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Other Important Reactions
of Haloalkanes

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Reaction of Haloalkanes with Metals

Most of the organic chlorides, bromides and iodides react with certain metals to form compounds containing carbon metal bond. Such compounds are called organometallic compounds.

Some important reactions of haloalkanes with metals are discussed below :

Formation of Grignard's reagent

Haloalkanes react with magnesium in dry ether to form alkyl-magnesium halides, also known as Grignard's reagents. The general reaction is :

General formula of grignard's reagents

Example : Ethylmagnesium bromide is formed when ethyl bromide reacts with magnesium.

Example of grignard's reagents : Ethylmagnesium bromide

Grignard's reagents are very reactive with compounds containing hydrogen (H+ ) and form alkanes.

Reaction of grignards reagents with water
Reaction of grignards reagents with alcohol

Because of this reason, it is necessary to avoid presence of moisture in the reactions involving Grignard's reagents.

Wurtz reaction

In Wurtz reaction, alkyl halides react with metallic sodium in dry ether to form symmetrical alkanes with double the number of carbon atoms present in the alkyl halide.

Wurtz reaction

Limitations of Wurtz reaction

  1. Wurtz reaction is not a good method for the preparation of unsymmetrical alkanes because a mixture of many compounds is formed.
    Limitations of Wurtz reaction with unsymmetrical alkyl halides
  2. In case of tertiary alkyl halides, elimination takes place because sodium is basic and the order of reactivity towards elimination reaction is tertiary > secondary > primary (discussed in elimination reactions).
    Limitations of Wurtz reaction with in case of tertiary alkyl halides

Reaction with lithium

Reaction of alkyl halide with lithium

Reduction of haloalkanes

Alkyl halides are reduced by many reducing agents like lithium aluminium hydride (LiAlH4), H2 in the presence of catalyst etc., to produce alkanes.

Reductiom of alkyl halides to alkanes using LiAlH4
Reduction of propyl bromide to propane using LiAlH4

Questions

Question : Grignard reagents should be prepared under anhydrous conditions. Explain why?

Answer : Grignard reagents, being very reactive, react with moisture present in the apparatus or the starting material. Hence, Grignard reagents must be prepared under anhydrous conditions.

Revision

Let's revise some important concepts.

Take a close look at the products :

Ethyl chloride

Convert 2-chlorobutane to 3,4-dimethylhexane

Convert chloroethane to bromobutane

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