Activation Parameters For Reaction Research Articles

CATALYTIC ACTION OF NITROGEN-CONTAINING BASES ON KINETICS OF ZINC AND HEXA- (m-TRIFLUOROMETHYLPHENYL)BENZOPORPHYRAZINE COMPLEX FORMATION

A complexation reaction of hexa(m-trifluoromethylphenyl)benzoporphyrazine with zinc acetate in the system “morpholine (piperidine) – benzene” was studied. Preliminary studies have shown that at concentrations of morpholine and piperidine in benzene less than 0.95 and 0.2 mol/l respectively, the reactions between hexa(m-trifluoromethylphenyl)benzoporphyrazine and zinc acetate not observed. The reaction takes place only at the range of concentrations of morpholine of 0.95 to 8.70 mol /l in benzene and at the range of concentrations of piperidine of 0.2 to 7.74 mol /l in benzene. The changes in the electronic absorption spectrum do not depend on the nature of the nitrogen-containing base, and accompanied by π - chromophore molecules from D2h to D4h symmetry increase. It was shown that complexation describes with the total kinetic equation of the third order. That is there is the first order on every reagent -hexa (m-trifluoromethylphenyl) benzoporphyrazine, zinc acetate and the base. A possible scheme of the mechanism in which the acid - base interaction of hexa (m-trifluoromethylphenyl) benzoporphyrazine with morpholine (piperidine), leading to the H – complex formation is the rate-limiting step of the process proposed. This complex unlike molecular form posseses higher reactivity at interaction with zink cation since an expenditure of energy for breaking intracyclic NH bonds is essentially lower. It was found that rate of hexa (m-trifluoromethylphenyl) piperidin benzoporfirazina coordination by zinc is higher in system “piperidine – benzene”. At replacement of piperidine with morpholine рКа of bases decreases by a factor of about 2.5. It results in the decrease in complexation rate judging by values of k298 by a factor of ~7 on the background of constancy of activation parameters of reaction. This fact is not surprising since less pronounced proton acceptor ability of morpholine complicates removal of intracyclic proton of NH - groups with formation of N - complex and, consequently, complicates zinc cation entrance into the coordination plane of the macrocycle.For citation:Petrov O.A., Sadovskaya I.N. Catalytic action of nitrogen-containing bases on kinetics of zinc and hexa (m-trifluorome-thylphenyl) benzoporphyrazine complex formation. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 36-41.

Oxidation of Unsaturated Aldehydes by Organic Peracids

The paper is dedicated to studies of kinetic regularities of oxidation of unsaturated aldehydes by organic peracids. The routes of products formation were considered, kinetic model of the oxidation reaction was designed and reaction activation parameters were calculated based on experimental data. New data on reactivity of aldehydes with various structures in the reaction with peracids were obtained.

Imidazole-catalyzed esterification of cellulose in ionic liquid/molecular solvents: A multi-technique approach to probe effects of the medium

Observed rate constants (kobs) for the imidazole-catalyzed acylation of microcrystalline cellulose by carboxylic acid anhydrides (ethanoic to hexanoic) were calculated from conductivity data. The reaction media consisted of the ionic liquid, IL, 1-allyl-3-methylimidazolium chloride and the molecular solvents, MSs, N,N-dimethylacetamide, DMAc, dimethylsulfoxide, DMSO, and sulfolane, Sulfn. The latter two carry the same dipole (S=O) and have some similar properties. Using FTIR, we showed that the acylating agent is N-acylimidazole. The reaction third order rate constants (k3) depend slightly on [IL] because the reactant is cellulose-IL complex. For ethanoic anhydride, values of k3 decrease in the order: IL-DMSO>IL-DMAc>IL-Sulfn. We analyze this dependence on the nature of the MS by considering the reaction activation parameters; some macroscopic and microscopic properties of the binary solvent mixtures and cellulose solutions therein, and the results of molecular dynamics simulations. Favorable activation enthalpy; lower solution viscosity; larger empirical polarity and basicity, and stronger biopolymer-solvent interactions are responsible for the faster reaction in IL-DMSO, relative to that in IL-Sulfn. The dependence of the values of (k3) on the number of carbon atoms in the acyl moiety showed a complex behavior (decrease from C2 to C4 and then increase), similar to that observed before, probably because of enthalpy/entropy compensation.

