Chapter 26: Alcohols, Phenols, and Ethers PDF
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This chapter details the properties and reactions of alcohols, phenols, and ethers. It covers preparation methods, physical characteristics, and a variety of chemical reactions involving these hydroxy compounds. The material is suitable for undergraduate-level organic chemistry courses.
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60 1196 Alcohol, Phenol and Ethers Chapter E3 26 Alcohol, Phenol and Ether Hydroxy compounds ID Markowniko ff'' s CH 3 CH CH 2 HOSO 2OH H 2O CH 3 CH CH 3 CH 3 CH CH 3 U Monohydric alcohols These are compound containing one hydroxyl group. Their general formula is Cn H 2n 2...
60 1196 Alcohol, Phenol and Ethers Chapter E3 26 Alcohol, Phenol and Ether Hydroxy compounds ID Markowniko ff'' s CH 3 CH CH 2 HOSO 2OH H 2O CH 3 CH CH 3 CH 3 CH CH 3 U Monohydric alcohols These are compound containing one hydroxyl group. Their general formula is Cn H 2n 2O rule Propene Hydroxy compounds are those compounds in which the hydroxy group, – OH is directly linked with the aliphatic or aromatic carbon. | CH 3 | | Boil OSO 2 OH OH Propan - 2 - ol CH 3 | C CH 2 H H 2O C CH 3 H 2 SO 4 Bromoethan e C2 H 5 Br Bromoethan e D YG (1) Preparation : (i) From alkyl halide C 2 H 5 Br KOH C 2 H 5 OH KBr (Aqueous) AgOH | C CH 3 C2 H 5 OH AgBr Moist silver oxide | OH Ethanol 1° alkyl halide gives good yield of alcohols. 2° alkyl halide gives mixture of alcohol and alkene. 3° alkyl halide gives alkenes due to dehydrohalogenation. CH 3 CH 3 Alcohol (b) Oxymercuration-demercuration CC Oxy mercuration H 2 O Hg(OAc )2 Mercuric acetate (Aqueous) ST CH 3 | CH 3 C CH 3 KBr H 2 O | OH Tert. buty l alcohol(side product) (ii) From alkenes : (a) Hydration Direct process : CC Alkene | | | | C C HOH dil H 2 SO 4 | NaBH 4 C C Demercuration | | OH H Alcohol 2-Methy lpropene (Major product) Br | | OH HgOAc CH 3 C CH 3 KOH CH 3 C CH 2 | | C C | U | CH 3 Ethanol OH H This reaction is very fast and produces the alcohol in high yield. The alcohol obtained corresponds to Markownikoff’s addition of water to alkene. (c) Hydroboration oxidation (Antimarkownikoff’s orientation) | | | | (HBO) | | | | : H O , OH C C H BH 2 C C 22 C C H BH 2 H OH Alcohol Alcohol Indirect process : CH 2 CH 2 HOSO 2 OH CH 3 CH 2 OSO 2 OH Ethene Sulphuric acid Ethy l hy drogen sulphate CH 3 CH 2 OH H 2 SO 4 H 2O Boil Ethanol In case of unsymmetrical alkenes Diborane is an electron defficient molecule. It acts as an electrophile reacting with alkenes to form alkyl boranes R 3 B. Alcohol, Phenol and Ethers RCH CH 2 R CH CH 2 H BH 2 R CH C H 2 | | H CH 3 CH 2 NH 2 HONO 2 NaNO / HCl Aminoethan e B H2 CH 3 CH 2OH N 2 H 2O Alky l borane Ethanol RCH CH 2 (R CH 2 CH 2 )2 BH (RCH 2 CH 2 )3 B Dialkyl borane Trialkyl borane Carbocation are not the intermediate in HBO hence no rearrangement take place. 2 R Mg X O2 2 R O Mg X. Primary alcohol Al 2 O 3 RCO R H 2 R CH R NaBH 4 Ketone 60 (a) With oxygen : Pd RCHO H 2 RCH 2 OH LiAlH 4 It is not a good method of preparation of alcohols because number of by product are formed like alkyl chloride alkenes and ethers. (vii) From Grignard reagent (iii) By reduction of carbonyl compounds Aldehyde | or Ni / Pt 2 HOH 2 ROH 2 Mg(X )OH OH CH2 CH3 CH3 H2O CH3 CH3 (b) With ethylene oxide : HO OH E3 Secondary alcohol H3O+ CH2 B 2 H6 1197 HO – CH2 R Mg X CH 2 CH 2 O CH2OH H 2O RCH 2CH 2 OMgX RCH 2CH 2OH Mg(X )OH LiAlH 4 also reduces epoxides into alcohol : (c) With carbonyl compounds : H H ID CH 2 CH 2 LiAlH 4 CH 3 CH 2 OH O | H | | H 2O R Mg X R C R C R R C R CH 3 CH 3 | O | H LiAlH 4 CH 3 C CH 3 H | OH D YG CH 3 C CH 2 (iv) By reduction of carboxylic acids and their derivatives (i) LiAlH 4 R COOH RCH 2 OH Carboxylic acid (ii) H 2 O primary alcohol H2 RCOOH RCOO R RCH 2 OH R OH Carboxy lic acid Ester Cataly st Esters are also reduced to alcohols (Bouveault Blanc reaction) U O || CH 3 C OCH 3 4[H ] 25 CH 3 CH 2 OH CH 3 OH Na / C H OH ST Methy l acetate (Ester) || | O | OMgX OH If R = H, product will be 1°alcohol. If R = R, product will be 2°alcohol. If carbonyl compound is a ketone, product will be 3° alcohol. It is the best method for preparation of alcohol because we can prepare every type of alcohols. (viii) The oxo process : It is also called carbonylation or hydroformylation reaction. A mixture of alkene carbon monoxides and hydrogen. Under pressure and elevated temperature in the presence of catalyst forms aldehyde. Catalyst is cobalt carbonyl hydride [CoH (CO)4 ] U Hydride selectively attacks the less alkylated carbon of the epoxide. Ethanol Methanol Reduction with aluminium isopropoxide is known as Meerwein-Ponndorff verley reduction (MPV) reduction. product is a mixture of isomeric straight chain (major) and branched chain (minor) aldehydes. Aldehydes are reduced catalytically to the corresponding alcohols. 