课件2012化硕有机aoc

1、第10章基反应10.1 引言1 基反应的特点:链反应1) 链（initiation: radicalformation）2) 链传递（propagation: successive steps generating new radicals）3) 链终止（termination: return to stable molecular species） 历史1900 Gomberg :发现三苯甲基1931 Michaelis: 提出生物反应过程中 基（J. Biol. Chem. 1931, 92, 211.） 基的中性neutralk离子型charged, ion-radicalsl双基bir

2、adicalsMoses Gomberg1866-1947the founder of radical chemistry(H3C)3CC(CH3)3 (H3C)3CC(CH3)3 Many Other ContributorsOCHOOCHOC(CH3)3C(CH3)3Galvinoxyl(H3C)3C(H3C)3C2有机基反应: 强调链的循环链终止链产物 2基 1反应物 1基 2反应物 2产物 1链链终止3反应物 1 + 反应物 2产物 1 + 产物 2乙烷的基氯代4均裂与异裂的区别5离子可高浓度，基通常只能以极稀浓度基终止反应的活化能很低 溶液中双基反应虽活化能为0，但由于反应组分在溶液

3、中的扩散，其反应速度取决于溶液的粘度。在通常温度下，速度为109 1010 M-1s-1.10.2基的产生与终止1热均裂法 (thermolysis)均裂能3040 kcal/mol, 温度在50200 C.The most easily cleaved bonds aomopolar bonds.Paneth experiment6Some Standard Bond Energies and Approximate Homolysis Temperatures7BondDkcal/ moleT CBondDkcal/ moleT CBondDkcal/ moleT CCC85670OO34

4、160OCl49280CH99850NN39230CI51350CO84680SS55440CBr674808Subsequent ReactionsH3CCH3 O O+(CH3)3CH3CO OC6H5CO2+ 92. 光化学均裂n 可见光能范围：可以将弱键均裂红色40 kcal/mol (167 kJ/mol)兰色70 kcal/mol (293 kJ/mol)n 紫外光 (200 nm)：140kcal/mol (586 kJ/mol)，足以将所有化学键均裂。Cl-Cl键离解能243 kJ/mol, 相当于光能 487.5 nm 247 kJ/mol.102. 光化学均裂 : 示例11

5、3单氧化还原法(redox methods)CrIICrIIIOH +ROOH+ORTiII+2H2O2TiIV2OH +2OH+Ar-N+ CuINCuIIAr+N2 +_Fenton 试剂C6H6OHC6H6+OHFe3+Fe2+H+C6H6OHC6H5OH+C6H6OH+ C6H6C12H12OH12Fe2+ + H2O2Fe3+ + OH + OH4. 氧化与还原反应中Na +Na+THFnaphthalene radical anionindicatorOONa +Na+PhPhTHFor EtherPhPhbenzophenone ketyldeep blue13Grignard反

6、应的可能机理1410.2.2 双基例如88 KN2NN15NN- N210.2.3 链终止（Termination and Inhibition）基淬灭过程相互偶合（combination）。既可直接形成化学键， 也可通过夺氢（disproportionation）转移到氧化剂或还原剂上16CH3CH3CH3CH3CH3C+CCH3CH3CCCH3 CH3CH3CH3CH3R +RR-RCH2HCH3CH2CH3CH3C+CCH3+HCCH3 CH3CH3CH3CH3CH3R +RR(H) + R(+H)例如17基阻抑剂:称为阻聚剂或抗氧剂例如Common inhibitorsoxygen(p

7、olyphenols such as hydroonesthiols,amines)18 抗氧剂机类化合物。三价膦还原过氧化氢类物质，使 产物。芳香胺、酚等也广泛用作抗氧剂In+ R-HR+ InH R+ O2R-O-OR-O-O+ R-HR-O-O-H + R氧分子与许多有机 物进行反应产生自 由基，在高温下润 滑油特别容易变质， 而抗氧剂能抓住过 氧基，切断链式过程，从而可阻 止烃类变质(autoxidation)10.3基结构与活性的脂肪烷烃中Cl夺氢的比例1 : 2 : 3 = 1:4.3:46Br 夺氢的比例1 : 2 : 3 = 1:250:6300More reactive on

8、es (F, Cl) are less selective and those oflower reactivity (Br) more selective.1910.4基取代反应1.卤代反应卤代反应的焓变：F：423； Cl：92; Br : 17; I : +67 kJ/mol氟代：过于激烈，难以氯代：需要，可顺利进行溴代：需较高温度碘代：很难发生。其逆过程，即碘代烷被HI还原 RI + HI R-H + I220卤代反应机理InitiationInitiatorXX+R+H-RX-XX-HpropagationSH2 机理RR-X+X2 RR-R +couplingR(+H)+R(H)t

9、erminationabstractiontransferR2 XX+R-XX2212. 自氧化反应分子氧处于三线态，具有顺磁性，相当于一个双排布情况如下：基，(s1s)2(s1s*)2(s2s)2(s2s*)2(s2px)2(p2py)2(p2pz)2(p2py*)1(p2pz*)1芳脂烃用氧进行氧化的相对活性PhCH(CH3)21.0PhCH2CH=CH2 Ph2CH2 PhCH2CH3PhCH30.0150.80.350.1822s2px*s2pxs2s*s2sOObond length: 121 pm23p2pz*p2py*p2pzp2py自氧化机理Propagation:+RR-O-

