Di-Hatogen Derivatives Preparation and Properties

Di-Hatogen Derivatives Preparation and Properties

→ When two hydrogen atoms of an alkane are substituted by halogen atoms, the compound obtained is known as di-halogen derivative.

Di-Hatogen Derivatives Preparation and Properties

On the basis of adjacent position of both halogen atoms, dihalogen derivatives are divided in to three parts:

→Gem-dihalides: If both halogen atoms are attached to the same carbon atom, the compound is known as gem-dihalide. For example,

Di-Hatogen Derivatives Preparation and Properties 1

→ Vic.Dihalides : In these compounds two halogen atoms are attached to adjacent carbons. For example,

Di-Hatogen Derivatives Preparation and Properties 2

→ α, ω-Dihalide : If halogen atoms are attacked to th€ first carbon and last carbon atom of carbon chain, then they are known as α, ω-dihalides. For examples,

Di-Hatogen Derivatives Preparation and Properties 3

→ General Methods of Preparation Gem-Dihalides

→ From Alkynes : By treating with halogen acids.

Di-Hatogen Derivatives Preparation and Properties 4

→ From Carbonyl Compounds : By treating with PCl5.

Di-Hatogen Derivatives Preparation and Properties 5

Vic-Dihalides

→ From Alkenes : Vic-dihalides are formed by treating halogen with ethene in the presence of CCl4.

Di-Hatogen Derivatives Preparation and Properties 6

From Glycol : Vic-dihalides are formed by the action of PCl5 on glycol.

Di-Hatogen Derivatives Preparation and Properties 7

α, ω DhaIide : When Silver salts of dicarboxylic acids reacts with bromine in the presence of CCl4.
α, ω-dihalides are obtained. This reaction is known as Hunsdicker reaction.

Di-Hatogen Derivatives Preparation and Properties 8

Physical Properties of Di-Hatogen Derivatives

Dihalogen derivatives are colourless, sweet smelling liquids. They are insoluble in water but soluble in organic solvents. They are heavier thaii water.

Chemical Properlies of Di-Hatogen Derivatives

Chemical reactions of di-halo deri”atives are similar to mono-halogen derivatives. Some reaction are as follows:

→ Hydrolysis : Gem-dihalides get hydrolysed with aqueous KOH or AgOH to give aldehyde or ketone whereas vic-dihalides gives glycol.

Di-Hatogen Derivatives Preparation and Properties 9
Di-Hatogen Derivatives Preparation and Properties 10

→ Dehalogenation : Reaction of gem-dihalide with Zn gives alkene with double number of carbon atoms, Vic-dihalide gives alkene with same number of carbon atoms and α, ω-dihalide forms cycloalkane with same number of carbon atoms.

Di-Hatogen Derivatives Preparation and Properties 11

Uses of Di-Hatogen Derivatives

Mono and dihalo derivatives has the following uses:

  • Methyl chloride and ethyl chloride are used in the preparations of methyl cellulose and ethyl cellulose.
  • Ethyl chloride is used in the preparation of tetra ethyl lead.
  • Methyl and ethyl chlorides are used as refrigerants and as anaesthetic.
  • Many important organic compounds are synthesized by monohalo derivatives.
  • Di-halo derivatives are used as solvent for rubber.
  • Methylene chloride is used as extraction solvent in medicine and food industries.

Chemistry Notes