2CH 3 CH CH 2 2CO 2 H2 CH3 – CH – CHO | CH3 H2 Zn – Cu CH3 – CH – CH2OH | CH3 Isobutyl alcohol (Minor) 2 Me 2 C O (CH 3 )2 CHOH Al(OCHMe ) Isopropy l alcohol Me 2 CHOH CH 3 CH 3 (v) By alkaline hydrolysis of ester O O || || R C O R HO Na (aq ) R C ONa R OH. Sod. salt of acid (vi) From primary amines Alcohol CH 3 CH 2 CH 2 CHO CO H2 Zn – Cu (Major) CH3 – CH2 – CH2 – CH2 – OH n- Butyl alcohol (2) Physical properties of monohydric alcohols (i) Character : Alcohols are neutral substances. These have no effect on litmus paper. This is analytical test for alcohols. 1198 Alcohol, Phenol and Ethers | | | H O : - - - - - H O : Solubility | | R H 1 Size of alkyl groups (i) Reaction involving cleavage of with removal of ‘H’ as proton Alcohols are stronger acids than terminal acetylene but are not acidic enough to react with aqueous NaOH or KOH. Acidic nature is in the order HOH ROH CH CH NH 3 RH. Acidic nature of alcohol decrease with increase of alkyl groups on – OH bonded carbon due to +I (inductive) effect of alkyl group. 60 | R R R R character to OH bond. (iv) Solubility : The lower alcohols are miscible in water. > Tertiary and C – O – cleavage reactivity order : Tertiary > Secondary > Primary alcohol R H H R C O | H R C O R | H Increase in carbon-chain increases organic part hence solubility in water decreases. R | R C O H E3 (ii) Physical state : The lower alcohols (upto C12) are colourless alcohol with characteristic smell and burning taste. The higher members with more than 12carbon atoms are colourless and odourless solids. (iii) Polar character : Oxygen atom of the – OH group is more electronegative than both carbon and hydrogen. Thus the electron density near oxygen atom is slightly higher. Hydrogen bonding shown below H O- - - - H O- - - H O- - - - H O. This gives polar H (a) Reaction with Na : (Active metals) 2 RO H 2 M 2 ROM H 2 (M = Na, K, Mg, Al, Isomeric 1°, 2°, 3° alcohols have solubility in order 1°> 2°> 3°. etc.) (v) Boiling points : Due to intermolecular hydrogen bonding boiling points of alcohols are higher than hydrocarbon and ethers. reaction show that alcohols are acidic in nature. Alcohols acts as Bronsted acids because they donate a ID 1 ; B.P. follows the trends : No. of branche s 1° alcohol > 2° alcohol > 3° alcohol (vi) Density : Alcohols are lighter than water. D YG Density Molecular masses. (vii) In toxicating effects : Methanol is poisonous and is not good for drinking purposes. It may cause blindness and even death. Ethanol is used for drinking purposes. (3) Chemical properties : Characteristic reaction of alcohol are the reaction of the – OH group. The reactions of the hydroxyl group consists of either cleavage of C – O bond or the cleavage of O – H bond. | C O H U | ST C – O bond is weaker in the case of tertiary alcohols due to +I effect of alkyl groups while – OH bond is weaker in primary alcohols as electron density increase between O – H bond and hydrogen tends to separates as a proton. | bond R C O H ; | H Primary R R CH OH ; Secondary Example :........ R O H : B R O : Alcohol (acid) Base BH Conjugate acid Alkoxide (conjugate base) On reaction of alkoxide with water, starting alcohol is obtained....... H O H R O : R O H Acid.. Conjugate acid OH Conjugate base Base This is the analytical test for alcohols. (b) Reaction with carboxylic acid [Esterification] : RCO OH H OR Conc. Alcohol H2SO4 acid RCOO R H 2O Ester When HCl gas is used as catalyst, the reaction is called fischer-speier esterification. Polar bond H weaker proton to a strong base (: B ). U B.P. Evolution of H 2 shows the presence of –OH and R R R C OH weaker bond Tertiary Thus primary alcohols give the most of reaction by cleavage of O – H bond while tertiary alcohols are most reactive because of cleavage of C – O bond. Hence – O – H cleavage reactivity order : Primary > Secondary Presence of bulky group in alcohol