• Friedel Crafts reaction takes place in the presence of AlCl3 which is acidic in nature but aniline is basic.
• This leads to aniline forming a salt.
• The acquired positive charge on the nitrogen atom makes it a strong deactivating group and hence aniline does not undergo Friedel Crafts reaction.
• In p-Methylaniline, Aniline is substituted with an electron releasing methyl group.
• This increases the electron density on the nitrogen atom making it more available for donation. Thus, p-Methylaniline is basic in nature.
• In the case of p-Nitroaniline, Aniline is substituted with an electron withdrawing nitro group which decreases the electron density on the nitrogen atom.
• This makes the lone pair of electrons on nitrogen less available for donation, making it less basic.
• Thus, p-Methylaniline is more basic than p-Nitroaniline.
• The lone pair of electrons on nitrogen atom of aniline shows resonancewith the aromatic ring.
• Also, as discussed above, aniline is basic in nature because it can donate these lone pair of electrons.
• Acetylation of aniline is necessary because else it will react with the catalyst used in electrophilic substitution reactions (AlCl3) which is acidic in nature to form the salt of aniline.
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