The Relative Rate Constants of Reactions of Oxygen Atoms with Several Olefins in Liquid Carbon Dioxide

Abstract

The relative rate constants of reactions of oxygen atoms with several olefins and 2-methylpropane have been determined in liquid carbon dioxide at −18 °C, using the γ-radiolysis of carbon dioxide in the presence of these hydrocarbons. They are : 1-butene, 1.0; cis-2-butene, 2.3; trans-2-butene, 3.0; 2-methylpropene, 2.9; 2,3-dimethyl-2-butene, 2.0; 2-methylpropane, 0.07. These relative values are very different from those obtained in the gas phase. A possible reason is discussed and a simple theoretical treatment is proposed for the competition between diffusion and reaction on the basis of the idea of a “collision set” in the liquid phase. The reaction of oxygen atoms with paraffin in liquid carbon dioxide seems to be faster than that in the gas phase. The reason is not clear at present.

Reactions of Microwave-Generated O(3P) Atoms with Unsaturated Hydrocarbons

“…cis -4-Octene. To confirm the observations previously reported that cis- or trans 1,2-disubstituted ethylenes yielded, among other products, both cis - and trans -epoxides, in the condensed phase,9i or in the vapor phase, the reaction of cis -4-octene was carried out using an O 2 /He plasma; see Table . The yield of epoxides (99%) formed at moderate (36%) conversion is fully consistent with the proposed mechanism, formation of the triplet diradical adduct, which undergoes internal rotation on a comparable or shorter time scale than intersystem crossing and epoxide formation.…”

“…When O( 3 P) atoms were generated using a microwave discharge of O 2 /He, the product ratios formed from the oxidation of styrene 9i or cis- stilbene 9a were not appreciably different. However, with all three of the microwave-promoted methods for the generation of O( 3 P) atoms, an appreciable amount of benzaldehyde (5−13%) was formed from the oxidation reactions of styrene 9i. The formation of a cleavage product, benzaldehyde, suggested that under the reaction conditions in all three cases ozone is formed.…”

“…A number of studies that generate ground-state oxygen, O( 3 P), have reported reactions carried out in the condensed phase or on solid surfaces. − The liquid-phase reactions have been carried out using γ-irradiation of substrates dissolved in liquid CO 2 , by the microwave discharge of CO 2 , with oxygen atoms generated by an O 2 /He plasma, or with a plasma formed from a mixture of N 2 and N 2 O …”

“…The mechanism proposed for the addition of O( 3 P) atoms to an olefin was shown to proceed via a triplet diradical since cis- or trans -stilbene yielded both cis- and trans- stilbene oxide as well as benzyl phenyl ketone. 9a,b The use of a O 2 /He plasma to generate O( 3 P) atoms has been questioned since the reactive species produced by the plasma were possibly contaminated with O 2 , O 2 ( 1 Σg), or O 3 9i. When O( 3 P) atoms were generated using a microwave discharge of O 2 /He, the product ratios formed from the oxidation of styrene 9i or cis- stilbene 9a were not appreciably different.…”