Hydrogen cyanide

Dissociation constant

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

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

yes

Remarks:

precedes guideline

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hydrogen cyanide

EC Number:

200-821-6

EC Name:

Hydrogen cyanide

Cas Number:

74-90-8

Molecular formula:

CHN

IUPAC Name:

hydrogen cyanide

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

Dissociation 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.