Tautomerism and octane quality in carbonyl-containing oxygenates

A subclass of the oxygenates for potential use in octane boosting of gasoline are molecular species containing carbonyl groups. We consider the kinetics of the radicals formed from carbonyl species and how they affect the overall radical propagation and termination during the combustion process. Using previous work on olefins, we deduce those chemical, characteristics of carbonyl molecules which will make them good octane boosters. We identify the CH bond on the ct carbon to be crucial to radical branching in the kinetic scheme. By a consideration of the molecular phenomena which affect the bond strength, we identify the gas-phase keto-enol tautomerism constant as a determining factor in radical propagation as well as the number of allylic hydrogens formed on the most stable enol dimer. We demonstrate a correlation for a limited data set between the experimental blending octane number and the independently measured gas-phase equilibrium constant for tautomerism and give a mechanistic explanation of the effect.