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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

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Environmental fate & pathways


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Description of key information

Key value for chemical safety assessment

Additional information

The abiotic dissociation of HCN depends on temperature and pH. Typical pH values of natural waters range from pH 6 to 8. The pKa value of the dissociation equilibrium of HCN  is 9.36 at 20°C. The HCN fraction will be 92% at pH 8.5 and > 99% at pH < 7 (Leduc et al,1982). In a model hard water, 98% of free cyanide was HCN at pH 7.7 (Murgatroyd et al, 1998).

Hydrolysis, to formic acid and ammonia, is normally a very slow reaction and it does not play a role under environmental conditions. The reaction is accelerated by strongly acidic or alkaline conditions.