Cyanides, Isocyanides and Diazonium Salts — Part 1: Cyanides, isocyanides and making diazonium salts: visual lesson, ISC Class 12 Chemistry

Lesson

C≡N compounds and diazonium salts

Part 1 — two isomeric functional groups, –C≡N and –N≡C, and the versatile diazonium ion ArN₂⁺.

In this lesson you will

Write equations for preparing alkyl cyanides from alkyl halides and amides
Write equations for preparing isocyanides from alkyl halides and primary amines
Compare cyanides and isocyanides
Write the diazotisation equation and explain why it is carried out at 273–278 K

Table of cyanides, isocyanides and diazonium salts and their uses
Compound	Where it matters
Propenenitrile (acrylonitrile)	Acrylic fibres (Orlon)
Ethanenitrile	Laboratory solvent
Isocyanides	Foul smell: test for primary amines
Benzenediazonium salts	Azo dyes, synthesis of many aromatic compounds

Concept

Structure and names

Alkyl cyanides (nitriles) R–C≡N: carbon of the CN group is bonded to R. IUPAC: alkanenitrile, counting the CN carbon (CH₃CN ethanenitrile). Alkyl isocyanides R–N≡C (R–N⁺≡C⁻): nitrogen bonded to R; named isocyanoalkanes (CH₃NC isocyanomethane, methyl isocyanide). They are functional isomers.

Table of names of cyanides and isocyanides
Formula	Common name	IUPAC name
CH₃CN	Methyl cyanide	Ethanenitrile
CH₃CH₂CN	Ethyl cyanide	Propanenitrile
C₆H₅CN	Phenyl cyanide	Benzonitrile
CH₃NC	Methyl isocyanide	Isocyanomethane
C₂H₅NC	Ethyl isocyanide	Isocyanoethane
C₆H₅NC	Phenyl isocyanide	Isocyanobenzene

Concept

Preparation of cyanides

From alkyl halides: heat with ethanolic KCN or NaCN (ionic; attack through C) → nitrile (one more C). From amides: dehydration with P₂O₅ (or SOCl₂, POCl₃) on heating.

\ce{CH3CH2CH2Br + KCN -> CH3CH2CH2CN + KBr}

\ce{CH3CH2CONH2 ->[P2O5][\Delta] CH3CH2CN + H2O}

Table of preparations of cyanides
Starting compound	Reagent	Product
1-Bromopropane	KCN, ethanol, heat	Butanenitrile
Propanamide	P₂O₅, heat	Propanenitrile
Benzamide	P₂O₅, heat	Benzonitrile
Benzenediazonium chloride	CuCN (Sandmeyer)	Benzonitrile

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