(i) Here, hydrolysis of benzene diazonium chloride in the presence of hypophosphorous acid converts it to benzene.
H3PO2 acts as a reducing agent in this reaction. Benzene diazonium chloride reduces to benzene by the addition of hydrogen and N2+ to N2. H3PO2 itself oxidises to H3PO3 where the oxidation number of P increases from +1 to +3. The presence of H2O facilitates the formation of HCl after the removal of Cl- from benzene diazonium chloride.
(ii) When a +R (Positive resonance effect) showing functional group joins phenol or benzene ring, their lone pairs participate in resonance or in delocalization. They show electron releasing tendency. The electrons are released towards benzene ring through delocalization. As a result of which the acidic strength of the compound is reduced due to the destabilization of the phenoxide ion due to concentration of negative charge. Eg. –NH2, -OR, R, OH, where R is an alkyl group. These are called ortho, para directing groups.
Due to the electron releasing effect of the –NH2 group on the benzene ring, the negative charge is delocalised at the ortho and para positions of the benzene ring. As a result the electrophile can easily attack at these positions where the negative charge is concentrated.
Resonance in aniline.
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