10、O-HR-O-O+O2R-HR-O-OR+R-O-O-R + O2Termination:2 R-O-O(R tertiary)RO O2ORR-O-O-O-O-R2RO + O224举例25O2CH3PhCH(CH3)2PhCCH3PhOH + (CH3)2C=O 115 CO OH0.05MPaH+异丙苯空气氧化制和苯酚CH3CH3PhCCH3H3CC OPh O+HOHOH十氢化萘6-羟基环葵酮O OO OHH SO24O+ HO+OHO HOO- H2O+H OOl醚类化合物，如乙醚、THF、1,2-二甲氧基乙烷等，自氧化生成爆炸性极强的过氧化物,如产物 EtO-(CHCH3-O-O-

11、)nH CHCl3自氧化能够产生极毒的光气，故市售氯仿多加入少量乙醇作为一个很应链终止剂基反263. 芳香族基取代反应 Gomberg-Bachmann 反应ROHAr-N-N=OHAr-N=N-OR + H OArNH+ RONO22Ar +N2+ ORNH2RONO+50%芳核基取代反应与亲电取代反应相比，受定位基团的效应的影响很小。取代主要发生在邻位，其次是对位。无论供基还是吸基，都能反应ArNN+Cu(I)Ar+Cu(II)+N2ArArNNAr+ArH+ Ar + N2 + H+10.5基加成与消除反应根据链转移的效率，基对双键的加成生成小分子或高分子XCC CC+Xktransfe

12、rXCC Y+ XXCCY+ X或者:kpolymerCCXCC +XCCCCPolymer当 ktransferktransfer kpolymer= CBrCl3hn CCl4 CH2Cl2 CH3Cl+ BrCCl3 CCl3+CClBr3Br 45%55%Brhn+ BrCCl3CCl3CCl3hn+ BrCCl330Br加醛、硫醇In+ RSHInH +RSRSCH2CHRRS+CH 2=CHRRS-CH2-CH2R+RS+RSHRSCH2CHRHHOCHCHC HOC+H3CCO2EtH3CHEtO2CCO2EtEtO2C31羧酸及其衍生物对烯烃的加成OOPhC O OCPhCH2

13、(CO2Et)2 + CH2=CH(CH2)9CO2Et(EtO2C)2CHCH2CH2(CH2)9CO2Et145 150 COSH CHCH3CCl CO2MeCuCl/Et3N.HClMeOSO2Cl+MeOCO2Me85 C, MeCN, 6hO100%MBSCsee V. Percec, J. Am. Chem. Soc. 1998, 120, 305-316.MBSCMMA32Frontier orbital diagram for the addition of radical to an alkene:CH2=CH2p*Me LUMOpSOMOpHOMO(a)Thestanda

14、rdofreferenceistheinteractionofmethylradicalwith ethylene,the radicalSOMOis approximately centered between the alkene HOMO and LUMO and interacts about equally with each33CH2=CHZpHOMO(b)If the alkene carries an electron-withdrawing substituent Z, its LUMO is lowered in energy and, as the molecules c

15、ome together, interacts more strongly with the radical SOMO than the HOMO does. The results is stabilization of theSOMO compared with the reference case (a) and faster reaction.34CH3SOMO p* LUMO352. 消除（Fragmentation of radicals）2 PhPh-C-O-O-C-Ph2 Ph-C-OCO2OOOEA = 27 kJ/molCH3+CO2CH3CO2 H。= 42 kJ/mol

16、=O+RRCO36( 190MeMeMe+MeMe(a)HOMe(a)HMeMeMeO1Me(b)Me+MeH(b)O3710.6基重排不如碳正离子普遍，但在上日益受到重视CH3CH3CH3t-BuOPhCCH2COPhCCH2PhCCH2CHO_COCH3CH3CH3Rearrangement of PhenylCH3RCHOor RSH1,2-shift(CH3)2CHCH2Ph(CH ) CCH PhPhCCH3 222CH3RCHO、RSH浓度加大，重排产物减少RCHOor RSHPhC(CH3)338Rearrangement of vinylHt-BuO- CODODDHHDD+反

17、-1-氘-1-丁烯D顺-1-氘-1-丁烯39Rearrangement of halogenHH+BrCl2CClHBrCl3CHHBrCl+BrClCl2CBrCl2C BrH402. Longer-range rearrangement of aryl groupsipso substitutionHR- RH413.1,5-氢迁移42See Barton, D. H. R. Aldrichimica Acta 1990, 23, 3. (Review)Petrovic,G.,Cekovic,Z.radicalalkylationoftheremotenonactivated -carbo

18、n atom. Tetrahedron Lett. 1997, 38, 627-630.43OOO HO HOONaNO2CH3HCHNOOOHOO HOH2OKonoike T, Takahashi K, Araki Y, et al, J. Org. Chem. 1997, 62, 960-966.CORO44Hofmann-Lffler 反应(also called Hofmann-Lffler-Freytag Reaction)45see: M. E. Wolff, Chem. Rev. 1963, 63, 55.4分子内加成和消除反应CH2CH3RH+RMajorCH2RH+R4647XXHH HHHHHHHHHHH HHH HHHH5-exo-trig6-endo-triggood SOMO-LUMOpoor SOMO-LUMO overlapoverlapBu3SnH+AIBN0.08 MBr+17%81%2%48当生成的基较，且无氢供体时，主要生成六CH2CH3CNCO2RCNCO2RRH+ RCNCCO