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King Hailu

Why sodium cyanoborohydride reactivity depends on pH?

Bertrand Wengher  Follow

sodium cyanoborhydride 's selectivity is achieved at mild basic solutions (pH= 7-10). In acidic solutions , it is not stable forming very toxic gas of HCN

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David Frigault  Follow

Acidic conditions are required for the reaction to occur. Selectivity for reductive aminations is more of a happy coincidence. The formation of iminium ions is favoured around pH 6, and iminium ions reduce much faster than ketones at that pH. 
Borch et al J. Am. Chem. Soc., 1971, 93 (12), pp 2897–2904

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Ayaz Wasay  Follow

Acid destabilizes the sodium cyanoborohydride which results in an activated state for kinetics and equilibrium. 

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Christopher Lucy  Follow

Acidic conditions are required for the reaction to occur. Selectivity for reductive aminations is more of a happy coincidence. The formation of iminium ions is favoured around pH 6, and iminium ions reduce much faster than ketones at that pH. 
Borch et al J. Am. Chem. Soc., 1971, 93 (12), pp 2897–2904

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Biochemistry world ??  Follow

In slightly acidic conditions it releases  HCN and also the hydride required for the reaction

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