ABSTRACT

The Knudsen mass-loss effusion technique was used to measure the vapor pressures at different temperatures of the following dihydroxybenzoic acids: 2,3-dihydroxybenzoic acid, between (345.22 and 363.18) K; 2,4-dihydroxybenzoic acid, between (376.22 and 392.11) K; 2,5-dihydroxybenzoic acid, between (372.14 and 388.92) K; 2,6-dihydroxybenzoic acid, between (347.14 and 365.17) K; 3,4-dihydroxybenzoic acid, between (387.12 and 403.26) K; and 3,5-dihydroxybenzoic acid, between (345.22 and 363.18) K. From the temperature dependences of the vapor pressure of the crystalline compounds, the standard (p0 = 105 Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. For each of the six isomers the standard (p0 = 0.1 MPa) molar enthalpy of formation in the crystalline phase was derived from the experimental standard molar energy of combustion, in oxygen, measured by static-bomb combustion calorimetry at T = 298.15 K. The combination of the standard molar enthalpy of formation in the crystalline phase with the standard enthalpy of sublimation yields the standard molar enthalpy of formation in the gaseous phase of the studied compounds.

Compounds

#	Formula	Name
1	CO2	carbon dioxide
2	H2O	water
3	O2	oxygen
4	C7H6O4	2,3-dihydroxybenzoic acid
5	C7H6O4	2,5-dihydroxybenzoic acid
6	C7H6O4	2,6-dihydroxybenzoic acid
7	C7H6O4	3,4-dihydroxybenzoic acid
8	C7H6O4	3,5-dihydroxybenzoic acid
9	C7H6O4	2,4-dihydroxybenzoic acid

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Phase	Method	#Points
POMD	4	Molar enthalpy of transition or fusion, kJ/mol ; Crystal		Crystal Liquid Air at 1 atmosphere	DSC	1
POMD	4	Normal melting temperature, K ; Crystal		Crystal Liquid Air at 1 atmosphere	DTA	1
POMD	4	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	30
POMD	5	Molar enthalpy of transition or fusion, kJ/mol ; Crystal		Crystal Liquid Air at 1 atmosphere	DSC	1
POMD	5	Normal melting temperature, K ; Crystal		Crystal Liquid Air at 1 atmosphere	DTA	1
POMD	5	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	22
POMD	6	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	26
POMD	7	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	21
POMD	8	Molar enthalpy of transition or fusion, kJ/mol ; Crystal		Crystal Liquid Air at 1 atmosphere	DSC	1
POMD	8	Normal melting temperature, K ; Crystal		Crystal Liquid Air at 1 atmosphere	DTA	1
POMD	8	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	21
POMD	9	Vapor or sublimation pressure, kPa ; Crystal	Temperature, K; Crystal	Crystal Gas	Calculated from knudsen effusion weight loss	30
RXND	4 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1
RXND	9 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1
RXND	5 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1
RXND	6 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1
RXND	7 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1
RXND	8 1 2 3	Specific internal energy of reaction at constant volume, J/g			Static bomb calorimetry	1

Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

Vapor Pressures and Enthalpies of Combustion of the Dihydroxybenzoic Acid Isomers

Monte, M. J. S.[Manuel J. S.], Goncalves, M. V.[Mariana V.], Ribeiro da Silva, M. D. M. C.[Maria D. M. C.]

ABSTRACT