The influence of the polarizability effect on the activation parameters of reactions of organometallic compounds

The literature data on the substituent influence on the energy, enthalpy, entropy, and free energy of activation for 21 series of organometallic compounds reactions have been analyzed. The activation parameters were first established to depend not only on the classic inductive, resonance, and steric effects but also on the polarizability effect of the substituents (the ion-dipole interaction in the transition state). In certain cases, the polarizability effect has the dominant influence on the considered parameters.

Investigation of the acid-catalyzed hydrolysis and reaction mechanisms ofN,N′-diarylsulfamides using various criteria

The mechanism of acid-catalyzed hydrolysis of a series of p-substituted N,N′-diarylsulfamides was investigated in aqueous mineral acid solutions. Rate profiles, reaction activation parameters, catalytic order of strong acids, solvent isotope effects, and analysis of the kinetic data by the excess acidity method suggest a change in the mechanism from A2 to A1. While the hydrolysis proceeds with an A2 mechanism in low acidity regions, an A1 mechanism takes place in high acid concentrations. Copyright © 2013 John Wiley & Sons, Ltd.

Kinetic Studies on the Oxidative Alkoxylation of Ethacrolein and Crotonaldehyde

Present work is dedicated to studies of kinetic regularities of α-ethylacrolein and crotonaldehyde oxidation in methanol, allyl alcohol and glycidol. Kinetic model of the reaction has been designed based on experimental data. Rate constants of hydrogen peroxide disappearance and rate constants of unsaturated acid and its ester formation for both aldehydes in different alcohols at various catalyst concentrations and temperatures have been calculated. The reaction activation parameters have also been calculated. Dependences of ester/ acid ratio on the reaction conditions have been ascertained. Our results indicate the dependence of the reaction rate and the reaction products composition on type of aldehyde and alcohol. Keywords: Crotonaldehyde, ester/acid ratio, α-ethylacrolein , H2SeO3 catalyst, Kinetic and activation parameters of reaction, Oxidation with hydrogen peroxide, Oxidative alkoxylation

Investigating the Mechanism of Heteroaromatic Decarboxylation Using Solvent Kinetic Isotope Effects and Eyring Transition-State Theory

An upper-level mechanistic organic experiment is outlined where undergraduates measure kinetic rate constants for decarboxylation of pyrrole-2-carboxylic acid by the initial-rates method. UV spectroscopy is used to monitor reactant disappearance in both hydrochloric acid and deuterium chloride at different temperatures. Individual data are pooled and utilized by the class to calculate solvent kinetic isotope effects and reaction activation parameters (the latter from Eyring plots). Students interpret experimental results and additional literature data to deduce likely operative decarboxylation mechanisms at varying acidities.

Reactivity of α-amino acids at their arenesulfonation in the water-1,4-dioxane and water-2-propanol systems

The kinetics of arenesulfonation of D,L-threonine, D,L-leucine and L-isoleucine with 3-nitrobenzenesulfonyl chloride in the water-1,4-dioxane and water-2-propanol solvents in the temperature range 298-313 K was studied. Calculations of effective values of activation parameters of reactions were carried out. Kinetic parameters of the studied processes were compared with the results of previous studies of the reaction of acyl transfer involving α-amino acids.

Bromination of butyl rubber with a sodium bromide-tert-butyl hypochlorite system

The kinetics of bromination of butyl rubber by a sodium bromide-tert-butyl hypochlorite system is studied. The orders of reaction with respect to reactants are determined, the empirical dependence of the reaction-rate constant on temperature is found, and the activation parameters of reaction are estimated. It is shown that the bromination of isoprenyl units of butyl rubber results in substitution products of a predominantly exomethylene structure that provides a high rate of rubber vulcanization by zinc oxide.

