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Phenols
- 1. PHENOLS B KARUNA DEVI ASSISTANTPROFESSOR PHARMACEUTICAL CHEMISTRY GOKARAJU RANGARAJU COLLEGE OF PHARMACY
- 2. LEARNING OUTCOMES ā¢ Classifyphenols. ā¢ Explain nomenclature. ā¢ Explain physico-chemical properties. ā¢ Explain methods of preparations. ā¢ Discuss the reactions of phenols. ā¢ Uses of phenol, o- cresol, resorcinol and naphthol.
- 3. NOMENCLATURE ā¢ Simplest memberof phenols. ā¢ Other members known as derivatives of phenols. OH Phenols
- 4. Classification of phenols: Phenols Monohydricalcohols Dihydric alcohols Trihydric alcohols OH OH OH Cl HOOC OH Phenols m - Cresol o - Chloro phenols p - hydroxybenzoic acid OH OH OH OH OH OH OH Resoscinol Hydroquine Catechol ļ”ļ ļ Naphthol OH OH OH Pyragallol OH OH OH Hydroxyquinone OH OH OH Phloroglucinol
- 5. PHYSICO-CHEMICAL PROPERTIES ā¢ Samefunctional group but similarity is to limited extent. ā¢ Similarity: Can be converted to esters and ethers. ā¢ Differences : Most of the properties and preparation methods are different. ā¢ So classified phenols and alcohols separately.
- 6. PHYSICO-CHEMICAL PROPERTIES ā¢ Phenolliquids or low melting solids because of H.B and have higher B.P. Nature ā¢ Phenol soluble in water and rest others insoluble in water.Solubility ā¢ Colorless unless coloring groups present.Color
- 7. HYDROGEN BONDING OH NO 2 OH NO2 OH NO 2 O - nitro phenol p - nitro phenol m - nitro phenol
- 8. METHODS OF PREPARATION Hydrolysisof diazonium salts Alkalifusion of sulfonates N2 + HSO 4 - Cl Cl OH m - chlorobenzene diazonium hydrogen sulphate m - chlorophenol H2O/H + /heat Ar ---NO2 Ar ------NH2 Ar -----N2 + HSO 4 - Ar -------OH Nitro Amine Diazonium salts Phenols SO3 - Na O - Na Sodium -2 - naphthalene sulfonate Sodium - 2 -naphthoxide 300ļ ļÆ ļ C / NaOH/ H 2O OH 2 - naphthol /ļ¢ - naphthol Dil H 2SO4
- 9. REACTIONS OF PHENOLS 1. ā¢Acidity/ salt formation 2. ā¢ Ester formation 3 ā¢ Ring substitution 4 ā¢ Ether formation
- 10. RING SUBSTITUTION REACTION Nitration Sulfonation Halogenation Friedalcrafts alkylation Friedal crafts acylation Nitration Coupling Kolbes reaction Reimer Tiemann raction Aldehyde formation Rxn with formaldehyde
- 11. ACIDITY/ SALT FORMATION ACIDITY:Phenols are weakly acidic. Order: Carboxylic acid > Phenols>Water. Phenols> Alcohols. Ka for phenols = 10-10 Ka for acids = 10-5 Ka for alcohols = 10-16 ā 10-18
- 12. ACIDITY/ SALT FORMATION Ka= More, Stronger acid Pka is less Ka = Less, Weaker acid Pka is more Kb = More, Stronger base Pkb is less Ka = Less, Weaker base Pkb is more PH = Pka + Log Salt/acid PH = Pka + Log ionized/unionized Phenols Salts (Acid) (Phenoxide) Insoluble in w ater Soluble in w ater
- 13. ACIDITY/ SALT FORMATION Ka=pH+ Log salt/acid
- 14.
