chap17chem12b

chap17chem12b - Chap 17 Rxns of Benzene General reaction of...

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1 Chap 17 Rxns of Benzene General reaction of electrophilic aromatic substitution 1. Halogenation of benzne. A) Br-Br + Fe-Br 3 [Br-Br-FeBr 3 ] B) Chlorination c) Iodine 2) Nitration of benzene Br Br FeBr 3 Br + Br + Br + H FeBr 4 - fast + Cl 2 AlCl 3 Lewis acid Cl + HCl + 1/2I 2 + HNO 3 I + NO 2 + H 2 O I + Br + HBr + FeBr 3 E + E + E + E + H Base fast E + HBase +
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2 3) sulfonation of benzene. 1) Substitution effects- + HNO 3 cat. H 2 SO 4 NO 2 + H 2 O gives O N O + + H 2 O + HSO 4 - O N O + N O O- H + + HSO 4 - two other resonnance N O O - + H 2 SO 4 + H 2 SO 4 + SO 3 S O O OH + H 2 O reversible O S O O - + O S O O two others S O O- H + HSO 4 - two other resonnance O S O O O S O OH O
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3 A) e’ donating- activating toward electrophilles. ED= donating, by resonance or induction. 1 Alkyl groups are e’ donating by induction. ED E + + ED ED + E ortho ED + meta- 2 less stable E ED E + para prtefers ortho para substitution CH 3 HNO 3 H 2 SO 4 CH 3 NO 2 + CH 3 NO 2 40% 57% sterics CH 3 O N O + First step ,is rate determing due to loss of aromaticity CH 3 + NO 2 CH 3 + NO 2 + CH 3 + NO 2 + CH 2 CH 3 Br 2 FeBr 3 CH 2 CH 3 Br + CH 2 CH 3 Br 38% 62% sterics
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chap17chem12b - Chap 17 Rxns of Benzene General reaction of...

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