or in acid decreases the rate of esterification. This is due to steric hindrance of bulky group. Reactivity of alcohol in this reaction is 1o 2 o 3 o. (c) Reaction with acid derivatives : (Analytical test of alcohol) O || CH 3 C Cl H O CH 2 CH 3 Ethanoy l chloride Ethanol O || CH 3 C OCH 2 CH 3 HCl Py ridine Ethy l ethanoate (Ethy l acetate) Alcohol, Phenol and Ethers O O || || In secondary and S N 1 mechanism operates Acylation : CH 3 C O C CH 3 H OCH 2 CH 3 Acetic anhy dride tertiary 1199 alcohols, the Ethanol H+ R OH O R OH 2 –H2O X R R X || CH 3 C OCH 2 CH 3 CH 3 COOH Ethy l ethanoate (d) Reaction with grignard reagents : (c) Reaction with PCl3 : Ethane 3 ROH PCl 3 3 RCl H 3 PO 3 (e) Reaction with ketene : Alcohol R O H CH 2 C O CH 2 C O R CH 3 C O R | || H O O (Keto form) (enol form) Py ridine ROH SOCl 2 RCl SO 2 HCl 360 o C R O H H N C H N C O R | O (d) Reaction with thionyl chloride [SOCl2] : Al 2 O3 ROH NH 3 RNH 2 || OH Primary amine ROH ROH R 2 NH R 3 N Al 2 O3 ID H NH C O R || O R OH conc. HNO 3 R O N (g) Reaction with ethylene oxide : ROH R O H CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 OH H 2O | OR OR | OR D YG 1, 2 -dialkoxy et hane (h) Reaction with diazomethane : R OH CH 2 N 2 R O CH 3 N 2 (Ether) (ii) Alkylation : ROH R2 SO 4 RO R RHSO 4 Tertiary amine (iii) Reaction involving cleavage of C OH with | | CH 3 CH 2 OH H 2 SO 4 removal or substitution of –OH group Conc. H2SO 17 4 0 110 H°2SO4 140°C (a) Reaction with hydrogen halides : Alcohols give alkyl halide. The reactivity of HX is in the order of HI > HBr > HCl and the reactivity of ROH is in the order of benzyl > allyl > 3° > 2°> 1°. The reaction follows a nucleophilic substitution mechanism. R X H 2 O ROH HX ZnCl 2 anhy drous If alcohols react with HI and red phosphorus, alkane will be formed. CH2 = CH2 Ethylene C2H5HSO4 Ethyl hydrogen sulphate C2H5O – C2H5 Diethyl ether U Grove’s process O H 2O O (g) Reaction with H2SO4 [Dehydration of alcohol] : The elimination of water from a compound is known as dehydration. The order of ease dehydration is Tertiary > Secondary > primary alcohol. The products of dehydration of alcohols are depend upon the nature of dehydrating agents and temperature. | | ST Al 2 O3 alky l nitrate U O | Secondary amine (f) Reaction with HNO3 : amino ester (Urethane) | Phosphorus acid (e) Reaction with ammonia : (f) Reaction with isocyanic acid : Alky l chloride Phosphorus trichloride E3 60 Ethy l magnesium br omide (Analytical test for alcohols) CH 3 OH C2 H 5 MgBr C2 H 6 CH 3 OMgBr Methy l alcohol (b) Reaction with PCl5 : ROH PX 5 RX POX 3 HX ; X = Cl –(H+) CH 3 OH CH 3 | | | | | | CH 3 C C C CH 3 H+/H2SO 4 Shiftin g + CH 3 CH 3 CH 3 C 2 H 5 OH 2 HI C 2 H 6 I2 H 2 O Red P heat Primary alcohols follow S N 2 mechanism. R OH 2 X X - - - R - - - OH 2 R X H 2 O Protonated 1o alcohol Alcohol leading to conjugated alkene are dehydrated to a greater extent than those of alcohols leading to nonconjugated alkene. Thus dehydration is in order 1200 Alcohol, Phenol and Ethers CH 2 CH C H CH 3 CH 3 CH 2 CH CH 3 | CH 3 | | OH | 2 -Methy lpropan - 2 -ol (Tert. alcohol) | H 2 SO 4 CH 3 C CH CH 3 CH 3 C CH CH 3 | H 2O | CH 3 OH | Important reagents used for oxidation of alcohols PCC [Pyridinium chloro chromate CH 3 CH 3 CH 3 | | CH 3 H CH 3 C CH CH 3 CH 3 C C | CH 3 CH 3 | H+ carboxylic acid. CrO3 H 2 SO 4 / Acetone to oxidise 2° alcohol to CH 2 CH CH 2 CH 3 E3 ketones. Jones reagents (chromic acid in aqueous acetone solution) oxidise 1° alcohol to aldehyde and 2° alcohol to ketone without affecting (C = C) double bond. MnO 2 selectively oxidises the –OH group of CH 2 CH CH CH 3 ID allylic and benzylic 1° and 2° alcohols to give aldehyde and ketone respectively. N 2 O 4 in CHCl 3 oxidises primary and secondary CH CH CH 2 CH 3 More amoun t (iv) General reaction of alcohols D YG (b) Oxidation : Difference between 1°, 2° and 3° alcohols. 