Kinetic and Mechanistic Studies of Uncatalysed Substitution of Coordinated Cyanide in Hexacyanoferrate(II) by Phenylhydrazine

The kinetics of uncatalyzed reaction between hexacyanoferrate(II) and 2,2'-Bipyridine (further designated as Bipy) has been followed spectrophotometrically by monitoring the increase in absorbance at 400 nm, the λmax of cherry red complex, [Fe(CN)4Bipy] 2– as a function of pH, Ionic strength, temperature and concentration of reactants. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) get replaced by incoming ligand Bipy under the following specified reaction conditions. Temperature = 30+0.1 o C, pH = 3.8+0.02 and I = 0.10 M (KNO3). The uncatalyzed reaction between [Fe(CN)6] 4– and Bipy is very slow. The reaction follows first order dependence each in [Fe(CN)6] 4– and [Bipy]. It was found that the initial rate varies linearly with increasing concentration of hexacyanoferrate(II), keeping other variables fixed at an optimum value. The initial rate is also found to increase in the beginning with increasing concentration of [Bipy] up to [Bipy] < 1.5×10 -4 M, passes through a maximum and then finally falls. The effect of pH, ionic strength on initial rate have also been studied and explained. The activation parameters for reaction have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations.

Kinetic study of the promazine oxidation to promazine 5-oxide by trisoxalatocobaltate(III) in basic aqueous media

The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([CoIII] = (0.6 − 2) × 10−3M, [ptz] = 6 × 10−5M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine 5-oxide. Linear dependences of the pseudo-first-order rate constants (k1 and k2) on [CoIII] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration of the H+ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive reducing species. The activation parameters for reactions studied were as follows: ΔH≠ = 44 ± 1 kJ mol−1, ΔS≠ = −100 ± 4 JK−1 mol−1 for the first step and ΔH≠ = 25 ± 1 kJ mol−1, ΔS≠ = −169 ± 4 J K−1 mol−1 for the second step, respectively. Mechanistic consequences of all the results are discussed.

The kinetics of pentoxyl oxidation by hypochlorite ions

The kinetics of pentoxyl (I) oxidation in aqueous media under the action of hypochlorite ions was studied at pH 8.8 and 273–298 K. The order of the reaction with respect to both participants was found to be one. The temperature dependence of the reaction rate obeyed the Arrhenius law. The reaction activation parameters were found to be Ea=11.08 kJ/mol, ΔH≠=8.73 kJ/mol, ΔS≠=−200.70 J/(mol K), and ΔG≠=66.88 kJ/mol. Reaction stoichiometry was studied, the chemical characteristics of the process considered, and a mechanism of the oxidative transformation of I under the action of OCl− suggested.

Mechanistic Study on the Oxidation of Promazine and Chlorpromazine by Hexaimidazolcobalt(III) in Acidic Aqueous Media

The kinetics of the oxidation of promazine and chlorpromazine by hexaimidazolcobalt(III) were studied in the presence of a large excess of cobalt(III) and H+ ions using u.v.–vis. spectroscopy ([CoIII] = (1–6) × 10−3 m, [ptz] = (2.5–10) × 10−5 m, [H+] = 0.05–0.8 m, I = 1.0 m (H+, Na+, Cl−), T = 333–353 K, l = 1 cm). In each case, the reversible reaction leads to formation of cobalt(II) species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (kobs) on [CoIII] with a non-zero intercept was established for both phenothiazine derivatives. A marked difference in the observed reaction rate for promazine and chlorpromazine is associated with the difference in its ability to undergo oxidation and is consistent with a trend in the redox potential changes for these reductants. The activation parameters for reactions studied were determined. Mechanistic consequences of all the results are discussed.

Bimetallo-radical carbon-hydrogen bond activation of methanol and methane.

