Alkyl halide, their properties/ types / preparation/ reactions, and Uses

 ALKYL HALIDE

            The alkyl halides are acyclic organic compounds made up of carbon, halogens, and hydrogen.  When we remove one hydrogen from any alkanes it is converted into alkyl, when this alkyl reacts with halogen atom then it is converted into alkyl halide.

          On the basis of a number of halogen atoms present in a compound they are designated as mono, di, tri, or poly haloalkane. These are halogen derivatives of alkane. These compounds are divided into three types.

·        Primary alkyl halide

          If halogen atom attached to that carbon atom which is further attached to one more carbon atom or no carbon atom, then this compound, is known as primary alkyl halide.

primary alkyl halide

·        Secondary alkyl halide

          If halogen atom attached to that carbon atom which is further attached to two more the carbon atom, then this compound is known as a secondary alkyl halide.

secondary alkyl halide

·        Tertiary alkyl halide

          If halogen atom attached to that carbon atom which is further attached to three more the carbon atom, then this compound, is known as a tertiary alkyl halide.

tertiary alkyl halide

Properties of alkyl halide

1.        The trivial name of alkyl halide is alkyl halide but IUPAC name is haloalkane.
2. .     They give substitution and elimination reactions.
3. .     Like the other homologs series, alkyl halide lower member also exist as a gas,            high member up to C -18 exist as a liquid, and a member having carbon greater than eighteen exist as solid.
4. .       Alkyl halides are polar molecules, so they slightly dissolve in water. These compounds also dissolve in organic solvents.
5. .      The boiling point and melting point of alkyl halide increase with the increase of chain length.
6. .      A lower member of alkyl has a pleasant odor but higher members are odorless.
7. .     They are colorless.
8. .     The general formula of alkyl halide is R-X.
9. .     Alkyl halide has a high heat of vaporization.

Preparation of alkyl halide

            Alkyl halides are prepared by different methods which are as follow:

v From alcohol

           We can prepare alkyl halide from alcohol by different methods.

• 1.     When alcohol reacts with halogen acids in the presence of zinc chloride, it is converted into alkyl halide.

 

alkyl halide

• 2.     When alcohol reacts with thionyl chloride and the solvent used in this reaction is pyridine, alkyl halides are formed.

 

alkyl halide

• 3.     When alcohol react with phosphorous pentachloride, chloride ion replace hydroxyl group of alcohol and converted them into alkyl halide.

• 

  alkyl halide

  
  

v Halogenation of alkanes

          Halogenation of alkane is carried out by a free radicle mechanism. This reaction occurs in the presence of sunlight or high temperature and UV light. Halogens replace the hydrogen atom from alkane and converted them into alkyl halide.

 

halogenation

v Addition of halogen acids to an alkene

          Alkene reacts with hydrogen halides to form alkyl halides.

 

alkyl halide 

v  Synthesis of an alkyl iodide

     We cannot prepare alkyl iodide directly, it can be prepared by the reaction of alkyl bromide or chloride with sodium iodide.

alkyl iodide

Reactions of alkyl halide

            Alkyl halides are reactive compounds.  It gives the following reaction:

v Substitution reaction

v Elimination reaction.

v Reduction of alkyl halide

v Reaction with sodium lead alloy

v Wurtz synthesis

1.    Substitution reaction

          Substitution reactions are those reactions in which halogen atom is replaced by another group (nucleophile).

v Reaction with the salt of acetic acid

          When alkyl halide reacts with the sodium salt of acetic acid, ethyl acetate is formed.

salt of acetic acid

v With ammonia, ethylamine, Diethylamine,  and triethylamine   

          When alkyl halide reacts with ammonia, ethylamine is formed. When ethylamine reacts with an alkyl halide, Diethylamine is formed. When Diethylamine reacts with an alkyl halide, triethylamine is formed. When trimethylamine reacts with alkyl halide then quaternary ethyl ammonium ion is formed.

           

amine derivatives

v Reaction with sodium hydroxide

          When alkyl halide reacts with sodium hydroxide than alcohols are formed.

ethyl alcohol

v Reaction with nitric acid

          When alkyl halide reacts with nitric acid then nitroethane is formed.

nitroethane

2.    Elimination reactions  

          Those reactions in which hydrogen halide remove from alkyl halide is known as an elimination reaction.

v  Reaction of an alkyl halide with potassium hydroxide

          When alkyl halide reacts with alcoholic KOH, undergo elimination reaction and alkene is formed.

3.    Reduction of alkyl halide

            Alkyl halide undergo reduction reaction when reacts with Zn in the presence of aqueous acid-like Hydrochloric acid.

reduction of alkyl halide

4.    Reaction with sodium lead alloy

        Methyl chloride reacts with sodium lead alloy and tetramethyl lead is formed.

 

tetraethyl lead

5.   Wurtz synthesis

        When alkyl halide reacts with sodium in an ether solvent than alkanes are formed.

 

wurtz synthesis

Uses of Alkyl halides

1.  Alkyl halides are used for the preparation of a variety of compounds by a nucleophilic substitution reaction.
2.     They are used as a solvent in many chemical reactions.
3.      Chlorofluorocarbons are used in refrigerators and propellants for aerosols.   
4.     They are also used as fire extinguishers.
5.      We can also use alkyl halides in different pharmaceuticals.  
6.      Ethyl chloride used as a cooling agent for skin in some hot areas.
7.     They are also used as a varnish.
8.     Dichloromethane is used in plastic welding.
9.