Formation of secondary ozonides in the gas phase low-temperature ozonation of primary and secondary alkenes

The gas-phase ozonation of a series of alkenes RCH=CH2 (R = Et, Hex), trans-RHC=CHR (R = Me, Et, Pr-i) and Me2C=CMe2 at -40 to 20 degrees C, and that of ethene H2C=CH2 at -120 to 0 degrees C at 10(-4) v/v concentrations in N-2 at atmospheric pressure have been studied. Using complementary product analysis by means of GC-FTIR and CC-MS techniques, we present conclusive evidence for the formation of secondary alkene ozonides as high-yield products in all instances except Me2C=CMe2. It is shown that the stereoselectivity for the conversion of trans-RHC=CHR (R = Me, Et, Pr-i) to trans-secondary ozonides in the gas phase is similar to that observed earlier in solution, and that the yields of secondary ozonides from RHC=CH2, but not those from RHC=CHR, significantly decrease with increasing temperature.