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New Way Chemistry for Hong Kong A-Level Book 3A1 New Way Chemistry for Hong Kong A-Level 3A 1 Benzeneand Electrophilic Aromatic Substitution.

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Presentation on theme: "New Way Chemistry for Hong Kong A-Level Book 3A1 New Way Chemistry for Hong Kong A-Level 3A 1 Benzeneand Electrophilic Aromatic Substitution."— Presentation transcript:

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2 New Way Chemistry for Hong Kong A-Level Book 3A1 New Way Chemistry for Hong Kong A-Level 3A 1 Benzeneand Electrophilic Aromatic Substitution

3 New Way Chemistry for Hong Kong A-Level Book 3A2 New Way Chemistry for Hong Kong A-Level 3A 2 Aromatic Hydrocarbons (Arenes) Simplest member : Benzene, C 6 H 6 Characteristic aroma Alkylbenzene, C n+6 H 2n+6 E.g. C 6 H 5 CH 3 C6H5C2H5C6H5C2H5

4 New Way Chemistry for Hong Kong A-Level Book 3A3 New Way Chemistry for Hong Kong A-Level 3A 3 Aromatic Hydrocarbons (Arenes) Generally less dense than water Insoluble in water but soluble in many organic solvents

5 New Way Chemistry for Hong Kong A-Level Book 3A4 New Way Chemistry for Hong Kong A-Level 3A 4 Aromatic Hydrocarbons (Arenes) PAHs : Polyaromatic hydrocarbons Fused aromatic rings

6 New Way Chemistry for Hong Kong A-Level Book 3A5 New Way Chemistry for Hong Kong A-Level 3A 5 Aromatic Hydrocarbons (Arenes) No heteroatoms Not PAH

7 New Way Chemistry for Hong Kong A-Level Book 3A6 New Way Chemistry for Hong Kong A-Level 3A 6 Aromatic Hydrocarbons (Arenes) PAHs : Polyaromatic hydrocarbons From incomplete combustion of wood, coal, diesel, fat, or tobacco Q.38 benzocyclobuta diene

8 New Way Chemistry for Hong Kong A-Level Book 3A7 New Way Chemistry for Hong Kong A-Level 3A 7 PAHs : Polyaromatic hydrocarbons Toxic and carcinogenic Benzo(a)pyrene : - first carcinogen discovered Found in : - tobacco smoke, - char-grilled food - burnt toast, - edible oils

9 New Way Chemistry for Hong Kong A-Level Book 3A8 New Way Chemistry for Hong Kong A-Level 3A 8 Preparation of Benzene

10 New Way Chemistry for Hong Kong A-Level Book 3A9 New Way Chemistry for Hong Kong A-Level 3A 9 1. Destructive Distillation of Coal Gives coal gas, ammoniacal liquor, coal tar and coke as products The coal tar produced is a mixture of many organic compounds (mainly aromatic ones) benzene and methylbenzene can be obtained by fractional distillation

11 New Way Chemistry for Hong Kong A-Level Book 3A10 New Way Chemistry for Hong Kong A-Level 3A Destructive Distillation of Coal A laboratory set-up of the destructive distillation of coal

12 New Way Chemistry for Hong Kong A-Level Book 3A11 New Way Chemistry for Hong Kong A-Level 3A 11 Industrial Preparation 2. Catalytic trimerization of ethyne

13 New Way Chemistry for Hong Kong A-Level Book 3A12 New Way Chemistry for Hong Kong A-Level 3A 12 Industrial Preparation 3. Catalytic Reforming of Petroleum Converts alkanes and cycloalkanes into aromatic hydrocarbons C 6 H 14  C 6 H 6 + 4H o C, 10 – 20 atm Pt

14 New Way Chemistry for Hong Kong A-Level Book 3A13 New Way Chemistry for Hong Kong A-Level 3A 13 Laboratory Synthesis 1. Decarboxylation of Sodium Salt of Benzoic Acid When sodium benzoate is fused with sodium hydroxide  the carboxylate group is removed

15 New Way Chemistry for Hong Kong A-Level Book 3A14 New Way Chemistry for Hong Kong A-Level 3A Reduction of Phenol Passing phenol vapour over heated zinc dust  produce benzene and zinc(II) oxide Benzene is separated by fractional distillation

