Cu(II) catalyzed reaction between phenyl hydrazine and toluidine blue—dual role of acid

The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB⁺) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions are the main products of the reaction. The diazonium ion further decomposes to phenol (PhOH) and nitrogen. At low concentrations of acid, H⁺ ion autocatalyzes the uncatalyzed reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, H⁺ hinders both the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to the uncatalyzed reaction, Pz+2 TB⁺+H₂O=PhOH+2 TBH+2 H⁺+N₂. Cu(II) catalyzed reaction occurs possibly through ternary complex formation between the unprotonated toluidine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed reaction is 2.1×10⁴ M⁻² s⁻¹. A detailed 13‐step mechanistic scheme for the Cu(II) catalyzed reaction is proposed, which is supported by simulations. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 271–276, 1999     

Uncatalyzed and ruthenium(III)‐catalyzed reaction of acidic chlorite with methylene violet

The kinetics and mechanism of the uncatalyzed and Ru(III)‐catalyzed oxidation of methylene violet (3‐amino‐7‐diethylamino‐5‐phenyl phenazinium chloride) (MV⁺) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo‐first‐order kinetics with respect to MV⁺. The uncatalyzed reaction had first‐order dependence on chlorite and H⁺ concentrations, but the catalyzed reaction had first‐order dependence on both chlorite and catalyst, and a fractional order with respect to [H⁺]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M^?2 s^?1, while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 10³ M^?1 s^?1. The basic stoichiometric equation is as follows: 2MV⁺ + 7ClO₂^? + 2H⁺ = 2P + CH₃COOH + 4ClO₂ + 3Cl^?, where P⁺ = 3‐amino‐7‐ethylamino‐5‐phenyl phenazinium‐10‐N‐oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15‐step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 294–303, 2003     

A kinetic study of the reduction of toluidine blue with thiourea in acidic solution

A detailed kinetic study of the reaction of toluidine blue (tolonium chloride) (TB⁺ Cl^?) with thiourea (TU) in aqueous hydrochloric acid solution is reported. The reaction was first order with respect to toluidine blue and the reductant and second order with respect to [H⁺]. Thiourea had a 2:1 stoichiometric ratio with TB⁺. Toluidine blue was reduced to a colorless base in two one-electron reduction steps and TU was oxidized to thioformamidinium ion, which dimerized rapidly to give stable dithioformamidinium ion. The energy parameters obtained for TB⁺-TU reaction were mean energy of activation (Ea′) = 26.7 ± 2.4 kJ M^?1; enthalpy of activation (ΔH^#) = 24.2 kJ M^?1; frequency factor (A) = 1.04 × 10⁴ M^?3 s^?1; and entropy of activation (ΔS^#) = ?176.35 J M^?1 s^?1. © John Wiley & Sons, Inc.     

Inorganic reactions of iodine(III) in acidic solutions and free energy of iodous acid formation

An analysis of the former works devoted to the reactions of I(III) in acidic nonbuffered solutions gives new thermodynamic and kinetic information. At low iodide concentrations, the rate law of the reaction IO + I^? + 2H⁺ ? IO₂H + IOH is k_+B [IO][I^?][H⁺]² – k_?B [IO₂H][IOH] with k_+B = 4.5 × 10³ M^?3s^?1 and k_?B = 240 M^?1s^?1 at 25°C and zero ionic strength. The rate law of the reaction IO₂H + I^? + H⁺ ? 2IOH is k_+C [IO₂H][I^?][H⁺] – k_?C [IOH]² with k_+C = 1.9 × 10¹⁰ M^?2s^?1 and k_?C = 25 M^?1s^?1. These values lead to a Gibbs free energy of IO₂H formation of ?95 kJ mol^?1. The pK_a of iodous acid should be about 6, leading to a Gibbs free energy of IO formation of about ?61 kJ mol^?1. Estimations of the four rate constants at 50°C give, respectively, 1.2 × 10⁴ M^?3s^?1, 590 M^?1s^?1, 2 × 10⁹ M^?2s^?1, and 20 M^?1 s^?1. Mechanisms of these reactions involving the protonation IO₂H + H⁺ ? IO₂H and an explanation of the decrease of the last two rate constants when the temperature increases, are proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 647–652, 2008     

