Presentation on theme: "Aromatic Hydrocarbons"— Presentation transcript:
1 Aromatic Hydrocarbons Nomenclature of the Derivatives of BenzenePhysical Properties of Aromatic HydrocarbonsPreparation of BenzeneReactions of BenzeneAlkylbenzenes
2 Nomenclature of Benzene Derivatives Nomenclature of the Derivatives of BenzeneNomenclature of Benzene Derivatives1. Monosubstituted benzenes(a) For certain compounds, benzene is the parent name and the substituent is simply indicated by a prefix
3 Nomenclature of the Derivatives of Benzene (b) For other compounds, the substituent and the benzene ring taken together may form a new parent name
4 Nomenclature of Benzene Derivatives There are three different ways that two groups can be attached to a benzene ring, so a prefix—ortho, meta, or para—can be used to designate the relative position of the two substituents.ortho-dibromobenzeneoro-dibromobenzeneor 1,2-dibromobenzenemeta-dibromobenzeneorm-dibromobenzeneor 1,3-dibromobenzenepara-dibromobenzeneorp-dibromobenzeneor 1,4-dibromobenzene
5 Nomenclature of Benzene Derivatives If the two groups on the benzene ring are different, alphabetize the names of the substituents preceding the word benzene.If one substituent is part of a common root, name the molecule as a derivative of that monosubstituted benzene.
6 Nomenclature of Benzene Derivatives For three or more substituents on a benzene ring:Number to give the lowest possible numbers around the ring.Alphabetize the substituent names.When substituents are part of common roots, name the molecule as a derivative of that monosubstituted benzene. The substituent that comprises the common root is located at C1.
8 Nomenclature of the Derivatives of Benzene When a substituent is one that when taken together with the benzene ring gives a new parent name, that substituent is assumed to be in position 1 and the new parent name is used
9 Nomenclature of Benzene Derivatives A benzene substituent is called a phenyl group, and it can be abbreviated in a structure as “Ph-”.Therefore, benzene can be represented as PhH, and phenol would be PhOH.
10 Example 31-1 Answer Solution: Nomenclature of the Derivatives of BenzeneExample 31-1Draw the structural formula for each of the following compounds:(a) 1,3,5-Trichlorobenzene(b) 2,5-Dibromophenol(c) 2,4-Dinitrobenzoic acidAnswerSolution:(a) (b)(c)
11 31.2 Nomenclature of the Derivatives of Benzene (SB p.150) Check Point 31-1Give the IUPAC name for each of the following compounds:(a) (b)(c)(d)(a) 1,2-Dimethylbenzene(b) 1-Methyl-2-nitrobenzene or 2-nitrotoluene(c) 3-Bromo-5-chlorobenzoic acid(d) 4-Bromo-2,6-dinitrophenolAnswer
12 Give the IUPAC name for each compound. PhCH(CH3)2isopropylbenzenem-butylphenol2-bromo-5-chlorotoluene
13 Which structure matches the given name? o-dichlorobenzene
15 Physical properties of aromatic hydrocarbons: have a fragrant smellgenerally less dense than water at 20°Cusually immiscible with watersoluble in organic solvents
16 Boiling point (°C) Melting point (°C) Density at 20°C (g cm–3) Physical Properties of Aromatic HydrocarbonsNameFormulaBoiling point (°C)Melting point (°C)Density at 20°C (g cm–3)Benzene220.127.116.118Methylbenzene111–950.867Ethylbenzene136–94
17 Boiling point (°C) Melting point (°C) Density at 20°C (g cm–3) Physical Properties of Aromatic HydrocarbonsNameFormulaBoiling point (°C)Melting point (°C)Density at 20°C (g cm–3)1,2-Dimethylbenzene144–25.20.8801,3-Dimethylbenzene139–47.40.8641,4-Dimethylbenzene13813.30.861
18 Industrial Preparation Catalytic Reforming of Alkanes Preparation of BenzeneIndustrial PreparationCatalytic Reforming of AlkanesCatalytic reforming converts alkanes and cycloalkanes into aromatic hydrocarbonse.g.PtC6H14 C6H6 + 4H2500°C, 10 – 20 atm
19 Destructive Distillation of Coal 31.5 Preparation of Benzene (SB p.157)Destructive Distillation of CoalHeating coal in the absence of air gives out coal gas, ammoniacal liquor, coal tar (قطران الفحم) and coke (فحم الكوك)Coal tar is a mixture of many organic compounds, mainly aromatic onesBenzene and methylbenzene can be obtained
20 Decarboxylation of Sodium Salt of Benzoic Acid Preparation of BenzeneLaboratory SynthesisDecarboxylation of Sodium Salt of Benzoic AcidWhen sodium benzoate is fused with sodium hydroxide, the carboxylate group is removed and benzene is formed
21 Preparation of Benzene Reduction of PhenolPhenol vapour is passed slowly over heated zinc dust to produce benzene and zinc(II) oxide
22 Reactions of BenzeneComparative Investigation of Chemical Properties of Cyclohexane, Cyclohexene and BenzeneReactionCyclohexane (a saturated alicyclic hydrocarbon)Cyclohexene (an unsaturated alicyclic hydrocarbon)Methylbenzene (an aromatic hydrocarbon)Action of Br2 in CH3Cl3 (in dark)No reactionBr2 decolourized and no HBr evolvedNo reaction with Br2 aloneIn the presence of FeBr3, Br2 decolourized and HBr fumes evolvedAction of H2 (with Ni catalyst)1 mole of cyclohexene reacts with 1 mole of H2 at room temperature1 mole of methylbenzene reacts 3 moles of H2 at high temperature and pressure
