Chapter17

Chapter17 - 17-17-1Reactions of Reactions of Benzene and...

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Unformatted text preview: 17-17-1Reactions of Reactions of Benzene and itsBenzene and itsDerivativesDerivativesChapter 17Chapter 1717-17-2Reactions of BenzeneReactions of Benzene◆The most characteristic reaction of aromatic compounds is substitution at a ring carbon++ChlorobenzeneHalogenation:HClCl2FeCl3HCl++NitrobenzeneNitration:HNO2HNO3H2SO4H2O17-17-3Reactions of BenzeneReactions of Benzene+Benzenesulfonic acidSulfonation:HSO3HSO3H2SO4++An alkylbenzeneAlkylation:RRXAlX3HX++Acylation:An acylbenzeneHRCXAlX3HXOCROH17-17-4Electrophilic Aromatic SubstitutionElectrophilic Aromatic Substitution◆Electrophilic aromatic substitution:Electrophilic aromatic substitution:a reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile◆We study•several common types of electrophiles •how each is generated•the mechanism by which each replaces hydrogen++HEE+H+17-17-5ChlorinationChlorinationStep 1: formation of a chloronium ionStep 2: attack of the chloronium ion on the ring+++Resonance-stabilized cation intermediate; the positivecharge is delocalized onto three atoms of the ring+slow, ratedeterminingClHHClHClClClClClClClFeClClClFeClClClFeCl4-+-A molecular complex with a positive charge on chlorineFerric chloride(a Lewis acid)Chlorine(a Lewisbase)++An ion pair containing a chloronium ion17-17-6ChlorinationChlorinationStep 3: proton transfer regenerates the aromatic character of the ringClHCl-FeCl3ClHClFeCl3ChlorobenzenefastCation intermediate+++-+17-17-7EAS: General MechanismEAS: General Mechanism◆A general mechanism◆General question: what is the electrophile and how is it generated?+E+HEH+slow, ratedeterminingStep 1:Step 2:EH+fast+H+EElectro- phileResonance-stabilized cation intermediate17-17-8BrominationBromination◆Energy diagram for the bromination of benzene17-17-9NitrationNitration◆Generation of the nitronium ion, NO2+•Step 1: proton transfer to nitric acid•Step 2: loss of H2O gives the nitronium ion, a very strong electrophileHSO3O HHONOOHSO4ONOOHHConjugate acidof nitric acid++SulfuricacidNitricacidThe nitroniumionONOOHHOHH+ON O17-17-1010NitrationNitrationStep 1: attack of the nitronium ion (an electrophile) on the aromatic ring (a nucleophile)Step 2: proton transfer regenerates the aromatic ringONOHNO2NO2HHNO2++++Resonance-stabilized cation intermediate+OHHOHHHNO2NO2OHHHOHHH++++++17-17-1111NitrationNitration◆A particular value of nitration is that the nitro group can be reduced to a 1° amino groupCOOHNO23 H2NiCOOHNH22H2O4-Aminobenzoic acid4-Nitrobenzoic acid+(3 atm)+17-17-1212SulfonationSulfonation◆Carried out using concentrated sulfuric acid containing dissolved sulfur trioxideB enzenesulfonic acidBenzene+SO3HSO3H2SO417-17-1313Friedel-Crafts AlkylationFriedel-Crafts Alkylation◆Friedel-Crafts alkylation forms a new C-C bond between an aromatic ring and an alkyl groupClAlCl3HCl+Benzene2-Chloropropane(Isopropyl chloride)Cumene(Isopropylbenzene)+17-17-1414Friedel-Crafts AlkylationFriedel-Crafts Alkylation...
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This note was uploaded on 09/19/2011 for the course CHM 262 taught by Professor Staff during the Spring '08 term at Purdue.

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Chapter17 - 17-17-1Reactions of Reactions of Benzene and...

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