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1、Chapter 23 Aromatic Nitrogen Compounds,23.1 Nitroarenes,23.1.1 Structure of Nitrobenzene,Preparation of Nitrobenzene,We have already seen many examples of the preparation of aromatic nitro compounds.By far the most important route to such compounds is electrophilic aromatic nitration with nitric aci
2、d.,23.1.3 Properties of Nitro Compounds,Nitrobenzene and related nitro compounds are generally high boiling liquids.Nitrobenzene have a characteristic odor of almonds.Nitrobenzene is readily absorbed through the skin and is poisonous.,b.p.210 211Pale yellow oil,2,4,6-Trinitrotoluene,TNT,m.p.81,TNT i
3、s an important explosive.It is relatively insensitive to shock and is used with a detonator(雷管,炸药).1,3,5-Trinitrobenzene is less sensitive than TNT to shock and has more explosive power,but is more difficult to prepare.,23.1.4 Reactions of Nitroarenes,Reactivities of Nitro Group,The nitro group is r
4、elatively stable to many reagents.It is generally inert to acids and most electrophilic reagents.It is also stable to most oxidizing agents.It reacts with RMgX and strongly basic reagents.The most important reaction of the nitro group in aromatic compounds is reduction.,Reduction,The reduction produ
5、cts depends on the reaction conditions used.,Monomolecular Reductions of Nitroarenes,Catalytic hydrogenation and chemical reducing agents in acidic media give the corresponding amines in high yield.,常用:Fe/HClZn/HCl,In acid the intermediate compounds cannot be isolated,but are reduced rapidly in turn
6、,In neutral media,a higher reduction potential is required and reduction is readily stopped at the hydroxylamine stage.,硝基苯还原关系图,Bimolecular Reductions of Nitroarenes,Reduction in basic media gives binuclear compounds.,芳环上的亲核取代反应,Mechanism,加成消除 机制,23.2 Arylamines(Aromatic Amines),23.2.1 Nomenclature
7、,Three common arylamines have the following names:,23.2.2 Physical Properties of Arylamines,23.2.3 Preparation of Arylamines,23.2.4 Basicity of Arylamines,Arylamines are less basic than alkylamines because the nitrogen lonepair electrons are delocalized by orbital overlap with the aromatic ring pi e
8、lectron system and are less available for bonding.As a general rule,substituents that increase the reactivity of an aromatic ring toward electrophilic substitution also increase the basicity of the corresponding arylamine.,Strongerbase,Weakerbase,23.2.5 Reactions of Arylamines,Electrophilic Aromatic
9、 SubstitutionOxidationBenzidine(对二氨基联苯)RearrangementDiazotization,Electrophilic Aromatic Substitution,Amino substituents are strongly activating groups in electrophilic aromatic substitution reactions.,100%,Friedel-Crafts Reactions of Amino-substituted Benzene Are Not Successful.,Vilsmeier Reaction,
10、Primary ReferenceVilsmeier,A.;Haack,A.Ber.,1927,60,119.,General Scheme,Example ReactionThe reaction proceeds by the formation of the electrophilic Vilsmeier complex followed by electrophilic substitution of the heterocycle.The formyl group is generated in the work up.Pyrrole,thiophene ad furan all u
11、ndergo this formylation which is highly selective for the C2 position.,References 1.Aromatic Heterocyclic Chemistry-David T.Davies2.Organic Chemistry-Clayden,Greeves,Warren and Wothers,Oxidation,Benzidine(联苯胺)Rearrangement,联苯胺重排,References 1.J AM Chem soc 1981 103 9552.STEDAM EN(36)4 1980 473-482,Me
12、chanism,Diazotization,Primary aromatic amines react with nitrous acid to yield stable arenediazonium salts,Arenediazonium salts are extremely useful in synthesis,because the diazonio group can be replaced by nucleophiles,注意事项,重氮盐是无色晶体，在干燥条件下不稳定，爆炸性强。重氮盐一般不溶于有机溶剂，可溶于水，其水溶液呈中性，在水中发生离子化，溶液具有导电性。重氮化反应要在
13、酸性条件下进行，酸的用量一般为1:1.5,重氮盐的轨道结构,23.3Synthetic Transformations of Aryl Diazonium Salts,Aryl diazonium salts can be converted into a range of systems as shown above.These reactions can be useful as the methodology can be complementary to other methods.Of particular note are the methods for introducing-F
14、 using HBF4(the Schiemann reaction)and-OH using H2O.The reactions of copper salts(CuCl,CuBr and CuCN)are known as the Sandmeyer reactions.Coupling with phenols gives azo-compounds which are important as yellow-red dyes or pigments.Aryl diazonium salts are prepared from aryl amines(previous page)whic
15、h in turn can be obtained by the reduction of nitrobenzene,Summary,Hydrolysis,Mechanism,Olah Reaction,Meerwein Reaction,Replacement by HydrogenDeamination by diazotization,Arenediazonium salts react with hypophosphorous acid(H3PO2)to yield products in which the diazonium group has been replaced by H
16、,The formation of hydrazine,肼,联氨,Diazonium Coupling Reactions,Electrophile,Summary,Aryl diazonium salts can be converted into a range of systems as shown above.Of particular note are the methods for introducing-F using HBF4(the Schiemann reaction)and-OH using H2O.The reactions of copper salts(CuCl,C
17、uBr and CuCN)are known as the Sandmeyer reactions.Coupling with phenols gives azo-compounds which are important as yellow-red dyes or pigments.Aryl diazonium salts are prepared from aryl amines(previous page)which in turn can be obtained by the reduction of nitrobenzene,23.4 Benzyne,问题的提出,苯环上没有吸电子取代基的卤代苯在常规条件下难于被亲核试剂取代,1,5-二甲基-2-碘苯不被NaNH2取代:,对氯甲苯与NaNH2反应生成二个产物:,反应机理,消除加成机制,苯炔存在的证据,23.4.1 苯炔的结构,23.4.2 苯炔的生成,23.4.3 苯炔的反应,1.二聚反应,2.亲核加成,3.亲电加成,4.环加成,23.4.4 芳香亲核取代反应的苯炔中间体机制,取代基对苯炔形成位置的影响,加成的方向,加成的方向取决于加成后形成的中间体稳定性,实例,
