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. 2022 May 31;14(11):2254.
doi: 10.3390/polym14112254.

A Theoretical Study on the Phosgenation of 2,4-Toluenediamine (2,4-TDA)

Ravikumar Thangaraj  1   2 , Tamás Horváth  1 , R Zsanett Boros  3 , Béla Viskolcz  1   2 , Milán Szőri  1
Affiliations

A Theoretical Study on the Phosgenation of 2,4-Toluenediamine (2,4-TDA)

Ravikumar Thangaraj et al. Polymers (Basel). .

Abstract

Industrially relevant phosgenation mechanisms of 2,4-toluenediamine (2,4-TDA) were investigated using G3MP2B3 model chemistry. Six reaction pathways had been explored, which resulted in the formation of toluene diisocyanate (2,4-TDI) including different scenarios of the 'phosgenations first' and 'consecutive phosgenations' mechanisms in both gas and condensed phases. Two possible 'phosgenations first' mechanisms show superior to the others in terms of energy, regardless of which phases are considered. Due to the o-dichlorobenzene (ODCB) solvation, the reaction barriers are dramatically reduced compared to the gas-phase reaction mechanism and the solvent effect can be described by linear relationship. Standard enthalpy of formation value was also recommended for 2,4-TDA (59.3 kJ/mol) and 2,4-TDI (-94.1 kJ/mol), as well as for the gas-phase intermediates (IM).

Keywords: G3MP2B3; carbamic chloride; phosgenation; toluene diisocyanate; toluenediamine.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Reaction scheme for the phosgenation of TDA.
Figure 2
Figure 2
Studied reaction mechanism of the 2,4-TDA phosgenation.
Figure 3
Figure 3
G3MP2B3 energy profile (zero-point corrected) for the phosgenation of 2,4-TDA in the gas phase.
Figure 4
Figure 4
G3MP2B3 energy profile (zero-point corrected) for the phosgenation of 2,4-TDA in ortho-dichlorobenzene (ODCB).
Figure 5
Figure 5
Transition-state structures for the phosgenation of 2,4-TDA in gas phase.
Figure 6
Figure 6
Transition state structures for the phosgenation of 2,4-TDA in gas phase.
Figure 7
Figure 7
Comparison of intermediate and transition-state energies between gas phase and ODCB obtained at G3MP2B3. Fitted plots are marked in dotted lines.
Figure 8
Figure 8
Comparison of intermediate and transition state energies in gas phase obtained by B3LYP/6-31G(d) level of theory and G3MP2B3. Fitted plots are marked in dotted lines.
Figure 9
Figure 9
Comparison of intermediate and transition-state energies in ODCB obtained by B3LYP/6-31G(d) level of theory and G3MP2B3. Fitted plots are marked in dotted lines.
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