Fatty acids, tall-oil, reaction products with acrylic acid

Dissociation constant

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dissociation constant

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

Comparison of dissociation constants for analogue structures

GLP compliance:

no

Statement on the lipophilicity of the substance fatty acid, tall oil, reaction product with acrylic acid

The substance fatty acid, tall oil, reaction product with acrylic acid also identified as Diacid 1550, is a dicarboxylic acid substance prepared from tall oil fatty acids. As all dicarboxylic acid, it is an ionisable substance that will be present under different dissociated forms depending on the environment conditions. The pKas of the substance will determine its state (dissociated or non-dissociated) in the environment.

Diacid 1550 is structurally related with two other dicarboxylic acids, Azelaic acid and 1,4-cis-cyclohexane dicarboxylic acid. pKas values are provided for a regular fatty acid (pKa is 4.96) and for the two other examples mentioned Azelaic (pKa is 4.55 / 5.41) and 1,4-cis-cyclohexane dicarboxylic acid (pKa is 4.4/5.7).

Based on the above and given the similarities between the diacids, a read-across is acceptable. The pKa values for the Diacid 1550 are expected to be between 4 and 6. This implies that at environmental pH, the Diacid 1550 will be mostly in its dissociated form. The pH diagram below shows the different dissociation forms in function of the pH.

Above pH 6, both carboxylic functions are expected to be dissociated. This implies that at environmental conditions the solubility of the Diacid 1550 will be close to the one from its salt (K, Na, etc.). Given the exposure concentrations and the experimental values obtained for the water solubility of the potassium salt of the Diacid 1550, the substance is expected to be mostly soluble in aqueous environment (environmental concentration below the solubility limit). In addition, the presence of the second carboxylic acid functional group in the middle of the fatty acid chain is expected to reduce any surface active properties, rendering the Diacid 1550 a poor surfactant compared to regular fatty acids.

Based on the above, it can be stated that under environmental conditions, the substance Diacid 1550 will not be very lipophilic.

Figures and schemes are included as attached background material.

Conclusions:

The pKa values of Diacid 1550 are expected to be between 4 and 6.

Executive summary:

Above pH 6, both carboxylic functions of the diacid are expected to be dissociated. This implies that at environmental conditions the solubility of the Diacid 1550 will be close to the one from its salt (K, Na, etc.). Given the exposure concentrations and the experimental values obtained for the water solubility of the potassium salt of the Diacid 1550, the substance is expected to be mostly soluble in aqueous environment (environmental concentration below the solubility limit). In addition, the presence of the second carboxylic acid functional group in the middle of the fatty acid chain is expected to reduce any surface active properties, rendering the Diacid 1550 a poor surfactant compared to regular fatty acids.

Based on the above, it can be stated that under environmental conditions, the substance Diacid 1550 will not be very lipophilic.

Reference 2

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

18 - 21 Aug 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

GLP compliance:

yes (incl. QA statement)

Dissociating properties:

not determined

Remarks on result:

other: No determination technically possible

The conductometric method could not be applied as the test item is a mixture and a distinct molecular mass is necessary for evaluation. Attempts to perform a photometric or titrimetric determination failed as the spectra in neutral, basic and acidic medium do not differ resp. no points of equivalence could be observed during titration with NaOH or HCl. All observations support the conclusion that the test item structure is independent from pH and shows no dissociation. Therefore, no dissociation constants could be determined for the test item DIACID 1550. No observations were made which might cause doubts concerning the validity of the study outcome.

Conclusions:

No dissociation constants could be determined for test item.
No observations were made which might cause doubts concerning the validity of the study outcome.

Executive summary:

The conductometric method could not be applied as the test item is a UVCB substance and a distinct molecular mass is necessary for evaluation. Attempts to perform a photometric or titrimetric determination failed as the spectra in neutral, basic and acidic medium do not differ resp. no points of equivalence could be observed during titration with NaOH or HCl. Therefore, no dissociation constants could be determined for the test item DIACID 1550.

No observations were made which might cause doubts concerning the validity of the study outcome.

Description of key information

No experimental study could be performed, due to


 The conductometric method could not be applied as the test item is a mixture and a distinct molecular mass is necessary for evaluation. No dissociation constants could be determined for the test item .

  
  
  

The pKa values of Diacid 1550 are expected to be between 4 and 6, from an acceptable read across with a similar substance.

Key value for chemical safety assessment

pKa at 20°C:

4

Additional information

The conductometric method could not be applied as the test item is a mixture and a distinct molecular mass is necessary for evaluation. No dissociation constants could be determined for the test item .

Diacid 1550 is structurally related with two other dicarboxylic acids, Azelaic acid and 1,4-cis-cyclohexane dicarboxylic acid. pKas values are provided for a regular fatty acid (pKa is 4.96) and for the two other examples mentioned Azelaic (pKa is 4.55 / 5.41) and 1,4-cis-cyclohexane dicarboxylic acid (pKa is 4.4/5.7).

Based on the above and given the similarities between the diacids, a read-across is acceptable. The pKa values for the Diacid 1550 are expected to be between 4 and 6. This implies that at environmental pH, the Diacid 1550 will be mostly in its dissociated form. Therefore it can be stated that under environmental conditions, the substance Diacid 1550 will not be very lipophilic.