Analytical and thermodynamic studies on some halogenated benzenoid compounds

Abstract

The bromination of 2-fluorophenol, 3-fluorophenol, 4-fluorophenol, 2-fluoroaniline, 3-fluoroaniline and 4-fluoroaniline was carried out inaqueous medium using an acidified mixture of potassium bromate andpotassium bromide as a source of bromine. The chlorination of thesecompounds was carried out using sulphuryl chloride as a chlorinatingagent in chloroform or diethyl ether. Anhydrous aluminium chloridewas used as a catalyst in the chlorination of the fluoroanilines.All the reaction products obtained were analyzed by fluorine-19 nuclear magnetic resonance spectroscopy (F n.m.r. spectroscopy), gas liquid chromatography (GLC) and high-performance liquid chromatography (HPLC).The identification and the structure of these products were established by comparison with the authentic compounds. For the thermodynamic studies:-(a) The enthalpies of solution (at saturation) of 2,4,6-tribromophenol (Br3C6H2OH), 4-bromoani1ine (BrC6H4NH2), 2,6-dibromoaniline (Br2C6H3NH2) and 2,4,6-tribromoaniline (Br3C6H2NH2) in toluene and n-propanol were determined from solubility measurements. ASO1H (Br3C6H2OH) in Toluene = 33.90 kJ mol -1Aso/ (Br3C6H2OH) in n-Propanol = 24.01 kJ mol-1AS0/ (BrC6H4NH2) in Toluene = 65.94 kJ mol -1Aso1H° (BrC6H4NH2) in n-Propanol = 61.95 kJ mol -1A SO1 H0 (Br2C6H3NH2) in Toluene = 46.65 kJ mol -1 sol ' 2 6 3 2'2AgQ-jH"0 (Br2C6H3NH2) in n-Propanol = 44.93 kj mol -1Aso1H° (Br3C6H2NH2) in Toluene = 28.09 kj mol -1Aso1H° (Br3C6H2NH2) in n-Propanol = 20.22 kJ mol -1Entropies of solution, enthalpies of transfer, free energiesof transfer and the entropies of transfer between the two solvents were also calculated.(b) Enthalpies of reaction of the bromination of 2-chloroaniline, 4-bromo-2-chloroaniline and 4-chloroaniline in aqueous medium (perchloric acid/sodium bromide) with aqueous bromine (sodium bromide/sodium bromate) were found using reaction calorimetry.arH0

(2-chloroaniline. + bromine. aq) = -207.84 - 0.63 kj mol-1r aqArH° (4-bromo-2-chloroaniline,c + bromine,aq ) = -91.29 - 0.96 kJ mol -1 ArH° (4-chloroaniline,c + bromine, aq) = -189.61 - 0.90 kJ mol-1.(c) A titration calorimetric technique was used to determine the enthalpies of bromination of 2-nitroaniline and 4-nitroanle in aqueous medium (perchloric acid/sodium bromide) with aqueous bromine (sodium bromide/sodium bromate).