Phenylnitroso Oxide Research Articles

Kinetics and Mechanism of the Reactions of Aromatic Nitroso Oxides with Tetracyanoethylene

The kinetics of reaction of phenylnitroso oxide and a number of its para-substituted analogues (R = Me2N, MeO, Me, and Br) with tetracyanoethylene in acetonitrile at room temperature was studied using flash photolysis. It was established that nitroso oxides exhibited nucleophilic properties in this reaction, and the rate constants for the trans forms of these species in the above series changed by seven orders of magnitude. In the presence of a strong electron-donating substituent (Me2N or MeO), the cis form, which is usually inert toward organic substrates, also reacted with the olefin along with the trans form. The reaction mechanism was studied using the density functional theory.

On the Mechanism of the [3+2]-Cycloaddition of Phenylnitroso Oxide to trans-Stilbene

The non-photolytic method for generation of arylnitroso oxides based on the reduction of nitrosobenzene by triphenylphosphine was used to study the products of the reaction of transphenylnitroso oxide with trans-stilbene. N,α-Diphenylnitrone and benzaldehyde were found to be the main stable products of the reaction, the first stage of which was [3+2]-cycloaddition to form the metastable 1,2,3-dioxazolidine intermediate. The obtained products were in agreement with our previous theoretical predictions.

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.

A new intramolecular transformation of aromatic nitroso oxides

The possibility of intramolecular interaction of a nitroso oxide group with an aromatic ring is investigated at the UB3LYP/6-311+G(d,p) and G3MP2B3 levels of theory for a wide series of aromatic nitroso oxides. It is found that this reaction leads to the formation of a dioxazole cycle, its subsequent decay resulting in opening of the benzene ring and formation of nitriloxide and carbonyl functional groups. The activation enthalpy of the transformation of phenylnitroso oxide is 75.1 kJ/mol. It is shown that various sub-stituents at ortho-position (with respect to the nitroso oxide fragment) considerably lower the activation barrier of the investigated transformation, particularly in case of o,p-dimethoxyphenylnitroso oxide ΔH≠ = 43.7 kJ/mol. It is concluded that in the case of polyaromatic nitroso oxides, for which intramolecular cyclization is more typical (ΔH≠ ∼ 50 kJ/mol), a factor favoring the attack on the ortho-carbon atom is the stabilization of the product’s diene group due to its inclusion in the polyaromatic system. It is established that sum of these effects leads to a low activation barrier for the transformation of nitroso oxide that forms during the photooxidizing of 2-azido-1-methoxyphenazine, ΔH≠ = 19 kJ/mol. It is proposed that due to the low activation energy of some nitroso oxides, their intramolecular cyclization may be the primary channel of their unimolecular decay.

Flash photolysis study of the reactivity of isomeric forms of arylnitroso oxides toward triphenyl phosphite

The kinetics of the reactions of phenylnitroso oxide and 4-CH3O-, 4-CH3-, and 4-Br-phenylnitroso oxides with triphenyl phosphite was studied in acetonitrile, benzene, and hexane by flash photolysis. The reaction occurs only with the trans-isomers of nitroso oxides. The value of the reaction rate constant increases with an increase in the electron-withdrawing power of substituents on the nitroso oxide aromatic ring, with the rate constant being almost the same in benzene and acetonitrile, and increasing by a factor of 2–3 in hexane. The temperature dependence for the decay rate constants of isomeric nitroso oxides in the presence of triphenyl phosphite was studied in acetonitrile.

The quantum-chemical modeling of the reaction of nitroso oxides with olefins

The density functional theory method was used to localize minima on the singlet potential energy surfaces of the nitroso oxide—ethylene, phenylnitroso oxide—tetramethylethylene, phenylnitroso oxide—hexene-1, and phenylnitroso oxide-styrene systems and on the triplet potential energy surfaces of the nitroso oxide—ethylene and phenylnitroso oxide-hexene-1 systems. The energetically favorable path was found to be that of (3 + 2) cycloaddition with the formation of five-membered rings, which decomposed into nitrone and carbonyl compound with the simultaneous dissociation of the C-C and C-O bonds. The influence of cis-trans isomerism of nitroso oxides on their reactivity with respect to olefins was studied.

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.

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 reactions between arylnitroso oxides and methyl vinyl ketone

The kinetics of the reactions of phenylnitroso oxide, (4-methylphenyl)nitroso oxide, (4-methoxyphenyl) nitroso oxide, 4-(N, N -dimethylamino)phenylnitroso oxide, (4-chlorophenyl)nitroso oxide, (4-bromophenyl) nitroso oxide, and (4-nitropenyl)nitroso oxide with methyl vinyl ketone in acetonitrile at 295 K was studied. With the use of 4-CH3O-C6H4-NOO as an example, it was found that only the trans isomers of nitroso oxides entered into the reaction. The rate constants of the reactions of the trans isomers of nitroso oxides with methyl vinyl ketone were measured. A linear correlation between the logarithms of reaction rate constants and the electronic properties of substituents in the aromatic rings of nitroso oxides on the Hammett scale was established: ρ = 1.11 ± 0.08; r = 0.990.

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.

Kinetics of the carbomethoxylation of methylacetylene-allene mixtures catalyzed by palladium complexes

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.

Strong Solvent Effect on the Reactivity of Polar Intermediates X–O–O: Isomerization of 4-(N,N-Dimethylamino)phenylnitroso Oxide

Strong Solvent Effect on the Reactivity of Polar Intermediates X–O–O: Isomerization of 4-(N,N-Dimethylamino)phenylnitroso Oxide

Phenylnitroso Oxide: Formation and Decay Kinetics

Phenylnitroso Oxide: Formation and Decay Kinetics