Cyanohydrins

Cyanohydrins are organic compounds that contain both a hydroxyl group and a cyano group on the same carbon atom, giving the general structure R-CH(OH)CN. They are typically described as the addition products of hydrogen cyanide to carbonyl compounds, such as aldehydes and ketones, forming a stereocenter at the carbon bearing the two functional groups.

Formation and sources: The classic route to cyanohydrins is the nucleophilic addition of HCN to carbonyl compounds, yielding benzaldehyde cyanohydrin for example. Practical syntheses often use safer cyanide sources such as hydrogen cyanide equivalents or trimethylsilyl cyanide (TMSCN) in the presence of acid or catalysts. The reaction is favored for aldehydes and less hindered ketones, and substituents on the carbonyl compound influence stability.

Properties and reactions: Cyanohydrins serve as versatile intermediates in organic synthesis. The nitrile group can be converted to carboxylic acids, amides, or amines, while the hydroxyl group provides a handle for further transformations such as etherification or oxidation. Cyanohydrins can be hydrolyzed or reduced to give alpha-hydroxy acids or corresponding amino alcohols. They also function as masked carbonyl compounds in retrocyanohydrin reactions, where base-induced cleavage regenerates the carbonyl compound and cyanide.

Applications and examples: Mandelonitrile is the cyanohydrin of benzaldehyde and serves as a precursor to benzoic acid and related compounds. Cyanohydrins are used as building blocks in asymmetric synthesis to access enantioenriched alpha-hydroxy nitriles and related products.

Safety: Cyanohydrins can release hydrogen cyanide under certain conditions, and their handling requires appropriate safety precautions and proper waste management.