Reaction of haloarenes – Electrophilic Substitution Reaction
Electrophile refers to an electron seeking specie. Thus, electrophilic substitution reaction refers to the reaction in which an electrophile substitutes another electrophile in an organic compound. Haloarenes undergo the usual electrophilic reactions of the benzene ring such as halogenation, nitration, sulphonation and Friedel-Crafts reactions. We will discuss about them one-by-one, but let’s first understand the behaviour of Reaction Of Haloarenes towards the attack of an electrophile:
- Due to –I effect (electron withdrawing nature) of halogen, benzene ring gets somewhat deactivated towards electrophilic substitution reaction.
- Due to its various resonating structures, there’s an excess of electron or negative charge over ortho- and para- positions of the ring than the meta- position. Thus, haloarenes are o- and p- directive towards electrophilic substitution reaction.
Due to the above reasons, haloarenes are somewhat deactivated than normal benzene ring towards the electrophilic substitution reaction. Thus, these reactions occur slowly and require more drastic conditions as compared to those in benzene.
In the above Reaction Of Haloarenes when a haloarene comes in the vicinity of chlorine in the presence of ferric chloride as solvent, then the chlorine molecule develops a polarity within itself and the chlorine with a slightly positive charge acts as electophile (electron seeking) and attacks the electron rich ortho and para position of haloarene. Both ortho and para compounds are formed out of which para isomer is the major product and ortho isomer is the minor product.
In this reaction, first NO2 is formed from nitric acid which is initiated by the presence of sulphuric acid; NO2 has an electrophilic centre over N due to the presence of two electronegative oxygen atoms in the molecule. NO2 attacks the electron rich ortho and para positions, out of which we get para isomer as the main product and ortho isomer as the minor product.
In this reaction, SO3 formed from sulphuric acid acts as an electrophile. SO3 attacks the electron rich ortho and para positions of the haloarene, out of which para isomer is obtained as the major product and ortho isomer as the minor product.
In this reaction, alkyl and acetonic group act as electrophile due to the presence of positive charge over the carbon atom. These groups attack the electron rich ortho and para positions of the haloarene, in which the para isomer of the product is obtained as the major product and ortho as the minor product.
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