Thermal decomposition reaction of 3,3,6,6-tetramethyl- 1,2,4,5-tetroxane in 2-methoxy- ethanol solution

The thermal decomposition study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide) was carried out in 2-methoxyethanol solution in the 130-166 °C temperature range. The overall reaction follows a first-order kinetic law up to at least 75% diperoxide conversion. The activation parameters (ΔH^# = 22.5 ± 0.7 kcal⋅mol^–1 and ΔS^# = -25.6 ± 0.5 cal⋅mol^–1⋅K^–1) for the unimolecular rupture of the O–O bond in the diperoxide molecule were obtained by measuring the remnant diperoxide at different reaction times by the CG technique. Acetone was detected by GC as the major organic product of the reaction.     

Kinetics and mechanism study of aniline addition to ethyl propiolate

The kinetics of the addition reaction of aniline to ethyl propiolate in dimethylsulfoxide (DMSO) as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants, and pseudo‐first‐order method was used to calculate the rate constant. This reaction was monitored by UV–Vis spectrophotometer at 399 nm by the variable time method. On the basis of the experimental results, the Arrhenius equation for this reaction was obtained as log k = 6.07 ‐ (12.96/2.303 RT). The activation parameters, E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 12.96, 13.55, 23.31 kcal mol^?1 and ?32.76 cal mol^?1 K^?1, respectively. The results revealed a first‐order reaction with respect to both aniline and ethyl propiolate. In addition, based on the experimental results and using also density functional theory (DFT) at B3LYP/6‐31G* level, a mechanism for this reaction was proposed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 144–151, 2006     

Investigation of kinetic and mechanism of triphenylphosphine addition to para‐naphthoquinone

This work reports the results of a kinetic and mechanistic investigations of the addition reaction of triphenylphosphine to para‐naphtoquinone in 1,2‐dichloromethane as solvent. The order of reaction with respect to the reactants was determined using initial rate method, and the rate constant was obtained on the basis of pseudo‐first‐order method. Variable time method using Uv–Vis spectrophotometry (at 400 nm) was utilized for monitoring this addition reaction, for which the following Arrhenius equation was obtained: The resulting activation parameters E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 13.63, 14.42, 18.75 kcal mol^?1, and ?14.54 cal mol^?1K^?1, respectively. The results suggest that the reaction is first order with respect to both triphenylphosphine and para‐naphthoquinone. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 427–433, 2005     

Kinetic study of triphenylphosphine addition to para‐benzoquinone

Kinetics of the addition reaction of triphenylphosphine to para‐benzoquinone in 1,2‐dichloroethane as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants. Pseudo‐first‐order method was also used to calculate the rate constant. This reaction was monitored by UV‐vis spectrophotometry at 520 nm by variable time method. On the basis of the obtained results, the Arrhenius equation of this reaction was obtained: The activation parameters, E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 5.701, 6.294, 19.958 kcal mol^?1 and ?45.853 cal mol^?1 K^?1, respectively. This reaction is first and second order with respect to triphenylphosphine and para‐benzoquinone, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:472–479, 2004     

Thermal decomposition of formaldehyde diperoxide in aqueous solution

Thermal decomposition of formaldehyde diperoxide (1,2,4,5-tetraoxane) in aqueous solution with an initial concentration of 6.22 × 10^?3 M was studied in the temperatures range from 403 to 439 K. The reaction was found to follow first-order kinetic law, and formaldehyde was the major decomposition product. The activation parameters of the initial step of the reaction (ΔH ^≠ = 15.25 ± 0.5 kcal mol^?1, ΔS ^≠ = ?47.78 ± 0.4 cal mol^?1K^?1, E _a = 16.09 ± 0.5 kcal mol^?1) support a mechanism involving homolytic rupture of one peroxide bond in the 1,2,4,5-tetraoxane molecule with participation of the solvent and formation of a diradical intermediate.     

