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Physical & Chemical properties

Dissociation constant

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Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2007
Reliability:
4 (not assignable)
Principles of method if other than guideline:
Method: other: potentiometric titration
GLP compliance:
no
Specific details on test material used for the study:
pure lactic acid
Dissociating properties:
yes
No.:
#1
pKa:
3.85
Temp.:
23 °C

1. “Holten” data

Paragraph 1.1 of chaptr V of “Holten” 1) 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.

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

G.H. Heesen 2) measured the dissociation constant of lactic acid and lactoyl lactic acid in 1970.

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

Conclusions:
The pKa of L-(+)-lactic acid is generally recognized to be 3.85.
Executive summary:

The pKa of L-(+)-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:
supporting study
Justification for type of information:
For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Dissociating properties:
yes
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

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.

Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For details and justification of read-across please refer to the attached report in section 13 of IUCLID.
Reason / purpose for cross-reference:
read-across source
Dissociating properties:
yes
No.:
#1
pKa:
3.86
Temp.:
25 °C
Remarks on result:
other: Acid-base constant: pKa = 3.86
Conclusions:
The dissociation constant was determined with 0.0001389 which leads to a pKa of 3.857 at 22.5 °C.
Executive summary:

According to Holten, the dissociation constant was determined with 0.0001389 which leads to a pKa of 3.857 at 22.5 °C.

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 °C is 3.85.

Key value for chemical safety assessment

pKa at 20°C:
3.85

Additional information