Alkil isocyanides

Alkil isocyanides

This is also known as isonitriles or carbylamines.

General methods of preparation

1By heating an alkyl iodide with silver cyanide in aqueous ethanolic solution; a small amount of cyanide is also formed :

RI   +   AgCN    ⟶    RNC   +   AgI

2  By heating a mixture of primary amine and chloroform with ethanolic potassium hydroxide:

 RNH₂   +   CHCl₃   +   3KOH    ⟶    RNC   +   3KCl   +   3H₂O

3 Dehydration of N-substituted formamides with phosphoryl chloride in pyridine produces isocyanides.

RNHCHO     (POCl₃) ⟶   RNC

General properties

The alkyl isocyanides are poisonous, most unpleasant-smelling liquids, with lower boiling points than the isomeric cyanides. They are not very soluble in water, the nitrogen atom not having a lone pair of electrons available for hydrogen bonding. Alkyl isocyanides absorb in the region 2185-2120 cm^-1.

Reaction

1.  Allkyl isocyanides are hydrolysed to an amine and formic acid by dilute acids, but are not hydrolysed by alkalis:

RNC   +   2H₂O    (acid) ⟶   RNH₂   +   HCO₂H

2.  Alkyl isocyanides are reduced to secondary amines either by dissolving metals or by catalytic reduction:

RNC    ⟶    RNHCH₃

3.  Alkyl isocyanides add on halogen to form alkyliminocarbonyl halides, sulphur to form alkyl isothiocyanates, and are readily oxidized by mercuric oxide to alkyl isocyanates:

RNC   +   X₂   ⟶    RNCX₂

RNC   +   S     ⟶     RMCS

RNC   +   HgO    ⟶   RNCO   +   Hg

4. When alkyl isocyanides are heated for a long time, they rearrange to the cyanide:

RNC    ⟶   RCN