Rearrangement of tertiary amine N-oxides—XXVII Mechanism of the reaction of isoquinoline N-oxide with substituted benzenesulfonyl chlorides

Kinetic experiments have been carried out on the reactions of isoquinoline N-oxide with p-toluenesulfonyl and other substituted benzenesulfonyl chlorides, varying solvent and salt compositions. The rate was correlated by the second-order equation, i.e., v = [N → O] × [ArSO₂Cl], and was found to be accelerated in polar media. The addition of chloride ion was found to increase the rate considerably, while the rates of the over-all reaction became greater with arenesulfonyl chlorides bearing stronger electron-withdrawing substituents ( = +2·0). By the use of 1-deuterated isoquinoline N-oxide a small kinetic isotope effect (k_H/k_D = 1·2) was observed for this reaction. Based on these kinetic observations the rate-determining step of this reaction is considered to be the cleavage of N---O bond. Meanwhile, from the ¹⁸O-tracer experiments in several solvents using uniformly ¹⁸O-labelled p-toluenesulfonyl or p-bromobenzenesulfonyl chloride the migration of arenesulfonate was found to proceed mainly via oxygen-bridged ion pair pathway.     

Inverse deuterium isotope effect on radiationless electronic transitions

Fluorescence quantum yields, Y, front photoselected vibrational states in the S₁ manifold of anthracene and of perdeuterated anthracene in planar supersonic jets reveal a large inverse deuterium isotope effect on the non-radiative relaxation from the S₁ origin (Y_H/Y_D = 5), while for high (1500 cm⁻¹) excess energies above the S₁ origin the inverse isotope effect is eroded (Y_H/Y_D ≈ 1). Novel information emerges on intermediating states involved in intersystem crossing.     

A novel photosynthetic mimic reaction catalysed by K[Ru(H-EDTA)Cl] · 2H2O; reduction of carbon dioxide to formate and formaldehyde in the presence of an aqueous suspension of Pt—CdS—RuO2

An efficient photocatalytic reduction of carbon dioxide to HCOOH and HCHO is reported using K[Ru(H-EDTA)Cl] · 2H₂O (1) as homogeneous catalyst and particulate Pt—CdS—RuO₂ as photon absorber at 505 nm. This system produces 0.22 M of HCOOH and 0.10 M of HCHO in 6 h of photolysis at rates of 3.05 × 10⁻² M h⁻¹ and 2.0 × 10⁻² M h⁻¹ respectively. Trace amounts of CH₃OH, CH₄ and CO are detected in the reaction vessel. The rates of formation of HCOOH and HCHO exhibit a first-order dependence on the catalyst and dissolved CO₂ concentrations. The reaction shows deuterium isotope effects (k_H/k_D) of 1.5 and 2.00 for the formation of HCOOH and HCHO respectively. Under identical experimental conditions, the rate of decomposition of formate was studied. The rate of decomposition of formate is slower (by two orders of magnitude compared with the formation of formate) even at high formate concentrations. A mechanism for the formation of HCOOH and HCHO is proposed.     

Temperature dependence of the reaction C2H (C2D) + O2 between 295 and 700 K

The rate coefficients for the reactions of C₂H and C₂D with O₂ have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with k_C2H+O2 = (3.15 ± 0.04) × 10⁻¹¹ (T/295 K)^{−(0.16 ± 0.02)} cm³ molecule⁻¹ s⁻¹. The kinetic isotope effect is k_C2H/k_C2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C₂H + O₂ kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting.     

The kinetics of the chromic acid oxidation of diphenylmethane

The kinetics of the chromic acid oxidation of diphenylmethane in aqueous acetic acid solution has been studied. The rate law is v = k[φCH₂φ][CrO₃]h₀ a kinetic isotope effect, k_H/k_D = 6·4 at 30°, was noted, and electron releasing groups were found to moderately facilitate the reaction (⁺ = −1·17). These, and related data, suggest that the initial reaction is the abstraction of a hydrogen atom forming a benzhydryl radical. The latter may then be further oxidized to give the product, benzphenone. It is noted that the chromic acid oxidations which must involve hydrogen abstraction all show a kinetic dependence on the total chromium (VI) concentration, whereas those which are believed to proceed via an ester mechanism have a kinetic dependence on only the acid chromate ion. This difference is suggested as a possible method of distinguishing between these two mechanisms. The effect of the water content of the solvent on the rate of the reaction is discussed, and a tentative, relative, H₋ scale for some of these solutions is suggested. This may permit one to determine the number of molecules of water which are involved in a reaction.     

