Theoretical kinetic investigation of thermal decomposition of nitropropane.

The thermal decomposition of nitropropane (CHCHCHNO) has been investigated at the CBS-QB3 level of theory. The pyrolysis of CHCHCHNO mainly includes the simple bond ruptures mechanism, hydrogen abstraction processes, isomerization and secondary reactions. As a result, for the simple bond ruptures mechanism, the formation of $${\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}$$ products is dominant with the energy barrier of 49.77 kcal mol. The process of H atom on the β-CH abstracted by one O atom of NO moiety in CHCHCHNO(CHCHCHNO → CHCH=CH + HONO) needs to overcome lower energy barrier than that of the rate-determining step (one of H atom on the α-CH and γ-CH abstracted of reaction) of the other hydrogen abstraction reactions. Therefore, we predict that the corresponding alkenes and HONO are the main products in the hydrogen abstraction reaction of nitroparaffin. Besides, the channel of the CHCHCHO + HNO formations (CHCHC(α)HNO → CHCHC(α)HONO → CHCHCHO + HNO), occurring through the H atom of C(α) abstracted by the N atom of NO moiety after the isomerization reaction from CHCHCHNO to CHCHCHONO, is favorable in the isomerization secondary reactions. Rate constants and branching ratios are estimated by means of the conventional transition state theory with zero curvature tunneling over the temperature range of 400-1500 K. The calculation shows that the overall rate constant in the temperature of 400-1500 K is mainly dependent on the competitive channels of formations of CHCH=CH + HONO and $${\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}$$ The three-parameter expression for the total rate constant is fitted to be k = 1.74 × 10 T exp(17038.7/ T) (s) between 400 and 1500 K. [ABSTRACT FROM AUTHOR]