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:

{\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:

{\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:

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

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

{\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]

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.
Morris, Joel (2001). "Acetyl Cyanide". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.ra026. ISBN 0471936235.
Hünig, Siegfried; Schaller, Rainer (1982). "The Chemistry of Acyl Cyanides". Angewandte Chemie International Edition in English. 21: 36–49. doi:10.1002/anie.198200361.
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.

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