Effect of additive polyfunctional substituents on the thermal decomposition rate of R1,R2,R3-nitromethanes

Abstract

Kinetics of thermal decomposition of polyfunctionally substituted nitromethanes has been studied by manometric method as well as IR and chromato-mass spectrometry. Activation parameters of the ratelimiting stage of C-NO 2 homolysis have been determined. The rate constant and the activation energy are correlated with additive steric constants of the substituents; this enables prediction of reactivity (thermal stability) of the unstudied mononitrocompounds which decompose with the break of C-NO 2 bond.Study of thermal decomposition kinetics of various nitrocompounds with relation to their structure is of great applied and fundamental interest. Extending the previously reported results [1, 2], herein we studied the influence of substituents structure on the rate and activation energy of thermal decomposition of polyfunctional nitrocompounds I-VII (Scheme 1).Thermal decomposition of compound II in the temperature range 160-180ºC and compound VI at 160ºC described by the first-order rate equation up to conversion of 45-50%. Changing of the ratio of substance mass to reaction volume m/V from 2 × 10 -4 to 28 × 10 -4 g/cm 3 had virtually no effect on the reaction rate constant at 160°С. Similarly, the rate constant was independent of the ratio of the reaction vessel surface to its volume S/V ranging between 2.8 and 4.9 cm -1 (in the cases of decomposition of compounds II and VI). Those observations evidenced about homogeneous mechanism of decomposition of compounds II and VI, not complicated by chain processes at the reaction vessel walls. Addition of