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Physical & Chemical properties

Partition coefficient

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Description of key information

The weighted n-octanol/water partition coefficients (log Kow) of  C16-18 DMAPA amidoamine at pH 4, 7 and 9 are 2.00, 2.01 and 2.57, respectively (EU method A.8; estimated by calculation based on the solubility of the test substance in n-Octanol and water; read-across from Stearic acid 3-(dimethylaminopropyl)amide).

Key value for chemical safety assessment

Log Kow (Log Pow):
2.01
at the temperature of:
20 °C

Additional information

C16-18 DMAPA amidoamine is a UVCB substance with variable chain length of the fatty acid moiety. Thus, the partition coefficient (log P) can only be estimated for distinct structures. An estimation for the mixture cannot be given. For the estimation the ACD PhysChem software ACD/Labs Release 12.00, Product version 12.01 (Build 38056 09 Feb 2010) was used.

The calculated log P for the main constituents of C16-18 DMAPA amidoamine are summarised in the table below.

 

Log Pcalculated

Hexadecanoic acid

6.81 ± 0.19

Octadecanoic acid

7.83 ± 0.19

N-(3-(dimethylamino)propyl)-hexadecanamide

6.6 ± 0.3

N-(3-(dimethylamino)propyl)-octadecanamide

7.62 ± 0.32

 

However, this calculation does not take into account, that the main constituents of the substance (N-(3-(dimethylamino)propyl)-hexadecanamide and N-(3-(dimethylamino)propyl)-octadecanamide) are mostly protonated at environmentally relevant pH.

 

Weighted log Kow values also considering protonation are available for one of the main constituents of C16-18 DMAPA amidoamine:

According to EU method A.8, 31 May 2008 the n-octanol/water partition coefficient (log Kow) of Stearic acid 3-(dimethylaminopropyl)amide was estimated by calculation based on the solubility of the test substance in n-Octanol and water.

 

solubility [g/L]

log Kow

n-octanol

water

free amine

151

0.01

4.18

protonated amine

22

0.22

2.04

 

Weighted log Kow were calculated taking into account the presence of the free and protonated amine at different pH values.

free amine [%]

protonated amine [%]

weighted log Kow

pH 4

0

100

2.00

pH 7

0.4

99.6

2.01

pH 9

26.2

73.8

2.57

The weighted log Kow at pH 4, 7 and 9 are 2.00, 2.01 and 2.57, respectively.

 

For chemical safety assessment these values are considered to be more realistic than the QSAR-based log Kow for C16-18 DMAPA amidoamine.

 

The following results from a supporting substance (C22-alkyltrimethylammonium chloride) are enclosed for justification of read-across:

Since the substance is a quaternary alkyltrimethylammonium chloride, it exhibits surface active properties. In such a case, the experimental determination of the partition coefficient Kow is afflicted with errors. Therefore, the Kow will be presented as the comparison between the measured solubilities in both solvents water and n-octanol respectively. In case of water-solubility the value of the critical micelle concentration (cmc) was used as suggested.

n-Octanol solubility: 19.7 g/L

water solubility: 10 mg/L

log Kow = 3.29