Phenol Notes

PHENOL Formula C6H5OH OH Structure Phenol is also known as carbolic acid or Benzenol or hydroxy benzene.In phenol —OH group is attached with sp2 hybridised carbon.It was discovered by Runge in the middle oil fraction of coaltar distillation and named it carbolic acid (carbo = coal; oleum = oil) .It is also present in traces in human urine. GENERAL METHODS OF PREPARATION (1) From benzene sulphonic acid : When sodium salt of benzene sulphonic acid is fused with NaOH phenol is obtained. C6H5SO3Na + NaOH  C6H5OH + Na2SO3 (2) From benzene diazonium chloride : When benzene diazonium chloride solution is warmed, phenol is obtained with evolution of nitrogen. OH NCl 2 (Steam distilled) H2O + N2 + HCl  (3) By distilling a phenolic acid with sodalime (decarboxylation): OH OH COOH (4) Salicylic acid From Grignard reagent : (The Grignard reagent on reaction with oxygen and subsequent hydrolysis by acid yields phenol) C6H5MgBr (5) [O] C6H5OMgBr H2O C6H5OH + Mg Br OH From benzene : + [O] (6) + Na2CO3 NaOH + CaO V2O5 300°C OH From chloro benzene : Aq. NaOH No NSR at normal condition R — Cl Aq. NaOH R — OH Ph—Cl Aq. NaOH 300°C Ph—ONa Ph — Cl Stable by resonance [NSR] ALCOHOL, PHENOL & ETHER Order of NSR : Cl Cl Cl NO2 < Cl NO2 < < NO2 NO2 NO2 max. –I, –M min. ed min. ESR max. NSR Aq. NaOH 300°C NO2 OH Aq. NaOH 25°C OH NO2 NO2 NO2 2, 4, 6–Trinitrophenol (Picric acid) (7) Industrial preparation of phenol: Phenol can be prepared commercially by : (a) (b) (c) (d) Middle oil fraction of coaltar distillation Cumene Raschig process Dow's process (a) Middle oil fraction of coaltar: (b) From cumene (Isopropyl benzene) : Cumene is oxidised with oxygen into cumene hydroperoxide in presence of a catalyst. This is decomposed by dil. H2SO4 into phenol and acetone. CH3 O CH3 OH C(CH3)2 CH O2 130°C Cumene OH H2SO4, H2O + H /100°C Cumene hydroperoxide + CH3 C O CH3 (c) o Raschig process : Chlorobenzene is formed by the interaction of benzene, HCl and air at 300 C in presence of o catalyst CuCl2 + FeCl3. It is hydrolysed by superheated steam at 425 C to form phenol and HCl. C6H6 + HCl + 1 O 2 2 CaCl2 / FeCl3 300°C C6H5Cl + H2O C6H5Cl + H2O C6H5OH + HCl 425°C (super heated steam) (d) Dow process : This process involves alkaline hydrolysis of chloro benzene-(large quantities of phenol formed). OH Cu  Fe C6H5Cl + NaOH + NaCl PHYSICAL PROPERTIES (i) (ii) Phenol is a colourless, hygroscopic crystalline solid. It attains pink colour on exposure to air and light. (slow oxidation) C6H5OH-------- O (iii) (iv) (v) (vi) O ----------- HOC6H5 Phenoquinone(pink colour) It is poisonous in nature but acts as antiseptic and disinfectant. Phenol is slightly soluble in water , readily soluble in organic solvents. Solublity of phenol in water is much lower than alcohols because of larger hydrocarbon part in the molecule. Due to intermolecular H-Bonding, phenol has relatively high boiling point than the corresponding hydrocarbons, aryl halides etc. but intermolecular H-bonding in o–derivatives is used in the preparation of dyes, drugs, bakelite and it's melting point (MP) is 43° C and boiling point (BP) is 182° C . CHEMICAL PROPERTIES (A) REACTIONS DUE TO –OH GROUP : Acidic Nature Phenol is a weak acid. The acidic nature of phenol due to formation of stable phenoxide ion in solution. The phenoxide ion is stable due to resonance. The negative charge is spread through out the benzene ring which is stabilising factor in the phenoxide ion. Electron withdrawing groups (–NO2, –Cl) increase the acidity of phenol while electron releasing groups (–CH3 etc.) decrease the acidity of phenol. C6 H 5OH ‡ˆ ˆˆ ˆ† ˆˆ 1  C 6 H 5 O + H 3O Phenol is stronger acid than alcohols but weaker than the carboxylic acids and even carbonic acid. The acidic nature of phenol is observed in the following: (i) Phenol changes blue litmas to red. (ii) Highly electro positive metals react with phenol. 