Inhibition of the H2+ O2 reaction by alkyl silanes

Abstract

The inhibiting action of SiEt4 and SiMe4 on the second limit of the H2+ O2 reaction has been examined in KCl-coated vessels. The inhibition characteristics observed with SiEt4 are essentially similar to those reported for C2H6, C4H8 and C4H10. The main inhibition process is the reaction of H atoms with SiEt4, but a significant contribution arises from the reaction of OH or O (or both) with the silance. The resultant triethylsilylethyl radicals appear to undergo multi-stage reactions to form C2H4, CH3CHO and presumably (SiO2)n, but at no time do they regenerate an active chain center. The experimental data are interpreted quantitatively and the velocity constant for the reaction H+SiEt4 has been evaluated as 2.18 × 109 1. mole–1 sec–1 at 520°C. The inhibition features of SiMe4 are similar to those observed with CH4 and CMe4. Thus SiMe4 does not inhibit directly, since the Me3SiCH2 radical, formed in the primary inhibition processes, reacts to regenerate an active centre and to form a “degenerate” inhibitor which has not reached a stationary concentration when the explosion boundary is reached. The consequent thermal nature of the explosion boundary has been confirmed by the effects of different inert gases on the ease of explosion.