1852
ALFREDA. SCALA AND WOO-TIEN Wu
The Reaction of (‘PJ Oxygen Atoms with Cyclopropane by Alfred A. Scala and Woo-Tien Wu Department of Chemistry, ~orcesterPolytechnic Institute, Worcester, Massachusetts 01609 (Received July ‘7, 1969)
The reaction of a (*PI)oxygen atom with cyclopropane in the gas phase has been investigated with regard for product analysis. Oxygen atoms were generated by the mercury-sensitized decomposition of nitrous oxide. Using nitrogen as an actinometer indicates that 40% of the oxygen in the system results in the production of water and 16% results in the production of carbon monoxide. The remainder of the oxygen is converted to formaldehyde which polymerizes. A mechanism for the reaction is proposed which involves electrophilic attack of the oxygen atom on the bent bond of cyclopropane forming a trimethylene oxide diradical. In the gas phase further decomposition of this product occurs and the initial products are formaldehydeand ethylene. Even at conversions of 0.2%, ethylene competes with cyclopropane for the oxygen atoms and a steady state is achieved. The data indicate that I c ~ / k c = ~ ~1.12 , X lod4. Since the rate of production of nitrogen is a function of the hydrocarbon which is preBent, it is questionable whether nitrogen is a reliable actinometer in these systems.
Introduction The reactions of oxygen atoms are of importance both in combustion processes and in photochemical smog formation. In the atmosphere, oxygen atoms produced by the photodecomposition of NO2 and Os are present in greater concentration than any other reactive atomic or free radical species.’ The simplest and most convenient method for the production of oxygen atoms in the laboratory is the mercury-sensitized decomposition of NzO shown in reaction 1. The advantages of HgWd
+ N2O
Hg(’So)
+
+ N2 + O(’P1)
(1)
this technique lie in the fact that the quantum yield for reaction 1 is LO2 and that the yield of nitrogen provides a convenient actinometer.3 Other advantages of this technique which have been pointed out by Cvetanovic4 are the ability to study reactions of atomic oxygen in the absence of molecular oxygen and the accessibility to higher pressure ranges than are possible by microwave discharge techniques. Cvetanovic6 has also utilized reaction 1 in determining relative quenching cross sections of other molecules for Hg(sPl). In this technique the yield of nitrogen serves~asa measure of the extent of reaction 1. This study was originally undertaken to determine the mechanism and the products of the reaction of e l e c t r ~ p h i l i coxygen ~ ~ ~ atoms with cyclopropane, a molecule of unusual structures which might be expected to be susceptible to electrophilic attack a t the carbon-carbon u bond. Recent theoreticale and experimentallo studies have shown that there is a region of high electron density on the edge of the cyclopropane ring. The results of this study, while elucidating the mechanism for this reaction, also raise the serious question of whether or not nitrogen is a reliable actinometer in these systems.
purified by repeated injection of small quantities on a 10 ft long squalane column. They were trapped at the exit of the chromatograph and subsequently passed over Drierite and distilled at low temperature to remove any traces of water. The only impurities present in the cyclopropane were 0.0024% propylene and
