Reactions of alkenes with ozone in the gas phase: a matrix-isolation studyof secondary ozonides and carbonyl-containing reaction products

Gas phase ozonolysis reactions of the alkenes ethene, cis- and trans-but-2- ene, isoprene and the monoterpenes alpha -pinene, beta -pinene, 3-darene, l imonene and beta -myrcene have been carried out and the reaction products h ave been trapped in O-2-doped-argon matrices onto a CsI window held at 12 K . Products have been identified by IR spectroscopy. Comparison with previou s matrix spectra, where secondary ozonides have been generated either in si tu by annealing or in solution reactions allows a positive identification o f the secondary ozonides of ethene and of cis- and trans-but-2-ene to be ma de. These observations are backed up by experiments utilising the isotopes C-13 and H-2 (D). It appears that secondary ozonides have also been formed from isoprene and the range of monoterpenes studied; this hypothesis is bas ed upon the similarity of spectral features seen in the products of these r eactions within those of the simpler alkenes. A number of other primary and secondary products are also identified from these reactions. Ethene gives formaldehyde as a primary product and acetaldehyde as a secondary product; it is found that the yield of acetaldehyde compared to formaldehyde increas es as the reaction times are increased. Formaldehyde, one of the expected p rimary products, is formed by ozonolysis of beta -pinene, although the othe r expected primary product, nopinone, is not seen. A range of secondary rea ction products have been identified from the ozonolysis of the monoterpenes studied (C) 2000 Elsevier Science B.V. All rights reserved.