Gas phase enthalpies of formation of monobromophenols

Abstract

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of the liquid 2-bromophenol and crystalline 4-bromophenol, respectively, Δ f H m ∘ ( l ) = - ( 133.5 ± 1.4 ) kJ · mol - 1 and Δ f H m ∘ (cr) = - ( 152.4 ± 1.4 ) kJ · mol - 1 , were derived from the standard molar energies of combustion, in oxygen, to yield CO 2(g) and HBr · 600H 2O(l), at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of vaporization or sublimation of the compounds, Δ 1 g H m ∘ = ( 55.5 ± 1.3 ) kJ · mol - 1 and Δ cr g H m ∘ = ( 83.1 ± 1.6 ) kJ · mol - 1 . These two thermodynamic parameters yielded the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 2- and 4-bromophenol, respectively, Δ f H m ∘ ( g ) = - ( 78.0 ± 1.9 ) kJ · mol - 1 and Δ f H m ∘ ( g ) = - ( 69.3 ± 2.1 ) kJ · mol - 1 . The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set.