Reaction sites Col R ■Benzene ring ■Side chain a -carbon
College Reaction sites of Science Benzene ring Side chain α-carbon R
林 I3,Electrophilic substitutions 一代三化反应：卤代、硝化、磺化、富氏化 An electrophilic substitution involves the substitution of one electrophile (a proton)from the aromatic ring with another electrophile.The aromatic ring remains intact. Electrophilic Aromatic Substitution X+ RC■Ot Halogenation Acylation Nitration, Alkylation NO NO. HSO,+ R+ Sulfonation SO3H
College I3、 Electrophilic substitutions of Science 一代三化反应:卤代、硝化、磺化、富氏化 An electrophilic substitution involves the substitution of one electrophile (a proton) from the aromatic ring with another electrophile. The aromatic ring remains intact
Reactions of benzene 1 Formation of aryl halides a substitution reaction,H is replaced with X catalyst +X2 +HX Example.Production of bromobenzene Fe or Br2 + +HBr FeBr3 12-54
College of Science 1
Reactions of other aromatics If toluene is used instead of benzene,we can get more than one product. CH3 (40%) +B2 Fe or HBr+ FeBr3 CH: No meta form is produced (60%) for this reaction. B 12-55
College of Science
2.亲电取代反应机制 Mechanism: ■--Step1:类似烯烃，亲电试剂进攻苯环的pi-键，形成碳 正离子 ■--Step2:这一步与烯烃不同，不是发生亲核试剂对苯环 进行加成，而是脱去一个质子，回复到稳定的芳香性苯环结 构，结果是取代反应。 ■Step1: ■Step2: Nu 6+ E -H -H" Nu + 6+ fast
College 2.亲电取代反应机制 of Science Mechanism: ---- Step 1: 类似烯烃，亲电试剂进攻苯环的pi-键，形成碳 正离子 ---- Step 2: 这一步与烯烃不同，不是发生亲核试剂对苯环 进行加成，而是脱去一个质子，回复到稳定的芳香性苯环结 构，结果是取代反应。 Step 1: Step 2: H E H E H E E+ + E H - H E + Nu - E Nu + E Nu slow fast