Kinetic study of some reactions related to the Mn(II)-catalyzed bromate-saccharide oscillating reactions

In the stirred batch experiment, the Mn(II)-catalyzed bromate-saccharide reaction in aqueous H₂SO₄ or HClO₄ solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second-order rate constants of the Mn(III)-saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M⁻¹ s⁻¹ in 1.00 M H₂SO₄ and (4.69, 7.51, 10.2, 13.5, and 36.2) M⁻¹ s⁻¹ in (2.00–4.00) M HClO₄ for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo-first-order rate constant of the Mn(III)-Br⁻ reaction is k_obs = (0.2 ± 0.1) [Br⁻] + (130 ± 5)[Br⁻]² + (2.6 ± 0.1) × 10³[Br⁻]³ + (1.2 ± 0.2) × 10⁴[Br⁻]⁴ s⁻¹ and the rate constant of the Br₂ Mn(II) reaction is less than 1 × 10⁻⁴ M⁻¹ s⁻¹. The second-order rate constants of the Br₂-saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10⁻⁴ M⁻¹ s⁻¹ at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.     

Kinetics and mechanism of indigo carmine-acidic iodate reaction. An indicator reaction for catalytic determination of Ru(III) ion

A kinetic study of uncatalyzed and Ru(III) catalyzed oxidation of indigo carmine(IC) (disodium 3,3′-dioxobi-indolin-2,2′-ylidene-5,5′-disulphonate) by iodate ion in aqueous sulphuric acid solution is reported. The uncatalyzed reaction order was found to be four; one each with respect to IC and iodate ion and second order with H⁺ ion. The Ru(III) catalyzed reaction was of fifth order, second order with respect to H⁺ and first order with respect to reductant, oxidant, and catalyst. Stoichiometric ratios of both reactions were the same with a 3:2 reductant-oxidant ratio. In both uncatalyzed and catalyzed reactions isatin-5-monosulphonic acid (2,3-dioxoindoline-5-sulphonic acid) was observed as the oxidation product. Rate constants for both the reactions are reported. Reaction mechanisms consistent with the experimental data are suggested. Further, a fixed time method is described for the determination of Ru(III), based on its ability to catalyze the oxidation of IC by acidic iodate. Using [H⁺] 2.25M, [iodate] 1.00 × 10^?3M and [IC] 5.0 × 10^?5M, in presence of Ru(III), the reaction followed first order kinetics with respect to IC. The interference of various cations, neutral salts, and potassium iodide on the determination of Ru(III) was studied using synthetic mixtures. The selectivity of the method and the recommended procedure are described.     

Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

Studies on toluidine blue reaction with sulfite in aqueous solution and role of Cu(II) as promoter

The kinetic and mechanistic details of the reaction between toluidine blue and sulfite were studied spectrophotometrically by monitoring the depletion of toluidine blue at 633 nm. The reaction had first‐order dependence on both the reactants, a stoichiometric ratio of 1:1 and a negative salt effect indicating the participation of TB⁺ and SO₃²⁻ ions in the rate‐limiting step. The reaction products were leuco base of toluidine blue and sulfate. The reaction was pH dependent and hence studied at its optimum pH 7.2. Cu(II) acted as promoter by facilitating the formation of a ternary complex with the reactants. The protonation and stability constants of the reactants were determined and used in validating the mechanism. The activation parameters for the reactions in absence and presence of Cu(II) were determined and compared with other systems. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 539–549, 1999     

Kinetics and mechanism of reaction of toluidine blue with acidic bromate

The detailed kinetics of the reaction of toluidine blue {phenothiazine-5-ium, 3-amino-7(dimethylamino)-2-methyl chloride, tolonium chloride, TB⁺Cl⁻} with potassium bromate and with aqueous bromine reaction were studied. In most of the experiments, the kinetics were monitored by following the rate of consumption of TB⁺ at 590 nm with excess acid and bromate. The reaction exhibited complex kinetic behavior. Initial reaction was slow and after an induction time, the TB⁺ concentration decreased fast. It had first-order dependence on both TB⁺ and bromate, and second-order dependence on H⁺. Under excess bromate conditions, the stoichiometric ratio of TB⁺ to bromate was 1:1. Demethylated sulfoxides were found at the reaction products. Sharp increase in the overall potential synchronized with the increase in bromine levels and the fast depletion of [TB⁺]. The role of bromide ion and bromine in the reaction was established. A multi-step reaction mechanism is proposed consistent with the experimental results. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 111–120, 1998.     

