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]

References

1. Liu, Bing; Wang, Yong; Chen, Ying; Wu, Qian; Zhao, Jing; Sun, Jianwei (2018). "Stereoselective Synthesis of Fully-Substituted Acrylonitriles via Formal Acylcyanation of Electron-Rich Alkynes". Organic Letters. 20 (12): 3465–3468. doi:10.1021/acs.orglett.8b01180. PMID 29873500. S2CID 46942109.
2. Morris, Joel (2001). "Acetyl Cyanide". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.ra026. ISBN 0471936235.
3. Hünig, Siegfried; Schaller, Rainer (1982). "The Chemistry of Acyl Cyanides". Angewandte Chemie International Edition in English. 21: 36–49. doi:10.1002/anie.198200361.
4. Demko, Zachary P.; Sharpless, K. Barry (2002). "A Click Chemistry Approach to Tetrazoles by Huisgen 1,3-Dipolar Cycloaddition: Synthesis of 5-Acyltetrazoles from Azides and Acyl Cyanides". Angewandte Chemie International Edition. 41 (12): 2113–2116. doi:10.1002/1521-3773(20020617)41:12<2113::AID-ANIE2113>3.0.CO;2-Q. PMID 19746613.