Calculation of Some Thermodynamic Properties and Detonation Parameters of 1‐Ethyl‐3‐Methyl‐H‐Imidazolium Perchlorate, [Emim][ClO4], on the Basis of CBS‐4M and CHEETAH Computations Supplemented by VBT Estimates

This paper estimates some thermochemical (in kcal mol^–1) and detonation parameters for the ionic liquid, [emim][ClO₄] and its associated solid in view of its investigation as an energetic material. The thermochemical values estimated, employing CBS‐4M computational methodology and volume‐based thermodynamics (VBT) include: lattice energy, U_POT([emim][ClO₄]) ≈? 123 ± 16 kcal · mol^–1; enthalpy of formation of the gaseous cation, Δ_fH°([emim]⁺, g) = 144.2 kcal · mol^–1 and anion, Δ_fH°([ClO₄]^–, g) = –66.1 kcal · mol^–1; the enthalpy of formation of the solid salt, Δ_fH°([emim][ClO₄],s) ≈? –55 ± 16 kcal · mol^–1 and for the associated ionic liquid, Δ_fH^o([emim][ClO₄],l) = –52 ± 16 kcal · mol^–1 as well as the corresponding Gibbs energy terms: Δ_fG°([emim][ClO₄],s) ≈? +29 ± 16 kcal · mol^–1 and Δ_fG^o([emim][ClO₄],l) = +24 ± 16 kcal · mol^–1 and the associated standard absolute entropies, of the solid [emim][ClO₄], S°₂₉₈([emim][ClO₄],s) = 83 ± 4 cal · K^–1 · mol^–1. The following combustion and detonation parameters are assigned to [emim][ClO₄] in its (ionic) liquid form: specific impulse (I_sp) = 228 s (monopropellant), detonation velocity (V_oD) = 5466 m · s^–1, detonation pressure (p_C–J) = 99 kbar, explosion temperature (T_ex) = 2842 K.     

Evidence for a Rapid Degenerate Hetero‐Cope‐Type Rearrangement in [Cp*W(S)2S‐CH2‐CHCH2]

Treatment of the salt [PPh₄]⁺[Cp*W(S)₃]^? ( 6 ) with allyl bromide gave the neutral complex [Cp*W(S)₂S‐CH₂‐CH?CH₂] ( 7 ). The product 7 was characterized by an X‐ray crystal structure analysis. Complex 7 features dynamic NMR spectra that indicate a rapid allyl automerization process. From the analysis of the temperature‐dependent NMR spectra a Gibbs activation energy of ΔG^≠ (278 K)≈13.7±0.1 kcal mol^?1 was obtained [ΔH^≠≈10.4±0.1 kcal mol^?1; ΔS^≠≈?11.4 cal mol^?1 K^?1]. The DFT calculation identified an energetically unfavorable four‐membered transition state of the “forbidden” reaction and a favorable six‐membered transition state of the “Cope‐type” allyl rearrangement process at this transition‐metal complex core.     

Kinetics and mechanism of the thermal decomposition reaction of acetone cyclic diperoxide in the gas phase

The kinetics of the thermal decomposition reaction of gaseous 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (ACDP) in the presence of n-octane was studied in the 403.2–523.2 K temperature range. This reaction yields acetone as the organic product. Under optimum conditions, first-order kinetics were observed, included when the S/V ratio of the Pyrex reaction vessel was increased by a nearly six-fold factor. In the range 443.2–488.2 K the temperature dependence of the rate constants for the unimolecular reaction in conditioned vessels is given by In k₁/(s^?1) = (31.8 ± 2.5) ? [(39.0 ± 2.5)/RT]. The value of the energy of activation in kcal/mol correspond to one O? O bond homolysis of the ACDP molecule in a stepwise biradical initiated decomposition mechanism. At the lower reaction temperatures as well in preliminary experiments participation of a surface catalyzed ACDP decomposition process could be detected. © 1994 John Wiley & Sons, Inc.     

Reaction of tetramethyl-1,2-dioxetane with triphenylphosphine: Activation parameters for the formation of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane

The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d₆ produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS^≠ = ?28 eu; k_30° = 1.8 m^?1sec^?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS^≠ = ?24 eu, k_30° = 1.3 M^?1sec^?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS^≠ = ?29 eu, k_30° = 4.9 M^?1 sec^?1.     

