The Standard Enthalpies of Formation of B(CH3)3, B(C2H5)3, B2(CH3)6, and B2(C2H5)6 Determined Using the Calibration Dependencies, as Well as Their Thermodynamic Properties
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In this study, the values of standard enthalpies of atomization (Δ ra H o ) and formation (Δ f H o ) of pyrophoric compounds B(CH 3 ) 3 (TMB) and B(C 2 H 5 ) 3 (TEB), as well as their dimers B 2 (CH 3 ) 6 (DTMB) and B 2 (C 2 H 5 ) 6 (DTEB), are determined using the DFT (M062X/6-311 + + G(d,p)) and the composite (CBS-QB3, G3B3) quantum chemical approaches. The coordination of the calculated and literature values of Δ f H o of these monomers within their reported uncertainties results in the values of Δ f H o (B(CH 3 ) 3 ) 3 = -111.3 ± 10.2 kJ/mol and Δ f H o (B(C 2 H 5 ) 3 ) 3 = -145.4 ± 7.8 kJ/mol. The best consistency with the literature values is observed in the case of G3B3 calculations. Thus, in these cases, their differences for both monomers are equal to 15 kJ/mol. The values of Δ f H o (B 2 (CH 3 ) 6 ) = -151.2 ± 15 kJ/mol and Δ f H o (B 2 (C 2 H 5 ) 6 ) = -189.8 ± 18 kJ/mol are determined using the thermochemistry of homodesmotic reactions and are reported for the first time. The temperature dependencies of Δ r1 G o and Δ r2 G o , determined for the reactions of dissociation of DTMB and DTEB, respectively, demonstrate their nearly complete dissociation even at T < 300 K . Therefore, it can be concluded that the contribution of dimers to the heat of combustion of TMB and TEB is negligible.
