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]

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]