3,5,5-trimethylhexanoic acid

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Study initiation date: 29 July 2009 Study completion date: 19 November 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)

Version / remarks:

adopted on 13 April 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.8 (Partition Coefficient)

Version / remarks:

Directive 92/69/EEC, Official Journal L 383 A 1992

Deviations:

no

GLP compliance:

yes

Type of method:

HPLC method

Partition coefficient type:

octanol-water

Analytical method:

high-performance liquid chromatography

Key result

Type:

log Pow

Partition coefficient:

3.2

Temp.:

25 °C

pH:

3

Type:

Pow

Partition coefficient:

1 580

Temp.:

25 °C

pH:

3

Details on results:

See IUCLID section "Any other information on results incl. tables"

Results of HPLC measurements for reference substances and test item:

Sample no.^1)	t_R1 [min]	t_R2 [min]	t_R [min]	k´	log k´(x)	log Pow (y)
0	1.16	1.15	1.16	--	--	--
1	1.46	1.46	1.46	0.259	-0.587	1.8^2)
2	1.60	1.60	1.60	0.379	-0.421	1.9^2)
3	1.76	1.76	1.76	0.517	-0.287	2.1^2)
4	1.85	1.85	1.85	0.595	-0.225	2.4^2)
5	1.95	1.95	1.95	0.681	-0.167	2.7^2)
6	11.17	11.19	11.18	8.638	0.936	4.2^2)
Test item	3.45			1.974	0.295	3.20^3)
Test item		3.45		1.974	0.295	3.20^3)
Mean value						3.2

1) For the names of the reference compounds see IUCLID section "Any other information on materials and methods incl. tables".

2) Results from the OECD guideline for the testing of chemicals No. 117: "Partition Coefficient (n-octanol/water), HPLC method" (13th April 2004).

3) Interpolated from linearized function log Pow = f(log k' ) of the calibration data.

The replicate log Pow data for the test item fall within a range of +/- 0.1 log units, thus the test is satisfactory.

Regression equation derived from plot of data for reference compounds [abscissa: log k´; ordinate: log Pow]:

y=1.6187*x+2.7193

The linear regression of the log k' of the calibration substances against their log Pow has a correlation coefficient of r = 0.9860.

Conclusions:

Partition coefficient n-octanol / water (Pow; OECD 117): Pow = 1580 / log Pow = 3.2 (25°C; pH 3.0)

Executive summary:

The partition coefficient n-octanol / water (Pow) of the test item was determined compliant with GLP according to OECD guideline no. 117 [adopted on 13 April 2004] and EU test method A.8 [Directive 92/69/EEC, Official Journal L 383 A 1992] with the HPLC method.

The submission substance is a carboxylic acid with a pKa of 4.8. Correspondingly, carboxylic acids were chosen as reference compounds and a buffered pH of 3.0 was selected for the HPLC to ascertain that organic acids are in their non-dissociated state (according to Henderson-Hasselbach equation, based on the pKa of 4.8 determined for the submission substance, at pH 3.0 the neutral fraction will amount to 98.44%).

The valid and reliable study produced the following result for the n-octanol-water partition coefficient for the submission substance (neutral state):

Partition coefficient n-octanol / water (Pow): Pow = 1580 / log Pow = 3.2 (20°C; pH 3.0)

Description of key information

log Pow (OECD 117): 3.2 at 25°C

Key value for chemical safety assessment

Log Kow (Log Pow):

3.2

at the temperature of:

25 °C

Additional information

The partition coefficient n-octanol / water (Pow) of the test item was determined compliant with GLP according to OECD guideline no. 117 [adopted on 13 April 2004] and EU test method A.8 [Directive 92/69/EEC, Official Journal L 383 A 1992] with the HPLC method.

The submission substance is a carboxylic acid with a pKa of 4.8. Correspondingly, carboxylic acids were chosen as reference compounds and a buffered pH of 3.0 was selected for the HPLC to ascertain that organic acids are in their non-dissociated state (according to Henderson-Hasselbach equation, based on the pKa of 4.8 determined for the submission substance, at pH 3.0 the neutral fraction will amount to 98.44%).

The valid and reliable study produced the following result for the n-octanol-water partition coefficient for the submission substance (neutral state):

Partition coefficient n-octanol / water (Pow): Pow = 1580 / log Pow = 3.2 (25 °C; pH 3.0)

Supporting data from an accepted QSAR model applicable for the substance type are available. However, no detailed description of QSAR model (QMRF) and no detailed justification of applicability and relevance of the model (QPRF) are given (reliability not assignable, RL4).

According to this study, the log Pow of the submission substance 3,5,5-trimethylhexanoic acid was estimated to be 3.34 using the program KOWWIN (v1.67; US EPA). This closely matches the experimentally determined value and thus gives additional confidence.