NH2/ND2-vapour pressure isotope effect of cyclopropylamine

The NH₂/ND₂-vapour pressure isotope effect has been determined between 283 and 333 K for cyclopropylamine, an amine with a strong ring strain. The measurements are represented by the relation ln[P(C₃H₅N²H₂)/P(C₃H₅NH₂)] = −(8821.73 ± 68.949) (K/T)² + (23.379 ± 0.223)K/T and correspond to a normal (P_D/P_H < 1) effect. They suggest an association that is slightly weaker than that of propylamine and nearly agrees with that of isopropylamine. The differences are discussed in terms of acidities and steric factors.     

Direct dynamics studies on the hydrogen abstraction reactions CF3O+CH4(CD4)→CF3OH(CF3OD)+CH3(CD3)

The dynamics properties of the hydrogen abstraction reaction CF₃O+CH₄→CF₃OH+CH₃ are studied by dual-level direct dynamics method. Optimization calculations are preformed by B3LYP and MP2 with the 6-311G(d,p) basis set, and the single-point calculations are done at the multi-coefficient correction method based on quadratic configuration interaction with single and double excitations (MC-QCISD) method. The rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200–2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is ‘normal’. The value of k_H/k_D is 2.38 at room temperature and it decreases with the temperature increasing.     

Time-resolved vibrational cemiluminescence: Rate constants for the reaction F + HC1 → HF + Cl and for the relaxtion of HF(v = 3) by HCl, CO2, N2O, CO, N2 and O2

The reaction: F + HCl→ HF (v 3) + Cl (1), has been initiated by photolysing F₂ using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k₁ = (7.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, and for the relaxation of HF(v = 3) by HCl, CO₂, N₂O, CO, N₂ and O₂: k_HCl = (1.18 ±0.14) × 10⁻¹¹ k_CO2 = (1.04 ± 0. 13) × 10⁻¹², k_N2O = (1.41 ± 0.13) × 10⁻¹¹ k_CO = (2.9 ± 0.3) × (10⁻¹², k_N2 = (7.1 ± 0.6) × 10⁻¹⁴ and k_O2 = (1.9 ± 0.6) × 10⁻¹⁴ cm³molecule⁻¹s⁻¹.     

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H₂O₂ has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10¹⁰M^-1s¹ and the activation energy E_A = 14.0 kJ mol^-1 (3.3 kcal mol^-1). For reaction with OH radicals the corresponding values are, k(20°C) = 3.1 × 10¹⁰M^-1s^-1 and E_A = 14.7 kJ mol^-1 (3.5 kcal mol^-1) determined in the temperature range 5–175°C. For reaction with H₂O₂ the values are, k(20°C) = 1.2 × 10¹⁰M^-1s^-1 and E_A = 15.6 kJ mol^-1 (3.7 kcal mol^-1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H₂PO₄^- was determined to k(20°C) = 1.5 × 10⁷M^-1s^-1 and E_A = 7.4 kJ mol^-1 (1.8 kcal mol^-1) in the temperature range 20–200°C.     

The temperature dependence of the kinetic isotope effect in the reaction of F atoms with CH4 and CD4

The kinetic isotope effect k_F+CH4/k_F+CD4 has been determined by reacting F atoms with mixtures of CH₄ and CD₄, using a discharge-flow-mass spectrometric technique. Experiments were carried out at four temperatures in the temperature range 183–298 K. The Arrhenius expression corresponding to the results is k_F+CH4/k_F+CD4=(0.99±0.02)×exp[(100±5)/T]. The present results are compared with previous published experimental and theoretical results.     

Direct kinetic studies of the reactions of 2-butoxy radicals with NO and O2

This Letter reports the first kinetic study of 2-butoxy radicals to employ direct monitoring of the radical. The reactions of 2-butoxy with O₂ and NO are investigated using laser-induced fluorescence (LIF). The Arrhenius expressions for the reactions of 2-butoxy with NO (k₁) and O₂ (k₂) in the temperature range 223–311 K have been determined to be k₁=(7.50±1.69)×10⁻¹²×exp((2.98±0.47) kJmol⁻¹/RT) cm³ molecule⁻¹ s⁻¹ and k₂=(1.33±0.43)×10⁻¹⁵×exp((5.48±0.69) kJmol⁻¹/RT) cm³ molecule⁻¹ s⁻¹. No pressure dependence was found for the rate constants of the reaction of 2-butoxy with NO at 223 K between 50 and 175 Torr.     

