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Which type of chemical reaction does given by arene compounds ? Give there suitable examples and reactions. |
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Answer» Solution :Benzene gives electrophilic ADDITION and electrophilic substitution reactions. They also gives oxidation reactions. (A) Electrophilic addition reactions are comparatively difficult. (i) Hydrogenation : Reaction with HYDROGEN at high temperature and/or at high pressure, in presence of nickel catalyst. (ii) Chlorination : They perform addition reactions with chlorine in presence of uv radiation. (B) Electrophilic substitution reaction : Benzene possess STABILITY, so substitution reaction in benzene is difficult with reactions, the reaction occurs by liberation of electrons from the electrophiles. (i) Nitration : A nitro group is introduced into benzene is heated with a mixture of concentrated nitric acid and concentrated sulphuric acid (nitrating mixture). Such reaction substitute H of benzene with `-NO_(2)`. (ii) Sulphonation : A mixture of benzene and fuming `H_(2)SO_(4)` or oleum `(H_(2)S_(2)O_(7))` or `(H_(2)SO_(4) + SO_(3))` when heated at 353 K temperature one hydrogen of benzene is replaced to give benzene sulphonic acid, the reaction isknown as sulphonation. (iii) Halogenation : Arenes react with `Cl_(2)` and `Br_(2)` (halogens) in the presence of a Lewis acid like anhydrous `FeCl_(3), FeBr_(3)` or `AlCl_(3)` to give chlorination and bromination respectively (halogenation). `{:(phi + Cl_(2) overset(FeCl_(3))rarr phi " Cl" ),(phi + Br_(2) overset(FeCl_(3))rarr phi " Cl"):}}` where `phi = C_(6)H_(5)` (iv) Friedel-Crafts ALKYLATION reaction : When benzene is treated with an alkyl halide in the presence of anhydrous aluminium chloride, alkybenene is formed. So , addition of alkyl group in benzene in place of H is known as Friedel-Crafts alkylation. (v) Friedel-Crafts acylation reaction : The reaction of benzene with an acyl halide (RCOCl) or acid anhydride `((RCO)_(2)O)` in the presence of Lewis acids `(AlCl_(3))` yields acyl benzene. So, addition of acyl group `(RCO-)` in benzene in place of H is known as Friedel-Crafts alkylation. (C) Oxidation reactions : (i) Reductive ozonolysis : When benzene is treated with `O_(3)` in presence of `Zn + H_(2)O`, the ozonolysis and oxidation of benzene is carried out. (ii) Combustion reaction : when arenes compounds are combusted in presence of enough amount of oxygens, they GET combusted by following reactions : `C_(x)H_(y) + (x+(y)/(4)) O_(2) rarr x CO_(2) + (y)/(2) H_(2)O` |
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