Kinetics of the reactions of CH3O with Cl and CIO

The kinetics of the reactions CH₃O + Cl → H₂CO + HCl (1) and CH₃O + ClO → H₂CO + HOCl (2) have been studied using the discharge-flow techniques. CH₃O was monitored by laser-induced fluorescence, whereas mass spectrometry was used for the detection or titration of other species. The rate constants obtained at 298 K are: k₁ = (1.9 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂ = (2.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. These data are useful to interpret the results of the studies of the reactions of CH₃O₂ with Cl and ClO which, at least partly, produce CH₃O radicals. © 1996 John Wiley & Sons, Inc.     

Consecutive reactions of diethoxydimethylsilane and triethoxymethylsilane with methoxide ions in methanol solution

The consecutive reactions of (CH₃)₂Si(OC₂H₅)₂ and CH₃Si(OC₂H₅)₃ with methoxide ions were investigated in methanol solutions. The reverse transesterification reactions with ethoxide ions could be neglected in both cases since the concentration of ethoxide in methanol solution was assumed to be low due to the fast equilibrium reaction C₂H₅O^? + CH₃OH ? C₂H₅OH + CH₃O^?. The progress of the reactions was followed by monitoring the formation of ethanol with a Fourier-transform infrared spectrometer. All rate constants were determined at 295 K. The reactions between the dialkoxydimethylsilanes and methoxide ions were assumed to consist of two consecutive steps that can be represented by the net reaction; (CH₃)₂Si(OC₂H₅)₂ + 2CH₃O^? → (CH₃)₂Si(OCH₃)₂ + 2C₂H₅O^?. The two consecutive rate constants were established as 1.93 ± 0.12M^?1s^?1 and 1.00 ± 0.12M^?1s^?1, respectively. The consecutive rate constants for the reactions between the trialkoxymethylsilanes and methoxide ions can be written according to the total reaction; CH₃Si(OC₂H₅)₃ + 3CH₃O^? → CH₃Si(OCH₃)₃ + 3C₂H₅O^?. The three rate constants corresponding to each consecutive step were established as 1.12 ± 0.09 M^?1s^?1, 0.82 ± 0.10 M^?1s^?1, and 0.51 ± 0.06 M^?1s^?1, respectively. © 1995 John Wiley & Sons, Inc.     

Flash photolysis of SiBr4: the UV spectrum of SiBr2

In the flash photolysis of SiBr₄ both the absorption and the emission spectra corresponding to the B̃²Σ−X̃²Π transition of SiBr have been observed. A broad, structureless absorption band has also been detected in the 340–400 nm region which could be assigned to the hitherto unreported à ¹B₁−x̃ ¹A₁ transition of SiBr₂. The decay of both absorption spectra followed first-order kinetics yielding the pseudo-first-order rate constants: k(SiBr)=2.6 × 10⁴s⁻¹ and k(SiBr₂) = 8.9 × 10³⁻¹. Assuming that the principal reactions consuming these intermediates are SiBr+SiBr₄→Si₂Br₅ and SiBr₂+SiBr₄→ Si₂Br₆, the second-order rate constants have the values k(SiBr)= 9.7×10⁹ M⁻¹s⁻¹ and k(SiBr₂)= 3.3×10⁸M⁻¹s⁻¹.     

A laser flash photolysis kinetic study of reactions of the Cl2− radical anion with oxygenated hydrocarbons in aqueous solution

