Registration Dossier

Physical & Chemical properties

Dissociation constant

Currently viewing:

Administrative data

Link to relevant study record(s)

Referenceopen allclose all

Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: The paper measured pKa1 only and references values from other studies.
Reason / purpose:
reference to same study
Principles of method if other than guideline:
The paper reports some titration and spectrometric studies which allow estimation of independent constants. pKa 1 was determined only for cyanuric acid.
GLP compliance:
no
Remarks:
Predates GLP
Dissociating properties:
yes
No.:
#1
pKa:
7
Remarks on result:
other: temperature not reported
No.:
#2
pKa:
10.6
Remarks on result:
other: temperature not reported
No.:
#3
pKa:
ca. 13
Remarks on result:
other: temperature not reported
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
The equilibrium constants relating to the hydrolysis of chloroisocyanurates have been measured spectrophotometrically. The results have been used to calculate the concentration of hypochlorous acid under various conditions in swimming pools treated with chloroisocyanurates and cyanuric acid.
Dissociating properties:
yes
No.:
#1
pKa:
6.8
Temp.:
23 °C
No.:
#2
pKa:
>= 10 - <= 11
Temp.:
23 °C
No.:
#3
pKa:
> 11
Temp.:
23 °C
Conclusions:
The lowest pKa of cyanuric acid was found by titration to be 6.80 and the two higher values of pKa were in the region 10-11.
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
The experimental determination of the dissociation constants was made by differential spectrometric titration.
GLP compliance:
no
Remarks:
Study predates GLP
Dissociating properties:
yes
No.:
#1
pKa:
6.88
Remarks on result:
other: temperature not stated
No.:
#2
pKa:
11.4
Remarks on result:
other: temperature not stated
No.:
#3
pKa:
13.5
Remarks on result:
other: temperature not stated
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well described paper
Principles of method if other than guideline:
The pH dependence of the ultravioalet absoprtion spectra of cyanuric acid has been attributed by previous workers to dissociation in alkaline solution, however the limited available spectral range doe not permit a full study or interpretation of the changes in spectra due to the various charged species. The paper is concerned with the ultraviolet spectra, extended to 1880 Ǻ of solutions of the cyanurate species, both chlorinated and unchlorinated. The interpretation of the spectra is augmented by a study of the spectra of barbital (5, 5-diethyl barbituric acid) which may form in aqueous solution as many as three species with net charge 0, 1- , 2-.
Dissociating properties:
yes
No.:
#3
pKa:
ca. 13
Remarks on result:
other: temperature not reported

The pH dependence of the ultraviolet absorption spectra of aqueous solutions of cyanuric acid and its chlorinated derivatives is attributed to dissociation leading to four species containing the cyanuric nucleus with net charge 0, 1 -, 2- and 3 -. Chlorination of cyanuric acid results in more diffuse spectra because several species of a given net charge may exist. At pH 14 the spectra of these solutions are essentially identical regardless of degree of chlorination and the principal organic ion present is the triply charged cyanurate. The value of pK3 of cyanuric acid was estimated from spectral changes to be about 13.

Conclusions:
The value of pK 3 of cyanuric acid was etimated from spectral changes to be about 13.
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Ionization constants for cyanuric acid are reported .
Principles of method if other than guideline:
Spectrophotometrically determined ionization constants are reported for cyanuric acid
Dissociating properties:
yes
No.:
#1
pKa:
6.5
Remarks on result:
other: temperature not reported
No.:
#2
pKa:
10.6
Remarks on result:
other: temperature not reported
Conclusions:
Values for pKa of 6.5 and 10.6 are reported for cyanuric acid

Description of key information

Several sources of literature are available which provide the dissociation constant of cyanuric acid as follows:

pKa1: = 6.5-7.0

pKa2: = 10 - 11

pKa3: ~13

Key value for chemical safety assessment

Additional information