Acyl cyanide

In organic chemistry, an acyl cyanide is a functional group with the formula R−C(O)CN and structure R−C(=O)−C≡N. It consists of an acyl group (R−C=O) attached to cyanide (−C≡N). Examples include acetyl cyanide, formyl cyanide, and oxalyl dicyanide. Acyl cyanides are reagents in organic synthesis.^[1][2]

General chemical structure of an acyl cyanide

Synthesis

Classically acyl cyanides are produced by the salt metathesis reaction of acyl chlorides with sodium cyanide:

${\displaystyle {\color {red}{\ce {R-C(O)}}}{\ce {Cl}}+{\ce {Na}}{\color {red}{\ce {CN}}}\longrightarrow {\color {red}{\ce {R-C(O)CN}}}+{\ce {NaCl}}}$

Alternatively, they can be produced by dehydration of acyl aldoximes:

${\displaystyle {\color {red}{\ce {R-C(O)C}}}{\ce {H=}}{\color {red}{\ce {N}}}{\ce {OH}}\longrightarrow {\color {red}{\ce {R-C(O)CN}}}+{\ce {H2O}}}$

Acetyl cyanide is also prepared by hydrocyanation of ketene:

${\displaystyle {\ce {CH2=}}{\color {red}{\ce {C=O}}}+{\ce {H}}{\color {red}{\ce {CN}}}\longrightarrow {\ce {H3C -}}{\color {red}{\ce {C(O)CN}}}}$

Reactions

They are mild acylating agents.^[2] With aqueous base, acyl cyanides break down to cyanide and the carboxylate:^[3]

${\displaystyle {\color {red}{\ce {R-C(O)CN}}}+{\ce {2 NaOH}}\longrightarrow {\color {red}{\ce {R-CO}}}{\ce {_2Na}}+{\ce {Na}}{\color {red}{\ce {CN}}}+{\ce {H2O}}}$

With azides, acyl cyanides undergo the click reaction to give acyl tetrazoles.^[4]