Naphthalene

preparation and reaction of naphthalene

1. Polynuclear hydrocarbon

2. Type The rings are isolated Diphenyl methane Triphenyl methane The rings are fused together in the ortho position Naphthalene Anthracene Phenanthrene

3. Structure of naphthalene

4. All ten carbons are sp2 hybridized Overlap of Sp2 With s orbital's of 8 hydrogen atom. All carbon and hydrogen lying in one plane. It is confirmed by X ray diffraction studies. It is aromatic satisfies the Huckle’s rule It is less aromatic than benzene.

5. Naphthalene It is the largest constituent of Coal tar It is obtained by cooling middle and Heavy oil The crude naphthalene is melted and treated with sulphuric aicid to remove basic impurities. Washed with water. Treated with aqueous sodium hydroxide to remove acidic impurities. Finally naphthalene is distilled to give pure product.

6. Resonance hybrid of naphthalene

7. Structure of naphthalene Erlenmeyer proposed the symmetrical formula for naphthalene in 1866

8. Graebe proved that it did consist of two benzene rings fused together in the ortho position in 1869

9. Naphthalene on oxidation gives phthalic acid

10. When nitrated naphthalene gives nitro naphthalene which, on oxidation , gave o-nitro phthalic acid. This indicates that nitro group is in benzene ring and that it is the side chain which are oxidised .

11. Nitro naphthalene reduced give amino naphthalene oxidised , phthalic acid was obtained. An amino group attached to the nucleus renders sensitivity to oxidation,

12. Inference: benzene ring in phthalic acid obtained by oxidation of amino naphthalene is not the same ring as that originally containing nitro group in nitro naphthalene i.e naphthalene contains two benzene ring

13. Synthesis of Naphthalene

14. O- xylene bromide combines with disodioethane tetra carboxylic ester when refluxed in acid solution, gives tetrahydronaphthalene dicarboxylic acid. When the silver salt of this acid is heated, naphthalene is formed

15. Position of double bond in naphthalene

16. Fries rule Fries compared the double bonds present in polynuclear compounds with benzoquinone . Structure II and III have structure similar to benzoquinone . Quinones are reactive than pure aromatic compound. Fries belived that stable form of polynuclear compound did not have this quinone structure.

17. Fries rule The most stable form of polynuclear aromatic compound is that form which has maximum number of benzenoid ring i.e three double bonds in each individual ring. According to fries naphthalene has structure I [ has two benzenoid ring] and not the structure of II and III [ has one benzenoid ring]

18. Reaction of naphthalene

19. Number of reduced product depend on the reducing agent used . If sodium in ethanol is used it gives 1:4 dialin m.p is 28C Naphthalene Na Ethanol 1:4 Dialin 1:4 dialin is unstable isomerise to form 1:2 dialin which also unstable to form naphthalene in the presence of sodium ethoxide

20. When reduced with isopentanol it forms tetralin mp 206-208ᵒC. Tetralin is used as varnishes.

21. When naphthalene is reduced in the presence of nickel it forms tetralin then it gives decalin

22. Naphthalene get oxidised in the presence of sulphuric acid,vanadium pentoxide,mercuric sulphate or air to phthalic anhydride.

23. Naphthalene on oxidation in presence of permanganate gives phthalic acid

24. Naphthalene on ozonolysis yield phthaldehyde

25. ozonolysis

26. Substitution product of naphthalene Orientation in naphthalene nucleus is more complicated than benzene nucleus due to presence of two rings in former. First group always enter the first position except in two cases when second derivative is the main product. Sulphonation at higher temperature Friedel craft reaction.

27. Introduction of second substituent can give rise to homonuclear substitution [ substitution in the same ring] or heteronuclear substitution [ second substitution in another ring]

28. Homonuclear substitution occur only when group already present is ortho para directing

29. Self polarisability is greater at position I than in position II in case of naphthalene. Self polarisability position and larger magnitude of self polarisability , the more reactive will be that point for the electrophillic reagent. Pie electron density is greater in 1:2 than 2:3 therefore former will be more reactive than the later.

30. Friedel craft reaction Naphthalene nucleus is attacked by aluminum chloride when vigorous conditions are used. Lower temperature is maintained to carry out the friedel craft reaction. Introduction of acyl group in presence of aluminium chloride gives 1 and 2 ketones , the nature of the solvent affects the yield. Acetyl chloride in carbondisulphide gives compound 1 and 2 in the ratio 3:1 and with nitrobenzene it is 1:9

31. Chloromethylation of naphthalene- Paraformaldehyde,HCl , phosphoric acid,Glacial acetic acid

32. Nitro naphthalene Nitric acid attacks naphthalene at room temperature to form 1 nitro naphthalene. Nitration of naphthalene at higher temperature give a mixture of 1:5 and 1:8 dinitro derivative. 2 nitro naphthalene is prepared by heating 2 naphthalene diazonium boro fluoride with sodium nitrite and copper powder.

33. Naphthalene sulphonic acid

34. When naphthalene is treated with concentrated sulphuric acid at 40C gives the I derivative and at 160C it yields II derivative. Β eta naphthalene sulphonic acid is the starting material for all beta naphthalene derivatives

35. Naphthyl amine

36. Reaction of naphthalene

37. Colourless cyrstal Mp 82 C Boil at 217 C