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Physical & Chemical properties

Partition coefficient

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Description of key information

The log octanol/water partition coefficient (log Kow) of terephthalic acid was estimated using the KOWWIN v1.67 QSAR model available from the US EPA. The estimated log Kow of terephthalic acid is 1.76.  Additionally, KOWWIN provides a measured log Kow value of 2.00 for terephthalic acid, retrieved from the data base of experimental results used to construct the QSAR model.  
Isophthalic acid is a structural analog of TPA that has an identical KOWWIN log Kow estimate of 1.76. The octanol/water partition coefficient of isophthalic acid has been determined according to the shake-flask procedure, in a system buffered to pH 7. The mean log Kow obtained for IPA under these conditions was -2.34. This value implies a much higher relative solubility of IPA in the aqueous phase than the log Kow indicated by KOWWIN QSAR. This is likely to have been caused by the presence of the buffer used to maintain the test system at pH 7: IPA would have been converted under these conditions to salts with higher aqueous solubility than that of the free acid. Similar behaviour, with a log Kow similarly lower than that of the free acid, may be expected for TPA under comparable conditions, following conversion of the parent monomer to its more soluble salts.
Wherever other models of the US EPA's EPISUITE QSAR programs have been used to generate estimates of physico-chemical or environmental fate and behaviour characteristics that require input of log Kow, these secondary models selected the database (measured) log Kow of 2.00 as the default value for terephthalic acid.

Key value for chemical safety assessment

Log Kow (Log Pow):
at the temperature of:
25 °C

Additional information