Oxidation of Substituted Benzyl Alcohols by Quinoxalinium Dichromate. A Kinetic Study

Quinoxalinium dichromate (QxDC) oxidizes benzyl alcohol and substituted benzyl alcohols smoothly in dimethyl sulfoxide (DMSO) and in the presence of acid to the corresponding aldehydes. The reaction has unit dependence on each of the alcohol, QxDC, and acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electron-withdrawing groups retard the reaction, and the rate data obey Hammetts relationship. The reaction constant was –1.09±0.01 at 303K. Oxidation of ,-dideuteriobenzyl alcohol indicated the presence of a substantial primary kinetic isotope effect (k_H/k_D=6.78 at 303K). The reaction failed to induce the polymerization of acrylonitrile. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The analysis of the dependence of the kinetic isotope effect on temperature indicated that the reaction involves a symmetrical cyclic transition state. A suitable mechanism is proposed.     

Direction of nucleophilic substitution in α, β-unsaturated imino compounds with a donor substituent in the beta position

A mechanism of conversion of -aminovinyl ketones into -aminovinylimines is disclosed. It has been found that in this and a series of other reactions (various conversions of -aminovinyl ketones, -aminovinylimines, and -alkoxyvinylimino salts and their vinyl analogs, cyano compounds, etc.), the intermediate determining the course of the reaction is an ,-unsaturated imino cation. The result of the reaction depends on the site and efficiency of the nucleophilic attack by tautomeric imino salt compounds possessing an unshared electron pair distributed over the various electrophilic sites of the molecule.     

Oxidation of Substituted Benzyl Alcohols by Quinoxalinium Dichromate. A Kinetic Study

Summary. Quinoxalinium dichromate (QxDC) oxidizes benzyl alcohol and substituted benzyl alcohols smoothly in dimethyl sulfoxide (DMSO) and in the presence of acid to the corresponding aldehydes. The reaction has unit dependence on each of the alcohol, QxDC, and acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electron-withdrawing groups retard the reaction, and the rate data obey Hammetts relationship. The reaction constant was –1.09±0.01 at 303K. Oxidation of ,-dideuteriobenzyl alcohol indicated the presence of a substantial primary kinetic isotope effect (k_H/k_D=6.78 at 303K). The reaction failed to induce the polymerization of acrylonitrile. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The analysis of the dependence of the kinetic isotope effect on temperature indicated that the reaction involves a symmetrical cyclic transition state. A suitable mechanism is proposed.     

Effect of the Nucleophile Structure on the Relative Mobility of the Nitro Group and Fluorine Atom in Reactions of 3,5-Dinitro- and 3-Fluoro-5-nitrobenzotrifluorides with Phenols in the Presence of Potassium Carbonate

The relative mobility of the nitro group and fluorine atom in 3,5-dinitro- and 3-fluoro-5-nitrobenzofluorides was estimated by the competing reaction technique using phenols in the presence of potassium carbonate (DMF, 65-95°C). Correlation analysis of the relative rate constants k(NO₂)/k(F) and of the differences in the activation parameters (H and S ) of competing reactions showed the existence of two reaction series for the examined phenols. The higher mobility of the nitro group was found to result from the entropy control of the reactivity of arenes. The mechanism of these reactions is discussed.     

Researches on the chemistry of carbazole derivatives

A method of preparing a number of 9-(-alkoxyethyl)-carbazoles by adding carbazole to the corresponding simple vinyl ethers in the presence of acid catalysts is described. Data relating to the effects of various factors on the reaction are given. The synthetic method developed for 9-(-alkylhydroxyethyl) carbazoles differs from that previously used in that reaction conditions are milder, yields of vinyl ethers lower, and yields of products higher.     

Quantum chemical reaction networks,reaction graphs and the structure of potential energy hypersurfaces

Global properties of the Born-Oppenheimer energy expectation value functional, defined over the nuclear configuration space R, are analyzed. Quantum chemical reaction graphs and reaction networks are defined in terms of intersection graphs of connected sets of nuclear geometries, representing various chemical structures. The set of all possible reaction mechanisms on the given energy hypersurface and the associated activation energy conditions are analyzed using reachability matrices defined over digraphs D ^s() and D ^s(, E).     

Kinetics and mechanisms of the reaction of acetylene with cyclohexa-1,3-diene and the decomposition of bicyclo[2.2.2]-octa-2,5-diene in the gas phase

The reaction of acetylene (A) with cyclohexa-1,3-diene (CHD) has been studied between 450 and 592 K. The pressures of A ranged from 25 to 112 torr and those of CHD from 8 to 62 torr. The reaction yields only ethene (E) and benzene (B) instead of bicyclo[2.2.2]octa-2,5-diene (BOD), the product that is expected for a 1,4,1′,2′ addition of the Diels–Alder type. It is first order with respect to each reagent. The rate constant (in L/mol·s) is given by The thermal decomposition of BOD has also been studied. In the ranges of 354–435 K and 0.5–6 torr, the reaction is first order and results in the formation of equal amounts of B and E as the reaction of A with CHD does. Its rate constant (in s^?1) is given by The following consecutive reactions are proposed for the reaction between A and CHD: where BOD is the primary product that is too unstable to be detected. This implies that the rate constant k is equal to k_a. The reaction mechanisms and the strain energy in BOD are discussed.     