1° RCH 2 OH R C O R C O H || O RCOOH CO 2 H 2 O O Drastic conditions CH 3 CH 3 | | 4 [O ] 3° CH 3 C OH CH 3 C O U (Under strong condition ) Acetone (Lesser number of carbon atoms) 4 [O ] CH 3 COOH CO 2 H 2 O ST (Under strong condition ) Acetic acid (Lesser number of carbon atoms) 3° alcohols are resistant to oxidation, but on taking stronger oxidising agent they form ketone. (c) Catalytic oxidation/dehydrogenation H H | | Cu , 573 K 1° CH 3 C O H CH 3 C O H 2 | Ethanal (Acetaldehy de) H Ethanol (Pri. alcohol) CH 3 | CH 3 | 2° CH 3 C O H CH 3 C O H 2 | H 2 -Propanol (Sec. alcohol) Cu , 573 K Propanone (Acetone) | R CH 2 CH 2 CH CH 2 OH OH Secondary alcohol CH 3 Tert. buty l alcohol (Tertiary ) R NaOC 2 H 5 , higher alcohol Carboxy lic acid CrO 3 2° R CH R R C R | | R | Aldehy de | benzyl alcohol. (d) Self condensation : Guerbet’s reaction R CH 2 CH 2 OH H CH CH 2 OH U (a) Reduction : R OH 2 HI R H H 2 O I2 OH and 2° alcohols to ketones. PDC [Pyridinium di chromate (C 5 H 5. NH )22 Cr2 O72 ] to oxidise 1° alcohols to aldehyde and 2° alcohol to ketones. H 2 CrO4 (chromic acid) to oxidise 1° alcohol to H2SO4 – H2O | (C6 H 5 N H Cl CrO3 ) ] to oxidise 1° alcohols to aldehydes 60 2 - alkene CH 2 CH CH 2 CH 3 OH 2-Methy lpropene (Alkene) CH 3 CH 3 | | 3° CH 3 C OH CH 3 C CH 2 H 2 O OH CH 3 CH 3 Cu , 573 K (e) Reaction with cerric ammonium nitrate : Cerric ammonium nitrate ROH Red colour solution of Yellow colour complex. This is analytical test for alcohols. (f) Iodoform test : When a few drops of alcohol are warmed with iodine and NaOH yellow precipitate of iodoform with characteristic smell is obtained. Any alcohol consists CH 3 CHOH group give iodoform test. Since reaction takes place with alkali solution as one of the reagents hence alkyl halide like CH 3 CH 2 Cl and CH 3 CH R will also give this test. | Cl (4) Uses of monohydric alcohol : (i) Uses of ethanol : It is used (a) In alcoholic beverages, (b) As a solvent in paints, varnishes, oils, perfumes etc., (c) In the preparation of chemical like chloroform, ether etc., (d) As a fuel in spirit lamps, (e) As an antifreeze for automobile radiators, (f) In the scientific apparatus like spirit levels, (g) As power alcohol. (ii) Uses of methanol : Alcohol, Phenol and Ethers (a) Methanol is an important industrial starting material for preparing formaldehyde, acetic acid and other chemicals. OH 1201 O | || CH 3 CH CH 3 CH 3 C CH 3 [O ] Propan - 2- ol (Iso- propy l alcohol) (2 alcohol) (b) As a fuel (a petrol substitute). A 20% mixture of methyl alcohol and gasoline is a good motor fuel. K 2 Cr2 O7 / H OMgBr OH | | H , H 2O CH 3 C CH 3 CH 3 C CH 3 CH 3 MgBr (c) As an antifreeze or automobile radiators. | | (d) To denature ethyl alcohol. The mixture is called methylated spirit. CH 3 CH 3 (e) In the preparation of dyes, medicines and perfumes. Methyl salicylate and methyl anthra anilate are used in perfumery. (iii) Primary alcohol into tertiary alcohol CH 3 CH 3 | H 2 SO 4 , Heat Dehy dration 2- Methy lpropan -1- ol (1) (Iso buty l alcohol) Ethanol (i) When CH3OH is heated on Cu coil it gives formalin like smell. (i) It does not give formalin like smell. (ii) When CH3OH is heated with salicylic acid in H2SO4 (conc.) then methyl salicylate is formed which has odour like winter green oil. (ii) No such odour is given. (iii) It does not give haloform or iodoform test. (iii) It haloform test Markowniko ff's rule CH 3 CH 3 E3 Methanol | CH 3 CH CH 2 OH CH 3 C CH 2 HBr Table : 26.1 Difference between methanol and ethanol | | CH 3 C CH 3 CH 3 C CH 3 aq. KOH | | Br OH 2- Methy lpropan - 2- ol (3) (tert. buty l alcohol) ID (iv) Lower alcohol into higher alcohol (ascent of series) HI KCN CH 3 OH CH 3 I CH 3 CN gives Methanol (1 carbon atom) 4 (H ) HONO CH 3 CH 2 NH 2 CH 3 CH 2 OH U Interconversion of monohydric alcohols (i) Primary alcohol into secondary alcohols SOCl 2 alc KOH C 3 H 7 OH C 3 H 7 Cl CH 3 CH CH 2 Propene D YG Propan -1-ol (1 alcohol) 60 2 - Methy lpropan - 2 - ol (3) (tert. buty l alcohol) K Cr O , H NaOH 7 C2 H 5 OH 2 2 CH 3 COOH CH 3 COONa | Br Ethanol (2 carbon atoms) (v) Higher alcohol into lower alcohol [Descent series] HBr aq. KOH CH 3 CH CH 3 CH 3 CH CH 3 | Reduction [O ] Ethanol (2 carbon atoms) OH Propan - 2- ol (2 alcohol) Cl 2 NaOH CaO aq. KOH CH 4 CH 3 Cl CH 3 OH (ii) Secondary alcohol into tertiary alcohol Heat Methanol (one carbon atom) Distinguish between primary, secondary and tertiary monohydric alcohols (i) Lucas test : A mixture of anhydrous ZnCl 2 conc. HCl is called as Lucas reagent. R CH 2 OH 2 R CH 2 Cl ppt. appears after heating conc. HCl / ZnCl Secondary conc. HCl / ZnCl 2 anhy. R2 CH OH R 2 CH Cl ppt. appears with in 5 minutes H 2O ST Tertiary anhy. H 2O U Primary ZnCl 2 / HCl R3 C OH R3C Cl ppt. appears immediately (ii) Victor mayer test : Also known as RBW test. RBW Red, Blue, White test. Primary Secondary