A Computational Study on the Redox Reactions of Ammonia and Methylamine with Nitrogen Tetroxide

Abstract

The redox reactions of NH 3 and CH 3 NH 2 with N 2 O 4 (NTO) have been studied by ab initio molecular orbital (MO) calculations at the UCCSD(T)∥UB3LYP/6-311+G(3df,2p) level of theory. These reactions are related to the well-known NTOhydrazine(s) propellant systems. On the basis of the predicted potential energy surfaces, the mechanisms for these reactions were found to be similar to the hydrolysis of NTO and the hypergolic initiation reaction of the NTO−N 2 H 4 mixture, primarily controlled by the conversion of NTO to ONONO 2 via very loose transition states (with NH 3 and CH 3 NH 2 as spectators in the collision complexes) followed by the rapid attack of ONONO 2 at the spectating molecules producing HNO 3 and RNO (R = NH 2 and CH 3 NH). The predicted mechanism for the NH 3 reaction compares closely with its isoelectronic process NTO + H 2 O; similarly, the mechanism for the NTO + CH 3 NH 2 reaction also compares closely with its isoelectronic NTO + NH 2 NH 2 reaction. The kinetics for the formation of the final products, HNO 3 + RNO (R = NH 2 , OH, CH 3 NH, and N 2 H 3 ), were found to be weakly pressure-dependent at low temperatures and affected by the strengths of H−NH 2 and H−OH but not in the RNH 2 case. We have also compared the predicted rate constant for the oxidation of NH 3 by N 2 O 4 with that for the analogous NH 3 + N 2 O 5 recently reported by Sarkar and Bandyopadhyay [J. Phys. Chem. A. 2020, 124, 3564−3572] under troposphere conditions. The rate of the latter reaction was estimated to be 2 orders of magnitude slower than that of the N 2 O 4 reaction under troposphere conditions.

A possible atmospheric source of HNO3: the ammonolysis reaction of t-N2O4 in the presence of water monomer, water dimer, and sulfuric acid

“…Our results shown in Fig. 1 were found to be very mechanistically and energetically similar to the work reported by Lin et al 13 All the relative energy values qualitatively matched (see Table S2 †). As seen in The calculated rate constants for the ammonolysis reaction of t-N 2 O 4 are listed in Table 1.…”

“…The ammonolysis reaction of t-N 2 O 4 has been extensively investigated from the theoretical viewpoint. 13 Here, this reaction has been reinvestigated at the CCSD(T)/aug-cc-pVTZ// B3LYP-D3/6-311++G(3df,2pd) level to check the catalytic effect of X. Our results shown in Fig.…”

“…In the atmosphere, the hydrolysis of t-N 2 O 4 to produce HONO is the most major loss route of t-N 2 O 4 . 10,11 As a complement to the loss of t-N 2 O 4 , the ammonolysis reaction of t-N 2 O 4 can form HNO 3 , 13 which could be competitive with the main source of HNO 3 , the gas-phase reaction of NO 2 with the hydroxyl (OH) radical 8,14 during the day and the hydrolysis reaction of N 2 O 5 [15][16][17] at night, in polluted areas of NH 3 . The ammonolysis of t-N 2 O 4 (shown in eqn ( 1) and ( 2)) investigated by Lin et al 13 reveals that the energy barrier of the t-N 2 O 4 + NH 3 reaction was determined to be 5.3 kcal mol −1 and the corresponding rate constant at low temperature was not pressure-dependent.…”

“…10,11 As a complement to the loss of t-N 2 O 4 , the ammonolysis reaction of t-N 2 O 4 can form HNO 3 , 13 which could be competitive with the main source of HNO 3 , the gas-phase reaction of NO 2 with the hydroxyl (OH) radical 8,14 during the day and the hydrolysis reaction of N 2 O 5 [15][16][17] at night, in polluted areas of NH 3 . The ammonolysis of t-N 2 O 4 (shown in eqn ( 1) and ( 2)) investigated by Lin et al 13 reveals that the energy barrier of the t-N 2 O 4 + NH 3 reaction was determined to be 5.3 kcal mol −1 and the corresponding rate constant at low temperature was not pressure-dependent. As far as we know, the effect of neutral and acidic gases on the ammonolysis of t-N 2 O 4 , which plays a signicant catalytic role in hydrogen abstraction reactions, 9,15,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] has not been explored.…”

Ab Initio Chemical Kinetics for Oxidation of CH3OH by N2O4: Elucidation of the Mechanism for Major Product Formation and Its Relevancy to Tropospheric Chemistry

“…In Figure 1, the reaction occurs through the N 2 O 4 :CH 3 OH (LM1) complex with a binding energy of 6.4 kcal/mol, which is slightly more stable than that of the N 2 O 4 /H 2 O complex, 5.0 kcal/mol, 13 but is very close to its isoelectronic N 2 O 4 / NH 2 NH 2 complex, 6.7 kcal/mol 11 , and N 2 O 4 /CH 3 NH 2 complex, 6.8 kcal/mol. 3 In the present reaction, the LM1 complex can undergo further reaction by lengthening N 2 O 4 's N−N bond to 3.343 Å concurrently rotating one of its NO 2 groups at TS1 forming the ONONO 2 /CH 3 OH (LM2) complex, which lies 2.9 kcal/mol above the reactants or 9.3 ]. Mulliken charge analysis shows that the NO and NO 3 group charges are +0.367 and −0.507e, respectively (Figure 3).…”