Reactivity of N-Phenylanthranilic Acid Derivatives: XIII. Electrical Conductivity of Solutions of Substituted 4-Nitro-N-phenylanthranilic Acids in the Dioxane-Water System

Conductometry was used to determine limiting equivalent electrical conductivity (₀), Pisarzhevskii-Valden product (₀₀), hydrodynamic ionic radii, ionization constants, thermodynamic parameters for substituted 4-nitro-N-phenylanthranilic acids (7 compounds) in the system dioxane-water at varioustemperatures. It was established that the ionization is endothermic and the entropy factor is prevailing. It was found that the reaction center is moderately sensitive to substituents and the sensitivity decreases with temperature. Multifactor correlation analysis showed that the reaction constants are roughly equal to r _I and _R but are half the values for substituted benzoic acids. The reaction series studied was found to be isoentropy. Inconsiderable solvation of the anions of the substituted anthranilic acids was revealed.     

Synthesis and reactions of the thioamide derivatives of methyl vinyl ketone

The reaction of isothiocyanates with in situ generated carbanions of α,β‐unsaturated ketones yielded α,β‐unsaturated keto thioamides which in the reaction with acids or bases cyclized to give 2,6‐disubstituted thiopyran‐4‐ones and in the reaction with α‐bromoesters gave thiazolidin‐4‐one derivatives. The thiopyran‐4‐ones reacted with α,β‐unsaturated aldehydes to yield tetrahydrothiopyran[2,3‐b]pyridin‐4‐ones, while thioanilides were formed in the reaction with phenyl isothiocyanate.     

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.     

The kinetics of the thermal bromination of CF3I. Determination of the bond dissociation energy D(CF3−I)

The kinetics of the thermal bromination reaction have been studied in the range of 173–321°C. For the step we obtain where θ=2.303RT cal/mole. From the activation energy for reaction (11), we calculate that This is compared with previously published values of D(CF₃?I). The relevance of the result to published work on k_c for a combination of CF₃ radicals is discussed.     

Effect of water on the enzymatic synthesis of vinyl sugar ester in hydrophilic organic solvent

The transesterification of divinyl adipate with glucose in N,N-dimethylformamide (DMF) catalyzed by alkaline protease from Streptomyces sp. and Bacillus subtilis at various water contents were examined. The enzymatic reaction by the Bacillus protease was carried out effectively in the presence of more than 2% of water, and a maximum reaction rate was observed at a water content of 20%. On the other hand, the reaction by the Streptomyces protease proceeded more effectively without the addition of water than in the presence of water. These results suggest that optimum water content is different, depending on the kind of enzyme protein used.

The effect of water on the enzymatic synthesis of vinyl glucose ester catalyzed by protease from Bacillus subtilis (B) in DMF. The reaction conditions are outlined in the Experimental Part .     

The reaction of 2,5-dimethylpyrrole with O2(a1Δg) in the gas phase

The chemical reaction of 2,5-dimethylpyrrole (C₆H₉N) with O₂(¹Δ_g) was studied in the gas phase in an isothermal flow reactor at room temperature and low pressures. The C₆H₉N concentration profiles were studied under pseudo-first order conditions [C₆H₉N]_° ? [O₂(¹Δ_g)] with mass-spectrometric detection of C₆H₉N. O₂(¹Δ_g) was produced either in a microwave discharge or in a chemical reaction. The value for the rate constant: was measured. The rate constant is compared to the value obtained for the quenching process. The primary product C₆H₉NO₂ was detected by mass spectrometry and the reaction mechanism is proposed. The possibility of using this reaction as a gas phase titration reaction for O₂(¹Δ_g) is discussed.     

Synthesis and Dynamic NMR Spectroscopic Study of Dialkyl 4-Ethoxy-1-(1-naphthyl)-5-oxo-4,5-dihydro-1<Emphasis Type="Italic">H</Emphasis>-pyrrole-2,3-dicarboxylates

Summary. Protonation of the reactive 1:1 intermediate produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates with ethyl 2-(1-naphthylamino)-2-oxoacetate, leads to a vinylphosphonium salt, which undergoes intramolecular Wittig reaction to produce dialkyl 4-ethoxy-1-(1-naphthyl)-5-oxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates in excellent yields. A dynamic NMR effect is observed in the ¹H NMR spectra of the title compounds as a result of restricted rotation around the single bond linking the naphthalene moiety and the heterocyclic system, which is attributed to the peri interaction between the pyrrole residue and the peri CH group. The free energy of activation (G ) for this process is 58±2kJmol^–1.Received December 6, 2002; accepted December 11, 2002 Published online June 12, 2003     

