1H-NMR Spectroscopy Study of Oleic Acid and Methyl Oleate Ozonation in different reaction conditions

Reactions of ozone with oleic acid or methyl oleate were carried out in presence of hexane, carbon tetrachloride, ethanol or water. All the reaction mixtures were studied by H Nuclear Magnetic Resonance Spectroscopy (H-NMR). Differences in the composition of the reaction mixture of the samples by 1H-NMR analysis were found. During the ozonation of oleic acid, the acyl-oxy-alquil-hydroperoxides were formed as major products in all the studied conditions. Nevertheless, during ozonation of methyl oleate, a striking dependence of reaction products with the solvent or additive used was found. In hexane, the corresponding ozonides/oligomers were obtained, whereas when ethanol is present, the ethoxy-hydroperoxides were the major products. The analysis in the presence of water only reveals the aldehyde and ozonides/oligomers signals. These results are discussed taking into account the Criegee mechanism, the characteristic of the bubbling reactor employed, and some properties of the solvents or additives used. INTRODUCTION Oleic acid (cis-9 octadecenoic acid) is one of the most important components of vegetable oils and the lipids present in the living organisms. For example, olive oil contains 60-70 % of oleic acid and sunflower oil 20-30 %. The oleic acid presents an unsaturation in its structure, and for that reason readily reacts with ozone, at a rate constant of 105-106 L mol s . The reaction of ozone with unsaturated compounds takes place through the well-known Criegee mechanism. This mechanism (Fig. 1) consists in an ionic, electrophilic attack of ozone, in a simultaneous way, at the carboncarbon double bond (1,3 dipolar cycloaddition), resulting the 1,2,3 trioxolane or primary ozonide. This intermediate is very unstable and it is decomposed forming a carbonylic compound (aldehyde or ketone) and the carbonyl oxide or zwitterion. In that moment, depending on the reaction conditions, different routes can be taken and different reaction products can be obtained. This mechanism (Fig. 1) consists in an ionic, electrophilic attack of ozone, in a simultaneous way, at the carboncarbon double bond (1,3 dipolar Oscar Ledea, Maritza Díaz, Jesús Molerio, Daniel Jardines, Aristides Rosado and