No abstract

Phosphorescence of methyl acetate formed by isomerization of electron-excited dimethyldioxirane is observed upon excitation at the wavelength of the absorption band of dimethyldioxirane in acetone at 77 K. The quantum yield of the photodeeomposition of dimethyidioxirane at 296 K is equal to 13.1+0.7 tool Einstein -l. The high quantum yield of photolysis is evidence for the chain mechanism of decomposition of dimethyldioxirane.

No abstract

The decomposition of dimethyldioxirane (1) in oxygen-free acetone solutions (46 ~ is accompanied by chemiluminescence (CL) in the visible spectral region. The emitter of CL is triplet-excited methyl acetate (2"('I')). For the decomposition of solutions of I in acetone and deuterated dimethyldioxirane in acetone-D 6 the decay of CL follows the first-order kinetics, and the kinetic isotope effect is observed. Two mechanisms of the formation of 2*(T) are discussed: ta) chain-radical process and (b) isomerization of 1 to 2.Key words: organic peroxides, dimethyldioxirane, chemiluminescence, mechanism of chemiluminescence.Formation of excited products in the decomposition accompanied by chemiluminescence (CL) is a general property of several cyclic peroxides. For example, the decomposition of dioxetanes gives ketones in singlet and triplet excited states, i,2 and the decomposition of some ozonides results in the formation of singlet oxygen. 3,4 In the majority of cases, these are precisely the products which are emitters of the luminescence appeared. Cyclic peroxides (dioxiranes 5,6) are not exceptions in this series. The energy released in the decomposition of dioxiranes to the corresponding ester is equal to -80 kcal real -1 al~d, hence, a chemiluminescence process is possible. 5,r In fact, we have shown 8 that the thermal decomposition of dimethyldioxirane (1) in the presence of an activator of CL, 9,10-dibromoanthracene (DBA), results in the appearance of CL caused, as we supposed, by the energy transfer from triplet-excited methyl acetate (2*(T)) (the main product of the decomposition of 1) to DBA. Later, 9 we observed a substantially more intense CL in the decomposition of compound 1 sorbed from the gas phase on the surface of Sitipor. However, zao CL was observed in a solution of i in acetone. We related this fact to the quenching process and, first of all, to the presence of oxygen, an efficient quenching agent of triplet-excited states. In this work, we first report on CL in the thermal decomposition of oxygenfree solutions of 1 in acetone. ExperimentalDioxirane 1 was obtained and analyzed as described in Ref. 10. The kinetics of the decomposition of 1 was monitored spectrophotometrically in a thermostated quartz ceil (the opti-" Dedicated to Prof, W. Adam on the occasion of his 60th birthday.cal path was 1 cm) by the decrease in the optical density at L 335 nm (e 10 L real -I cm-t) t~ on a Specord M-40 instrument (Carl Zeiss, Jena). Chemiluminescence was monitored on an installation of an FEU-140 photomultiplier calibrated in absolute units according to a procedure described previously. It Phosphorescence spectra of methyl acetate (2) were recorded on a Hitachi MPF-4 spectrofluorimeter at 77 K. Oxygen from a solution of 1 in acetone was removed by subsequent "freezing-evacuating-thawing out" procedures repeated 5--6 times until the release of gas bubbles stopped completely. After this, a solution of I in acetone was placed in a therrnostated cell arranged above the photocathode of the photomultiplier, and CL ...

ABSTRACT:In the present work the results of the study of oxidative destruction of chitosan effected by ozone and hydrogen peroxide are listed. The results obtained verify the rupture of 1,4-␤-D-glucoside bonds in macromolecule to be the basic process during amino groups of chitosan protection by acids. The rate of ozone with chitosan interaction depends on the concentration of ions in reaction mass. Destruction of chitosan by hydrogen peroxide leads to the formation of oligosaccharides in contrast to ozonolysis. Hydrogen peroxide oxidizes functional groups of chitosan only under tough conditions.