The features of the kinetics of radical reactions of quinone imines with 2-mercaptobenzothiazole

Kinetics of the reactions of N-phenyl-1,4-benzoquinone monoimine and N,N′-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole in chlorobenzene at T = 343 K has been studied by using kinetical spectrophotometry method (periodic spectral measurements and/or monitoring the wavelengths of the absorption band of quinone imines in the visible region). Two general features of the reactions, namely, radical mechanism and the existence of two steps were found. Kinetic features depend on the structure of a quinone imine. A reaction between N,N′-diphenyl-1,4-benzoquinone diimine and 2-mercaptobenzothiazole at first (initial) steps proceeds in an autoinhibition mode and has two independent channels, one of which being radical-chain. The addition of an initiator strongly accelerates the reaction only at the initial step, on completion of which the reaction rate decreases significantly and do not depend on the presence of the initiator. This testifies to the proceeding of the reaction by a non-chain mechanism subsequently to the initial step. The interaction involving N-phenyl-1,4-benzoquinone monoimine proceeds by a radical non-chain mechanism from the very beginning up to the end, and at the initial steps it proceeds in the autoaccelerating mode. The initiator has no influence on the reaction rate. For the process of the interaction of N,N′-diphenyl-1,4-benzoquinone monoimine and 2-mercaptobenzothiazole in the presence of 4-hydroxydiphenylamine, a radical mechanism was proposed, that serves to describe the kinetic features of the reaction and to obtain a quantitative estimation of some of its kinetic parameters.     

Kinetic and thermodynamic parameters for the equilibrium reactions of phenols with the dpph. radical

The kinetics and energetics of the reversible reaction of phenols with the dpph. radical have been studied; steric shielding of the divalent N by the o-NO2 in dpph. seems to be the main cause of the entropic barriers of this reaction.     

Catalytic effect of aliphatic amine on the reaction of quinone diimine with 2-mercaptobenzothiazole

Russian Chemical Bulletin - A secondary aliphatic amine, N-benzylmethylamine, significantly increases the rate of the chain reaction of N,N′-diphenyl-1,4-benzoquinone diimine with...     

Kinetic solvent effects on peroxyl radical reactions

Kinetic solvent effects on peroxyl radical reactions are easily determined using a new peroxyester-based radical clock method.     

Kinetic effects in radical addition reactions to radicophiles

Beyond expectation from polar effects rate acceleration is observed when captodative (cd) substituted 1,1-diphenylethylenes 6 and styrenes 7 undergo addition of isobutyronitrile radicals. The effect can be rationalised in terms of frontier orbital interactions.     

3+2] cycloaddition reactions of cyclopropyl imines with enones

A nickel-catalyzed [3+2] cycloaddition of cyclopropyl aldimines and enones has been developed. The process provides direct access to trisubstituted cyclopentanes, and the scope exceeds that of the corresponding reactions involving cyclopropyl ketones. A basis for the improved performance of cyclopropyl aldimines compared with cyclopropyl ketones is provided.     

Multiorbital interactions during Acyl radical addition reactions involving imines and electron-rich olefins

Ab initio and DFT calculations reveal that acyl radicals add to imines and electron-rich olefins through simultaneous SOMO --> pi*, pi --> SOMO, and HOMO --> pi*C=O interactions between the radical and the radicalophile. At the CCSD(T)/aug-cc-pVDZ//QCISD/cc-pVDZ level, energy barriers of 15.6 and 17.9 kJ mol(-1) are calculated for the attack of the acetyl radical at the carbon and nitrogen ends of methanimine, respectively. These barriers are 17.1 and 20.4 kJ mol(-1) at BHandHLYP/cc-pVDZ. In comparison, barriers of 34.0 and 23.4 kJ mol(-1) are calculated at BHandHLYP/cc-pVDZ for reaction of the acetyl radical at the 1- and 2-positions in aminoethylene, repectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO --> pi*imine, pi imine--> SOMO, and LPN --> pi*C=O interactions are worth 90, 278, and 138 kJ mol-1, respectively, in the transition state (2) for reaction of acetyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multiorbital interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions. NBO analyses for the remaining systems in this study support the hypothesis that the acetyl radical is ambiphilic in nature.     

Reaction of superoxide radical with quinone molecules

When the superoxide radical O(2)(?-) is generated on reaction of KO(2) with water in dimethyl sulfoxide, the decay of the radical is dramatically accelerated by inclusion of quinones in the reaction mix. For quinones with no or short hydrophobic tails, the radical product is a semiquinone at much lower yield, likely indicating reduction of quinone by superoxide and loss of most of the semiquinone product by disproportionation. In the presence of ubiquinone-10, a different species (I) is generated, which has the EPR spectrum of superoxide radical. However, pulsed EPR shows spin interaction with protons in fully deuterated solvent, indicating close proximity to the ubinquinone-10. We discuss the nature of species I, and possible roles in the physiological reactions through which ubisemiquinone generates superoxide by reduction of O(2) through bypass reactions in electron transfer chains.     

