Registration Dossier

Administrative data

Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1962
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: This study is similar to, but precedes the development of OECD Guideline 112.

Data source

Reference
Reference Type:
publication
Title:
Thermodynamics of Metal-Cyanide Coordination I. pK, ∆Ho and ∆So values as a function of temperature for hydrocyanic acid dissociation in aqueous solution
Author:
Izatt RM, JJ Christensen, RT Pack, R Bench
Year:
1962
Bibliographic source:
Inorganic Chemistry 1: 828-831

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
yes
Remarks:
precedes guideline
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Stock HCN solution was prepared by passing a 0.05 F NaCN solution through an Amberlite GC-120, Type 1 ion exchange column until the Na concentration as determined by a flame test was less than 0.05% of that originally present.

Results and discussion

Dissociating properties:
yes
Dissosciation constant
No.:
#1
pKa:
ca. 9.36
Temp.:
20 °C
Remarks on result:
other: 95 % Confidence Limit ± 0.012

Applicant's summary and conclusion

Conclusions:
The pKa of hydrocyanic acid is 9.36 at 20°C and 9.11 at 30°C.
Executive summary:

The pKa of hydrocyanic acid is 9.36 at 20 °C.The predominant speciation of all inorganic cyanide in the body is HCN due to this weak acid dissociation constant.