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Physical & Chemical properties

Dissociation constant

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Description of key information

pKa estimated to be around 30

Key value for chemical safety assessment

Additional information

Acetonitrile is both a very weak acid and a very weak base. For acidity and basicity this weak, the reported values of Pka are often only estimates, as they are in this case with acetonitrile, because the pK's can sometimes only be measured in solvents other than water.

pKa values in the range of -4.2 to -10.13 have been reported for the reaction of acetonitrile with very strong acid. The basicity of acetonitrile seems to depend on the acid it reacts with, hence the different values.

pK values in the range of 29.1 to 31.3 have been reported for the reaction of acetonitrile with strong base, as measured in dimethyl sulfoxide. Authors of this work state that it may be possible to extrapolate to estimate the pKa of acetonitrile in water to be around 30.