Zc. Tan et S. Raphael, THERMODYNAMIC STUDY OF THE 3 ISOMERS OF BROMOBENZOIC ACID, Science in China. Series B, Chemistry, life sciences & earth sciences, 37(6), 1994, pp. 641-652
The enthalpies of sublimation and fusion and triple-point temperatures
of 2-bromo-, 3-bromo- and 4-bromobenzoic acids have been determined p
recisely by sublimation calorimetry, drop calorimetry and differential
thermal analysis. The measurements of sublimation enthalpy of the thr
ee acids were made at 333, 348 and 363 K, respectively, using a Tian-C
alvet microcalorimeter equipped with Knudsen effusion cells. The deriv
ed standard molar enthalpies of sublimation at 298.15 K are (95.94 +/-
0.41), (99.20 +/- 0.18), and (103.08 +/- 0.59) kJ . mol(-1) for the 2
-bromo- , 3-bromo- and 4-bromobenzoic acids, respectively. In addition
, the saturated vapour pressure of these compounds was also calculated
on the basis of the sublimation experiments. The enthalpy of fusion,
the triple-point temperatures' and the mole fraction purities of the s
amples of the investigated substances were measured using the mean tem
perature version DTA apparatus developed by the CTM of the CNRS in Mar
seille. The triple-point temperature and the molar enthalpies of fusio
n of the 2-bromo-, 3-bromo and 4-bromobenzoic acids have been found to
be (422.37 +/- 0.01) K, (24.54 +/- 0.07) kJ . mol(-1); (429.68 +/- 0.
01) K, (21.27 +/- 0.09) kJ . mol(-1) and (527.61 +/- 0.02) K, (28.70 /- 0.08) kJ . mol(-1) respectively. Using the contribution of benzene
ring, carboxylic and bromine groups, determined from literature data,
we have calculated the enthalpy of sublimation of 4-bromobenzoic acid
and compared the value with our experimental result. It is also possib
le to demonstrate and explain the existence of an intramolecular hydro
gen bond in 2-bromobenzoic acid molecule.