2C6H5OH + 2Na  2C6H5ONa + H2 (iii) Phenol reacts with strong alkalies to form phenoxides. C 6 H 5 OH + NaOH (iv) 1   C 6 H 5 O N a +H 2O However phenol does not decompose Na2CO3 or NaHCO3 because phenol is weaker than carbonic acid. C6H5OH + Na2CO3 or NaHCO3  No reaction ALCOHOL, PHENOL & ETHER Ph — OH + Acid-I Ph—ONa Base-I Acid-I Base-I (v) NaHCO3 < < Acid-II Base-II + Base-II H2CO3 Acid-II Reaction in reverse direction . Phenol does not react with NaHCO3. CH3 C OH + NaHCO3 CH3 Acid-I (vi) H2CO3 [H2O + CO2] O O Acid-I Base-I C ONa + Base-I > > Acid-II Base-II Base-II Reaction in forward direction . Acetic acid reacts with NaHCO3 and gives effervesence of CO2. Reaction with PCl5 : Phenol reacts with PCl5 to form chloro benzene. The yield of chlorobenzene is poor and mainly triphenyl phosphate is formed. C6H5OH + PCl5  C6H5Cl + POCl3 + HCl 3C6H5OH + POCl3  (C6H5)3PO4 + 3HCl Reaction with Zn dust: When phenol is distilled with zinc dust benzene is obtained. C6H5OH + Zn CH2 Ex. Sol. OH Zn ? Zn ? Zn ? Zn ? No reaction CH3 OH Ex. CH3 Sol. CH3 Ex. Sol. Ex. CH3 No reaction COOH OH COOH Sol. Acid-II  C6H6 + ZnO Reaction with NH3( Bucherer reaction): Phenol reacts with NH3 in presence of anhydrous ZnCl2 to form aniline. Anhydrous ZnCl2 or (NH 4) 2 SO 3 / NH 3 150°C C6H5OH + NH3 C6H5NH2 + H2O Reaction with FeCl3: Phenol gives violet colouration with FeCl3 solution (neutral) due to formation of a complex. C6H5OH + FeCl3  Voilet colour This reaction is used to differentiate phenol from alcohols. Acetylation (Schotten-Baumann reaction) : Phenol reacts with acid chlorides or acid anhydrides in alkali solution to form phenyl esters. NaOH C6H5OH + ClCOCH3  HCl C6H5 O—C— CH3 O C6H5OH + Cl C6H5 NaOH HCl C C6H5O C— C6H5 O O Ether formation (Alkylation) : Phenol reacts with alkyl halides in alkali solution to form phenyl ethers. (Williamson's synthesis) C6H5OH + NaOH RX C6H5ONa   C6H5OR –NaX alkali solution Sodium phenoxide  C6H5OH + CH2N2 Reaction with P2S5 : 5C6H5OH + P2S5 (B) C6H5OCH3 + N2   5C6H5SH + P2O5 REACTION OF BENZENE RING : The —OH group is ortho and para directing. It activates the benzene nucleus. Halogenation : Phenol reacts with bromine in CCl4 to form mixture of o–and p–bromo phenol. OH OH OH + Br2 Br CHCl 3 or CS2 or CHCl 4 low temp. + Br Phenol reacts with bromine water to form a white ppt. of 2,4,6 tribromo phenol. OH OH Br Br + 3Br2 + 3HBr H2O Br Nitration : Phenol reacts with dil. HNO3 at 0°–10° C to form o- and p- nitro phenols. OH OH OH NO2 dil. HNO3 0 - 10°C (40%) + NO2 (10%) ALCOHOL, PHENOL & ETHER When phenol is treated with nitrating mixture to form 2,4,6- trinitro phenol (picric acid) OH OH NO2 NO2 conc. HNO3 conc. H2SO4 [2, 4, 6–Trinitrophenol (Picric acid)] NO2 Sulphonation: Phenol reacts with fuming H2SO4 to form o–and p–hydydroxy benzene sulphonic acid at different temperatures. OH SO3H 25°C OH + conc. H2SO4 OH 100°C SO3H Friedel-Craft's reaction : Phenol when treated