Equilibrium constants for triphenylmethyl bromide and 3-bromo-3-phenyldiazirine in acetonitrile

The equilibrium constants at 25°C are 7.6 x 10⁻³ and 2.0 x 10⁻⁵ for triphenylmethyl bromide and bromodiazirine respectively.     

Study of the kinetics and equilibrium of the benzyl-radical association reaction with molecular oxygen

The forward rate constant, k₁, and the equilibrium constant, K_p, for the association reaction of the benzyl radical with oxygen have been determined. The rate constant k₁ was measured as a function of temperature (between 298 and 398 K) and pressure (at 20 and 760 torr of N₂) by two different techniques, argon-lamp flash photolysis and excimer-laser flash photolysis, both of which employed UV absorption spectroscopy (at 253 nm and 305 nm, respectively) to monitor the benzyl radical concentration. Over the range of conditions studied, we find that the reaction is independent of pressure and is almost independent of temperature, which is in accord with two early studies of the reaction but in apparent disagreement with more recent work. For our results in 760 torr of N₂ and for 298 < T/K < 398, a linear least-squares fitting of the data yield the expression: k₁ = (7.6 ± 2.4) × 10^?13 exp[(190 ± 160) K / T ] cm³ molecule^?1 s^?1. With the flash-photolysis technique, we determined K_p over the temperature range 398–525 K. Experimental values were analyzed alone and combined with theoretically determined entropy values of the benzyl and benzylperoxy radicals to determine the enthalpy of reaction: ΔH = (?91.4 ± 4) kJ mol^?1. Previous work on the benzyl radical enthalpy of formation allows us to calculate ΔH°_{f 298} (Benzylperoxy) = (117 ± 6) kJ mol^?1. In addition, we carried out an RRKM calculation of k₁ using as constraints the thermodynamic information gained by the study of K_p. We find that all the studies of the association reaction are in good agreement once a fall-off effect is taken into account for the most recent work conducted at pressures near 1 torr of helium. © 1994 John Wiley & Sons, Inc.     

Kinetics and mechanism of the reaction of benzyl bromide with copper in dimethylacetamide in the presence of oxygen

The reaction of copper metal with benzyl bromide in dimethylacetamide in the presence of oxygen has been studied. Oxidative dissolution of copper follows the single-electron transfer mechanism with formation of benzaldehyde, benzyl alcohols, and copper(II) coordination compounds. The kinetic and thermodynamic parameters of the process have been determined by resistometry. Intermediately formed species have been identified and quantitated, and the reaction stereochemistry has been studied. The reaction mechanism is discussed.     

The mechanism of the elimination kinetics of 2-bromo-2-butene in the gas phase

The kinetics of the gas phase elimination of 2-bromo-2-butene were determined in a static system over the temperature range of 340–380°C and pressure range of 37–134 torr. The reaction in seasoned vessels, even in the presence of a free radical inhibitor, is catalyzed by hydrogen bromide. Under maximum catalysis of HBr, the kinetics were found to be of order 1.0. The reaction, when maximally catalyzed with HBr, appears to undergo a molecular elimination of HBr which follows first-order kinetics. The products are 1,2-butadiene and hydrogen bromide. The rate coefficients. under maximum catalysis, are given by the Arrhenius equation log ??₁(s^?1) = (13.57 ± 0.56) ? (200.4 ± 6.8) kJ mol^?1 (2.303RT)^?1. The catalyzed pyrolysis of 2-bromo-2-butene appears to proceed through a six-membered cyclic transition-state type of mechanism.     

Resolution of the non-steady-state kinetics of the two-step mechanism for the Diels-Alder reaction between anthracene and tetracyanoethylene in acetonitrile

The Diels-Alder reaction between anthracene and tetracyanoethylene in acetonitrile does not reach a steady-state during the first half-life. The reaction follows the reversible consecutive second-order mechanism accompanied by the formation of a kinetically significant intermediate. The experimental observations consistent with this mechanism include extent of reaction-time profiles which deviate markedly from those expected for the irreversible second-order mechanism and initial pseudo first-order rate constants which differ significantly from those measured at longer times. It is concluded that the reaction intermediate giving rise to these deviations cannot be the charge-transfer (CT) complex, which is formed during the time of mixing, but rather a more intimate complex with a geometry favorable to the formation of the Diels-Alder adduct. The kinetics of the reaction were resolved into the microscopic rate constants for the individual steps. The rate constants, as shown in equation 1, at 293 K were observed to be 5.46 M(-)(1) s(-)(1) (k(f)), 14.8 s(-)(1) (k(b)), and 12.4 s(-)(1) (k(p)). Concentration profiles calculated under all conditions show that intermediate concentrations increase to maximum values early in the reaction and then continually decay during the first half-life. It is concluded that the charge-transfer complex may be an intermediate preceding the formation of the reactant complex, but due to its rapid formation and dissociation it is not detected by the kinetic measurements.     

