THERMODYNAMIC STUDY OF THE 3 ISOMERS OF IODOBENZOIC ACID

2-Iodo-, 3-iodo- and 4-iodobenzoic acids have been investigated by sub limation calorimetry, drop calorimetry and thermal analysis. The measu rements of sublimation enthalpy of these three compounds were carried out at 363 K using a Tian-Calvet microcalorimeter equipped with a Knud sen effusion cell. The saturated vapour pressures of these acids at th e sublimation temperature 363 K were also calculated. The derived valu es of standard molar enthalpies of sublimation at 298.15 K are 92.59 /- 0.20, 96.38 +/- 0.29, and 99.32 +/- 0.36 kJ mol-1 for 2-iodo-, 3-io do- and 4-iodobenzoic acid, respectively. The enthalpies of fusion, th e temperatures of triple point and the mole fraction purities of these three compounds were determined using the mean temperature version DT A apparatus developed by the Centre de Thermodynamique et de Microcalo rimetrie of the CNRS in Marseille. The triple point temperatures and t he molar enthalpies of fusion for the 2-iodo-, 3-iodo- and 4-iodobenzo ic acid have been found to be 435.02 +/- 0.02 K, 21.38 +/- 0.19 kJ mol -1; 460.30 +/- 0.01 K, 28.70 +/- 0.21 kJ mol-1 and 543.70 +/- 0.03 K, 35.24 +/- 0.13 kJ mol-1, respectively. Using the contributions of benz oic acid and iodine group, determined from literature data, we have ca lculated the enthalpy of sublimation of 4-iodobenzoic acid and compare d the calculated result with the experimental value. It has also been possible to demonstrate and explain the existence of an intramolecular hydrogen bond in 2-iodobenzoic acid molecule.