P I2 AgNO 2 HONO NaOH C2 H 5 OH C2 H 5 I C2 H 5 NO 2 CH 3 C NO 2 CH 3 C NO 2 || || NOH NONa Nitrolic acid P I2 Sod. salt of nitrolic acid (Red colour) (CH 3 )2 CHOH (CH 3 )2 CHI (CH 3 )2 C NO 2 (CH 3 )2 C N O 2 No AgNO 2 HONO | H NaOH | reaction NO colour) Tertiary P I2 AgNO 2 HONO (CH 3 )3 COH (CH 3 )3 Cl (CH 3 )3 CNO 2 No reaction (colourless) Dihydric alcohols (Blue 1202 Alcohol, Phenol and Ethers These are compound containing two hydroxyl groups. These are dihydroxy derivatives of alkanes. Their general formula is Cn H 2n 2 O 2. The simplest and most important dihydric alcohol is ethylene glycol. They are classified as , , ….. glycols, according to the relative position of two hydroxyl groups. is 1, 2 glycol, is 1, 3 glycol. (1) Preparation (i) From ethylene : (a) Through cold dilute alkaline solution of Bayer’s reagent | | – C=C – | C– | OH 60 | –C= | OH (i) dil. (ii) dil. KMnO 4 OH– Chlorohydrin RCO2OH OH | | –C– C– | | OH H2O H+ O (Antihydroxylation) (b) With O2 in presence of Ag : CH 2 || CH 2 CH 2 1 Cataly st O2 | Ag , 200 400 C CH 2 2 Ethy lene CH 2 OH H 2O O | dil. HCl Ethy lene oxide ID | | –C–C– E3 (Synhydroxylation) CH 2 OH Ethy lene gly col D YG U (c) With HOCl followed by hydrolysis : (Industrial method) CH 2 CH 2 OH || | HOCl CH 2 CH 2 Cl Ethy lene chlorohy drin NaHCO 3 CH 2 OH | CH 2 OH NaCl CO 2 Gly col (ii) From 1, 2 dibromo ethane [Lab method]: CH 2 Br CH 2OH | Na 2 CO 3 H 2O | 2 NaBr CO 2 CH 2 Br CH 2OH CH 2 Br CH 2 OOCCH 3 CH 3 COOH 2CH 3 COOK | 2 KBr CH 2 Br CH 2 OOCCH 3 ST U | Gly col diacetate CH 2OH NaOH | 2CH 3 COONa CH 2OH (2) Physical properties (i) It is a colourless, syrupy liquid and sweet in taste. Its boiling point is 197°C. (ii) It is miscible in water and ethanol in all proportions but is insoluble in ether. (iii) It is toxic as methanol when taken orally. (iv) It is widely used as a solvent and as an antifreeze agent. (3) Chemical properties Na 50° C PCl 5 CH2 ONa | CH2 OH CH2Cl | CH2 OH N 160° a C PCl5 CH2 ONa | CH2 ONa Dialkoxide (Disodium glycollate) CH2 Cl | CH2 Cl 1,2 Dichloroethane Alcohol, Phenol and Ethers 4 R CO R 2 HCHO Aldehyde is more reactive than ketone in dioxalane formation. O O HIO + CH2OH – CH2OH CHO C O This part does not react due to steric hindrance O CH2 – OH CH3 | CH2 – OH H3C CH Cl CH OH | O CH3 O H2 CH 2 CHCHO CH 2 CHCH 2 OH cataly st H 2O2 / O H HOCH 2CHOHCH 2OH Glycerol (2) Physical properties (i) It is a colourless, odourless, viscous and hygroscopic liquid. (ii) It has high boiling point i.e., 290°C. The high viscosity and high boiling point of glycerol are due to association through hydrogen bonding. (iii) It is soluble in water and ethyl alcohol but insoluble in ether. (iv) It is sweet in taste and non toxic in nature. (3) Chemical properties (i) Reaction with sodium CH 2 OH CH 2ONa CH 2ONa | CH 2 OH D YG | U CH OOCR 3 H 2 O CH OH 3 RCOOH | | steam CH 2 OOCR ST NaOH | CH 2 OOCR | | NaOH (a) CH OH | Monosodium gly cerol 3 PCl 5 CH 2OH | | (b) CH OH | 3RCOONa CH 2 OH Sodium salt of higher fatty acids Yeast C6 H12 O6 C3 H 8 O3 CH 3 CHO CO 2 Glycerol CH 2Cl Gly cery l richloride t (1, 2, 3 - Trichloropropane) CH 2 Br PBr 3 CH 2OH | || CH 2 propene | Cl 2 CH o 600 C || CH 2 Ally lchloride | H 3 PO 3 CH Br | CH 2 Br 1, 2, 3 - Tribromopr opane CH 2 CH 2 I || | (c) CH OH PI 3 CH I CH I 2 | | | CH 2OH CH 2 I CH 2 I Ally liodide CH 2OH | | o 110 C CH OH CH OH CH 2 OH CH 2 OH | HCl Acetaldehyde || CH 2 Ally lalcohol | CH Cl | CH 2 OH - Gly cerol monochloro hy drin (66%) - Gly cerol monochloro hy drin (34%) CH 2 Cl Excess of HCl o 110 C | CH Cl | CH 2 OH Gly cerol , - dichlorohy drin (56%) | NaOH (dil ) CH | (iii) From propene [Modern method] CH 3 CH 2 Cl CH 2 OH CH 3 POCl 3 3 HCl | (ii) By fermentation of sugar Na 2SO 3 CH 2ONa Disodium gly cerolate CH Cl CH 2OH | Oil or fat Glucose | Room temperatur e CH 2 OH (Unstable) CH 2 OH CH OOCR NaOH CH OH Hy droly sis CH OH (iii) Reaction with HCl or HBr CH 2 OH CH 2 Cl CH 2 OH Gly cerol | | Na | Room temperatur e Fatty acids CH 2 OH Oil or fat CH 2 OOCR CH OH (ii) Reaction with PCl5, PBr3 and PI3 CH 2OH CH 2Cl Trihydric alcohols. The only important trihydric alcohol is glycerol (propane-1, 2, 3-triol). It occurs as glycosides in almost all animal and vegetable oils and fats. (1) Preparation (i) From oils and fats CH 2 OOCR CH 2 OH | CH OH Na | (iii) As a solvent and as a preservatives. (iv) As