Amines, C16-18-alkyl

Partition coefficient

Description of key information

 Weight of evidence is based on various studies performed according to relevant guidelines: due to the substance properties (strong bases, fully ionized at environmental pH; surface active compounds), according to EU method A.9, Pow was determined as the ratio of solubility in n-octanol (free amine) and water (hydrochloride of n-alkylamine). The highest resulting value from a homologous series of n-alkylamines is used for the category (worst case).

Key value for chemical safety assessment

Log Kow (Log Pow):

4.33

at the temperature of:

25 °C

Additional information

Sorption characteristics and the potential to form aggregates (surface active compounds) prevent a reliable measurement of the partition coefficient for primary fatty amines (PFA). PFA are difficult substances with regard to the determination of the partitioning coefficient n-octanol water (Pow): the compounds are strong bases (pKa 10.6), such that at neutral pH (pH 7) these compounds are ionised (primary ammonium ion) by 99.98%. The resulting primary ammonium derivative is surface active.

According to EU method A.9 (Partition Coefficient), neither of the two alternative methods outlined do fully apply:
The shake-flask method is not applicable to surface active materials: In conclusion, it could only be applied to a highly alkaline solution (pH 13 or higher), where less than 1% is present as primary ammonium ion and surface activity is thus minimal.
The HPLC method is neither applicable to surface active materials nor to strong bases. While ionisable compounds may be tested in buffered solutions, column properties do not allow for pH-values above 8, such that only the primary ammonium derivative can be tested, which is surface active.

According to EU method A.9, for such compounds Pow should be calculated from the solubilities in water and n-octanol. The present WOE approach follows this recommendation:

The relevant water solubility is the one of the alkyl ammonium derivative, i.e. the hydrochloride of the respective n-alkylamine.

Given the equilibrium in water between the alkyl ammonium ion and the free amine, relevant for octanol solubility is the one determined from the free amine (uncharged).

 

To choose a relevant worst-case key value for risk assessment, the following table presents available experimentally determined water solubilities (CMCs) of alkylamine hydrochlorides, together with experimental values for octanol solubilities of their respective free amine. Resulting calculated partition coefficients n-octanol/water are given in the table:

 

Table 1: Resulting partition coefficient n-octanol water (Pow) calculated from water solubilities (alkyl amine hydrochlorides) and n-octanol solublities (free amines):

 

Substance name	Solubility in octanol (20°C) [g/L]	Reference	Solubility in water (25°C) (CMC) [g/L]	Reference	Pow	log Pow
Dodecylamine	539	Clariant, 2009j	3.5	Clariant, 2008e	154.00	2.19
Tetradecylamine	310	Clariant, 2009k	0.69	Clariant, 2009r	449.28	2.65
Hexadecylamine	148	Clariant, 2009i	0.063	Clariant, 2010v	2349.21	3.37
Octadecylamine	126	Clariant, 2009g	0.013	Clariant, 2010w	9692.31	3.99
(Z)-Octadec-9-enylamine	813	Clariant, 2009h	0.038	Clariant, 2009q	21394.74	4.33

 

As could be expected, a clear increasing trend for Pow becomes obvious with increasing carbohydrate chain length.

The highest log Pow value (4.33) is resulting for(Z)-Octadec-9-enylamine, and this value is used as the worst-case key value for the whole category:

 

key value log Pow: 4.33 ((Z)-Octadec-9-enylamine)

 

References:

Clariant (2008e): Dodecylamine Hydrochloride, Solubility in water, Critical micelle concentration, Report No.: 08-36296.1

Clariant (2009g): Octadecylamine, Solubility in n-Octanol, Report No.: 09-59852

Clariant (2009h): Oleylamine, Solubility in n-Octanol, Report No.: 09-59853

Clariant (2009i): Hexadecylamine, Solubility in n-Octanol, Report No.: 09-59854

Clariant (2009j): Dodecylamine, Solubility in n-Octanol, Report No.: 09-59855

Clariant (2009k): Tetradecylamine, Solubility in n-Octanol, Report No.: 09-59856

Clariant (2009q): Oleylamine Hydrochloride, Solubility in water, Critical micelle concentration, Report No.: 09-67123

Clariant (2009r): Tetradecylamine Hydrochloride, Solubility in water, Critical micelle concentration, Report No.: 09-63643-1

Clariant (2010v): Hexadecylamine hydrochloride, Solubility in water, Critical micelle concentration, Report No.: 09-67119

Clariant (2010w): Octadecylamine hydrochloride, Solubility in water, Critical micelle concentration, Report No.: 09-67120-1