C16-18-(even numbered)-alkyl fatty acid, compound with C16-18-(even numbered)-alkylamine

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

Variability of the determined concentrations was higher than 30% between the two test columns. However, the concentration was around 10-20 µg/L, which is a sufficiently accurate range.

GLP compliance:

yes (incl. QA statement)

Type of method:

column elution method

Key result

Water solubility:

11.4 µg/L

Conc. based on:

test mat.

Incubation duration:

19 h

Temp.:

20 °C

pH:

7

Remarks on result:

other: see remarks

Remarks:

Recirculation flow rate was 12.5 mL / h

Key result

Water solubility:

20.9 µg/L

Conc. based on:

test mat.

Incubation duration:

19 h

Temp.:

20 °C

pH:

7

Remarks on result:

other: see remarks

Remarks:

Circulation flow rate was 25 mL/h

Details on results:

See Table 2.

Contact time (h)	Concentration column 1 (µg/L)	Concentration column 2 (µg/L)
15	23.15	13.67
16	20.76	12.47
17	20.79	9.73
18	20.29	9.28
19	19.43	11.9
Mean	20.9	11.4

Table 2: Concentration of the test substance (expressed in equivalent of the test item) throughout the study.

Conclusions:

The water solubility of fatty acids, C16-18, compds. with C16-18 alkylamines was 16.2 µg/L at 20°C and pH 7.

Executive summary:

The water solubility of the test item was determined according the OECD guideline 105. A preliminary test estimated the water solubility < 10 mg/L. So the column elution method was applied. The test item concentration was calculated after

quantification of amines from C7 to C20 in ultrapure water by HPLC-MS. The water solubility of fatty acids, C16-18, compds. with C16-18 alkylamines was 16.2 µg/L at 20°C and pH 7. It is important to note that the shortest compounds (C10 - C12) are the main observed and strongly contributes to the solubility.

Description of key information

The water solubility of the test item was determined according the OECD guideline 105. A preliminary test estimated the water solubility < 10 mg/L. So the column elution method was applied. The test item concentration was calculated after quantification of amines from C7 to C20 in ultrapure water by HPLC-MS. The water solubility of fatty acids, C16-18, compds. with C16-18 alkylamines was 16.2 µg/L at 20°C and pH 7. It is important to note that the shortest compounds (C10 - C12) are the main observed and strongly contributes to the solubility.

In addition, CMC of individual alkylamines were determined in order to assess the log Kow of each of them separately. 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:

15 µg/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 10^3
Tetradecan-1-amine	6.9 x 10^2
Hexadecan-1-amine	6.3x 10^1
Octadecan-1-amine	1.3 x 10^1
(Z)-Octadec-9-enylamine	3.8 x 10^1

 

 

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.