a cooling agent in aeroplanes. (v) As an explosives in the form of dinitrate. | Gly cerol (iv) From propenal : U O (4) Uses (i) Used as an antifreeze in car radiators. (ii) Used in the manufacture of dacron, dioxane etc. | CH 2 OH - monochloro hy drin | O | aq. NaOH CH 2 OH ID O H3C CH 2 OH | E3 H CH 2 OH HOCl 60 Dioxalane formation provides a path of protecting a carbonyl group in reaction studied in basic medium in which acetals are not affected. The carbonyl compound may be regenerated by the addition of periodic acid to aqueous solution of the dioxalane or by acidic hydrolysis. R R O CH 2 C H 2 OH C O | C | CH 2 OH R R O CH 2 1203 (iv) Reaction with HI CH 2 Cl | CH OH | CH 2 Cl Gly cerol , - dichlorohy drin (44%) 1204 Alcohol, Phenol and Ethers CH 2 I | CH 2 | (a) CH OH 3 HI CH I Warm | | CH 2OH CH 2 I 1,2,3 - Tri- iodopropan e (Unstable) CH 2 || CH 3 | | CH 3 CH | | HI || CH 2 I CH 2 I CH 2 Ally liodide Unstable Propene CH I | CH 3 Isopropy l iodide (v) Reaction with oxalic acid (a) At 110°C Glycerol is formed CH 2 OH | I2 CH 2 I Ally liodide | I2 CH CH 3 | HI CH I (b) CH || (viii) Reaction with nitric acid CH 2 OOC COOH | 100 110 o C 60 CH 2OH CH 2OH CH 2ONO 2 | | CH OH HOOC COOH CH OH CH OH 3 HNO 3 CH ONO 2 3 H 2 O CH 2 OH CH 2OH | H 2O Oxalic acid | conc. H 2 SO 4 | CH 2 OH | CH 2ONO 2 Gly cerolmono - oxalate Dynamite is prepared from T.N.G. || CH 2 O C H | CH 2 OH | 2 CH OH H COOH H O | | CH 2 OH CH 2 OH Gly cerolmono formate Formic acid Gly cerol || 2 CO 2 CH CH 2 OH Ally lalcohol | CH OH | CH 2OH D YG (vi) Dehydration CH 2OH CH 2 COOH CHOH CH2OH CH2OH COOH Glyceraldehy de Glyceric acid Tartronic acid U | ST | | | [O CHOH [O] ] | CHOH | CH2OH | CHOH COOH | CHO Fenton’ sreage nt | Acrolene or acraldehy de | CH2OH 2H 2O CH CHO (vii) Oxidation CHO [O] dil. HNO3 || conc. H 2 SO 4 / P2 O5 / KHSO 4 | CHOH + CH2OH CH2OH | [O KMnO ] 4 acidifi ed [O] | Dihydroxy acetone Hydroxy Pyruvic acid COOH | Oxalic acid 2CH2O + CO | COOH COOH 2HIO | [O] CO | CH2OH [O] COOH | CO [O] Cordite : It is obtained by mixing glyceryl trinitrate with gun cotton and vaseline it is smokeless explosive. (4) Uses (a) As antifreeze in automobile radiator. (b) In the preparation of good quality of soaphand lotions shaving creams and tooth pastes. (c) As a lubricant in watches. (d) As a preservatives. (e) As a sweetening agent in confectionary, beverages and medicines being non toxic in nature. (f) In dynamite. manufacture of explosives such as (i) Acrolein test : When glycerol is heated with KHSO 4 a very offensive smell is produced due to | CH2OH Glyceraldehy Dihydroxy de acetone Glyceros e CH2OH Blasting gelatin : A mixture of glyceryl trinitrate and cellulose nitrate (gun cotton). (5) Analytical tests of glycerol C=O | CH2OH C3 H5 (ONO)3 12CO2 10 H 2O 6 N 2 O2 U (b) At 260°C, allyl alcohol is formed CH 2 OH CH 2 OOC | | | HOOC 2 H O 2 | CH OH CH OO C | | HOOC CH 2 OH CH 2 OH CH 2 Dynamite : A mixture of T.N.G. and glyceryl dinitrate absorbed in kieselguhr is called dynamite. It was discovered by Alfred. Nobel in 1867. It releases large volume of gases and occupy 10,900 times the volume of nitroglycerine. ID CO 2 CH OH Gly cery l rinitrate t (T.N.G.) E3 O COOH Mesoxalic acid CO2 + H2O formation of acrolein. Its aqueous solution restores the colour of schiff’s reagent and reduces Fehling solution and Tollen’s reagent. (ii) Dunstan’s test : A drop of phenolphthalein is added approximately 5 ml of borax solution. The pink colour appears on adding 2-3 drops of glycerol, pink colour disappears. The pink colour appears on heating and disappears on cooling again. Alcohol, Phenol and Ethers Unsaturated alcohols (Allyl alcohol) as carbolic acid. It is also present in traces in human urine. (1) Preparation (1) Preparation CH 2 CH CH 2 Br H 2 O CH 2 CH CH 2 OH HBr (i) From benzene sulphonic acid C6 H 6 Benzene Ally lalcohol (ii) By heating glycerol with oxalic acid : | HOOC | HOOC CH OH CH 2 OH | CH 2 OOC | 2 H 2O Heat CH OO C CH 2 CO 2 | CH 2 OH | CH 2 OH Ally lalcohol OK 2 Br2 CH2Br – CHBrCH2OH 2, 3-dibromopropanol-1 HBr CH2BrCH2 CH2OH 3-Bromopropanol-1 HOCl CH3 pCresol HNO 3 C6 H 6 C6 H 5 NO 2 o Benzene H 2 SO 4 , 45 C Nitrobenze ne NaNO 2 HCl , 0 5 o C NH2 Sn / HCl C6 H 5 NH 2 Aniline C6 H 5 N 2 Cl Benzene diazonium chloride H 2O C6 H 5 OH Warm N2Cl Phenol OH CH2 OH – CHOH – CH2OH HNO 2HCl D YG Glycerol Na CH2 = CH – CH2ONa