D. V. Kazakov

Kinetics of thermal decomposition of dimethyldioxirane in oxygen atmosphere

Dimethyldioxirane decomposition in oxygen atmosphere follows a first-order kinetic law. Decomposition rate constant (k, s−1) in acetone in the temperature range from 30 to 50°C has been determined as lgk=(7.1±0.9)−(16.0±1.4)/θ, θ=2.303RT kcal/mol.

Kinetics and mechanism of the highly efficient generation of singlet oxygen in dimethyldioxirane decomposition induced by the chloride ion

The decomposition of dimethyldioxirane induced by the chloride anion has been investigated by methods of infrared chemiluminescence and quantum chemistry. The reaction leads to efficient generation of singlet excited molecular oxygen 1O2 (the excitation yield in acetone is 61%). A mechanism of peroxide decomposition is proposed in which the key reactions are the addition of the chloride ion to an oxygen atom of dioxirane, resulting in dioxirane ring opening and the formation of the 2-chlorooxy-2-hydroxy propane alcoholate (k1), and the interaction of the latter with another dimethyldioxirane molecule. This interaction results either in the formation of an adduct, which further decomposes to evolve 1O2, and catalyst regeneration (k2) or in the formation of the 2-chloroxyisopropyl radical, which leads to the irreversible consumption of the chloride ion catalyst (k3). The decay kinetics of the infrared chemiluminescence of 1O2 has been studied in a wide range of reactant concentrations. The temperature dependence of the rate constant of the reaction of dimethyldioxirane with the chloride ion has been determined by a kinetic analysis of the mechanism proposed: log(2k1) = (11.1 ± 0.7) − (46 ± 4)/Θ, where Θ = 2.3RT kJ/mol. Estimation of the ratio of the rates of the reaction of the 2-chlorooxy-2-hydroxy propane alcoholate with dimethyldioxirane via two pathways (k3/k2) has demonstrated that the fraction of the process involving electron transfer does not exceed 1.5% under the experimental conditions examined. Nevertheless, the latter reaction, which withdraws the chloride ion from the catalytic cycle of dimethyldioxirane decomposition yielding singlet oxygen, has a marked effect on the overall kinetics of the process.

Kinetics and mechanism of the reaction of dimethyldioxirane with cumene

The reaction of dimethyldioxirane with cumene (22–52°C) follows a chain-radical mechanism. The kinetic regularities of this reaction were studied by the chemiluminescence and kinetic UV spectrophotometry methods by monitoring the consumption of dioxirane. The process is inhibited by oxygen. In the absence of O2, the process is accelerated due to the decomposition of dimethyldioxirane induced by alkyl radicals. In this case, the reaction occurs according to a complicated kinetic law including the first and second orders with respect to dioxirane. Based on the kinetics and reaction products, the scheme of the process was proposed.

Chemiluminescence in the reaction of the RuII trisbipyridyl complex with dimethyldioxirane

The reaction of dimethyldioxirane (1) with the RuII trisbipyridyl complex accompanied by chemiluminescence (CL) was studied. It is established that the intensity of CL and the rate of its decay increase proportionally with the concentration of RuII. The bimolecular rate constant (k2) of the reaction of1 with RuII was determined. The activation parameters (Ea and logA) for this reaction were calculated from the temperature dependence ofk2. The excitation yield of RuII* (ηRu*) was estimated. The quenching of RuII* by dioxirane was studied, and the bimolecular quenching constant and the coefficient of excitation regeneration were determined. It was suggested that the catalysis of the decomposition of1 and the excitation of RuII occurvia a mechanism of chemically initiated electron exchange.

Kinetics of the reaction between dimethyldioxirane and 2-methylbutane

The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O2, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10−4 s−1) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between the alkyl radical and dimethyldioxirane was estimated.

CHEMILUMINESCENCE OF OXYGEN-FREE ACETONE SOLUTIONS OF DIMETHYLDIOXIRANE

The decomposition of dimethyldioxirane (1) in oxygen-free acetone solutions (46°C) is accompanied by chemiluminescence (CL) in the visible spectral region. The emitter of CL is triplet-excited methyl acetate (2*(T)). For the decomposition of solutions of1 in acetone and deuterated dimethyldioxirane in acetone-D6 the decay of CL follows the first-order kinetics, and the kinetic isotope effect is observed. Two mechanisms of the formation of2*(T) are discussed: (a) chain-radical process and (b) isomerization of1 to2.

Kinetics of dimethyldioxirane decomposition in the presence of cumene

Dimethyldioxirane consumption increases considerably in the presence of cumene. The product composition (cumic alcohol, acetophenone, α-methylstyrene) and the inhibiting effect of oxygen prove a radical reaction mechanism. The kinetic order for dimethyldioxirane increases with the conversion from 1.5 to 2.

Formation of radicals during dimethyldioxirane decomposition

Thermal decomposition of dimethyldioxirane is followed by the formation of radicals registered by ESR spectroscopy using aC-phenyl-N-tert-butylnitronc spin trap. The intensity of the ESR signal increases linearly with increasing temperature; the dependence is extreme in character.

Decomposition of triphenyl phosphite ozonide catalyzed by pyridine

Pyridine accelerates the decomposition of triphenyl phosphite ozonide in CH2Cl2. The addition of alcohol to the system (PhO)3PO3−C5H5N−CH2Cl2 increases the rate of this process. The kinetics of (PhO)3PO3 decomposition in pyridine, in ethanol-pyridine, 2-propanol-pyridine mixtures and in CH2Cl2 were investigated.

Chemiluminescence arising from the decomposition of 1,4-dimethylnaphthalene endoperoxide applied to silica gel in the presence of NdIII, YbIII, and EuIII β-diketonates

Visible and near-IR chemiluminescence was observed upon the decomposition of 1,4-dimethylnaphthalene endoperoxide applied to silica gel in the presence of the β-diketonate complexes Nd(L)3·nH2O, Yb(L)3·nH2O, and Eu(L)3·nH2O (L is 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dionate, 1,1,1-trifluoro-3-thenoylacetonate, and acetylacetonate). Excited lanthanide ions serve as luminescent emitters with emission maxima at λ = 870 and 1060 nm for NdIII, 990 nm for YbIII, and 615 nm for EuIII. Singlet oxygen generated by decomposing endoperoxide was found to play a key role in the chemiluminescence mechanism.