Experimental and computational thermochemistry of 1,4-benzodioxan and its 2-R derivatives

The standard molar energies of combustion, at T = 298.15 K, of crystalline 1,4-benzodioxan-2-carboxylic acid and 1,4-benzodioxan-2-hydroxymethyl were measured by static bomb calorimetry in an oxygen atmosphere. The standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in the gas phase at T = 298.15 K: 1,4-benzodioxan-2-carboxylic acid -(547.7 ± 3.0) kJ · mol^-1 and 1,4-benzodioxan-2-hydroxymethyl -(374.2 ± 2.3) kJ · mol^-1. In addition, density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, 6-311G^** and cc-pVTZ, have been performed for the compounds studied. We have also tested two more accurate computational procedures involving multiple levels of electron structure theory in order to get reliable estimates of the thermochemical parameters of the compounds studied. The agreement between experiment and theory gives confidence to estimate the enthalpies of formation of other 2-R derivatives of 1,4-benzodioxan (R = -CH₂COOH, -OH, -COCH₃, -CHO, -CH₃, -CN, and -NO₂).