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Dissociation constant

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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
Reference:
Composition 0
Principles of method if other than guideline:
Method: other: potentiometric titration
GLP compliance:
no
Test material information:
Composition 1
Dissociating properties:
yes
Remarks on result:
other: Acid-base constant: pKa = 3.85
No.:
#1
pKa:
3.85
Temp.:
23 °C
Conclusions:
At 23 °C, the following values were measured.
Crystalline lactic acid (3-9-1970) Ka 1.42 x 10-4, pKa 3.85
Executive summary:

The ionization constant was determined by means of potentiometric titration with 0.1 N NaOH and determination of the pH at 50% neutralization by graphical interpolation. At 23 °C, the following values were measured.

Crystalline lactic acid (3-9-1970) Ka = 1.42 x 10-4, pKa = 3.85.

Endpoint:
dissociation constant
Type of information:
other: handbook data
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Reference:
Composition 0
Principles of method if other than guideline:
Method: other: several methods
GLP compliance:
no
Test material information:
Composition 1
Dissociating properties:
yes
No.:
#1
pKa:
3.86
Temp.:
22.5 °C
Remarks on result:
other: Acid-base constant: pKa = 3.86
Executive summary:

The dissociation constant was determined with 0.0001389 which leads to a pKa of 3.857 at 22.5ºC.

Endpoint:
dissociation constant
Type of information:
other: expert statement
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: expert statement
Remarks:
based on handbook data and experimental study
Reference:
Composition 0
Principles of method if other than guideline:
Method: other: potentiometric titration
GLP compliance:
no
Test material information:
Composition 1
Dissociating properties:
yes
Remarks on result:
other: Acid-base constant: pKa = 3.85
No.:
#1
pKa:
3.85
Temp.:
23 °C

1. “Holten” data

Paragraph 1.1 of chapter IV of “Holten” is about the dissociation constant of lactic acid.

The results show a broad dispersion. IUPAC have characterised the determination by Martin and

Tartar as very reliable. They found that a maximum of dissociation constant (0.0001389) was

reached at 22.5 °C. The dissociation constant for lactic acid could be expressed in the following formula: pKa= 3.857 + 5.10-5.(t-22.5)2

The dissociation constant of 0.0001389 leads to a pKa of 3.857 at 22.5°C.

[ H.Holten: Properties and Chemistry of lactic acid and derivatives. 1971. Paragraph 1.1 of chapter IV (Physical Chemistry). Page 62-67.]

2. PURAC measurements on the dossociation constant of lactic acid.

G.H. Heesen measured the dissociation constant of lactic acid and lactoyl lactic acid in 1970.

At 23°C he found a Ka for lactic acid of 1.42 x 10-4 and a pKa of 3.85.

[PURAC report: Bepaling van de zuursterkte van melkzuur en lactoylmelkzuur. G.J. Heesen. 15 September 1970]

Conclusions:
The pKa of lactic acid is generally recognized to be 3.85.
Executive summary:

The dissociation constant of 0.0001389 leads to a pKa of 3.857 at 22.5ºC according to Holten 1971. PURAC measurements determined at 23ºC a Ka for lactic acid of 1.42 x 10-4 and a pKa of 3.85. The conclusion of the expert statement is that the pKa of lactic acid is generally recognized to be 3.85.

Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
This information is used in a read-across approach in the assessment of the target substance.
Reason / purpose:
read-across source
Related information:
Composition 1
Principles of method if other than guideline:
Method: other: potentiometric titration
GLP compliance:
no
Test material information:
Composition 1
Dissociating properties:
yes
Remarks on result:
other: Acid-base constant: pKa = 3.85
No.:
#1
pKa:
3.85
Temp.:
23 °C

1. “Holten” data

Paragraph 1.1 of chapter IV of “Holten” is about the dissociation constant of lactic acid.

The results show a broad dispersion. IUPAC have characterised the determination by Martin and

Tartar as very reliable. They found that a maximum of dissociation constant (0.0001389) was

reached at 22.5 °C. The dissociation constant for lactic acid could be expressed in the following formula: pKa= 3.857 + 5.10-5.(t-22.5)2

The dissociation constant of 0.0001389 leads to a pKa of 3.857 at 22.5°C.

[ H.Holten: Properties and Chemistry of lactic acid and derivatives. 1971. Paragraph 1.1 of chapter IV (Physical Chemistry). Page 62-67.]

2. PURAC measurements on the dossociation constant of lactic acid.

G.H. Heesen measured the dissociation constant of lactic acid and lactoyl lactic acid in 1970.

At 23°C he found a Ka for lactic acid of 1.42 x 10-4 and a pKa of 3.85.

[PURAC report: Bepaling van de zuursterkte van melkzuur en lactoylmelkzuur. G.J. Heesen. 15 September 1970]

Conclusions:
The pKa of lactic acid is generally recognized to be 3.85
Executive summary:

The dissociation constant of 0.0001389 leads to a pKa of 3.857 at 22.5ºC according to Holten 1971. PURAC measurements determined at 23ºC a Ka for lactic acid of 1.42 x 10-4 and a pKa of 3.85. The conclusion of the expert statement is that the pKa of lactic acid is generally recognized to be 3.85.

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

The pKa of lactic acid at 23 degrees C is 3.85

Key value for chemical safety assessment

pKa at 20°C:
3.85

Additional information