Regioselective addition of protic acids to tricarbonyliron complexes of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane. Crystal structure of (C10H10O)Fe2(CO)6

The main product of the thermal reaction between the title oxatetraene (I) and Fe₂(CO)₉ in ether/pentane is the bimetallic complex (C₁₀H₁₀O)Fe₂(CO)₆-diexo (II), which has C_2υ symmetry both in the solid state (X-ray analysis) and in solution. Whereas the protonation of the free ligand leads usually to polymerisation, the addition of a protic acid such as CF₃CO₂H to II proceeds cleanly at 0°C giving first a (η 3-allyl)Fe(CO)₃O₂CCF₃ complex (III). The intermediate III adds a second equivalent of acid in a slower step (k₂/k₁ = 0.1, CF₃CO₂D/CHCl₃, 0°C) giving the trans-bis(η³-allyl) isomer IV with high regioselectivity. The addition of CF₃CO₂D yields the corresponding deuteriomethylallyliron tricarbonyl trifluoroacetates III′ and IV′. No further deuterium incorporation is observed at 0°C, thus confirming the kinetic control of the regioselective double addition of protic acid to II.     

Far-UV laser flash photolysis in solution. A study of the chemistry of 1,1-dimethylsilene in hydrocarbon solvents

The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λ_max 255 nm. Characteristic rapid quenching is observed for the silene with methanol (k_McOH = (4.9 ± 0.2) × 10⁹ M⁻¹ s⁻¹), tert-butanol (k_BuOH = (1.8 ± 0.1) × 10⁹ M⁻¹ s⁻¹) and oxygen (k_O2 = (2.0 ± 0.5) × 10⁸ M⁻¹ s⁻¹). The Arrhenius activation parameters for the reaction with methanol have been determined to be E_a = −2.6 ± 0.6 kcal mol⁻¹ and log A = 7.7 ± 0.3.     

Interconversion kinetics and ordering of 1,4- and 1,1-dimethylcyclohexane in liquid-crystalline solutions by 1D and 2D deuterium NMR

Deuterium NMR spectra of perdeuteriated 1,4-dimethylcyclohexane-d₁₆ and 1,1-dimethylcyclohexane-d₁₆ dissolved in the nematic solvent ZLI 2452 are reported for the temperature range -40 to +80°C. Between -30 and +60°C the spectra exhibit characteristic exchange broadening and coalescence due to the ring inversion process. In the extreme slow exchange regime, peak assignment and determination of relative signs of the deuterium quadrupole interactions were made using 2D exchange spectroscopy and structural parameters derived from molecular mechanics calculations. In the intermediate temperature range the lineshapes were interpreted quantitatively in terms of the ring interconversion kinetics yielding the kinetic equations, k = 1.38 × 10¹³ exp (-45.2/RT)s^-1 for 1,4-dimethylcyclohexane, and k = 4.05 × 10¹³ exp (-49.0/RT)s^-1 for 1,1-dimethylcyclohexane, where R is in kJ mol^-1. The complete ordering matrix of both compounds was determined over the whole temperature range of the measurements.     

Kinetics and mechanism of the oxidation of aliphatic aldehydes by sodium n-bromoarylsulphonam1des in acid solution

The oxidation of aliphatic aldehydes to the corresponding carboxylic acids by sodium N-bromoarylsulphonamides (N-bromoamines) is first order with respect to the oxidant, the aldehyde and hydrogen ions. In the oxidation of acetaldehyde at 298 K, the primary kinetic isotope effect, k_H/k_D is 4.91 ± 0.14 and the solvent isotope effect, k(H₂O)/k(D₂O), is 0.43. Addition of the parent sulphonamide does not affect the rate. The reduction of six substituted N-bromoamines exhibited a reaction constant of 1.22 at 298 K. (ArSO₂NH₂Br)⁺ is postulated as the reactive oxidising species. Separate rate constants for the oxidation of aldehyde hydrate and free aldehyde forms have been computed. The rates of the oxidation of the aldehyde hydrates correlate well with Taft's substituent constants with negative reaction constants. A mechanism involving hydride transfer from the aldehyde hydrate to the oxidant is proposed.     

Kinetics and mechanisms of the redox reaction of hexaaquotitanium(III) and the ethylenediamine tetraacetato titanium(III) complex by aqueous solutions of bromine

At 25°C, I = 1.0 M (CF₃SO₃⁻Li⁺+CF₃SO₃H), [H⁺] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H₂O), ₆³⁺ by bromine was found to be: −d/[Br₂]T/dt=kK/[Br₂][Ti^III]/[H⁺]+K+kK/[Br₃⁻][Ti^III]/[H⁺+K, where k = 9.2 × 10⁻³ M ⁻¹ s ⁻¹ and K = 4.5 × 10⁻³ M. At [H⁺] = 1.0 M, [Br⁻] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br⁻] increases.