Kinetic measurements on methylidyne radical reactions with several hydrocarbons at low temperatures

The temperature dependences of the methylidyne radical reactions with methane, allene, methylacetylene and propene were studied. This work was carried out in a supersonic flow reactor coupled with pulsed laser photolysis (PLP) and laser-induced fluorescence (LIF) techniques. Three Laval nozzles were designed to provide uniform supersonic expansions of nitrogen at Mach 2 and of argon at Mach 2 and 3 to reach low temperatures, e.g. 170, 128 and 77 K, respectively. CH radicals were produced by PLP of CHBr3 at 266 nm and probed by LIF. The exponential decays of the CH fluorescence were acquired, hydrocarbons being introduced in excess. The rate constants for the CH+CH4 reaction are in good agreement with the temperature dependence proposed by Canosa et al. (A. Canosa, I. R. Sims, D. Travers, I. W. M. Smith and B. R. Rowe, Astron. Astrophys., 1997, 323, 644-651, ) i.e. 3.96x10(-8)(T/K)(-1.04) exp(-36.1 K/T) in the range 23-298 K. The rate constants of the CH+C3H4(allene), CH+C3H4(methylacetylene) and CH+C3H6(propene) reactions exhibit a small temperature dependence between 77 and 170 K, with a maximum rate around 100 K close to (4.3-4.6)x10(-10) cm3 molecule-1 s-1.     

Kinetic study of the reactions of the hydroxyl radical with ethane and propane

Absolute rate coefficients for the reactions of the hydroxyl radical with ethane (k₁, 297–300 K) and propane (k₂, 297–690 K) were measured using the flash photolysis–resonance fluorescence technique. The rate coefficient data were fit by the following temperature-dependent expressions, in units of cm³/molecule·s: k₁(T) = 1.43 × 10^?14T^1.05 exp (?911/T) and k₂(T) = 1.59 × 10^?15T^1.40 exp (-428/T). Semiquantitative separation of OH-propane reactivity into primary and secondary H-atom abstraction channels was obtained.     

Enantioselective radical addition reactions to imines using binaphthol-derived chiral N-triflyl phosphoramides

Binaphthol-derived chiral phosphoric acid catalysts were applied to enantioselective radical addition reactions of imines and provided chiral amines with good enantioselectivities (73-84% ee). Furthermore, the enantioselectivities were not affected by either electronic properties of phenyl imines or radical precursors.     

Multi-component orbital interactions during oxyacyl radical addition reactions involving imines and electron-rich olefins

Ab initio and DFT calculations reveal that oxyacyl radicals add to imines and electron-rich olefins through simultaneous SOMO-pi*, SOMO-pi and pi*-HOMO interactions between the radical and the radicalophile. At the BHandHLYP/aug-cc-pVDZ level, energy barriers of 20.3 and 22.0 kJ mol(-1) are calculated for the attack of methoxycarbonyl radical at the carbon and nitrogen ends of methanimine, respectively. In comparison, barriers of 22.0 and 8.6 kJ mol(-1) are calculated at BHandHLYP/aug-cc-pVDZ for reaction of methoxycarbonyl radical at the 1- and 2-positions in aminoethylene, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*, SOMO-pi and pi*-LP interactions are worth 111, 394 and 55 kJ mol(-1) respectively in the transition state (8) for reaction of oxyacyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.     

Kinetic studies of NHx radical reactions

Combined experimental and theoretical studies of the reactions

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and

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were carried out in the present work. The rate constant of reaction (1) was investigated in the temperature range 293 K T612 K using the laser photolysis continuous-wave laser-induced fluorescence technique for the production and detection of NH₂. The results are well described by k₁(T)=5.43×T^−4.02 exp(−1034K/T) cm³ molecule⁻¹ s⁻¹. Stationary points on the potential energy surface were characterized using the gaussian-2 (G2) ab initio method. The surface is complex, with hydrogen-atom transfers and cis—trans isomerization connecting five stable adduct species.The product distribution of reaction (2) was studied at room temperature using the discharge flow technique with mass spectrometric detection of the reaction products. Measured branching fractions for the production of N₂O+H(D) were k_2a/k₂ = 0.84±0.4 for NH+NO and k_2a/k₂ = 0.87±0.17 for ND+NO. Stationary points on the ground ²A′ surface were calculated using the G2 method. The transition state energy for the dissociation of the cis isomer into H+N₂O was found to be lower than the transition state energy for dissociation into OH+N₂. Additionally, trans-HNNO was found to isomerize to cis-HNNO before dissociation.For reaction (3), the molecular properties of all relevant intermediates and transition states on the ground state potential energy surface were determined using the G2 method. The results predict the formation of three intermediates, H₂NO, trans-HNOH and cis-HNOH, all exothermic relative to the reactants. The transition states separating these intermediates from one another and their products (H₂+NO, H+HNO(¹A′) or NH+OH) were also characterized, several for the first time.     