16 New Way Chemistry for Hong Kong A-Level Book 3A15 New Way Chemistry for Hong Kong A-Level 3A 15 Reactions of Benzene

17 New Way Chemistry for Hong Kong A-Level Book 3A16 New Way Chemistry for Hong Kong A-Level 3A 16 Reactivity of Benzene Unreactive towards addition reactions due to stabilization of the system by delocalization of  -electrons

18 New Way Chemistry for Hong Kong A-Level Book 3A17 New Way Chemistry for Hong Kong A-Level 3A 17 Reactivity of Benzene Not oxidized by KMnO 4

19 New Way Chemistry for Hong Kong A-Level Book 3A18 New Way Chemistry for Hong Kong A-Level 3A 18 Reactivity of Benzene Resistant to electrophilic addition

20 New Way Chemistry for Hong Kong A-Level Book 3A19 New Way Chemistry for Hong Kong A-Level 3A 19 Reactivity of Benzene Resistant to catalytic hydrogenation

21 New Way Chemistry for Hong Kong A-Level Book 3A20 New Way Chemistry for Hong Kong A-Level 3A 20 Addition reactions occur only under drastic conditions.

22 New Way Chemistry for Hong Kong A-Level Book 3A21 New Way Chemistry for Hong Kong A-Level 3A 21 The  -electron cloud is susceptible to electrophilic attack. Substitution is preferred to addition since the former retains aromaticity. Electrophilic aromatic substitution (S E )

23 New Way Chemistry for Hong Kong A-Level Book 3A22 New Way Chemistry for Hong Kong A-Level 3A 22 Electrophilic Aromatic Substitution Reactions where E + denotes an electrophile

24 New Way Chemistry for Hong Kong A-Level Book 3A23 New Way Chemistry for Hong Kong A-Level 3A 23 General Reaction Mechanism Step 1: Benzene reacts with the electrophile A carbocation intermediate is formed Rate determining step

25 New Way Chemistry for Hong Kong A-Level Book 3A24 New Way Chemistry for Hong Kong A-Level 3A 24 General Reaction Mechanism The carbocation formed has a positive charge on the carbon atom of benzene Stabilized by delocalization of  electrons

26 New Way Chemistry for Hong Kong A-Level Book 3A25 New Way Chemistry for Hong Kong A-Level 3A 25 General Reaction Mechanism Step 2: The carbocation loses a hydrogen ion  forms the substitution product

27 New Way Chemistry for Hong Kong A-Level Book 3A26 New Way Chemistry for Hong Kong A-Level 3A Halogenation Benzene does not react with Cl 2 and Br 2 in 1,1,1-trichloroethane When catalysts (e.g. AlCl 3, FeCl 3 or FeBr 3 ) are present  benzene react readily with Cl 2 and Br 2  form chlorobenzene and bromobenzene

28 New Way Chemistry for Hong Kong A-Level Book 3A27 New Way Chemistry for Hong Kong A-Level 3A Halogenation No apparent reaction

29 New Way Chemistry for Hong Kong A-Level Book 3A28 New Way Chemistry for Hong Kong A-Level 3A Halogenation fast slow

30 New Way Chemistry for Hong Kong A-Level Book 3A29 New Way Chemistry for Hong Kong A-Level 3A Halogenation - Mechanism Step 1: The catalyst (FeBr 3 ) combines with bromine to give a complex

31 New Way Chemistry for Hong Kong A-Level Book 3A30 New Way Chemistry for Hong Kong A-Level 3A 30 Step 2: Formation of carbocation intermediate Rate determining step Stabilized by delocalization of  -electrons

32 New Way Chemistry for Hong Kong A-Level Book 3A31 New Way Chemistry for Hong Kong A-Level 3A 31 Step 3: The loss of a proton from the carbocation intermediate Forms the bromination product The catalyst (FeBr 3 ) is regenerated Fumes of HBr(g) are produced, indicating substitution rather than addition has occurred.

