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.

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

Acyl cyanides are mild acylating agents and the traditional acylant in the Reissert reaction.

In aqueous base, acyl cyanides break down to cyanide and the carboxylate: $${\displaystyle {\color {red}{\ce {R-C(O)CN}}}+{\ce {2 NaOH}}\longrightarrow {\color {red}{\ce {R-CO}}}{\ce {_2Na}}+{\ce {Na}}{\color {red}{\ce {CN}}}+{\ce {H2O}}}$$ Nickel(II) catalyzes benzoyl cyanide decarbonylation to the benzonitrile.^{: Rxn. (13)}

Acyl cyanides are hetero (oxa) dienophiles.^{: Rxn. (8)} They click onto azides to give acyl tetrazoles.

References