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. 2020 Jan 9;5(2):1277-1286.
doi: 10.1021/acsomega.9b03967. eCollection 2020 Jan 21.

Theoretical Study of the Kinetics of the Gas-Phase Reaction between Phenyl and Amino Radicals

Tien V Pham  1 , Hoang T Tue Trang  2 , Trinh Le Huyen  3 , Tue Ngoc Nguyen  1
Affiliations

Theoretical Study of the Kinetics of the Gas-Phase Reaction between Phenyl and Amino Radicals

Tien V Pham et al. ACS Omega. .

Abstract

The potential energy surface (PES) of the C6H5 + NH2 reaction has been investigated by using ab initio CCSD(T)//B3LYP/6-311++G(3df,2p) calculations. The conventional transition-state theory (TST) and the variable reaction coordinate-TST (VRC-TST) have been used to predict the rate constants for the channels possessing tight and barrierless transition states, respectively. The Rice-Ramsperger-Kassel-Marcus/Master equation (RRKM/ME) theory has been utilized to determine the pressure-dependent rate constants for these reactions. The PES shows that the reaction begins with an exothermic barrierless addition of NH2 to C6H5 producing the vital intermediate state, namely, aniline (C6H5NH2, IS1). Once IS1 is generated, it can further isomerize to various intermediate states, which can give rise to different products, including PR4 (4,5,6-trihydro-1-amino phenyl + H2), PR5 (3,4,5,6-tetrahydro phenyl + NH3), PR6 (2,3,5,6-tetrahydro-1-imidogen phenyl + H2), PR9 (3,4,5,6-tetrahydro-1-imidogen phenyl + H2), and PR10 (2,5,6-trihydro-1-amino phenyl + H2), of which the most stable product, PR5, was formed by the most favorable channel going through the two advantageous transition states T1/11 (-28.9 kcal/mol) and T11P5 (-21.5 kcal/mol). The calculated rate constants for the low-energy channel, 1.37 × 10-9 and 2.16 × 10-11 cm3 molecule-1 s-1 at T = 300, P = 1 Torr and T = 2000 K, P = 760 Torr, respectively, show that the title reaction is almost pressure- and temperature-dependent. The negative temperature-dependent rate coefficients can be expressed in the modified Arrhenius form of k 1 = 8.54 × 1013 T -7.20 exp (-7.07 kcal·mol-1/RT) and k 2 = 2.42 × 1015 T -7.61 exp (-7.75 kcal·mol-1/RT) at 1 and 10 Torr, respectively, and in the temperature range of 300-2000 K. The forward and reverse rate coefficients as well as the high-pressure equilibrium constants of the C6H5 + NH2 ↔ IS1 process were also predicted; their values revealed that its kinetics do not depend on pressure at low temperature but strongly depend on pressure at high temperature. Moreover, the predicted formation enthalpies of reactants and the enthalpy changes of some channels are in good agreement with the experimental results.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Simplified potential energy surface (PES) for the C6H5 + NH2 reaction calculated at the CCSD(T)//B3LYP/6-311++G(3df,2p) + zero-point vibrational energies (ZPVE) level of theory (energies are in kcal/mol).
Figure 2
Figure 2
Geometries of the intermediate states, complexes, reactants, and products optimized at the B3LYP/6-311++G(3df,2p) level (bond lengths are in angstrom and bond angles are in degrees).
Figure 3
Figure 3
Geometries of the main transition states optimized at the B3LYP/6-311++G(3df,2p) level (bond lengths are in angstrom and bond angles are in degrees).
Figure 4
Figure 4
Plots of predicted rate constants for the C6H5 + NH2 → C6H5NH2 process in the temperature range of 300–2000 K at various pressures of 1–76 000 Torr Ar.
Figure 5
Figure 5
Plots of predicted rate constants for the decomposition process, C6H5NH2 → C6H5 + NH2, in the temperature range of 300–2000 K at various pressures of 1–76 000 Torr Ar.
Figure 6
Figure 6
Plots of predicted rate constants for the C6H5 + NH2 → PR5 reaction in the temperature range of 300–2000 K at various pressures of 1–76 000 Torr Ar.
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