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
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