A nitrilium ion is a nitrile that has been protonated, RCNH+, or alkylated, RCNR′+.[IUPAC Gold Book: nitrilium ions]
Synthesis
Nitriles are only weakly basic
and are poor nucleophiles, but they will attack very reactive electrophiles such as
.
Nitrilium salts can be prepared by reacting nitriles with Oxonium ion. 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′.
As intermediates
Nitrilium ions are believed to be intermediates in the hydrolysis of nitriles,
the Beckmann rearrangement, the Friedel-Crafts
cyclization of amines to
isoquinolines,
the
Schmidt reaction with ketones,
and the
Ugi reaction,
Ritter reaction,
Pinner reaction and Passerini reactions.
