Objectives. Preparation of Haloalkanes by Halogenation. Preparation Aryl Chlorides by Electrophilic Substitution. Halogen Exchange. Halogenation.
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Preparation of Haloalkanesby Halogenation
Preparation Aryl Chlorides by Electrophilic Substitution
Free radical chlorination or bromination of alkanes gives a complex 287 Haloalkanes and Haloarenes mixture of isomeric mono- and polyhaloalkanes, which is difficult to separate as pure compounds.
CH4 + Cl2 CH3Cl + HCl
F2 > Cl2 > Br2 > I2.
Attack of or on an alkane is selective
Order of reactivity is 3° > 2° > 1°
Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts like iron or iron(III) chloride.
Alkyl iodides are often prepared by the reaction of alkyl chlorides/ bromides with NaI in dry acetone. This reaction is known as Finkelstein reaction.
The synthesis of alkyl fluorides is best accomplished by heating an
alkyl chloride/bromide in the presence of a metallic fluoride such as
AgF, Hg2F2, CoF2 or SbF3. The reaction is termed as Swarts reaction.