CH3COOH CH2 = CH – CH2OOCCH3 Allyl acetate HCl CH2 = CH – CH2Cl Allyl chloride COOH + | COOH U Br2 | | | Br OH CH3 mCresol (iii) From Grignard reagent C 6 H 5 Br Bromobenze ne Formic acid Br CH3 m-Toluene diazonium chloride Diazonium salts are obtained from aniline and its derivatives by a process called diazotisation. HCOOH CH2 – CH – CH2 H2 O CH3 mToluidine Ether Mg C 6 H 5 MgBr Phenyl magnesium bromide O2 H 2O C 6 H 5 OMgBr C 6 H 5 OH Oxalic acid ST CH3 (ii) From benzene diazonium chloride U CH2OHCHClCH2OH Glycerol -monochlorohydrin Oxidati on H+/H2O ID 1-propanol Phenol OH p-Toluene sulphonic acid CH3CH2CH2OH Pt (Allyl alcohol) Solid Fuse KOH CH3 (3) Chemical properties H or CO 2 / H 2 O E3 (b) It is soluble in water, alcohol and ether in all proportion. Sodium phenoxide This is one of the laboratory methods for the preparation of phenol. Similarly methyl phenols (cresols) can be prepared. (a) It is colourless, pungent smelling liquid. Alk. KMnO (O + 4 H2O) Fuse SO3H (2) Physical properties CH2 = CH – CH2OH – Sodium benzene sulphonate || NaOH Benzene sulphonic acid H / H 2O NaOH C6 H 5 ONa C6 H 5 OH C6 H 5 SO 3 Na CH 2 | H 2 SO 4 (f uming ) C6 H 5 SO 3 H 60 (i) From allyl halide CH 2 OH 1205 H Phenol (iv) From salicylic acid : OH HNO [O] OH COOH 3 CH2 – CH – COOH | Br + 2NaOH | Br Zn dust (CH3OH ) CH2 = CH – COOH Acrylic acid Phenol (Carbolic acid), C6H5OH or Hydroxy benzene It was discovered by Runge in the middle oil fraction of coal-tar distillation and named it ‘carbolic acid’ (carbo = coal, oleum = oil) or phenol containing 5% water is liquid at room temperature and is termed Salicylic acid CaO + Na2CO3 + H2O Phenol (v) Middle oil of coal tar distillation : Middle oil of coal-tar distillation has naphthalene and phenolic compounds. Phenolic compounds are isolated in following steps. Step I : Middle oil is washed with H 2 SO 4. It dissolves basic impurities like pyridine (base). Step II : Ecessive cooling separates naphthalene (a low melting solid) 1206 Alcohol, Phenol and Ethers Step III : Filtrate of step II is treated with aqueous NaOH when phenols dissolve as phenoxides. Carbon dioxide is then blown through the solution to liberate phenols. C6 H5 OH NaOH C6 H5 ONa H 2O CO 2 , H 2 O C6 H5 OH Na2CO3 H Step IV : Crude phenol (of step III) is subjected to fractional distillation. 180°C xylols (hydroxy xylenes) (vi) Raschig’s process Benzene 1 CuCl 2 / FeCl 3 O 2 C 6 H 5 Cl H 2 O 2 250 o C Chlorobenz ene o Phenol steam (vii) Dow process High pressure Chlorobenz ene sodium phenoxide on treatment with mineral acid yields phenol. (viii) Oxidation of benzene (3) Chemical properties V2 O5 2C 6 H 6 O 2 2C 6 H 5 OH o D YG 315 C (ix) Oxidation of isopropyl benzene [Cumene] H3C AlCl3 + CH3CH2CH2Cl CH3 (i) Acidic nature : Phenol is a weak acid. The acidic nature of phenol is due to the formation of stable phenoxide ion in solution. C6 H 5 OH H 2 O ⇌ C 6 H 5 O H 3 O Phenoxide ion CH AlCl3 + CH3CH = CH2 Due to intermolecular H- bonding and high dipole moment, melting points and boiling points of phenol are much higher than that of hydrocarbon of comparable molecular weights. (iii) It has a peculiar characteristic smell and a strong corrosive action on skin. (iv) It is sparingly soluble in water but readily soluble in organic solvents such as alcohol, benzene and ether. (v) It is poisonous in nature but acts as antiseptic and disinfectant. U 2C6 H 5 ONa H 2 SO 4 2C6 H 5 OH Na 2 SO 4 ID o 300 C C 6 H 5 Cl 2 NaOH C 6 H 5 ONa NaCl H 2 O | – O-------H – – (crossed intermolecular H-bonding between water and phenol molecules) 425 C C 6 H 5 Cl H 2 O C 6 H 5 OH HCl Chlorobenz ene + – O-------H E3 C 6 H 6 HCl H + | H – O-------H –– O------- o, m, p-cresols 211°235°C + – 60 fraction distillati al on Crude phenols + The phenoxide ion is stable due to resonance. O– O O O –.. Cumene –.. O – OH U | C(CH3)2 ST O2 Cataly st.. – OH H2O/H + (CH3)2CO + Acetone Cumene hydroperoxi de Phenol (2) Physical properties (i) Phenol is a colourless crystalline, deliquescent solid. It attains pink colour on exposure to air and light. (ii) They are capable of forming intermolecular Hbonding among themselves and with water. Thus, they have high boiling points and they are soluble in water. The negative charge is spread throughout the benzene ring. This charge delocalisation is a stabilising factor in the phenoxide ion and increase