CHARACTERISATION OF THE CHLOROBENZOATE HYDROPHOBICITY USING THE 1-OCTANOL/WATER PARTITIONING SYSTEM

摘要

Environmental fate of chlorobenzoates will depend on their hydrophobicity which in turn depends on the pH of contaminated environments. At present, only experimental hydrophobicities of non-ionised forms of chlorobenzoates are available. Therefore behaviour of the ionised forms in the 1-octanol/water partition system are reported here for 2-chlorobenzoic acid, 3-chlorobenzoic acid, 4-chlorobenzoic acid, 2,4-dichlorobenzoic acid, 2,6-dichlorobenzoic acid and 3,5-dichlorobenzoic acid. Rate constant of the phase transfer from water into the 1-octanol phase (l_1) ranged from 0.45 × 10~(-2) to 2.87 × 10~(-2) dm/min. The l_1 values varied with the initial chlorobenzoate concentrations in the 1-octanol phase and the changing chlorine substitution pattern. However, no systematic trends could be established with either variable. Rate constants of phase transfer from the 1-octanol phase into water (l_2) ranged from 0.93 × 10~(-2) to 2.73 × 10~(-2) dm/min. The l_2 values were directly proportional to the initial chlorobenzoate concentrations in the 1-octanol phase for mono-chlorobenzoates and indirectly for di-chlorobenzoates. Chlorination in the para-position increased the l_2 values. Logarithms of the 1-octanol/water partition coefficient varied between -0.783 for 2,4-dCBA and 0.368 for 3-CBA. Both l_1 and l_2 exhibit previously observed bilinear dependences on the partition coefficients. Results indicate that chlorobenzoates will be mobile in contaminated environments, most likely causing groundwater contamination. Data for 3-CBA provide some explanations of previously reported data on its toxicity towards Pseudo-monas stutzeri during PCB biodegradation.