Carbon-hydrogen bond cleavage reactions of CH3OH and CH4 by a dirhodium(II) diporphyrin complex with a m-xylyl tether (.Rh(m-xylyl)Rh.(1)) are reported. Kinetic-mechanistic studies show that the substrate reactions are bimolecular and occur through the use of two Rh(II) centers in the molecular unit of 1. Second-order rate constants (T = 296 K) for the reactions of 1 with methanol (k(CH3OH) = 1.45 x 10-2 M-1 s-1) and methane (k(CH4) = 0.105 M-1 s-1) show a clear kinetic preference for the methane activation process. The methanol and methane reactions with 1 have large kinetic isotope effects (k(CH3OH)/k(CD3OD) = 9.7 +/- 0.8, k(CH4)/k(CD4) = 10.8 +/- 1.0, T = 296 K), consistent with a rate-limiting step of C-H bond homolysis through a linear transition state. Activation parameters for reaction of 1 with methanol (DeltaH = 15.6 +/- 1.0 kcal mol-1; DeltaS = -14 +/- 5 cal K-1 mol-1) and methane (DeltaH = 9.8 +/- 0.5 kcal mol-1; DeltaS = -30 +/- 3 cal K-1 mol-1) are reported.

Ligand substitution reactions of the CpMn(CO)2(cyclohexane) intermediate studied by time-resolved infrared absorption spectroscopyElectronic supplementary information (ESI) available: Complete tables of pseudo-first order rate constants kobs as a function of [L] and of temperature. See http://www.rsc.org/suppdata/dt/b3/b302023a/

Time-resolved infrared absorption spectroscopy is used to observe the ligand substitution reactions of the photolytically generated solvated intermediate CpMn(CO)2(CyH) (CyH = cyclohexane) with L = cyclopentene, THF, furan, and pyrrolidine to form CpMn(CO)2(L). Second-order rate constants and reaction activation parameters are derived. Although the pseudo-first order reaction rate constant is a linear function of ligand concentration over the entire concentration range studied, the observed kinetics for these reactions are most consistent with a dissociative interchange mechanism. A lower limit of 34 ± 3 kJ mol−1 for the [Cp(CO)2Mn]–CyH bond dissociation enthalpy is derived. Reactivity trends among the ligands are discussed, and comparisons are made between the ligand substitution behavior of CpMn(CO)2(CyH) and that of other alkane-solvated transition metal intermediates. From these comparisons, it appears that for reaction of a coordinatively unsaturated transition-metal in a given solvent, the relationship between ΔH‡ and ΔS‡ is determined by the solvent independent of the particular metal complex reacting.

A kinetic study of the oxidation of 2-pyridinemethanol, 2-pyridinecarboxaldehyde and 2,6-pyridinedimethanol by chromium(VI) in acidic aqueous media

Oxidation of 2-pyridinemethanol (2-pyol), 2,6-pyridinedimethanol (2,6-pydol) and 2-pyridinecarboxaldehyde (2-pyal) by CrVI was studied under pseudo-first-order conditions in the presence of a large excess of reductant and at various H+ aq concentrations; [CrVI] = 8 × 10−4 M, [reductant] = 0.025–0.20 M, [HClO4] = 1.0 and 2.0 M (I = 1.2 and 2.1 M) or 0.5–2.0 (I = 2.1 M). A parabolic dependence of the pseudo-first-order rate constant (k obs) versus [H+] was observed for all the reductants. A linear dependence of k obs on [2,6-pydol] and, unusually, higher than first-order dependence on [2-pyol] and [pyal] was established. The apparent activation parameters for reactions studied at constant [H+] at I = 1.2 and 2.1 M were determined. The presence of chromium species at the intermediate oxidation states: CrV, CrIV and CrII, was deduced based on e.s.r. measurements and the kinetic effects of MnII or O2 (Ar), respectively. Comparison of the available second-order rate constants for aromatic alcohols and aldehydes demonstrated that chelating abilities of the reductant facilitates the redox process, whereas the electron-withdrawing effect caused by protonating the pyridine nitrogen atom acts in the opposite direction. The unusual low reactivity of 2-pyol was ascribed to intramolecular hydrogen bond formation.

