低温酸化反応機構から考えるオクタン価

抄録

It is well known that octane number systematically changes depending on the chemical structure. According to this empirical rule, octane number increases with the number of branches, and decreases with the separation between branches. This paper aims to provide some insight into the chemical interpretation of octane number. At first, the low temperature oxidation and H₂O₂ loop mechanism are introduced in order to understand the auto-ignition process of hydrocarbon compounds, and then, the effects of branched structure on the low temperature oxidation mechanism have been discussed by using a steady state analysis. This analysis shows that both tertiary and quaternary carbon decrease the effective rate constants of chain branching process for alkylperoxy radical (ROO•) reactions. A tertiary carbon inhibits intramolecular hydrogen shift reaction of hydroperoxyalkylperoxy radical (•OOQOOH). On the other hand, a quaternary carbon inhibits mainly intramolecular hydrogen shift reactions of ROO• and promotes cyclic-ether formation reactions of hydroperoxy radical (•QOOH). The correlations between chemical structure and octane number can be partly explained by these kinetic effects.