R. L. Safiullin

Isomeric forms of arylnitroso oxides: Electronic spectra and reactivity

The electronic spectra were measured and the kinetics of unimolecular decomposition of the isomeric forms (cis and trans) of phenylnitroso oxide, (4-methylphenyl)nitroso oxide, (4-nitropenyl)nitroso oxide, (4-bromophenyl)nitroso oxide, 4-(N,N-dimethylamino)phenylnitroso oxide, and (4-methoxyphenyl)nitroso oxide in acetonitrile, benzene, and n-hexane was studied using flash photolysis. In all of the nitroso oxides except for 4-(N,N-dimethylamino)phenylnitroso oxide, the cis form absorbed in a shorter wavelength region and was more labile than the trans form. The difference between the reactivity of the two species increased on going from n-hexane to acetonitrile. The temperature dependence of reaction rate constants was studied for both of the isomeric forms. Unlike the trans isomer, the cis isomer almost did not react with tetramethylethylene.

A Revised Mechanism of Thermal Decay of Arylnitroso Oxides

The electronic spectra were measured and the unimolecular decay kinetics of the isomeric forms (cis and trans) of 4-methoxyphenylnitroso oxide in acetonitrile, benzene, and hexane was studied using flash photolysis. The cis form absorbed in a shorter wavelength region and was more labile than the trans form. The difference between the reactivity of the two species increased on going from hexane to acetonitrile. The temperature dependences of reaction rate constants were studied for both isomeric forms. The analysis of products of flash photolysis of 4-methoxyphenyl azide in the presence of oxygen allowed for understanding the mechanism of thermal decay of nitroso oxides. It was shown that the trans nitroso oxide is converted into cis nitroso oxide. The latter undergoes an unusual ring cleavage reaction to form 4-methoxy-6-oxohexa-2,4-dienenitrile N-oxide derivative. We conclude that the nitro- and nitrosobenzenes, which are the main products of the steady-state photolysis of aromatic azides in the presence of oxygen, are formed by the photochemical transformation of the nitroso oxides.

Kinetics of the liquid-phase oxidation of 1,4-dioxane in the presence of inhibitors

The kinetics of 1,4-dioxane oxidation initiated by azodiisobutyronitrile in the temperature range from 323 to 353 K are studied from the rate of oxygen absorption. The oxidation proceeds in the regime of a nonbranched chain reaction with quadratic-law chain termination. The apparent rate constants (fk7) of 1,4-dioxane oxidation inhibition by 2,6-ditert-butyl-4-methylphenol and quercitin are measured. Quercitin is not inferior to ionol in inhibition efficiency.

Reactivity of arylnitroso oxides to triphenylphosphine

The kinetics of reactions between phenylnitroso oxide, 4-CH3O-, 4-CH3-, or 4-Br-phenylnitroso oxide and triphenylphosphine in acetonitrile at 295 ± 2 K were studied using pulsed photolysis. Only trans-nitroso oxides enter this reaction. The rate constants of the reaction increase with increasing electron-acceptor properties of the substituent in the aromatic ring of nitroso oxide; they are on the order of 105 to 106 l mol−1 s−1. The extinction coefficient for trans-4-methylphenylnitroso oxide at 420 nm was estimated at 3.9 × 103 l mol−1 cm−1.

Effect of the structure of reactants on the reaction rate constants of aromatic nitroso oxides with olefins

The reactivity of phenylnitroso oxide, (p-methylphenyl)nitroso oxide, (p-nitrophenyl)nitroso oxide, (m-nitrophenyl)nitroso oxide, and (p-bromophenyl)nitroso oxide toward a number of olefins in acetonitrile at room temperature was studied using flash photolysis. It was found that the reaction rate constant decreased with decreasing energy of a molecular orbital with a maximum contribution from the atomic orbitals of carbon atoms in the C=C bond of olefins. This, along with a positive slope of the Hammett function for the reactions of substituted phenylnitroso oxides with 1-hexene and styrene, suggest an electrophilic character of these species. The temperature dependence of the rate constant of the reaction of phenylnitroso oxide with 1-hexene was studied: log A = 7.9 ± 0.4 [l mol-1 s-1]; Ea = 38 ± 2 kJ/mol.