- 15. EFFECT OF SUBSTITUENTSON ACIDITY ā¢ Three factors that effect acidity: 1. Nature of substituent. Ex. e-donating or e-withdrawing 2. Position of the substituent. Ex. Ortho, meta and para 3. No: of electron donating and withdrawing groups
- 16. NATURE OF SUBSTITUENT. ā¢Effect of electron withdrawing substituent: Ex. Cl-, CN-, NO2, CHO, COOH. ā¢ OH O2N + O2N O - + H + p - nitro phenol p - nitro phenoxide
- 17. ā¢ Effect ofelectron donating /releasing substituent: -CH3, -OCH3, -NH2 NATURE OF SUBSTITUENT. + H + OH NH2 O - NH2 p -amino phenol p - amino phenoxide
- 18. POSITION OF THESUBSTITUENT. Ortho or para position o Delocalize the negative charge on phenoxide ion more effectively. o 5 resonating structures Meta position o Delocalize the negative charge on phenoxide ion less effectively. o 4 resonating structures
- 19. NUMBER OF ELECTRONDONATING AND WITHDRAWING GROUPS
- 20. ESTER FORMATION ArSO2 --OHArSO2 ---Cl ArSO2 --OAr Aryl sulphonic acid Aryl sulphonic acid chloride Esters Ar ----OH ArCOCl ArCO ---OAr Aryl carboxylic acids Aryl acid chlorides Esters OH COCl O O + NaOH Phenol Benzoyl chloride Phenyl benzoate Acids ---------------Esters ----------Single stepReversible & Slow process Acids -----Acid chloride -------Esters --------Two stepIrreversible and fast process
- 21. ESTER FORMATION Schotten Baumann technique AqNaOH Calatyst and neutralize HCl that is liberated Pyridine converts acid chloride into powerful acylating agent
- 22. RING SUBSTITUTION REACTION OH 1.Nitration Dil HNO 3 / 20 ļÆ ļ C OH NO2 OH NO2 + ļļ ļ nitro phenol p - nitro phenol Polysubstitution Oxidation So at low temperature & dil acids Conc HNO 3 Polysubstitution OH NO2 NO2 O2N 2, 4, 6 trinitro phenol 2. Sulphonation 15 -20 o C/ H 2SO4 OH SO3H O - phenol sulphonic acid OH SO3H p - phenol sulphonic acid 100 o C / H 2SO4 Phenols
- 23. RING SUBSTITUTION REACTION OH 3.Halogenation Br2 /H2O OH BrBr Br ļ²,4,6 tribromo phenol Br2/ CS 2/ CHCl 3 Low polar solvents OH Br p - bromo phenol Aq Br2 Phenols Aq bromine all o & p position halogenated Even displacement of other groups occur Mono halogenation OH BrBr Br ļ²,4,6 tribromo phenol OH SO3H p -phenol sulphonic acid Replacement occurs
- 24. RING SUBSTITUTION REACTION OH 4.Friedal crafts alkylation HF OH CH3 CH3 CH3 5. Friedal crafts acylation Fries rearrangement OCOCH 3 CH3 m-cresyl acetate 6. Nitrosation NaNO 2, H2SO4 OH CH3 NO Phenols CH3Cl CH3CH3 t - butyl chloride p -tertiary butyl phenol OH CH3 m-cresol (CH3CO) 2O OH CH3 COCH 3 OH CH3 CH3CO 2 - methyl 4 -hydroxy acetophenone 4 - methyl 2 -hydroxy acetophenone para migration(acyl group) ortho migration(acyl group) OH CH3 o - cresol 4 -nitroso -2 -methyl phenol
- 25. RING SUBSTITUTION REACTION OH Phenols + Cl - N2 + Diazoniumsalts CouplingOH N N Azo compound Ar ---N2 + + Ar' ----H Mildly alkaline condition Ar ---N=N----Ar' + H + Diazoniumsalts Aromatic compounds Azo compounds
- 26. RING SUBSTITUTION REACTION NaO CO2/ 125 o C/4 -7 atmos OH COONa Sodiumphenoxide Sodiumsalicylate Kolbes reaction Applications
- 27. REIMER TIEMANN REACTION OH Phenols +CHCl 3 + Aq 3 NaOH OH CHO Salicylaldehyde + 3 NaCl + 2H2O Electrophilic aromatic substitution reaction Step 1: Abstraction of proton by base from chloroform
- 28. REIMER TIEMANN REACTION Step:2 Generation of dichlorocarbene Step:3 Addition of CCl2 to phenoxide ion
- 29. REIMER TIEMANN REACTION Step:4 Abstraction of proton from water Step:5 Tautomerism to give substituted phenol
- 30. REIMER TIEMANN REACTION Step:6 Displacement of halide ion by hydroxide ion Step:7 Tautomerism to give substituted phenol
- 31.