Mechanistic Aspects of Ligand Substitution on the Hydroxopentaaquarhodium(III) Ion in Aqueous Solution by Sulfur‐Containing Bioactive Ligands

The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k₁ ～10^?3 s^?1 and k₂ ～10^?5 s^?1) and activation parameters (for thioglycolic acid: ΔH₁^≠ = 22.4 ± 3.0 kJ mol^?1, ΔS₁^≠ = ?220 ± 11 J K^?1 mol^?1, ΔH₂^≠ = 38.5 ± 1.3 kJ mol^?1, ΔS₂^≠ = ?204 ± 4 J K^?1 mol^?1; for 2‐thiouracil: ΔH₁^≠ = 42.2 ± 2.0 kJ mol^?1, ΔS₁^≠ = ?169 ± 6 J K^?1 mol^?1, ΔH₂^≠ = 66.1 ± 0.5 kJ mol^?1, ΔS₂^≠ = ?124 ± 2 J K^?1 mol^?1; for glutathione: ΔH₁^≠ = 47.2 ± 1.7 kJ mol^?1, ΔS₁^≠ = ?155 ± 5 J K^?1mol^?1, ΔH₂^≠ = 73.5 ± 1.1 kJ mol^?1, ΔS₂^≠ = ?105 ± 3 J K^?1 mol^?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as      

Cross‐Aldol Reaction of Isatin with Acetone Catalyzed by Leucinol: A Mechanistic Investigation

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin ( 1 a ) and acetone, catalyzed by L ‐leucinol ( 3 a ), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn‐enamine 6 , catalyzed by isatin, was identified as the rate‐determining step by both the calculations (ΔG^≠=26.1 kcal mol^?1 for the analogous L ‐alaninol, 3 b ) and the kinetic isotope effect (k_H/k_D=2.7 observed for the reaction using [D₆]acetone). The subsequent reaction of the syn‐enamine 6 with isatin produces (S)‐ 2 a (calculated ΔG^≠=11.6 kcal mol^?1). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin‐catalyzed formation of the syn‐enamine 6 , which is thermodynamically favored over its anti‐rotamer 7 by 2.3 kcal mol^?1; and 2) the high preference of the syn‐enamine 6 to produce (S)‐ 2 a on reaction with isatin ( 1 a ) rather than its enantiomer (ΔΔG^≠=2.6 kcal mol^?1).     

Heat of formation of Benzophenone Oxide

The heat of formation of benzophenone oxide, Ph₂CO₂, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph₂CN₂ + O₂ → Ph₂CO₂ + N₂ was found to be ?48.0 ±0.8 kcal mol^?1 and ΔH_f(Ph₂CN₂) was determined by measuring the reaction enthalpy for Ph₂CN₂ + EtOH → Ph₂CHOEt + N₂ (?53.6 ±1.0 kcal mol^?1). Taking ΔH_f(PhCHOEt) = ?10.6 kcal mol^?1 led to ΔH_f(Ph₂CN₂) = 99.2 ± 1.5 kcal mol^?1 and hence to ΔH_f(Ph₂CO₂) = 51.1 ± 2.0 kcal mol^?1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph₂CO₂ → 2Ph₂CO + O₂ is exothermic by ?76.0 ±4.0 kcal mol^?1.     

Kinetics and mechanism of decomposition of intermediate complex during oxidation of pectate polysaccharide by potassium permanganate in alkaline solutions

The kinetics of decomposition of an [Pect·Mn^VIO₄^2?] intermediate complex have been investigated spectrophotometrically at various temperatures of 15–30°C and a constant ionic strength of 0.1 mol dm^?3. The decomposition reaction was found to be first‐order in the intermediate concentration. The results showed that the rate of reaction was base‐catalyzed. The kinetic parameters have been evaluated and found to be ΔS^≠ = ? 190.06 ± 9.84 J mol^?1 K^?1, ΔH^≠ = 19.75 ± 0.57 kJ mol^?1, and ΔG^≠ = 76.39 ± 3.50 kJ mol^?1, respectively. A reaction mechanism consistent with the results is discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 67–72, 2003     

Synthesis,structure, and kinetic studies on [RuCl2(NCCH3)2(cod)]

[RuCl₂(NCCH₃)₂(cod)], an alternative starting material to [RuCl₂(cod)] _n for the preparation of ruthenium(II) complexes, has been prepared from the polymer compound and isolated in yields up to 87% using a new work-up procedure. The compound has been obtained as a yellow solid without water of crystallization. The complexes [RuCl₂(NCR)₂(cod)] spontaneously transform into dimers [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph). ¹H NMR kinetic experiments for these transformations evidenced first-order behavior. [RuCl₂(NCPh)₂(cod)] dimerizes slower by a factor of ten than [RuCl₂(NCCH₃)₂(cod)]. The following activation parameters, ΔH ^#?=?114?±?3?kJ?mol^?1 and ΔS ^#?=?66?±?9?J?K^?1?mol^?1 for R?=?CH₃CN (ΔG ^#?=?94?±?5?kJ?mol^?1, 298.15?K) and ΔH ^#?=?122?±?2?kJ?mol^?1 and ΔS ^#?=?75?±?6?J?K^?1?mol^?1 for R?=?Ph (ΔG ^#?=?100?±?4?kJ?mol^?1, 298.15?K), have been calculated from the first-order rate constants in the temperature range 294–323?K. The kinetic parameters are in agreement with a two-step mechanism with dissociation of acetonitrile as the rate-determining step. The molecular structures of [Ru₂Cl(μ-Cl)₃(cod)₂(NCR)] (R?=?Me, Ph) have been determined by X-ray diffraction.     

