Crossed ozonide formation in the ozonolysis of styrene
Styrene–benzaldehyde mixtures (unsubstituted and the p-nitro, p-chloro, and p-methyl systems) were ozonized in CDCl3 at 0 °C. The yields of styrene ozonide and of the two crossed ozonides (stilbene and ethylene ozonides) were determined. The cleavage direction ratios of the primary ozonides were also determined. In a computer simulation of the yields five rate expressions were employed, giving relative rate coefficient information on the cycloaddition reactions between the carbonyl oxides and the aldehydes. This analysis of the various competing reactions during ozonolysis indicated that electron-withdrawing substituents increased crossed ozonide formation by enhancing the dipolar character of the carbonyl oxide and the dipolarophilicity of the aldehyde. The substituent also influences the cleavage direction of the primary ozonide and the solvent cage effect. A Hammett correlation of the crossed ozonide rate constants [k(stilbene ozonide)/(k(ethylene ozonide)] had a slope (ρ) of 1.4 (0.1).