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Physical & Chemical properties

Water solubility

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Description of key information

In a worst case approach, the solubility of the Alkyl phosphate and stearyl amine salts (EC = 952-252-4) was considered as driven by the properties of the alkylammonium part which has a CMC = 38 mg/L at 20°C.

Key value for chemical safety assessment

Water solubility:
38 mg/L
at the temperature of:
20 °C

Additional information

Alkyl phosphate and stearyl amine salts (EC = 952-252-4) is a multi-constituent manufactured as a solid block. The registered substance is mainly composed by primary alkylamines (CAS 90640-32-7, UVCB), Monoalkyl dihydrogenophosphate and Dialkyl hydrogenophosphate salts (CAS 39471-52-8, Multi-Constituant). This different chemical structures are constituted by saturated and variable chain lenght with C16 and C18.

 

N-hydrogenated tallow alkyl amine (CAS 90640-32-7) among which C16 and C18 n-alkylamines are one of the major constituents. Primary fatty amines in their free (non-protonated) form are very poorly soluble in water.

 

Measurements must be performed at very high pH (pKa 10.6) and due to the very low concentrations experimental determination is often technically not possible. Therefore, values given in Table 1 below are calculated with the exception of C12-, C14- and C16-alylamines. Calculation for the remaining compounds was performed based on their C-Chain distribution according to the formula presented in the publication by Matuura et.al. [1]. As would be expected, a clear trend of decreasing water solubility with increasing chain length is obvious:

Table 1: water solubilities of the commercial substances derived from the water solubilities of the C-chain pure amines (unprotonated).

Substance Name

solubility [mg/L]

Dodecan-1-amine

3.70

Tetradecan-1-amine

0.213

Hexadecan-1-amine

1.08 x 10-2

C12-18-(even numbered)-alkylamine

4.63 x 10-3

C16-18-(even numbered, C18 unsaturated)-alkylamine

7.89 x 10-4

C16-18-(even numbered)-alkylamine

7.98 x 10-4

(Z)-Octadec-9-enylamine

6.20 x 10-4

Octadecan-1-amine

5.59 x 10-4

 

Because of their high pKa-values (10.6, i.e. strong bases), at environmentally relevant pH these compounds are fully protonated (99.98% at pH7), i.e. present as alkylammonium-ions.

 

While determining the water solubility of the alkylamine hydrochlorides, a further difficulty is their surface active property: single hydrated molecules are found up to their respective critical micelle concentration (CMC), only. At higher concentrations, molecules will be aggregating to from micelles. Therefore, as a substitute of the water solubility, the CMC is used for surface active compounds. As will be obvious from the following data table, there is a clear decreasing trend for water solubility with increasing hydrocarbon chain legth, as would be expected:

Table 2: Water solubilities of the commercial substances derived from the water solubilities of the hydrochlorides of the C-chain pure amines (protonated form of amine)

 

Substance Name

solubility [mg/L]

Dodecan-1-amine

3.5 x 103

Tetradecan-1-amine

6.9 x 102

Hexadecan-1-amine

6.3x 101

Octadecan-1-amine

1.3 x 101

(Z)-Octadec-9-enylamine

3.8 x 101

 

Conclusion :

Regarding the other main constituants, the Phosphoric acid, octadecyl ester (CAS 39471-52-8), it was observed that the water solubility is less than 0.162 mg/L according an TG OECD 105. To assess the solubility of Alkyl phosphate and stearyl amine salts (EC = 952-252-4) it is of importance to consider the most conservative reliable values found for each endpoint. In a worst case approach, the environmental fate (e-fate) and ecotoxicity of the Alkyl phosphate and stearyl amine salts (EC = 952-252-4) was considered as driven by the properties of the alkylammonium part.

 

In spite of the clear trend observed for water solubility across category members, water solubility for (Z)-octadec-9-enylamine is selected as key value for the whole category, on the following grounds: as opposed to water solubility, a clear increasing trend of log Kow is obvious with increasing carbohydrate chain length. Because of the highest log Kow value (4.33) is resulting for(Z)-octadec-9-enylamine, this value is used as the worst-case key value for the whole category.

 

Moreover, it is of importance to note that a new study on the Alkyl phosphate and stearyl amine salts will be performed according the TG OECD 105 and GLP to reinforce this approach.