Study of the oxidation of unsymmetrical ethers (ETBE, TAME) and tentative interpretation of their high octane numbers

This work aims at a better understanding, from the reaction mechanism point of view, of the antiknock effect of two unsymmetrical ethers: tert-amyl methyl ether (TAME) and ethyl tert-butyl ether (ETBE).An experimental investigation of the reactions of equimolecular mixtures of these ethers in the presence of oxygen shows that these ethers oxidize less easily than the alkanes of similar structures.Taking into account the distribution of the primary reaction products at ca. 300°C and by using the techniques of Thermochemical Kinetics due to BENSON et al. for the estimation of kinetic parameters, it has been shown that these ethers do not oxidize according to a “low” temperature scheme, like the neighbouring alkanes. Their reaction with O2 seems to have the characteristics of a thermal degradation and not those of a genuine oxidation. In line with the experimental results, it appears that in the co-oxidation of one of the above-mentioned ethers and a hydrocarbon, the effect of the ether is that of a “negative catalyst” transforming reactive radicals, chain carriers of the hydrocarbon oxidation, through a rather complex reaction scheme into unreactive ones, unable to propagate the reaction at a sufficient rate to trigger the auto-ignition reactions, responsible for the occurrence of knock phenomena