with methyl chloride in presence of anhydrous AlCl3 p-cresol is main product. OH OH OH + CH3Cl CH3 Anhydrous AlCl3 + CH3 o-cresol OH p-cresol OH OH + CH3COCl COCH3 Anhydrous AlCl3 + COCH3 o – and p – hydroxy acetophenone Gattermann aldehyde synthesis : When phenol is treated with liquid HCN and HCl gas in presence of anhydrous AlCl3 yields mainly p- hydroxy benzaldehyde (formylation) HCl + HCN AlCl3 HN CHCl OH OH OH + HN CHCl H2O AlCl3 HCl NH3 CH NH CHO Riemer-Tiemann reaction : Phenol on refluxing with chloroform and NaOH (aqueous) followed by acid hydrolysis yields o–hydroxy benzaldehyde. When CCl4 is used salicylic acid is formed. MECHANISM : CCl2 is neutral attacking electrophile (formed by elimination reaction) CHCl3 KOH : CCl2 Kolbe 's Schmidt reaction : This involves the reaction of C6H5ONa with CO2 at 1400 C followed by acid hydrolysis salicylic acid is formed followed. Hydrogenation: Phenol when hydrogenated in presence of Ni at 150-2000C forms cyclohexanol. ALCOHOL, PHENOL & ETHER Fries rearrangement reaction : C6H5OH + CH3COCl Anhydrous AlCl3 C6H5OCOCH3 Duff 's reaction: This method gives only the o-compound which is hindered by the presence of a –I group in the ring. Coupling reactions: Phenol couples with benzene diazonium chloride in presence of an alkaline solution to form a dye (p- hydroxy azobenzene) red only. Phenol couples with phthalic anhydride in presence of conc. H2SO4 to form a dye (phenolphthalien) used as an indicator. Lederer Manasse (Condensation with formaldehyde) : Phenol condenses with HCHO (excess) in presence of NaOH or weak acid (H+) to form a polymer known as bakelite (aresin). Leibermann's nitroso reaction : When phenol is reacted with NaNO2 and conc. H2SO4 it gives a deep green or blue colour which changes to red on dilution with water. When made alkaline with NaOH original green or blue colour is restrored. This reaction is used as a test of phenol. 2NaNO2 + H2SO4  2HNO2 + Na2SO4 Reaction with acetone: (Condensation with acetone) ALCOHOL, PHENOL & ETHER Oxidation: TESTS OF PHENOL (i) Phenol turns blue litmus to red. (ii) Aqeous solution of phenol gives a violet colour with a drop of ferric chloride. (iii) Phenol gives Lieber mann 's nitroso test. Phenol in conc. H2SO4 NaNO2 excess of water Red colour NaOH excess Blue colour (iv) Aqeous solution of phenol gives a white ppt. of 2,4,6 tribromophenol with bromine water. (v) Phenol combines with phthalic anhydride in presence of conc. H2SO4 to form phenolphthalein which gives pink colour with alkali. (vi) With ammonia and sodium hypochlorite , phenol gives blue colour. Differences between phenol and alcohol (C2H5OH) : (i) Phenol is more acidic than aliphatic alcohol due to resonance in phenoxide ion. (ii) Phenol gives violet colour with FeCl3 while aliphatic alcohol does not give. (iii) Phenol gives triphenyl phosphate with PCl5 while aliphatic alcohol gives alkyl chloride. (iv) Phenol has phenolic odour whereas alcohol has pleasent odour. (v) Phenol on oxidation gives quinone while alcohol gives aldehyde or ketone and acids. Uses of Phenol : Phenol is used : (a) As an antiseptic in soaps and lotions. "Dettol" (2,4-Dichloro-3,5-dimethyl phenol) (b) In manufacture of azodyes, phenolphthalein , picric acid (explosive), cyclohexanol (Solvent for rubber), plastics (bakelite) etc. (c) In manufacture of drugs like aspirin salol, phenacetin etc. (d) As preservative for ink.