Haloalkane are one of the most
reactive classes of organic compounds. Their reactivity is due to the presence
of polar carbon – halogen bond in their molecules. The reactions of haloalkane
may be divided into the following types
Nucleophilic substitution reactions
Reaction with metals
As polar bond C?+ – X?-
is present in halo alkane, nucleophilic reagents are attracted by partially
positively charged carbon atoms and substitutes halogen. The substitution
reactions that take place through nucleophiles are called nucleophilic
substitution reactions. In short it is called SN reaction.
with aqueous alkali or moist silver oxide.(Hydrolysis)
Haloalkane react with aqueous solution of KOH or
moist silver oxide (Ag2O/H2O) to form alcohols.
R – X + KOH(aq) R – OH + KX (14.15)
R – X + AgOH(moist) R – OH + AgX (14.17)
with alcoholic ammonia (Ammonolysis)
react with alcoholic ammonia solution to form alkyl amines.
R – X + H – NH2
R – NH2 +
CH3 – CH2
– Br + H – NH2 CH3
– CH2 – NH2 + HBr (14.20)
Bromo ethane Ethyl amine
However, with excess of halo alkane,
secondary and tertiary amines along with quartenary ammonium salts are obtained
Nucleophiles such as cyanide and
nitrite ion which can attack nucleophilic centre from two sites are called
ambident nucleophiles. These nucleophiles can attack from either of these sites
depending upon the reaction conditions and the reagent used.
with alcoholic KCN
react with alcoholic KCN solution to form alkyl cyanides.
– X + KCN ? RCN + KX (14.22)
CH3 – CH2
– Br + KCN ? CH3 – CH2 – CN + KBr (14.23)
Bromo ethane Ethyl cyanide
with alcoholic AgCN
react with alcoholic AgCN solution to form alkyl isocyanide.
– X + AgCN ? R – C + AgX (14.24)