Thermal reaction of hydrogen–butene-2-cis mixtures at 500°C: Hydrogenation,hydrogenolysis, and thermal reaction of the olefin

The thermal reaction of hydrogen–butene-2-cis mixtures has been studied in a static system at low extent of reaction around 500°C. Hydrogen does not affect the thermal reaction itself of the olefin, but gives rise to new stoichiometries of hydrogenolysis and hydrogenation, which are specified: The reaction is described in terms of a molecular and free-radical mechanism. It is shown that the key process for the hydrogenolysis–hydrogenation reaction is (1) and that the rate constant of this process can be determined from either propylene, or methane, or butene-1 formations: with θ = 4.57 × 10^?3 T kcal/mol. Other rate constants are estimated and agree with literature data.     

Synthesis and Dynamic NMR Spectroscopic Study of Dialkyl 4-Ethoxy-1-(1-naphthyl)-5-oxo-4,5-dihydro-1 H-pyrrole-2,3-dicarboxylates

Protonation of the reactive 1:1 intermediate produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates with ethyl 2-(1-naphthylamino)-2-oxoacetate, leads to a vinylphosphonium salt, which undergoes intramolecular Wittig reaction to produce dialkyl 4-ethoxy-1-(1-naphthyl)-5-oxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylates in excellent yields. A dynamic NMR effect is observed in the ¹H NMR spectra of the title compounds as a result of restricted rotation around the single bond linking the naphthalene moiety and the heterocyclic system, which is attributed to the peri interaction between the pyrrole residue and the peri CH group. The free energy of activation (G ) for this process is 58±2kJmol^–1.     

Directly Linked and Fused Oligoporphyrin Arrays from Oxidation of Metalloporphyrins

The Ag^I-promoted oxidative meso-meso coupling reaction of 5,15-diaryl Zn^II-porphyrins is advantageous in light of its high regioselectivity as well as its easy extension to large porphyrin arrays. Linear meso-meso linked porphyrin 128-mer and three-dimensionally arranged grid porphyrin 48-mer were isolated in a discrete form by repetitive oxidation reaction and subsequent gel-permeation chromatography (GPC)-HPLC. 5,15-Diaryl Cu^II-, Ni^II-, and Pd^II-porphyrins were converted to meso- doubly-linked diporphyrins by oxidation with(p-BrC₆H₄)₃NSbCl₆. End-aryl-capped meso-meso linked Cu^II-, Ni^II-, and Pd^II- diporphyrins were converted to completely fused meso-meso - -triply-linked diporphyrins through the oxidative ring closure (ODRC) reaction with (p-BrC₆H₄)₃NSbCl₆. Finally, we found that Sc^III-catalyzed oxidation with DDQ gave a very efficient ODRC reaction and hence allowed the synthesis of triply-linked oligoporphyrins up to 12-mer.     

Consistency of theory and experiment in the ethane–methyl radical system

The thermal decomposition of ethane has been reinvestigated using the single pulse, reflected shock technique. Reflected shock temperatures were corrected for boundary layer-induced nonidealities using the thermal decomposition of cyclohexene as a kinetic standard. The rate constant for the reaction was calculated from the rate of formation of methane under conditions of very low extent of reaction, over a temperature range of 1000–1241 K. Ethane compositions of 1% and 3% in argon at total reaction pressures of 3 and 9 atm were used, and a small pressure dependence of k₁ was observed. An RRKM model is described which gives excellent agreement with this and other recent dissociation and recombination rate constant data in light of a recent revision to the thermochemistry of the methyl radical. In the range of 1000–1300 K an RRKM extrapolated k is given by the expression, log k = 17.2 ? 91,000/2.3RT, while at 298 K the calculation gives log k (l/mol sec) = 10.44, where k is calculated from k and the equilibrium constant.     

The kinetics of the gas phase decomposition reactions of the hexafluoro-t-butoxy radical

Hexafluoro-t-butoxy radicals have been generated by reacting fluorine with hexafluoro-2-methyl isopropanol: Over the temperature range of 406–600 K the hexafluoro-t-butoxy radical decomposes exclusively by loss of a CF₃ radical [reaction (-2)] rather than by loss of a CH₃ radical [reaction (-1)]: (1) The limits of detectability of the product CF₃COCF₃, by gas-chromatographic analysis, place a lower limit on the ratio k_?2/k_-1 of ～80. The implications of this finding in relation to the reverse radical addition reactions to the carbonyl group are briefly discussed. A thermochemical kinetic calculation reveals a discrepancy in the kinetics and thermodynamics of the decomposition and formation reactions of the related t-butoxy radical: