Nitrilium

The general structures of nitrilium ions

A nitrilium ion is a nitrile that has been protonated, [RCNH]^+, or alkylated, [RCNR′]^+.[1]

Synthesis

Nitriles are only weakly basic[2] and are poor nucleophiles, but they will attack very reactive electrophiles such as carbocations.[3]

Nitrilium salts can be prepared by reacting nitriles with trialkyloxonium salts. The nitrilium ions thus formed can then be reduced to secondary amines with sodium borohydride in diglyme. This is a convenient route to secondary amines of the form RCH₂—NH—R′.[4]

As intermediates

Nitrilium ions are believed to be intermediates in the hydrolysis of nitriles,[5] the Beckmann rearrangement, the Friedel-Crafts cyclization of amines to isoquinolines,[6] the Schmidt reaction with ketones,[7] and the Ugi, Ritter, Pinner and Passerini reactions.

References

1. IUPAC Gold Book: nitrilium ions
2. Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. p. 200. ISBN 978-0-19-850346-0.
3. Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. p. 436. ISBN 978-0-19-850346-0.
4. March, J.; Smith, M. (2007). Advanced Organic Chemistry (6th ed.). New York: John Wiley & Sons. p. 1814. ISBN 978-0-471-72091-1.
5. Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. p. 294. ISBN 978-0-19-850346-0.
6. March, J.; Smith, M. (2007). Advanced Organic Chemistry (6th ed.). New York: John Wiley & Sons. p. 716. ISBN 978-0-471-72091-1.
7. March, J.; Smith, M. (2007). Advanced Organic Chemistry (6th ed.). New York: John Wiley & Sons. p. 1613. ISBN 978-0-471-72091-1.