Quantum Chemical Study of the Thermochemical Properties of Organophosphorous Compounds

Abstract

Organophosphorous compounds are involved in many toxic compounds such as fungicides, pesticides, or chemical warfare nerve agents. The understanding of the decomposition chemistry of these compounds in the environment is largely limited by the scarcity of thermochemical data. Because of the high toxicity of many of these molecules, experimental determination of their thermochemical properties is very difficult. In this work, standard gas-phase thermodynamic data, i.e., enthalpies of formation (ΔfH298°), standard entropies (S298°), and heat capacities (Cp°(T)), were determined using quantum chemical calculations and more specifically the CBS-QB3 composite method, which was found to be the best compromise between precision and calculation time among high accuracy composite methods. A large number of molecules was theoretically investigated, involving trivalent and pentavalent phosphorus atoms, and C, H, O, N, S, and F atoms. These data were used to propose 83 original groups, used in the semiempirical group contribution method proposed by Benson. Thanks to these latter group values, thermochemical properties of several nerve agents, common pesticides and herbicides have been evaluated. Bond dissociations energies (BDE), useful for the analysis the thermal stability of the compounds, were also determined in several molecules of interest.

Benson group additivity values of phosphines and phosphine oxides: Fast and accurate computational thermochemistry of organophosphorus species

“…Out of the wealth of data on phosphorus‐based Benson groups reported by Glaude et al only two groups, C‐(H) 2 (C)(PO) and P(O)‐C 3 , are common with the current study. The CBS‐QB3 enthalpy, entropy, and heat capacity contributions reported by Glaude et al are, in respective order, −17 kJ mol −1 , 37 J K −1 mol −1 and 21 J K −1 mol −1 for C‐(H) 2 (C)(PO), and −289 kJ mol −1 , −8 J K −1 mol −1 and 48 J K −1 mol −1 for P(O)‐C 3 , in excellent agreement with the data in Table .…”

“…For larger molecules, this is nowadays considered the best available alternative to obtain thermochemical properties with near chemical accuracy . The approach has in the past been used in the context of phosphorus compounds by Glaude et al and Dorofeeva and Moiseeva, who have reported values for roughly a 100 phosphorus‐based Benson groups.…”

Kinetic modeling of the thermal destruction of lewisite

“…Arsenic contains a large number of electrons (Z = 33) and the calculation methods used for the elements of the first rows for such thermochemical investigations in combustion (Khalfa et al, 2015;Lizardo-Huerta et al, 2018) are unsuitable. It is necessary to consider the relativistic effects due to the core electrons, which are generally described by pseudopotentials in the orbital bases.…”

Combustion and Pyrolysis Kinetics of Chloropicrin

“…This methodology has proven its precision with molecules containing hetero-atoms 15,16,24 . In addition, the low frequency vibration modes, corresponding to internal rotations, were treated as hindered rotors instead of harmonic oscillators, using THERMROT 25 .…”