33 New Way Chemistry for Hong Kong A-Level Book 3A32 New Way Chemistry for Hong Kong A-Level 3A Nitration Benzene reacts readily with a mixture of conc. HNO 3 and conc. H 2 SO 4 Conc. H 2 SO 4 increases the rate of reaction by increasing the concentration of the electrophile, NO 2 +

34 New Way Chemistry for Hong Kong A-Level Book 3A33 New Way Chemistry for Hong Kong A-Level 3A 33 acidbase electrophile 2HNO 3 NO 3  + H 2 O + NO 2 +

35 New Way Chemistry for Hong Kong A-Level Book 3A34 New Way Chemistry for Hong Kong A-Level 3A 34 Optional

36 New Way Chemistry for Hong Kong A-Level Book 3A35 New Way Chemistry for Hong Kong A-Level 3A Sulphonation Benzene reacts with fuming sulphuric acid at room temp  form benzenesulphonic acid ++ (H 2 SO 4 + SO 3 )

37 New Way Chemistry for Hong Kong A-Level Book 3A36 New Way Chemistry for Hong Kong A-Level 3A Sulphonation Sulphonation is a reversible process By heating an aqueous solution of benzenesulphonic acid to above 100 o C  benzene and sulphuric acid are formed

38 New Way Chemistry for Hong Kong A-Level Book 3A37 New Way Chemistry for Hong Kong A-Level 3A Friedel-Crafts Alkylation When benzene is warmed with a haloalkane in the presence of AlCl 3 as a catalyst  alkylbenzene is formed

39 New Way Chemistry for Hong Kong A-Level Book 3A38 New Way Chemistry for Hong Kong A-Level 3A 38 Important starting step in the manufacture of styrene, phenol and detergents Example 29-6 Example 29-6 Check Point 29-6 Check Point Friedel-Crafts Alkylation

40 New Way Chemistry for Hong Kong A-Level Book 3A39 New Way Chemistry for Hong Kong A-Level 3A 39 The END

41 New Way Chemistry for Hong Kong A-Level Book 3A40 New Way Chemistry for Hong Kong A-Level 3A Nomenclature of the Derivatives of Benzene (SB p.191) Draw the structural formula for each of the following compounds: (a)1,3,5-Trichlorobenzene (b)2,5-Dibromophenol (c)2,4-Dinitrobenzoic acid Answer Back (a)(b)(c)

42 New Way Chemistry for Hong Kong A-Level Book 3A41 New Way Chemistry for Hong Kong A-Level 3A Nomenclature of the Derivatives of Benzene (SB p.192) Give the IUPAC name for each of the following compounds: (a) (b) Answer (a)1,2-Dimethylbenzene (b)1-Methyl-2-nitrobenzene or 2- nitrotoluene

43 New Way Chemistry for Hong Kong A-Level Book 3A42 New Way Chemistry for Hong Kong A-Level 3A Nomenclature of the Derivatives of Benzene (SB p.192) Give the IUPAC name for each of the following compounds: (c) (d) Answer Back (c)3-Bromo-5-chlorobenzoic acid (d)4-Bromo-2,6-dinitrophenol

44 New Way Chemistry for Hong Kong A-Level Book 3A43 New Way Chemistry for Hong Kong A-Level 3A Structure of Benzene and Aromaticity (SB p.195) The basic structural requirement for aromatic compounds is that the molecule must be planar, cyclic and with (4n + 2)  electrons delocalized in the ring. n must be a natural number (i.e. n = 1, 2, 3, and so on). There are aromatic compounds without benzene ring. An example is the 1,3-cyclopentadienyl anion. Can you draw its structure and explain its aromaticity? Answer

45 New Way Chemistry for Hong Kong A-Level Book 3A44 New Way Chemistry for Hong Kong A-Level 3A Structure of Benzene and Aromaticity (SB p.195) Back Cyclopentadienyl anion is an aromatic anion. It has six π electrons delocalized over a completely conjugated planar monocyclic system of five sp 2 hybridized carbon atoms. Cyclopentadienyl anion

46 New Way Chemistry for Hong Kong A-Level Book 3A45 New Way Chemistry for Hong Kong A-Level 3A Physical Properties of Aromatic Hydrocarbons (SB p.197) PAHs are formed from partial combustion and pyrolysis of aromatic compounds. They are in common occurrence in our environment. List some important uses of aromatic hydrocarbons and how they release PAHs to our environment. Answer