The pH-dependence of the oxidation of Ti^III-edta by bromine is interpreted in terms of the change in identity of the Ti^III-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k₀^edta)² weighting into an equation of the form: k₀^edta =k₁+k₂K₁[H⁺]⁻¹+k₃K₁K₂[H⁺]^−2/1+K₁[H⁺[H⁺⁻¹+K₁K₂[H⁺]⁻², with K₁ and K₂ fixed as earlier determined at 9.55 × 10⁻³ and 2.29 × 10⁻⁹ M, respectively, for the oxidation of bromine. k₁=k₂=(3.1±0.32)×10³M⁻¹s⁻¹ k₃=(2.3±0.45)×10⁶N⁻¹s⁻¹.

It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br₂^.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for Ti^III-edta+Ti^IV-edta is estimated at 32 M⁻¹ s⁻¹.     

Kinetics study of the gas-phase reactions of C2F5OC(O)H and n-C3F7OC(O)H with OH radicals at 253–328 K

The rate constants, k₁ and k₂ for the reactions of C₂F₅OC(O)H and n-C₃F₇OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k₁ and k₂ were determined as (9.24 ± 1.33) × 10⁻¹³ exp[−(1230 ± 40)/T] and (1.41 ± 0.26) × 10⁻¹² exp[−(1260 ± 50)/T] cm³ molecule⁻¹ s⁻¹. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k₁ and k₂. The atmospheric lifetimes of C₂F₅OC(O)H and n-C₃F₇OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively.     

State-selected reaction and relaxation of CH with H2

The state-selected reaction of CH(X₂Πν″ = 0, 1) with H₂ has been studied, in which CH was generated by IRMPD of a precursor gas, CH₃OH. The subsequent evolution of CH (ν″ = 0, 1) was monitored by the sensitive LIF technique. For the ground state and vibrationally excited state CH, the reaction with H₂ is found to depend on the total pressure in the sample cell at room temperature, which suggests that the reaction proceeds through an intermediate adduct, CH₃. The backward dissociation process is found to depend on the buffer pressure, which can be rationalized via a collision-induced backward dissociation. The decay rates of CH (ν″ = 0, 1) due to collisions with H₂ and Ar at a buffer pressure of 10 Torr are k_H2 (ν″ = 1) = (2.3±0.1) × 10⁻¹ cm³ molecule⁻¹ s⁻¹ and k_Ar (ν″ = 1) = (4.4±0.1) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. Possible effects of the vibrational excitation on the reaction rate of CH (ν″ = 1) are discussed.     

Kinetic study of gas-phase Lu(D3/2) with O2, N2O and CO2

The second-order rate constants of gas-phase Lu(²D_3/2) with O₂, N₂O and CO₂ from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule⁻¹ cm³ s⁻¹) are described in Arrhenius form by k(O₂)=(2.3±0.4)×10⁻¹⁰exp(−3.1±0.7 kJmol⁻¹/RT), k(N₂O)=(2.2±0.4)×10⁻¹⁰exp(−7.1±0.8 kJmol⁻¹/RT), k(CO₂)=(2.0±0.6)×10⁻¹⁰exp(−7.6±1.3 kJmol⁻¹/RT), where the uncertainties are ±2σ.     

Experimental and theoretical investigation of the reaction CF3 + NO + M → CF3NO + M from 0.5 to 12 Torr and from 253 to 373 K

The kinetics of the association reaction of CF₃ with NO was studied as a function of temperature near the low-pressure limit, using pulsed laser photolysis and time-resolved mass spectrometry. CF₃ radicals were generated by photolysis of CF₃I at 248 nm and the kinetics was determined by monitoring the time-resolved formation of CF₃NO. The bimolecular rate constants were measured from 0.5 to 12 Torr, using nitrogen as the buffer gas. The results are in very good agreement with recent data published by Vakhtin and Petrov, obtained at room temperature in a higher pressure range and, therefore, the two studies are quite complementary. A RRKM model was developed for fitting all the data, including those of Vakhtin and Petrov and for extrapolating the experimental results to the low- and high-pressure limits. The rate expressions obtained are the following: k₁(0) = (3.2 ± 0.8) × 10⁻²⁹ (T/298)^{−(3.4±0.6)} cm⁶ molecule⁻² s⁻¹ for nitrogen used as the bath gas and k₁(∞) = (2.0 ± 0.4) × 10⁻¹¹ (T/298)^(0±1) cm³ molecule⁻¹ s⁻¹. RRKM calculations also help to understand the differences in reactivity between CF₃ and other radicals, for the same association reaction with NO.