The rate and mechanism of oxidative addition of H2 to the Cr(CO)3C5Me5 radical—generation of a model for reaction of H2 with the Co(CO)4 radical

Abstract The rate of reaction of hydrogen with the 17 e − metal centered radical Cr(CO) 3 C 5 Me 5 obeys the third-order rate law d[P]/d t = k obs [ Cr] 2 [H 2 ] in toluene solution. In the temperature range 20–60°C, k obs =330±30 M −2 s −1 , Δ H ≠ =0±1 kcal mol −1 , Δ S ≠ =−47±3 cal mol −1 deg −1 . The rate of oxidative addition is not inhibited by added pressure of CO. The rate of binding of D 2 is slower than that of H 2 : k (H 2 )/ k (D 2 )=1.18. These results are combined with earlier work to generate a complete reaction profile for hydrogenation of the metal–metal bonded dimer [Cr(CO) 3 C 5 Me 5 ] 2 +H 2 →2H–Cr(CO) 3 C 5 Me 5 . A similar reaction profile for Co 2 (CO) 8 +H 2 →2H–Co(CO) 4 under high pressures of CO is constructed based on literature data and estimated activation parameters for reaction of the Co(CO) 4 radical with hydrogen.

Application of the Pseudo-Inverse Matrix Method in Non-Isothermal Kinetic Analysis

A method is proposed for evaluation of the activation parameters for reactions which occur under non-isothermal conditions. This method can discriminate between possible differential conversion functions. The proposed method, which was coded into a software package available to the scientific community, is designed to solve an overdetermined systems of equations: dai/dt=k(Ti)f(ai) where i equations are to be considered (i can be the number of experimental points). Solution of this overdetermined system with a pseudo-inverse matrix method furnishes the activation parameters and the parameters of the conversion function f(a). Some examples of application of this method in non-isothermal kinetic analysis are presented.

Photochemistry of M(PP3)H2 (M = Ru, Os; PP3 = P(CH2CH2PPh2)3): Preparative, NMR, and Time-Resolved Studies

Photochemical reaction of Ru(PP3)H2 (PP3 = P(CH2CH2PPh2)3) in THF under a rigorously inert atmosphere yields the cyclometalated complex Ru[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H. The latter is converted back to Ru(PP3)H2 under H2 and reacts even with traces of N2 to yield Ru(PP3)(N2). The dinitrogen complex may be synthesized directly by a number of methods. NMR spectroscopy shows that photolysis of Ru(PP3)H2 under C2H4 and CO yields Ru(PP3)(C2H4) and Ru(PP3)(CO), respectively. Photolysis of Ru(PP3)H2 with HSiEt3 in THF yields Ru(PP3)(SiEt3)H, while photolysis in mixtures of THF and benzene at low temperature yields Ru(PP3)(Ph)H. The latter is also generated by reduction of Ru(PP3)Cl2 in the presence of benzene. Os(PP3)(Ph)H is formed either by photolysis of Os(PP3)H2 or by reduction of Os(PP3)Cl2 in the presence of benzene. Irradiation of Os(PP3)H2 in THF or THF/hexane mixtures initially yields the THF C−H activation product, Os(PP3)(2-C4H7O)H. This complex is also generated by reduction of Os(PP3)Cl2 with sodium naphthalenide under N2 in the presence of THF. Os(PP3)(2-C4H7O)H is converted to the cyclometalated complex, Os[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H, on irradiation in THF and to Os(PP3)(Ph)H on irradiation in benzene. Reaction of Os(PP3)H2 with CH3OTf (Tf = triflate) yields Os(PP3)(OTf)H, which is converted to the labile Os(PP3)(CH3)H on reaction with methyllithium. Laser flash photolysis of Ru(PP3)H2 in cyclohexane (laser wavelength 308 nm) yields transient Ru(PP3) with an absorption maximum at 395 nm. The transient reacts with H2, C6H6, HSiEt3, CO, N2, C2H4, and THF with little discrimination; the second-order rate constants for these reactions lie in the range 5 × 105−2 × 106 dm3 mol-1 s-1 at 295 K. Kinetic isotope effects have been determined for the reaction with benzene and THF, as 1.5 (0.2) and 1.1 (0.2), respectively. Activation parameters for reaction of Ru(PP3) are as follows: with HSiEt3 ΔH⧧ = 35 (2) kJ mol-1, ΔS⧧ = −18 (6) J K-1 mol-1; with C6H6 ΔH⧧ = 39 (4) kJ mol-1, ΔS⧧ ≈ 0 J K-1 mol-1. The reaction with THF yields a short-lived adduct, probably bound through oxygen, which is rapidly converted to the cyclometalated product. Laser flash photolysis of Os(PP3)H2 generates transient Os(PP3) (λmax = 390 nm). The transient kinetics of Os(PP3) are substantially different from its ruthenium analogue. It reacts with alkanes and shows different behavior toward THF but is unaffected by addition of H2. Rate constants in the range 6 × 104−6 × 105 dm3 mol-1 s-1 (295 K) are presented for reaction with C6H6, THF, HSiEt3, CO, C2H4, N2, and several alkanes. Kinetic isotope effects have been determined for the reactions with methylcyclohexane and benzene as 5.6 (1.5) and 0.6 (0.1), respectively. The rate constants for reaction with alkanes rise in the order, methylcyclohexane < pentane < heptane < methane. The rate constants for reaction with methane and benzene are insignificantly different. Following reaction of Os(PP3) with THF to form Os(PP3)(THF), C−H insertion occurs with a first-order rate constant of 4.2 (8) × 103 s-1 with kH/kD = 2.6 (0.4). The activation parameters for reaction of Os(PP3) with substrates are as follows: with pentane ΔH⧧ = 27 (1) kJ mol-1, ΔS⧧ = −59 (4) J K-1 mol-1; with HSiEt3 ΔH⧧ = 31 (5) kJ mol-1, ΔS⧧ = −27 (12) J K-1 mol-1; with C6H6 ΔH⧧ = 38 (3) kJ mol-1, ΔS⧧ = −7 (9) J K-1 mol-1.

