Organic chemistry I. Aromatic hydrocarbons. Zdeněk Friedl. Chapter 9. Solomons & Fryhle: Organic Chemistry 8th Ed., Wiley 2004

Transcription

1 Organic chemistry I Zdeněk Friedl Chapter 9 Aromatic hydrocarbons Solomons & Fryhle: Organic Chemistry 8th Ed., Wiley 2004

2 Aromatic hydrocarbons structure of aromates, delocalization energy Hückel s rule type of aromatic hydrocarbons reaction scheme of aromates electrophilic aromatic substitution S E Ar Friedel-Crafts alkylation and acylation further important S E Arreactions substituent regioselectivity in S E Ar reactions side-chain reactions oxidation and reduction of aromates 2

3 The orbital structure of benzene An electrostatic potential map of benzene (a) 6 sp 2 orbitals connected into a ring by σ-bonds (b) 6 p z orbitals of benzene ring (c) overlap of p z orbitals a delocalized structure of benzene 3

4 The delocalization energy of benzene A difference between heats of hydrogenation of cyclohexatriene (theor) and benzene 4

5 The Hückel s rule of aromaticity (4n+2) p electrons (n=0,1,2,3...) 5

6 Polycyclic aromatic hydrocarbons PAHs An enzymatic oxidation to reactive epoxides a alkylation of DNA 6

7 Nonbenzenoid aromatic compounds AZULENE delocalization energy of 205 kj mol -1 The electrostatic potential map of azulene: there is substantial separation of charge between the rings a an appreciable dipole moment 7

8 Nonbenzenoid aromatic compounds FULLERENES (C 60 buckminsterfullerene) 8

9 Heterocyclic aromatic compounds p-orbital structure of PYRIDINE PYRROLE 9

10 Summary of benzene reactivity 10

11 The reaction scheme of aromatic compounds oxidation S R R CH 2 CH 2 CH 2 CH 3 a a S E Ar A E A R CH CH R 11

12 S E Ar Summary of basic substitution reactions 12

13 S E Ar A general mechanism for the reaction 13

14 S E Ar The reaction coordinate of substitution reaction 14

15 S E Ar The electrophilic aromatic bromination 15

16 S E Ar Bromination of condensed aromates α β α - kinetic controlled β - thermodynamic controlled Br H Br Br 2 g - HBr g Br H 16

17 S E Ar The electrophilic aromatic nitration 17

18 S E Ar An alternative course of electrophilic aromatic nitration 18

19 S E Ar The electrophilic aromatic sulfonation 19

20 S E Ar Friedel-Crafts alkylation I 20

21 S E Ar Friedel-Crafts alkylation II 21

22 S E Ar Friedel-Crafts alkylation III An industrial synthesis of STYRENE 22

23 S E Ar Friedel-Crafts acylation I 23

24 S E Ar Friedel-Crafts acylation II Ageneration of the REAGENT (acylium cation) 24

25 S E Ar Friedel-Crafts acylation III Amechanism for the substitution reaction 25

26 S E Ar Selected electrophilic substitution reactions CHLOROMETHYLATION CH 2 =O + HCl + ZnCl 2 g CH + 2 -OH [ZnCl 3 ]- a a Ar-CH 2 -Cl GATTERMANN-KOCH GATTERMAN C O + HCl + AlCl 3 g CH + =O [AlCl 4 ] - a Ar-CH=O HOUBEN-HOESCH REIMER-TIEMANN HCN + HCl + AlCl 3 g CH + =NH [AlCl 4 ] - R-CN + HCl + AlCl 3 g RC + =NH [AlCl 4 ] - CHCl 3 + NaOH g CCl 2 a a Ar-CH=O a a Ar-CH=O a a Ar-(C=O)-R (activated aromates) 26

27 S E Ar Restrictions of Friedel-Crafts reactions 27

28 S E Ar The synthesis of a-tetralone F-C acylation a Clemmensen reduction a F-C acylation 28

29 S E Ar Substitution effects vs. regioselectivity I 29

30 S E Ar Substitution effects vs. regioselectivity II A classification of substituents 30

31 S E Ar Activating substituents a ortho-para orientation (+ I, + M) ; (- I, + M) effect 31

32 S E Ar Halogenes a ortho-para orientation (- I + M) effect: a deactivation of aromatic ring 32

33 S E Ar The reaction coordinates of benzene vs. chlorobenzene 33

34 S E Ar Deactivating substituents a meta orientation (- I) ; (- M) ; (- I M) effect 34

35 S E Ar Stability of s-complex vs. nature of substituent 35

36 S E Ar Summary of electrophilic aromatic substitution reactions 36

37 Oxidation of alkylbenzene side-chain 37

38 A E /A R Addition on C=C bond of alkenylbenzenes Aregioselectivity of A E a A R reactions 38

39 S R Halogenation of alkylbenzene side-chain 39

40 The regioselectivity of benzyl halogenation 40

41 An oxidation of aromatic hydrocarbons O O 2 V 2 O 5 g COOH COOH O O O 2 V 2 O 5 O g COOH COOH 41

42 An industrial problem to be solved Ox cat OH INNOCENTIVE Direct oxidation of benzene to phenol Deadline: November 29, 2004 Reward: $ 45,000 Further problems can be found at 42

43 A R Reduction of aromatic hydrocarbons 43

44 Summary of aromate synthetic reactions 44