2-[[6-[(5-chloro-2,6-difluoro-4-pyrimidinyl)amino]-1-hydroxy-3-sulpho-2-naphthyl]azo]naphthalene-1,5-disulphonic acid, sodium salt

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

March 16, 2018 - March 23, 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD 105

Deviations:

not applicable

Principles of method if other than guideline:

OECD 105 flask method

GLP compliance:

no

Type of method:

flask method

Partition coefficient type:

octanol-water

Analytical method:

high-performance liquid chromatography

Key result

Type:

log Pow

Partition coefficient:

-2.9

Temp.:

20 °C

Remarks on result:

other: pH not determined

Preliminary visual estimation of the n-octanol solubility

Defined amounts of the test item were stirred with increasing volumes of n-octanol at room temperature and visually checked for any undissolved particles.

Table3: Results of the preliminary visual estimation of the n-octanol solubility

Amount of test item / mg	Added volume of n-octanol / mL	Total volume of n-octanol / mL	Stirring time / h	Appearance of mixture
7.3	10	10	~2	not dissolved
	90	100	~65	not dissolved (slightly cloudy)

According to this preliminary test the solubility of the test item in n-octanol was below 73 mg/L (without correction for the purity).

Calculation of the partition coefficient log P_OW from the preliminary test

The partition coefficient P_{O W}may be estimated from the saturation concentrations in n-octanol and water. The estimated partition coefficient was calculated with the water solubility data determined in project PS20180017-4 (c_S = 1.85 g/L) and the data obtained above. It was calculated to be: log P_OW < -1.4.

 Also the program KOWWIN (part of EPI Suite) was used for calculating the log P_OW of the test item. The calculated value was -1.7.

Due to the calculations the partition coefficient was estimated based on the ratio of the solubilities in water and octanol. The octanol solubility was determined using the flask method. The shake flask method and the HPLC method were not applicable due to the low log P_OW.

Determination of the solubility in n-octanol: Flask method

The individual saturation solubility of the test item in n-octanol was performed within this study. After that, the partition coefficient was estimated based on the ratio of the test item solubility in n-octanol and water. The flask method was performed as described above. The data for the evaluation are given in Table4.The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in Table4.

Table4: n-Octanol solubility experiments of the test item

Experiment	24 h experiment	48 h experiment	72 h experiment	blank experiment (72 h)
Amount of test item / mg	21.6	21.8	19.8	--
Amount of octanol / mL	50	50	50	50
Stirring time at 30 °C / h	24	48	72	72
Dilution factor	40	40	40	40
Measured concentration / mg/L	0.032 / 0.032	0.050 / 0.051	0.056 / 0.055	≤ 0.013* /≤ 0.013*
Mean concentration / mg/L	0.032	0.050	0.055	≤ 0.013*
n-Octanol solubility / mg/L	1.29	2.01	2.22	≤ 0.51*

* Quantification limit for measurement (lowest calibration standard)

As a conservative approach the highest measured value was taken into account for the n-Octanol solubility. The n-octanol solubility of the test item at 20 °C was determined to be 2.22mg/L.

Calculation of the partition coefficient log P_OW from the individual solubilities

In the project PS20180017-4 the water solubility of the test item at 20 °C was determined to be1.85 g/L (± 0.06 g/L). Within this project the n-octanol solubility of the test item at 20 °C was determined to be2.22 mg/L.

The partition coefficient P_OW of the test item was determined to be: 

log P_OW = -2.9

Executive summary:

The partition coefficient (n-octanol/water) of the test item Reactive Orange 64 was estimated based on the ratio of the individual solubilities of the test item in water and n-octanol. The solubilities were determined according to the flask method.The shake flask method and the HPLC method were not applicable due to the low log P_OW.

It was found to be:

 

log P_OW =  -2.9

 

Description of key information

The partition coefficient (n-octanol/water) of the test item Reactive Orange 64 was estimated based on the ratio of the individual solubilities of the test item in water and n-octanol. The solubilities were determined according to the flask method.The shake flask method and the HPLC method were not applicable due to the low log P_OW.

It was found to be:

 

log P_OW =  -2.9

 

Key value for chemical safety assessment

Log Kow (Log Pow):

-2.9

at the temperature of:

20 °C