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Water solubility

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Description of key information

 Water solubility (CMC) based on the alkylamine hydrochloride with the highest resulting Kow-value as calculated from the ratios of n-octanol solubility (free amine) and water solubility (hydrochloride).

Key value for chemical safety assessment

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

Additional information

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. Thus, they are best represented by their corresponding hydrochlorides. Therefore, environmentally relevant is the water solubility of the hydrochloride of the respective alkylamine, which - due to the positive charge - is pronouncedly higher than that of the free amine.

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 micells. 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 and derivation of key values for risk assessment:

Due to their pKa-value of approximately 10.6, primary amines generally appear fully protonated under environmental conditions. Therefore, environmentally relevant is the water solubility of the respective hydrochloride.

 

To choose a relevant key value for risk assessment, the following table (Table 3) presents water solubilities (CMCs) of alkylamine hydrochlorides where experimentally determined, together with experimental values for octanol solubilities of their respective free amine, used to calculate partition coefficients n-octanol/water.

 

Table 3: Water solubilities (alkyl amine hydrochlorides) and n-octanol solublities (free amines) used to calculate Kow-values from the ratio of octanol solubility and water solubility:

 

Substance name

Solubility in octanol (20°C) [g/L]

Reference

Solubility in water (25°C) (CMC) [g/L]

Reference

Kow

log Kow

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

 

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 (see section partition coefficient). Thus, it is straight forward to use the corresponding value for water solubility as the category-wide key value for water solubility for PFAs.

 

key value water solubility: 38 mg/L ((Z)-Octadec-9-enylamine)

 

References:

[1]: N. Nishikido, Y. Moroi, R. Matuura, "The Micelle Formation of Mixtures of Polyoxyethylene Type Nonionic Surfactants in Aqueous Solutions", Bulletin of the Chemical Society of Japan, Vol. 48 (5), 1387-1390 (1975)

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