Exploring the reaction kinetics of methyl formate + NO 2 : implication for ignition behavior of methyl formate/NO 2 mixtures.

The reaction pathways and potential energy profiles are theoretically explored for H-abstraction, addition and addition-dissociation reactions of methyl formate (MF, HC(O)OCH 3 ) + NO 2 using the high level quantum chemical compound method CCSD(T)/cc-pV x Z( x = T, Q)//M062X/6-311+G(2df,2p). Notably, three different HNO 2 isomers ( cis -HONO, trans -HONO and HNO 2 ) are all considered in each reaction pathway. The corresponding temperature- and pressure-dependent rate constants are then computed by RRKM/ME simulations with one-dimensional hindered rotor approximation and asymmetric Eckart tunneling corrections. The calculations show that the rate constants are pressure independent. Although trans -HONO is the most stable HNO 2 isomer, the results reveal that the dominant channels are cis -HONO + HC(O)OCH 2 /C(O)OCH 3 and cis -HC(O)(ONO)OCH 3 for the H-abstraction and addition, respectively. Moreover, the lowest energy barrier for the H-abstraction channel ( cis -abs) is 11.2 kcal mol -1 lower than the addition channel ( cis -add), and thus the addition channel is less kinetically favored. The computed rate constants for the MF + NO 2 reaction are then incorporated into a kinetic model and the importance of the title reaction in predicting the ignition behavior of MF/NO 2 mixtures is demonstrated by kinetic modeling. The detailed reaction kinetics in this work will be helpful for kinetic model development of other ester-based fuels.