A laser photolysis–long path laser absorption (LP‐LPLA) experiment has been used to determine the rate constants for H‐atom abstraction reactions of the dichloride radical anion (Cl₂⁻) in aqueous solution. From direct measurements of the decay of Cl₂⁻ in the presence of different reactants at pH = 4 and I = 0.1 M the following rate constants at T = 298 K were derived: methanol, (5.1 ± 0.3)·10⁴ M⁻¹ s⁻¹; ethanol, (1.2 ± 0.2)·10⁵ M⁻¹ s⁻¹; 1‐propanol, (1.01 ± 0.07)·10⁵ M⁻¹ s⁻¹; 2‐propanol, (1.9 ± 0.3)·10⁵ M⁻¹ s⁻¹; tert.‐butanol, (2.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; formaldehyde, (3.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; diethylether, (4.0 ± 0.2)·10⁵ M⁻¹ s⁻¹; methyl‐tert.‐butylether, (7 ± 1)·10⁴ M⁻¹ s⁻¹; tetrahydrofuran, (4.8 ± 0.6)·10⁵ M⁻¹ s⁻¹; acetone, (1.41 ± 0.09)·10³ M⁻¹ s⁻¹. For the reactions of Cl₂⁻ with formic acid and acetic acid rate constants of (8.0 ± 1.4)·10⁴ M⁻¹ s⁻¹ (pH = 0, I = 1.1 M and T = 298 K) and (1.5 ± 0.8) · 10³ M⁻¹ s⁻¹ (pH = 0.42, I = 0.48 M and T = 298 K), respectively, were derived. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C‐H‐bond of log k_2nd = (32.9 ± 8.9) − (0.073 ± 0.022)·BDE/kJ mol⁻¹ is derived. From temperature‐dependent measurements the following Arrhenius expressions were derived: k (Cl₂⁻ + HCOOH) = (2.00 ± 0.05)·10¹⁰·exp(−(4500 ± 200) K/T) M⁻¹ s⁻¹, E_a = (37 ± 2) kJ mol⁻¹ k (Cl₂⁻ + CH₃COOH) = (2.7 ± 0.5)·10¹⁰·exp(−(4900 ± 1300) K/T) M⁻¹ s⁻¹, E_a = (41 ± 11) kJ mol⁻¹ k (Cl₂⁻ + CH₃OH) = (5.1 ± 0.9)·10¹²·exp(−(5500 ± 1500) K/T) M⁻¹ s⁻¹, E_a = (46 ± 13) kJ mol⁻¹ k (Cl₂⁻ + CH₂(OH)₂) = (7.9 ± 0.7)·10¹⁰·exp(−(4400 ± 700) K/T) M⁻¹ s⁻¹, E_a = (36 ± 5) kJ mol⁻¹ Finally, in measurements at different ionic strengths (I) a decrease of the rate constant with increasing I has been observed in the reactions of Cl₂⁻ with methanol and hydrated formaldehyde. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 169–181, 1999     

Nonlinear chemical reaction between Na2S2O3 and Peroxide compound

Kinetics of reaction between Na₂S₂0₃ and peroxide compound (H₂0₂ or Na₂S₂O₃) in a batch reactor and in a continuous stirring tank reactor (CSTR) were studied. Steady oscillations in uncatalyzed reactions in a CSTR were first discovered. In Na₂S₂0₃-H₂O₂-H₂S0₄ reaction system, Pt potential and pH of higher and lower flow rates beyond oscillation flow rates were in around the same extreme values. The reaction catalyzed by Cu²⁺ consists of the catalyzed oscillation process and the uncatalyzed osciliation one. On the basis of experiment, a reaction mechanism consisting of three stages was put forward. The three stages are H⁺ positive-feedback reactions, proton negative-feedback (uncatalyzed negative-feedback and catalyzed negative-feedback) reactions and transitional reactions. The mechanism is able to explain reasonably the nonlinear chemical phenomena appearing in the thiosulfate oxidation reaction by peroxide compounds. Project supported by the National Natural Science Foundation of China.     

Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ-R-5α,14β-androstane-14,17ξ-diols under [NH4]+ chemical ionization conditions1

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH₄]⁺ ions formed from epimeric tertiary steroid alchols 14 OH_β, 17OH_α or 17 OH_β substituted at position 17 have been studied. They give rise to formation of [M + NH₄? H₂O]⁺ dentoed as [MH_sH]⁺, [M_sH? H₂O]⁺, [M_sH? NH₃]⁺ and [M_sH? NH₃? H₂O]⁺ ions. Stereochemical effects are observed in the ratios [M_sH? H₂O]⁺/[M_sH? NH₃]⁺. These effects are significant among metastable ions. In particular, only the [M_sH]⁺ ions produced from trans-diol isomers lose a water molecule. The favoured loss of water can be accounted for by an S_N2 mechanism in which the insertion of NH₃ gives [M_sH]⁺ with Walden inversion occurring during the ion-molecule reaction between [M + NH₄]⁺ + NH₃. The S_N1 and S_Ni pathways have been rejected.     

