioxane-water (8020% w/w) and ethanol-water (9010% w/w) mixed solvents has been studied at 25, 35 and 50 °C. The exchange reaction was found to proceed via a bimolecular S_N2, limiting mechanism with reaction rates depending on the solvent used. Inhibition of the exchange in ethanol-water is probably due to solvation of chloride ion through hydrogen bond formation. The rate laws for the exchange reactions are: R_e=3.24×10⁹ e^–65550/RT [Rh₃SnCl] [NaCl] in dioxanewater and R_e=6.61×10⁸ e^–69600/RT [Ph₃SnCl] [NaCl] in ethanol-water, where is the degree of dissociation of NaCl and R_e is the rate of exchange in mol l^–1 s^–1. The activation parameters H^*, S^* and G^* are reported.     

Kinetik der unkatalysierten Urethanbildung

Summary The kinetics of the reaction of phenylisocyanate with 1-butanol have been studied at low concentrations in carbon tetrachloride solution at three temperatures. The present paper describes the relation between the reaction rate and the concentration of the alcohol dimer and the 1:1 alcoholurethane associate. Therefrom we conclude that the monomeric alcohol does not play any significant part in the reaction. We explain the observed rate equation with the second-order term of the reactants with the equality of the productsk _AA K _AA andk _AU K _AU (rate constant and association constant of alcohol dimer and 1:1 alcohol-urethane associate).For the reaction of alcohol dimer H =45.4 kJ mol^–1 and S =– 142J mol^–1K^–1. We interpret this result in terms of a six-cyclic transition state.

     

Kinetics and mechanism of chromium(VI) oxidation of L-methionine

The kinetics and mechanism of chromium(VI) oxidation of L-methionine in acidic medium have been studied spectrophotometrically. The reaction proceeds via the formation of a transient intermediate (_max = 410–420 nm) which decomposes by a proton catalyzed pathway. The rate law is:

Transfer of F− in the reaction of SF 6 − with SOF4: Implications for SOF4 production in corona discharges

The temperature (T) and electric field-to-gas pressure (E/P) dependences of the rate coefficientk for the reaction SF ₆ ^– +SOF₄SOF ₅ ^– +SF₅ have been measured. ForT<270 K,k approaches a constant of 2.1×10^–9 cm³/s, and for 433>T>270 K,k decreases withT according tok (cm³/s)=0.124 exp [–3.3 lnT(K)]. ForE/Pk has a constant value of about 2.5×10^–10 cm³/s, and for 130 V/cm·torr>E/P>60 V/cm·torr, the rate is approximately given byk (cm³/s)7.0×10^–10 exp (–0.022E/P). The measured rate coefficient is used to estimate the influence of this reaction on SOF₄ production from negative, point-plane, glow-type corona discharges in gas mixtures containing SF₆ and at least trace amounts of O₂ and H₂O. A chemical kinetics model of the ion-drift region in the discharge gap is used to fit experimental data on SOF₄ yields assuming that the SF ₆ ^– +SOF₄ reaction is the predominant SOF₄ loss mechanism. It is found that the contribution of this reaction to SOF₄ destruction falls considerably below the estimated maximum effect assuming that SF ₆ ^– is the predominant charge carrier which reacts only with SOF₄. The results of this analysis suggest that SF ₆ ^– is efficiently deactivated by other reactions, and the influence of SF ₆ ^– +SOF₄ on SOF₄ production is not necessarily more significant than that of other slower secondary processes such as gas-phase hydrolysis.     

Kinetic exchange studies of metal ion substitution in EDTA chelates Fe(III)- UO2 EDTA exchange

A kinetic study of the exchange reaction between UO₂EDTA complex and Fe(III), at a constant ionic strength of 0.1, over the concentration range of 5×10^–3–1×10^–2 M of each reactant and pH 4.5–5.5 has been carried out radiometrically. The rate of the exchange process can be expressed by the equation: R=k₁[UO₂EDTA][Fe]+k₂[EDTA][H⁺]^–1. The activation parameters calculated were H^*=25.95 kJ mol^–1 and S^*=0.67 kJ mol^–1 K^–1.     

Kinetics of the manganese(III)-oxalate reaction in acidic sulphate media

The kinetics of the reaction of manganese(III) with oxalic acid (OA) has been studied in H₂SO₄ solutions. Under the experimental conditions of 6 × 10^–3 <>₀ < 0.4=" mol=">^–3 and [H₂SO₄]₀ 0.2 mol dm^–3 the observed pseudo-first order rate constant k _obs follows the expression