- 32. WILLIAMSONS SYNTHESIS ArO - + R----XArO ----R + X -- Phenoxide Alkyl halides Alkyl aryl ethers OH C2H5I /Aq NaOH ļÆļ Heat O C2H5 Phenol Ethyl phenyl ether Alkyl aryl ether OH + CH3 O S O CH3 O O Phenol Dimethyl sulphate O CH3 CH3 O S O Na O O + Anisole Methyl sodiumsulphate In Williamsons synthesis aryl halides cannot be used b.cos of low reactivity towards NSR Alkyl aryl ethers & aryl ethers
- 33. QUALITATIVE TESTS FORPHENOLS ā¢ Acidity: Carboxylic acids>Phenols>H2O. ā¢ Solubility: Soluble in Aq NaOH. Insoluble in Aq NaHCO3 ā¢ Colored reactions: performed in polar solvents. Or In non polar solvents then add pyridine.
- 34. QUALITATIVE TESTS FORPHENOLS 1. Phenols + Ferric chloride -------Green to Blue or Violet to Red. 2. Neutral fecl3 test: Colored solution 1- 2 drops of 5 % neutral fecl3 solution 1 ml of dil solution(Aq or Aq ethanol 0.2%) +
- 35. Phenols, resorcinol andcresol = Blue or violet ā¢ Catechol = Green p- bromo phenol= violet ā¢ Salicylaldehyde = violet Trichloro phenol = No color ā¢ P- chloro phenol=violet Alpha- naphthol=White color Salicylic acid =blue color QUALITATIVE TESTS FOR PHENOLS
- 36. ā¢ Color producenot permanent so observe immediately after addition. ā¢ Negative test: o-nitro phenol and m & p āhydroxy benzoic acid. QUALITATIVE TESTS FOR PHENOLS
- 37. ā¢ LIBERMANN REACTION(phenols with free para position) QUALITATIVE TESTS FOR PHENOLS Blue(Sodium salt of indophenol) Red(Indophenol) Blue green or blue violet 1 ml of conc H2SO4 +few crystlas of NaNO2 0.1 gm of phenol in dry test tube+ Dilute with water Dilute with NaOH
- 38. 0.2 gm ofsample 0.2 gm of sample + H2SO4 + H2SO4 QUALITATIVE TESTS FOR PHENOLS 10% NaOH solution in beaker Phenol, catechol, hydroquinone = blue color p-cresol= No color Alpha & beta naphthol=Faint green PHTHALEIN TEST:
- 39.
- 40. ā¢ Antiseptic anddisinfectant. ā¢ 5% to 10% ointment used to treat psoriasis and eczema. ā¢ 2% solution in treating hay fever and whooping cough ā¢ Bactericidal properties used cosmetic and dermatological drugs. ā¢ Anti dandruff shampoos and sunscreen lotions. ā¢ Used in preparation of molisch reagent. ā¢ Detection of arginine in proteins by sakaguchi test. ā¢ Antiseptic in perfumes. ā¢ Synthesis of fungicides ā¢ As antioxidant in rubber. ā¢ Precursor for synthesis of sudan dyes. STRUCTURE & USES OH OH Resorcinol OH ļ”ļ ļļ ļ naphthol