47 New Way Chemistry for Hong Kong A-Level Book 3A46 New Way Chemistry for Hong Kong A-Level 3A Physical Properties of Aromatic Hydrocarbons (SB p.197) Aromatic hydrocarbons are the raw materials for the manufacture of monomers and plasticizers in polymers, commonly used as solvents and important constituents of lead-free gasoline. Incomplete combustion and pyrolysis process favour the production of PAHs. These compounds are encountered abundantly in the atmosphere, soil and elsewhere in the environment from sources that include engine exhaust, wood stove smoke, cigarette smoke and charbroiled food. Coal tar and petroleum residues such as road and roofing asphalt have high levels of PAHs. Back

48 New Way Chemistry for Hong Kong A-Level Book 3A47 New Way Chemistry for Hong Kong A-Level 3A Reactions of Benzene (SB p.203) Complete each of the following by supplying the missing reactant or product as indicated by the question mark: (a) (b) (c) Answer Back (a) (b)conc. H 2 SO 4, conc. HNO 3 (c)fuming H 2 SO 4

49 New Way Chemistry for Hong Kong A-Level Book 3A48 New Way Chemistry for Hong Kong A-Level 3A Reactions of Benzene (SB p.203) (a)One mole of benzene reacts with three moles of chlorine under special conditions. What are the conditions required for the reaction? (a)UV radiation or diffuse sunlight must be present for the free radical addition reaction to take place. Answer

50 New Way Chemistry for Hong Kong A-Level Book 3A49 New Way Chemistry for Hong Kong A-Level 3A Reactions of Benzene (SB p.203) (b)Draw the structure of the reaction product in (a). Answer (b)

51 New Way Chemistry for Hong Kong A-Level Book 3A50 New Way Chemistry for Hong Kong A-Level 3A Reactions of Benzene (SB p.203) (c)Methylbenzene undergoes two different types of chlorination reaction by different mechanisms. Compare the two different types of chlorination reaction in terms of reaction conditions as well as the products formed. Answer

52 New Way Chemistry for Hong Kong A-Level Book 3A51 New Way Chemistry for Hong Kong A-Level 3A Reactions of Benzene (SB p.203) (c)The two different types of chlorination reaction of methylbenzene are: Type I: free radical substitution reaction Type II: electrophilic aromatic substitution reaction Back

53 New Way Chemistry for Hong Kong A-Level Book 3A52 New Way Chemistry for Hong Kong A-Level 3A 52 ReactionCyclohexane (a saturated alicyclic hydrocarbon) Cyclohexene (an unsaturated alicyclic hydrocarbon) Methylbenzen e (an aromatic hydrocarbon) Action of bromine in 1,1,1- trichloro- ethane (in dark) No reactionBromine is decolourized and no hydrogen bromide is evolved No reaction with bromine alone. In the presence of iron(III) bromide, bromine is decolourized and hydrogen bromide fumes are evolved Comparison of some reactions of cyclohexane, cyclohexene and methylbenzene

54 New Way Chemistry for Hong Kong A-Level Book 3A53 New Way Chemistry for Hong Kong A-Level 3A 53 ReactionCyclohexane (a saturated alicyclic hydrocarbon) Cyclohexene (an unsaturated alicyclic hydrocarbon) Methylbenzen e (an aromatic hydrocarbon) Action of hydrogen (with nickel catalyst) No reactionOne mole of cyclohexene reacts with one mole of hydrogen at room temperature One mole of methylbenzene reacts with three moles of hydrogen at high temperature Comparison of some reactions of cyclohexane, cyclohexene and methylbenzene

55 New Way Chemistry for Hong Kong A-Level Book 3A54 New Way Chemistry for Hong Kong A-Level 3A 54 ReactionCyclohexane (a saturated alicyclic hydrocarbon) Cyclohexene (an unsaturated alicyclic hydrocarbon) Methylbenzen e (an aromatic hydrocarbon) Action of acidified potassium manganat e(VII) No reactionAcidified potassium manganate(VII) solution is decolourized No reaction Comparison of some reactions of cyclohexane, cyclohexene and methylbenzene

56 New Way Chemistry for Hong Kong A-Level Book 3A55 New Way Chemistry for Hong Kong A-Level 3A 55 ReactionCyclohexane (a saturated alicyclic hydrocarbon) Cyclohexene (an unsaturated alicyclic hydrocarbon) Methylbenzen e (an aromatic hydrocarbon) Action of concentrat ed nitric acid and concentrat ed sulphuric acid No reactionCyclohexene is oxidized and the colour darkens A yellow liquid is formed Comparison of some reactions of cyclohexane, cyclohexene and methylbenzene


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