Reduction of toluidine blue by stannous ion at low pH: Kinetics and simulations

A detailed kinetic study of the reaction between toluidine blue (tolonium chloride) (TB⁺Cl^?) and stannous chloride is carried out in aqueous hydrochloric acid. The depletion kinetics of toluidine blue were spectrometrically monitored at 626 nm. The reaction had fractional order with respect to toluidine blue (one half), three halves with respect to Sn²⁺, and first-order dependence on H⁺ ion. Stoichiometric ratio between reductant and oxidant is 1:1. During the reaction Sn²⁺ is oxidized to Sn⁴⁺ and toluidine blue is reduced to colorless base in two univalent steps. © 1993 John Wiley & Sons, Inc.     

Kinetics of phenol oxidation by peroxidase

Studies of the kinetic behavior of horseradish peroxidase (HRP) at pH 8 and at room temperature indicate that the reaction of phenol with H₂O₂ catalyzed by HRP exhibits normal Michaelis-Menten saturation kinetics. An irreversible reaction mechanism for the steady-state kinetics of HRP, which is consistent with the experimental data, is considered. The second-order rate constants for the reactions of HRP with H₂O₂ and compound II with phenol are 4.14 × 10⁵ M^-1s^-1 and 5.54 × 10⁴M^-1s^-1, respectively.     

Oxidation of manganese(II) by ozone and reduction of manganese(III) by hydrogen peroxide in acidic solution

Manganese(II) is oxidized by ozone in acid solution, k=(1.5±0.2)×10³ M⁻¹ s⁻¹ in HClO₄ and k=(1.8±0.2)×10³M⁻¹ s⁻¹ in H₂SO₄. The plausible mechanism is an oxygen atom transfer from O₃ to Mn²⁺ producing the manganyl ion MnO²⁺, which subsequently reacts rapidly with Mn²⁺ to form Mn(III). No free OH radicals are involved in the mechanism. The spectrum of Mn(III) was obtained in the wave length range 200–310 nm. The activation energy for the initial reaction is 39.5 kJ/mol. Manganese(III) is reduced by hydrogen peroxide to Mn(II) with k(Mn(III)+H₂O₂)=2.8×10³M⁻¹ s⁻¹ at pH 0–2. The mechanism of the reaction involving formation of the manganese(II)-superoxide complex and reaction of H₂O₂ with Mn(IV) species formed due to reversible disproportionation of Mn(III), is suggested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 207–214, 1998.     

Discharge flow‐chemiluminescence study of the rate coefficients for O(3P) + CF2CCl2 and O(3P) + CF3CFCF2 reactions at 298 K

The kinetics of the reactions O(³P) + CF₂CCl₂ and O(³P) + CF₃CFCF₂ were studied at room temperature in a discharge flow tube system. The overall rate constants based on the measured afterglow reactions were (3.10 ± 0.40) × 10⁻¹³ and (3.00 ± 0.60) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, respectively. The experiments were carried out under pseudo‐first‐order conditions with [O(³P)]₀ ≪ [alkene]₀. These results are compared with previous relative measurements using different experimental techniques. The effect of substituent atoms or groups on the overall rate constants is analyzed in comparison with other alkenes in the literature. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 867–872, 1999     

Bimolecular radical scavenging processes for laser isotope separation: NH2D + O2

Infrared multiphoton photooxidation of NH₂D in NH₃ mixtures was observed to produce exclusively HDO, suggesting a single step deuterium separation efficiency of [D₂O]/([D₂0]+[H₂O]) ⩾ 50% which is significantly higher than that of the theoretical value, 33%. The results are explained by the large rate differences in the radical scavenging steps, i.e. k(D+O₂) = 2.2 × 10⁹M⁻¹ s⁻¹, k(NH₂+O₂) ⩽ 5 × 10⁶ M⁻¹ s⁻¹ and k(NH₂+NH₂)=1.6 × 10¹⁰ M⁻¹ s⁻¹. With Ti solid powder as a catalyst, we observed that the formation yields of HDO are at least three to four times higher than those without a catalyst.