Phenyl-to-Oxo Migration in an Electrophilic Rhenium(VII) Dioxo Complex

Reaction of (HBpz3)ReO(Ph)(OTf) with oxygen atom donors leads to oxidation of the phenyl group [HBpz3 = hydrotris(1-pyrazolyl)borate, OTf = triflate, OSO2CF3]. Reaction with Me2SO gives the adduct [(HBpz3)ReO(Ph)(OSMe2)]OTf, which undergoes phenyl-to-oxo migration at 25 °C to give the phenoxide complex [(HBpz3)ReO(OPh)(OSMe2)]OTf and Me2S. The Me2SO adduct readily and reversibly loses Me2S (k = 2.9(4) s-1 at 25 °C) as indicated by isotope exchange reactions and magnetization transfer. The Me2SO adduct also slowly oxidizes Me2SO to Me2SO2. These reactions all proceed via an intermediate rhenium(VII) dioxo complex, [(HBpz3)ReO2(Ph)]OTf. This dioxo complex can be observed at low temperature on reaction of (HBpz3)ReO(Ph)(OTf) with pyridine N-oxide. It rearranges at 0 °C by phenyl-to-oxo migration to give phenoxide products and the catecholate complex (HBpz3)ReO(O2C6H4). The kinetics of this migration have been measured (ΔH⧧ = 14.8(7) kcal/mol, ΔS⧧ = −20.5(25) eu). From these data and the activation parameters for reactions of [(HBpz3)ReO(Ph)(OSMe2)]OTf, a detailed free energy surface for the reactions of [(HBpz3)ReO2(Ph)]OTf is constructed. The dioxo complex reacts very rapidly with Me2S (1.7 × 105 M-1 s-1) with essentially no enthalpic barrier, consistent with the action of a highly electrophilic oxo ligand. Electrophilicity of the oxo groups is suggested to be a critical factor in facilitating the phenyl-to-oxo migration. A general explanation for the relative ease of various organometallic migration reactions, based on analogies with organic [1,2]-shifts, is presented.