Infrared spectra and kinetics of decomposition of primary ozonides in the liquid phase at low temperatures

Abstract

A low-temperature i.r. cell has been developed for in situ studies of the intermediates of the ozonolysis of alkenes in the liquid phase at temperatures down to –178°C. The i.r. spectra of 1,2,3-trioxolans (primary ozonides) formed from the following alkenes have been observed: hex-1-ene, cis-di-isopropylethylene, trans-diethylethylene, trans-di-isopropylethylene, and trans-di-t-butylethylene. All have characteristic bands in three spectral regions, 690, 970, and 1 100 cm^–1 and at higher temperatures decompose with the formation of 1,2,4-trioxolans (final ozonide) and peroxy-compounds. The decay of the i.r. bands at 690 cm^–1 has been used to study the kinetics of the decomposition of the primary ozonides over a range of temperatures. The reactions are first order and have the following A and E factors: trans-diethylethylene, 10^5.3 s^–1, 29 ± 6 kJ mol^–1; trans-di-isopropylethylene, 10^8.4 s^–1, 40 ± 3 kJ mol^–1; trans-di-t-butylethylene, 10¹¹ s^–1, 60 ± 13 kJ mol^–1. The activation energies for the decomposition of the primary ozonides from cis-di-isopropylethylene and hex-1-ene are estimated to be lower than 14 kJ mol^–1. The observed parameters and the effects of substitution indicate incipient π-bonding and charge separation in the C–O bonds of the transition state and also considerable orientation of solvent molecules.