Dynamic proton magnetic resonance studies on complex spin systems. Non-mutual three-spin exchange in N-(trideuteriomethyl)-2-cyanoaziridine

At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH⁰ = ?475±20 cal mol^?1 (?1.987 ± 0.084 kJ mol^?1) and ΔS⁰ = 0.43±0.08 cal mol^?1 K^?1 (1.80±0.33 J mol^?1 K^?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔH_tc^≠ = 17.52±0.18 kcal mol^?1 (73.30±0.75 kJ mol^?1), ΔS_tc^≠ = ?2.08±0.50 cal mol^?1 K^?1 (?8.70±2.09 J mol^?1 K^?1) and ΔG_tc^≠ (300 K) = 18.14±0.03 kcal mol^?1 (75.90±0.13 kJ mol^?1) for the trans → cis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.     

Kinetic and thermochemical parameters of chlorine atom transfer reactions from CF3Cl,CF3CF2Cl,CF2ClCF2Cl,and CF2ClCFCl2 in gas phase

The following reactions: (1) were studied over the temperature ranges 533–687 K, 563–663 K, and 503–613 K for the forward reactions respectively and over 683–763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔH_r°(1) = ?3.95 ± 0.45 kcal mol^?1 was calculated and from this value the ΔH∮(C₂F₅Cl) = ?2.66.3 ± 2.5 kcal mol^?1 and D(C₂F₅-Cl) = 82.0 ± 1.2 kcal mol^?1 were obtained. Besides, the ΔH_r°(2) was estimated leading to D(CF₂ClCF₂Cl) = 79.2 ± 5 Kcal mol^?1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.     

Data on the thermochemistry of azoalkanes

The rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetrical azoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔH_? (CH₃N₂) = 51.5 ± 1.8 kcal mol^?1, ΔH_? (C₂H₅N₂) = 44.8 ± 2.5 kcal mol^?1, ΔH_? (2?C₃H₇N₂) = 37.9 ± 2.2 kcal mol^?1, [N_A-(C)] = 27.6 ± 3.7 kcal mol^?1, [N_A-(?_A) (C)] = 61.2 ± 3.1 kcal mol^?1.     

Chemistry of trifluorostyrenes and their dimmers: 3. Solvent effect on the kinetic parameters of the thermal cyclodimerization of α, β, β-trifluorostyrene1

Rate constants for the thermal cyclodimerization of α, β, β-trifluorostyrene (TFS) were determined in six solvents at 393°K. The products of this reaction were mixtures of roughly equal amounts of cis-trans isomers. The rate constants in 3 solvents, were calculated according to Arrhenius equation. In n-hexane, log A = 6.02±0.18, E_a= 19.5±0.3 kcal.mol^?1; in glyme, logA = 5.31 ± 0.19, E_a= 18.0±0.3 kcal.mol^?1; in methanol, IogA=4.93±0.13, E_a=17.1±0.3 kcal mol^?1. All data are consistent with a stepwise radical mechanism, and our reaction in this solvent series obeys an isokinetic relationship, with β = 478°K.     

Die Bildungsenthalpie von Zinndijodid,SnJ2 (c)

The heat of reaction for SnJ₂ (c)+J₂ (c)+4045 CS₂ (l)=[SnJ₄; 4045 CS₂] (sol) has been determined to be (?41.12±0.55) kJ mol^?1, [(?9.83±0.13) kcal mol^?1] by isoperibol solution calorimetry. Combining this result with the heat of formation of SnJ₄ in CS₂ determined in a previous investigation¹¹ the value (?153.9±1.40) kJ mol^?1, [(?36.9±0.33) kcal mol^?1] has been derived for the heat of formation, ΔH _f ^ι (SnJ₂;c; 298.15 K), of tin diiodide.     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006