Direct bond fission and hydrogen migration as the trigger forces in the pyrolysis of n-pentyl nitrate at low pressure

Nitrates are a potential class of substances as cetane improvers of diesel fuel and are critical raw materials for some military explosives. Thus, an in-depth investigation of the thermal decomposition mechanism of nitrates is important for further improving their effects. Herein, a combination of experimental and computational studies was performed for the pyrolysis of n-pentyl nitrate in the temperature range of 400‒900 K. Using synchrotron radiation vacuum ultraviolet photoionization, some intermediates and products, such as ethylene, formaldehyde, propene, ethenol, pentanal, NO2, and HONO, were identified according to their photoionization efficiency curves. Quantum chemical calculations at the CBS-QB3 level were conducted to elucidate the overall reaction mechanism of n-pentyl nitrate pyrolysis. Along the direct bond fission of n-pentyl nitrate, primary products, C5H11O• radical and NO2, and butyl radical and CH2ONO2, can further dissociate into many products, in which formaldehyde is the most dominant. In addition, two hydrogen-atom migration channels followed by decomposition are verified for the decomposition of n-pentyl nitrate according to the observation of trans-HONO, pentanal, and 1-pentene. These evidences highlight that both bond fission and hydrogen migration play comparable roles as potential driving forces in the pyrolysis of n-pentyl nitrate at low pressure. This thermal decomposition mechanism of n-pentyl nitrate provides some useful clues for developing combustion models of long chain nitrates in future.