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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Study period:
1991-12-23
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study performed according to appropriate guideline and under GLP.
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Deviations:
no
GLP compliance:
yes
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Type:
log Pow
Partition coefficient:
0.005
Temp.:
22 °C
pH:
7
Remarks on result:
other: It is unlikley that IPA remained in the free acid form under the pH 7-buffered conditions of the test and this is likely to be reflected in the results.

There was no trend in the partition coefficient in response to varying amounts of water and the mean log Kow for the triplicates of each treatment ranged from -2.32 to -2.38. Recoveries were complete ( mean: 95.4%).

The mean Kow was 0.00468 and the mean log Kow was -2.34. These values imply a much higher relative solubility of IPA in the aqueous phase than the log Kow of 1.76 (identical to that predicted for TPA) indicated by KOWWIN QSAR. This is likely to be due to the presence of the pH 7 buffer in the test system, which probably caused IPA to be converted to salts with higher aqueous solubility than that of the free acid.

Conclusions:
The octanol/water partition coefficient of isophthalic acid was determined according to the shake-flask procedure, in a system buffered to pH 7. The mean log Kow obtained with IPA under these conditions was -2.34. Since IPA and terephthalic acid are structural analogs, 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.
Executive summary:

The octanol/water partition coefficient of isophthalic acid was determined according to the shake-flask procedure, in a system buffered to pH 7. The mean log Kow obtained under these conditions was -2.34.

This value implies a much higher relative solubility of IPA in the aqueous phase than the log Kow of 1.76 indicated by KOWWIN QSAR. This is likely to be due to the presence of the pH 7 buffer in the test system, which probably caused IPA to be converted 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 terephthalic acid under comparable conditions, following conversion of the parent monomer to its more soluble salts.

Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
11-Aug-2020
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
1. SOFTWARE
Estimation Programme Interface (EPI) Suite programme for Microsoft Windows v4.11.


2. MODEL (incl. version number)
KOWWIN v1.68


3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
SMILES: O=C(O)c(ccc(c1)C(=O)O)c1


4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
Please refer to attached justification.


5. APPLICABILITY DOMAIN
Please refer to attached justification.


6. ADEQUACY OF THE RESULT
Please refer to attached justification.
Guideline:
other: ECHA's Guidance on information requirements and chemical safety assessment Chapter R.6: QSARs and grouping of chemicals.
Version / remarks:
May 2008
Principles of method if other than guideline:
The prediction of log Kow for terephthalic acid was performed using the model KOWWIN v.1.68 (September 2008). The KOWWIN program estimates the log octanol/water partition coefficient of organic chemicals using an atom/fragment contribution method.

- Software tool(s) used including version:
Estimation Programme Interface (EPI) Suite programme for Microsoft Windows v4.11.

- Model(s) used:
KOWWIN v1.68
GLP compliance:
no
Remarks:
Not relevant (calculated endpoint).
Type of method:
other: (Q)SAR calculated endpoint
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
SMILES: O=C(O)c(ccc(c1)C(=O)O)c1
Type:
log Pow
Partition coefficient:
1.76
Temp.:
25 °C
pH:
ca. 3.9
Remarks on result:
other: Temperature and pH are assumed values, the pH of a staurated aqueous solution of the free acid is given as 3.88 at 25 ºC (see Point 4.19)
Key result
Type:
log Pow
Partition coefficient:
2
Remarks on result:
other: expermental data from QSAR database

The predicted log Kow value for terephthalic acid is 1.76.

 

Additionally, KOWWIN provides a measured log Kow value of 2.00 for terephthalic acid (attributed to Hansch, C., Leo, A. and Hoekman, D., 1995: Exploring QSAR. Hydrophobic, electronic and steric constants. ACS Professional Reference Book. Washington DC: American Chemical Society), retrieved from the database used to construct the QSAR model. 

Conclusions:
KOWWIN predicts a log Kow value of 1.76 for terephthalic acid. The experimental data contained within the database of this QSAR model corroborates with this finding with a log Kow of 2.00.
Executive summary:

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.

Description of key information

Log Kow: 2.00; KOWWIN v1.68; H.-H. Maguire (2020)

Key value for chemical safety assessment

Log Kow (Log Pow):
2
at the temperature of:
25 °C

Additional information

In a study using QSARs (Maguire, 2020) the log octanol/water partition coefficient (log Kow) of terephthalic acid was estimated using the KOWWIN v1.68 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.  The log

As study on Isophthalic acid (Hatoum & Garthwaire, 1992), a structural analogue of TPA that has an identical KOWWIN log Kow estimate of 1.76, was also available.  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.  As such, and considering the above, this value (log Kow = 2) has also been used as the key value for the chemical safety assessment as well as for any other regulatory purpose.