23 Cyclohexane (a saturated alicyclic hydrocarbon) Reactions of BenzeneReactionCyclohexane (a saturated alicyclic hydrocarbon)Cyclohexene (an unsaturated alicyclic hydrocarbon)Methylbenzene (an aromatic hydrocarbon)Action of acidified KMnO4No reactionKMnO4decolourizedAction of conc. HNO3 and conc. H2SO4Cyclohexene oxidized and colour darkensA yellow liquid is formed
24 Reactions of BenzeneMethylbenzene is highly unsaturated, but it is resistant to oxidation and addition reactionsThe resistance of oxidation and addition reactions of aromatic compounds is used to distinguish from unsaturated alkenesMethylbenzene reacts with Br2 in the presence of FeBr3. It is through substitution reaction
25 Electrophilic Aromatic Substitution Reactions Reactions of BenzeneElectrophilic Aromatic Substitution ReactionsMost characteristic reaction of aromatic compounds:Electrophilic substitution reactionsThe electrophiles attack the benzene ring, replacing one of the hydrogen atoms in the reactionElectrophiles are either a positive ion (E+) or some other electron-deficient species with a partial positive charge (+)
26 Reactions of BenzeneNitrationConc. H2SO4 increases the rate of reaction by increasing the concentration of the electrophile, NO2+ (nitronium ion)
27 Reactions of BenzeneSulphonationBenzene reacts with fuming sulphuric(VI) acid at room temperature to give benzenesulphonic acidHeating aqueous solution of benzenesulphonic acid above 100°C, benzene and sulphuric(VI) acid are formed
28 Reactions of BenzeneHalogenationBenzene reacts with chlorine and bromine in the presence of catalysts such as AlCl3, FeCl3, FeBr3, to give chlorobenzene and bromobenzene respectively
29 Reactions of BenzeneAlkylationWhen benzene is warmed with a haloalkane in the presence of catalysts such as AlCl3, an alkylbenzene is formedImportant step in chemical industry to produce polystyrene, phenol and detergents
30 Reactions of BenzeneExample 31-2Complete each of the following by supplying the missing reactant or product as indicated by the question mark:(a)(b)(c)Solution:(a)(b) conc. H2SO4, conc. HNO3(c) fuming H2SO4Answer
31 Reactions of BenzeneCheck Point 31-2(a) One mole of benzene reacts with three moles of chlorine under special conditions. What is the reaction condition required for the reaction?(b) Draw the structure of the reaction product in (a).Answer(a) UV radiation or diffuse sunlight must be present for the free radical addition reaction to take place.(b)
32 AlkylbenzenesAlkylbenzenes are a group of aromatic hydrocarbons in which an alkyl group is bonded directly to a benzene ringalso known as arenese.g.
33 This type of oxidation is limited to those molecules with AlkylbenzenesAlkylbenzenes are oxidized to benzoic acid by strong oxidizing agents such as hot alkaline potassium manganate(VII)This type of oxidation is limited to those molecules with
35 AlkylbenzenesThe C = C double bond and acyl groups in the side chain are oxidized by hot alkaline potassium manganate(VII)e.g.
36 AlkylbenzenesExample 31-3State the conditions under which methylbenzene can be converted in the laboratory to(a) C6H5CH2Cl(b) C6H5COOHAnswerSolution:(a) Reagent: Cl2Condition: in the presence of light(b) Reagent: (1) KMnO4–, OH–, (2) H3O+Condition: heating under reflux
37 AlkylbenzenesCheck Point 31-3Methylbenzene 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
38 31.7 Alkylbenzenes (SB p.164)Two different types of chlorination reaction of methylbenzene are:Type I: free radical substitution reactionType II: electrophilic aromatic substitution reaction
39 Orientation effects of substituents in electrophilic aromatic substitution reactions of monosubstituted BenzenesAlkyl groups and groups with lone pairs (electron donating groups) direct new groups to ortho-, para-positions and speed-up the reaction (i.e. o & p directors and activating groups).Halogens direct new groups to ortho-, para- positions but they slow down thereaction (i.e. halogens are o & p directors and deactivating groups).Electron withdrawing groups such as nitro, nitrile, and carbonyl direct newgroups to the meta-position and slow the reaction down (i.e. i.e. m directors and deactivating groups).Thus the order of reactivity of benzene and monosubstituted benzene derivatives in E.Ar.sub. is as in the following chartSubstituted benzene with o,p directors > Benzene > Halobenzene derivatives > Substituted benzene with m- directors
40 Orientation effects of substituents in electrophilic aromatic substitution reactions of monosubstituted BenzenesMeta directorsOrtho , para directors-NO2-SO3H-COOH, -COOR-CHO, -COR-CN-OH, -OR-NH2, -NHR, -NR2-C6H5-CH3, -R (alkyl)-F, -Cl, -Br, -I
41 Q2: What is the final product of the following reaction? Q1: What are the major products of the following reaction?Q2: What is the final product of the following reaction?a) o-chlorobenzaldehyde b) m-chlorobenzaldehyde c) p-chlorobenzaldehyde d) a,cQ3:Which one of the following compounds has aromatic character?