3,4,5-trihydroxybenzoic acid

Dissociation constant

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

pKa provided in acute toxicity test to Daphnia

GLP compliance:

not specified

Specific details on test material used for the study:

3,4,5-Trihydroxybenzoic (gallic) acid (98% minimum purity) from Nacalai tesque, Kyoto, Japan

Dissociating properties:

not determined

pKa:

3.13

Remarks on result:

other: endpoint provided without additional details

Conclusions:

pKa of 3.13 is reported in acute toxicity test of gallic acid to Daphnia magna.

Executive summary:

pKa of 3.13 is reported in acute toxicity test of gallic acid to Daphnia magna.

Reference 2

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

pKa provided in water solubility test

GLP compliance:

not specified

Specific details on test material used for the study:

Gallic acid (≥98% purity; CAS No. 149-91-7) was obtained from Sigma-Aldrich.

Dissociating properties:

not determined

pKa:

4.51

Temp.:

24.85 °C

Conclusions:

pKa of 4.51 at 24.85°C is reported in water solubility determination of gallic acid.

Executive summary:

pKa of 4.51 at 24.85°C is reported in water solubility determination of gallic acid.

Reference 3

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

documentation insufficient for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

pKa provided in acute toxicity test to fish

GLP compliance:

not specified

Specific details on test material used for the study:

Gallic acid (98 % purity) was obtained as dry powder from Acros Organics (no. 410860010).

Dissociating properties:

not determined

pKa:

3.34

Remarks on result:

other:

Remarks:

endpoint provided without additional details

Conclusions:

pKa of 3.34 is reported in acute toxicity test of gallic acid to fish.

Executive summary:

pKa of 3.34 is reported in acute toxicity test of gallic acid to fish.

Description of key information

As explained by Škorňa et al. (2016), in the case of gallic acid, carboxylic group shows the highest acidity (pKa = 4.4). Acidities of three phenolic groups were found in the range from pKa = 8.8 (4-OH)

to pKa = 11.4 (5-OH).

Experimental determination of the pKas based on deprotonation of gallic acid using Raman spectrometer is provided by Huguenin et al. (2015).

The bond from COOH function is the first bond impacted by the increase of pH. This modification corresponds to the reaction LH4 -> LH3(-) + H(+) with pK1 of 4.4

For OH(2) bond break, corresponding to LH3(-) -> LH2(2-) + H(+), pK2 is 8.8

For OH(3) bond break, corresponding to LH2(2-) -> LH(3-) + H(+), pK3 is 10.0

For OH(4) bond break, corresponding to LH(3-) -> L(4-) + H(+), pK4 is 11.4

The following values are reported in the literature and are to considered as the pKa of the carboxylic group, whereas not specified in the supporting publications:

A) Kamaya et al., 2005       

pKa of gallic acid: 3.13

B) Motta et al., 2008     

pKa of gallic acid: 4.51 at 24.85°C

C) Techner et al, 2015     

pKa of gallic acid: 3.34