Effect of oxygen vacancies in anodic titanium oxide films on the kinetics of the oxygen electrode reaction

The effect of oxygen vacancies in the anodic oxide film on passive titanium on the kinetics of the oxygen electrode reaction has been studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Oxide films of different donor density were prepared galvanostatically at various current densities until a potential of 20.0 V_SHE was achieved. The semiconductive properties of the oxide films were characterized using EIS and Mott-Schottky analysis, and the thickness was measured using ellipsometry. The film thickness was found to be almost constant at ∼44.7 ± 2.0 nm, but Mott-Schottky analysis of the measured high frequency interracial capacitance showed that the donor (oxygen vacancy) density in the n-type passive film decreased sharply with increasing oxide film formation rate (current density). Passive titanium surfaces covering a wide range of donor density were used as substrates for ascertaining relationships between the rates of oxygen reduction/evolution and the donor density. These studies show that the rates of both reactions are higher for passive films having higher donor densities. Possible explanations include enhancement of the conductivity of the film due to the vacancies facilitating charge transfer and the surface oxygen vacancies acting as catalytic sites for the reactions. The possible involvement of surface oxygen vacancies in the oxygen electrode reaction was explored by determining the kinetic order of the OER with respect to the donor concentration. The kinetic orders were found to be greater than zero, indicating that oxygen vacancies are involved as electrocatalytic reaction centers in both the oxygen evolution and reduction reactions. This paper was submitted in honor of the many contributions to electrochemistry that have been made by Professor Boris Grafov. The article is published in the original.     

Effect of molecular oxygen on concentration autooscillations and autowaves in the Belousov-Zhabotinskii reaction

It has been established that molecular oxygen is responsible for the differences in the concentration regions for existence of autooscillations and autowaves in the Belousov-Zhabotinskii reaction when the reaction mixture is in contact with air. When gaseous oxygen is passed through the solution, it affects the oscillation parameters through two mechanisms: chemical interaction with malonic acid radicals, and removal of free bromine from the solution. The influence of stirring intensity on the autooscillation parameters in Belousov-Zhabotinskii reactions is related mainly to changes in the rate of access of molecular oxygen to the reaction mixture.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 661–666, November–December, 1988.     

Effect of binary aqueous‐organic solvents on the reaction of phenacyl bromide with nitrobenzoic acid(s) in the presence of triethylamine

Second‐order rate constants (k₂) of the reaction between phenacyl bromide and equimolar mixture of nitrobenzoic acid(s)–triethylamine have been determined in dimethylformamide (DMF)/acetonitrile (ACN)/acetone and aqueous mixtures of these solvents by conductometric method at 30°C. The rates of nitrobenzoic acids are found to be in the order: 4‐NO₂ > 3‐NO₂ > 3,5‐(NO₂)₂. Changes in the rate just by the addition of water (1% (v/v)) into organic component is rationalized. Decrease in the values of k₂ on increasing water content in organic solvent is explained on the basis of preferential solvation phenomenon. Single and dual regression analysis using the various solvent parameters of aqueous mixtures (E_T(30), Z, π*, β, α, and Y) resulted in π* and α as the best parameters to explain solvation of nitrobenzoates. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 401–409, 2004     

Kinetics and mechanism of the reaction of 5-bromo-2- carbonyl derivatives of furan with amines

The kinetics of exchange of bromine in 5-bromo-2-carbonyl derivatives of furan by dimethylamino and morpholino groups was studied. The reaction is kinetically complicated for 5-bromofurfural (I) — aldehyde I initially reacts simultaneously at both the carbonyl group to give the aminocarbinol and at the bromine atom with exchange by an amino group. The accumulation of the ammonium salt in the latter reaction leads to the development of an autocatalytic reaction, the product of which is 5-N,N-dialkylaminofurfurylidene-N,N-dialkylammonium bromide. Amines react with the ketones without complications; the second-order rate constants are presented. The rate of exchange decreases in the order CHO > COC₆H₅ > COCH=CHC₆H₅ > COCH₃ > CH=CHCOC₆H₅.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1465–1470, November, 1976.     