Reactions of Arylnitroso Oxides with Substituted Styrenes: Kinetics and Products

The kinetics of the reactions of phenylnitroso oxide and 4-CH3O- and 4-Cl-phenylnitroso oxides with a series of substituted styrenes (4-X-C6H4-CH=CH2; X = H, CH3O, Cl, CN) in acetonitrile at 22 ± 2°C was studied using the flash photolysis technique. It was shown for 4-CH3O-C6H4NOO as an example that only the trans isomers of the nitroso oxides are involved in the reaction. There is a linear correlation between the logarithm of the rate constant and the electronic properties of the substituent in the nitroso oxide aromatic ring on the Hammett scale: ρ = 2.3 ± 0.3 (r = 0.993) for 4-CH3O-styrene ρ = 2.03 ± 0.07 (r = 0.995) for styrene, and ρ = 1.77 ± 0.05 (r = 0.9996) for 4-Cl-styrene. Both the electron-donating and electron-withdrawing substituents in the aromatic ring of styrene increase its reactivity toward a given nitroso oxide. An analysis of the products of phenyl azide photooxidation in the presence of styrene showed that the product of phenylnitroso oxide [3+2]cycloaddition to the double bond of the olefin decomposes into benzalaniline and carbonyl oxide.

Kinetics of copper(II)-catalyzed cyclopropanation of olefins

Kinetics of the copper(II) acetylacetonate-catalyzed cyclopropanation of styrene and 2,5-dimethylhexa-2,4-diene is reported. A kinetic analysis of a catalytic olefin cyclopropanation scheme is suggested.

Thermal intramolecular transformation of key intermediates in the photooxidation of para-allyl-substituted phenyl azide.

The electronic spectra, kinetic regularities, and the mechanism of decay of the cis and trans isomeric forms of 4-[(2E)-1-methylbut-2-en-1-yl]phenylnitroso oxide (2) were studied by flash photolysis and product analysis. The mechanism of the consumption of this nitroso oxide is the same as the one proposed earlier for 4-methoxyphenylnitroso oxide. The trans-2 isomer is converted into cis-2, which undergoes cyclization to the substituted benzo[d][1,2,3]dioxazole 3. The reopening of the dioxazole ring yields nitrile oxide 4. The final product (3,4-dimethyl-3a,4-dihydro-2,1-benzisoxazol-5(3H)-ylidene)acetaldehyde (5) is formed by the intramolecular [3 + 2]-cycloaddition of the nitrile oxide group of 4 to the allylic double bond. To support the proposed mechanism, the quantum chemical calculations have been employed.

Analysis of the reactivities of organic compounds in hydrogen atom abstraction from their C-H bonds by the sulfate radical anion SO4·−

An experimental rate constant data array (>50 values) for the reactions of the sulfate radical anion with the C-H bonds of various organic compounds is analyzed by Denisov’s intersecting parabolas method. The data array is divided into the following four groups according to the type of the C-H bond attacked and the bre value: compounds with primary C-H bonds (bre = 13.14 ± 0.17), compounds with secondary C-H bonds remote from the polar groups (bre = 12.64 ± 0.34), compounds with secondary α-C-H bonds (bre = 13.28 ± 0.24), and compounds with tertiary C-H bonds. It is demonstrated by DFT calculations that the rate constant of the reaction SO4·− + RH is determined by nonspecific solvation and by the ion-dipole interaction in the transition state of the reaction.

Free-radical chain oxidation of 1,4-dioxane and styrene in the presence of fullerene C60

The antiradical activity of fullerene C60 was studied for the oxidation of 1,4-dioxane and styrene initiated by azobisisobutyronitrile and benzoyl peroxide as model reactions. The effective rate constants of the reaction of peroxyl radicals with fullerene C60 (k7) and the stoichiometric inhibition factor (feff) were determined in air (