Amines, C16-18 (even numbered)-alkyl , salts with phosphoric acid, mono- and di-C16-18 (even numbered) alkyl esters

Partition coefficient

Description of key information

Alkyl phosphate and stearyl amine salts (EC = 952-252-4) are mainly composed by primary alkylamines (CAS 90640-32-7, UVCB), Monoalkyl dihydrogenophosphate and Dialkyl hydrogenophosphate salts (CAS 39471-52-8, Multi-Constituent). This different chemical structures are constituted by variable chain lenght with C16 and C18. 

For primary alkylamines, a weight of evidence is based on available studies. 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.

Phosphoric acid, octadecyl ester (CAS 39471-52-8) has a log Kow value less than 0.3 to 2.31 according to a TG OECD 117 and GLP study.

Moreover, it is of importance to note that a new study on partition coefficient (log Kow) on the registered salt, the Alkyl phosphate and stearyl amine salts (EC = 952-252-4) is not technically feasible according to its high insolubility in water and octanol. Even if the log kow is waived for the overall registered salt, a log kow value information is reported because it is essential for CSA, classification and labelling and PBT assessment (according REACH guidance document R7a section R.7.1.8 page 76).

 

Key value for chemical safety assessment

Log Kow (Log Pow):

4

at the temperature of:

20 °C

Additional information

For primary alkylamines, a weight of evidence is based on various studies performed under technical guidelines OCDE. Alkylamines are difficult substances with regard to the determination of the partitioning coefficient n-octanol water: 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.

 

In the Chapter R.7A of the REACH guidance (Section R.7.1.8.3; Guidance on regulatory compliant Kow determination for surfactants), it is indicated that none of the experimental methods is very well suited for determining the Kow of surface active chemicals.

 

 The slow stirring method (OECD 123) seems to be the best in theory, but still not demonstrated to be perfect. Indeed, due to the physico-chemical properties of surfactants, specifically their tendency to either accumulate at the octanol/water interface or to coat the surfaces of the above-described HPLC adsorbent phase, the log Kow of surfactants cannot be accurately measured for these substances.

 

According to the REACH guidance Chapter R.7a v6 (July 2017), the ratio solubility in octanol / solubility in water is acceptable for such compounds. The present weight of evidence approach follows this recommendation. 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.