Studies on mechanism and kinetics of reaction of CuSO4 with Cu2SO2

The reaction of CuSO₄ with Cu₂SO₂ to give Cu₂SO₄ was studied. The influence of the degree of reaction, the initial mixture composition and the temperature upon the reaction rate and the product composition was discussed. It was found that the reaction starts above 710 K and pure Cu₂SO₄ can be obtained under strictly defined conditions.     

2-Nitro-and 2-bromo-2-nitroethylphosphonates in the reaction with sodium azide

The reactions of phosphorylated 2-nitro-and 2-bromo-2-nitroethenes with sodium azide involve 1,3-dipolar cycloaddition to form triazoles, aziridines and isomeric vinyl azides. The latter products were isolated as a mixture of structural isomers. The structure of the obtained compounds was determined by IR and ¹H and ³¹P NMR spectroscopy.     

On the grignard reaction of 2-bromo-3-iodo- and 3-bromo-2-chlorothiophene

2-Bromo-3-iodo- and 3-bromo-2-chlorothiophene react with magnesium in the presence of 1,2-dibrornoethane to give 2-halo-3-thiophene magnesium halide which opens a useful route to 2,3-disubstituted thiophenes having an electron-withdrawing group in the 3-position.     

Kinetics and mechanism of nickel reaction with benzyl bromide in dimethylformamide

Abstarct  The reaction of nickel with benzyl bromide in DMF has been studied. The reaction intermediates were investigated by different methods and the kinetic and thermodynamic parameters were determined. The reaction of benzyl bromide with nickel was shown to occur on the metal surface by the Langmuir-Hinshelwood scheme, with the formation of benzyl radicals which are recombined and isomerized in solution to form 1,2-diphenylethane and trace amounts of 4.4′-dimethylbiphenyl. Original Russian Text ? A.M. Egorov, S.A. Matyukhova, I.S. Kocherova, A.A. Novikova, A.V. Anisimov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 3, pp. 455–463.     

Kinetics and mechanism of the reaction of 1-chloro-2,4,6-trinitrobenzene with the N,N-dimethylaminohydrazone of furfural in acetonitrile

Kinetics of the arylation of the N,N-dimethylaminohydrazone of furfural with picryl chloride in acetonitrile at 298 K has been studied. The reaction is not catalyzed by nucleophiles. The mechanism includes the rapid equilibrium formation of σ-adduct with its slow unimolecular decomposition. Rate and equilibrium constants for the individual steps were calculated. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 173–176, May–June, 2000.     

Aminolysis of Y-substituted-phenyl 2-methoxybenzoates in acetonitrile: effect of the o-methoxy group on reactivity and reaction mechanism

Second-order rate constants (k(N)) were measured for aminolyses of Y-substituted-phenyl 2-methoxybenzoates 2a-i and 4-nitrophenyl X-substituted-benzoates 3a-j in MeCN at 25.0 °C. The Br?nsted-type plot for the reactions of 2a-i with piperidine curves downward, indicating that a change in rate-determining step (RDS) occurs. The Hammett plot for the reactions of 3a-j with piperidine consists of two intersecting straight lines, which might be taken as evidence for a change in RDS. However, the nonlinear Hammett plot has been suggested not to be due to a change in RDS but rather to the stabilization of the ground state of substrates possessing an electron-donating group (EDG) (e.g., 3a-c) through a resonance interaction, since the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ρ = 0.54 and r = 1.54. The ρ value found for the reactions of 3a-j in MeCN is much smaller than that reported previously for the corresponding reactions in H(2)O (i.e., ρ = 0.75). It is proposed that the reactions of 3a-j in MeCN proceed through a forced concerted mechanism due to instability of T(±) in the aprotic solvent, while the reactions of 2a-i proceed through a stepwise pathway with a stabilized T(±) through an intramolecular H-bonding interaction.     

The reaction of perfluoroalkylcopper compounds with 1-bromo-1-perfluoroalkylethylenes

Perfluoroalkylcopper compounds [F_FCU], when they react with 1-bromo-1-perfluoroalkylethylenes 1, do not give the expected gem-disubstituted compounds 3, but the vic-disubstituted products 2 in 60–70% yields. These results show that the reaction does not proceed through a simple vinylic substitution. ¹H and ¹⁹F NMR data are given for the new compounds.