Kinetic analysis of nitroxide radical coupling reactions mediated by CuBr

In a previous paper, we described the room temperature rapid, selective, reversible, and near quantitative Cu‐activated nitroxide radical coupling (NRC) technique to prepare 3‐arm polystyrene stars. In this work, we evaluated the Cu‐activation mechanism, either conventional atom transfer or single electron transfer (SET), through kinetic simulations. Simulation data showed that one can describe the system by either activation mechanism. We also found through simulations that bimolecular radical termination, regardless of activation mechanism, was extremely low and could be considered negligible in an NRC reaction. Experiments were carried out to form 2‐ and 3‐arm PSTY stars using two ligands, PMDETA and Me₆TREN, in a range of solvent conditions by varying the ratio of DMSO to toluene, and over a wide temperature range. The rate of 2‐ or 3‐arm star formation was governed by the choice of solvent and ligand. The combination of Me₆TREN and toluene/DMSO showed a relatively temperature independent rate, and remarkably reached near quantitative yields for 2‐arm star formation after only 1 min at 25 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2214–2223, 2010     

Direct-type catalytic Mannich reactions of amides with imines

Direct-type catalytic Mannich reactions of amides with imines proceeded smoothly using barium phenoxide as a catalyst to afford the desired adducts in high yields with high anti selectivities.     

Molecular complexes and solvation interactions in the reaction of quinone imines with thiols

This study aims to investigate the role of complexation between reagents and the role of solvation of reagents by solvents in the kinetics of chain reactions of quinone imines with thiols. The thermodynamic characteristics of the complexation of quinone imines with thiophenol in CCl₄, chlorobenzene, and ethanol, as well as of the complexation of quinone imines and thiophenol with these solvents were calculated by quantum chemical methods (DFT calculations at the PBE/cc-pVDZ level of theory) and in terms of the additive-multiplicative model. Both approaches give consistent results. The formation of molecular complexes in quinone imine–thiphenol systems is accompanied by a 10–30 kJ mol^–1 decrease in enthalpy and has only a slight effect on the reaction mechanism.     

Rate parameters for the reactions of the bromomethyne radical

Absolute rate parameters were measured for the gas phase reactions of CBr($\text{～}\text{X}$²Π) produced in the flash photolysis of CHBr₃ with a variety of paraffins, olefins, O₂ and NO. The rate of cycloaddition to unsaturated bond increases with alkyl substitution, pointing to the electrophilic nature of CBr. In comparison with published data on CCI and CH the reactivity follows the trend CBr ≈ CCl < CH.     

Kinetic study of the CN radical reaction with 2-methylfuran

The gas phase reaction of the ground state cyano-radical (CN (X²∑⁺)) with 2-methylfuran (2-MF) is investigated in a quasi-static reaction cell at pressures ranging from 2.2 to 7.6 Torr and temperatures ranging from 304 to 440 K. The CN radicals are generated in their ground electronic state by pulsed laser photolysis of gaseous cyanogen iodide (ICN) at 266 nm. Their concentration is monitored as a function of reaction time using laser-induced fluorescence at 387.3 nm on the B²∑⁺ (ν′ = 0) ← X²∑⁺ (ν″ = 0) vibronic band. The reaction rate coefficient is found to be rapid and independent of pressure and temperature. Over the investigated temperature and pressure ranges, the rate coefficient is measured to be 2.83 (± 0.18) × 10⁻¹⁰ cm³ molecules s⁻¹. The enthalpies of the stationary points and transition states on the CN + 2-MF potential energy surface are calculated using the CBS-QB3 computational method. The kinetic results suggest the lack of a prereactive complex on the reaction entrance channel with either a very small or nonexistent entrance energy barrier. In addition, the potential energy surface calculations reveal only submerged barriers along the minimum energy path. Based on comparisons between previous CN reactions with unsaturated hydrocarbons, the most likely reaction pathway is CN addition onto one of the unsaturated carbons followed by either H or methyl elimination. The implications for the transformation of biomass-derived fuels in nitrogen-rich flames is discussed.