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NEET Chemistry Notes Organic Compounds Containing Nitrogen – Hofmann Mustard Oil Reaction

NEET Chemistry Notes Organic Compounds Containing Nitrogen – Hofmann Mustard Oil Reaction

 Hofmann Mustard Oil Reaction

Hofmann Mustard Oil Reaction

Amines, when warmed with CS2, alkyl or aryl thiocyanate with a characteristic smell of mustard oil is formed.
NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 1

Uses of Amines

  •  Amines are used as intermediates in drug manufacturing and as reagents in organic synthesis.
  • Aromatic amines are used for manufacture of polymers, dyes and as intermediates for additives in rubber industiy.
  •  Quarternary ammonium salts of long chain aliphatic tertiary amines are used as detergents.

Diazonium Salts

Diazonium salts are obtained when primary aromatic amines react with nitrous acid. These salts are used in the preparation of azo dyes and a number of useful halogen substituted arenes.

Preparation of Diazonium Salts

Primary aromatic amines when reacts with HN02 form diazonium salts at low temperatures (0-5°C). The reaction is called diazotisation.
NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 2

Physical Properties

Benzene diazonium chloride is a colourless crystalline solid. It is readily soluble in water. It is stable in cold but reacts with water.

Chemical Properties

Diazonium salts mainly show two types of reactions:

Reactions Involving Displacement of Nitrogen
The following are the reactions involved in the displacement of nitrogen in the benzene can be given as:

  •  Sandmeyer’s Reaction Benzenediazonium chloride heated with cuprous chloride or cuprous bromide respectively dissolved in HCl or HBr yield chlorobenzene or bromobenzene, respectively.
    NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 3
  • Gattermann Reaction In Gattermann reaction, benzenediazonium chloride is warmed with copper powder and HCl or HBr to produce chlorobenzene and bromobenzene can be produced using Gattermann reaction by warming benzenediazonium chloride with copper powder and HCl or HBr respectively.
    NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 4
    The yield of Sandmeyer’s reaction is found to be greater than the Gattermann reaction.
  • Other Reactions
    NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 5
    NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 6
    NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 7

Reactions Involving Retention of Diazo Group

Coupling reactions are the example of electrophilic substitution reaction.
NEET Chemistry Notes Organic Compounds Containing Nitrogen - Hofmann Mustard Oil Reaction 8
Coupling with phenols is carried out in weakly alkaline medium (pH 9 to 10) because phenate ion produced is coupled with diazonium salt more readily. Above pH 10, diazonium salt reacts with hydroxide ion to form diazotate ion which does not take part in coupling reaction.

Uses of Diazonium Salts

Diazonium salts are used for the preparation of a large number of aromatic compounds viz substitution and coupling compounds.

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