Effects of pH on the water solubility and 1-octonal partition coefficient of tetrabromobisphenol A

Kuramochi, H.; Katsuya, K.; Sakai, S. (2008) Organohalogen Compounds, 70: 000193-000196
Introduction To predict the behaviour of tetrabromobisphenol A (TBBP-A), which has two phenolic groups, in the environment, it is necessary to know its physicochemical properties (water solubility (Sw), 1-octanol/water partition coefficient (Kow), and Henry's law constant (Hw)). Although the Sw and Kow of TBBP-A at a pH of about 3, that is, the non-ionic form, were measured in our previous work1, those values are not useful for accurate prediction of its environmental distribution. The reason is that ionization of the phenolic group of TBBP-A is expected to begin in a solution pH of higher than 5.5, as shown in Fig. 1. This shows that TBBP-A may exist in both the ionic and non-ionic form in the environment and also that Sw and Kow for a mixture of the ionic and non-ionic forms are more important. In this study, the Sw and Kow of TBBP-A in different aqueous solutions prepared by varying the solution pH were measured using the shake flask method to understand the properties of the ionic and non-ionic forms of TBBP-A. The effect of pH on Sw and Kow was first revealed from the present experimental data. The pHeffect and the environmental partition of TBBP-A were discussed through comparing the properties of TBBP-A with those of 2,4,6-tribromophenol (TBP), which has a phenolic group. In addition, the pH effect on Sw was represented using an analytical expression based on mass balance equation and the dissociation constants of the phenolic groups (Ka1 and Ka2), to evaluate if these literature values2 are reasonable.