acidity of phenol. [No resonance is possible in alkoxide ions (RO–) derived from alcohols. The negative charge is localised on oxygen atom. Thus alcohols are not acidic]. Phenols are much more acidic than alcohols but less so than carboxylic acids or even carbonic acid. This is indicated by the values of ionisation constants. The relative acidity follows the following order K a (approx. ) (10 5 ) (10 7 ) (10 10 ) (10 14 ) (10 18 ) RCOOH H 2 CO 3 C6 H 5 OH HOH ROH Carboxy lic acid Carbonic acid Phenol Water Alcohols Effects of substituents on the acidity of phenols : Presence of electron attracting group, (e.g., NO 2 , – + – + – H – O-------H – O-------H – O-------H – + – + – O------- (intermolecular H-bonding among phenol Alcohol, Phenol and Ethers increases the acidity of phenol as it enables the ring to draw more electrons from the phenoxy oxygen and thus releasing easily the proton. Further, the particular effect is more when the substituent is present on o- or p-position than in m-position to the phenolic group. The relative strengths of some phenols (as acids) are as follows : p-Nitrophenol > o-Nitrophenol > m- Nitrophenol > Phenol Presence of electron releasing group, (e.g., CH 3 , C 2 H 5 , OCH 3 , NR 2 ) on the benzene ring decreases the acidity of phenol as it strengthens the negative charge on phenoxy oxygen and thus proton release becomes difficult. Thus, cresols are less acidic than phenol. However, m-methoxy and m-aminophenols are stronger acids than phenol because of –I effect and absence of +R effect. (b) Ether formation : Phenol reacts with alkyl halides in alkali solution to form phenyl ethers (Williamson’s synthesis). The phenoxide ion is a nucleophile and will replace halogenation of alkyl halide. C 6 H 5 OH NaOH C 6 H 5 ONa H 2 O Sod. phenoxide C 6 H 5 ONa ClCH 3 Chloro phenols : o- > m- > pCresols : m- > p- > o- C 6 H 5 ONa Cl HC(CH 3 )2 C 6 H 5 O HC(CH 3 )2 Isopropy l chloride Isopropy l pheny l ether Ethers are also formed when vapours of phenol and an alcohol are heated over thoria (ThO 2 ) or Al 2 O3. , ThO 2 C6 H 5 OH HOCH 3 C6 H 5 O CH 3 Methoxy benzene (c) Ester formation : Phenol reacts with acid chlorides (or acid anhydrides) in alkali solution to form phenylesters (Acylation). This reaction (Benzoylation) is called Schotten-Baumann reaction. C6 H 5 OH NaOH C6 H 5 ONa H 2 O U D YG (a) Phenol changes blue litmus to red. O || Acety lchloride (c) Phenol reacts with strong alkalies to form phenoxides. C6 H 5 OH NaOH C6 H 5 ONa H 2 O C 6 H 5 OH (CH 3 CO ) 2 O Acetic anhydride C 6 H 5 OOCCH 3 CH 3 COOH Pheny l acetate (ester) O || NaOH C 6 H 5 OH Cl C C 6 H 5 Benzoy l chloride O || However, phenol does not decompose sodium carbonate or sodium bicarbonate, i.e., CO 2 is not ST U evolved because phenol is weaker than carbonic acid. (ii) Reactions of –OH group (a) Reaction with FeCl3 : Phenol gives violet colouration with ferric chloride solution (neutral) due to the formation of a coloured iron complex, which is a characteristic to the existence of keto-enol tautomerism in phenols (predominantly enolic form). O Pheny l acetate NaOH (b) Highly electropositive metals react with phenol. 2C6 H 5 OH 2 Na 2C6 H 5 ONa H 2 C 6 H 5 O C C 6 H 5 NaCl H 2 O Pheny l benzoate The phenyl esters on treatment with anhydrous AlCl 3 undergoes Fries rearrangement to give o- and phydroxy ketones. OOCCH3 OH OH COCH3 AlCl3 (anhydrous) hea t + Phenyl acetate COCH3 o - Keto phydroxy acetophenone (d) Reaction with PCl5 : Phenol reacts with PCl 5 to OH 3– 6 NaCl Ethoxy benzene (Phenetol) Sodium phenoxide The acidic nature of phenol is observed in the following : Enol C 6 H 5 OCH 3 Methy l phe ny l ether (Anisole) C 6 H 5 ONa Cl C CH 3 C 6 H 5 OOCCH 3 NaCl Dihydric phenol : m- > p- > o- OH C 6 H 5 OK IC2 H 5 C 6 H 5 O C 2 H 5 KI ID m-methoxy phenol > m-amino phenol > phenol > o-methoxy phenol > p-methoxy phenol This is the test of phenol. 60 –CN, –CHO, –COOH) on the benzene ring E3 X, NR 3 , 1207 + FeCl3 3H + FeO + + 3HCl 6 form chlorobenzene. The yield of chlorobenzene is poor and mainly triphenyl phosphate is formed. C6 H 5 OH PCl 5 C6 H 5 Cl POCl 3 HCl 1208 Alcohol, Phenol and Ethers 3C6 H 5 OH POCl 3 (C6 H 5 )3 PO 4 3 HCl (e) Reaction with zinc dust : When phenol is distilled with zinc dust, benzene is obtained. C6 H 5 OH Zn C6 H 6 ZnO (f) Reaction with ammonia : Phenol reacts with ammonia in presence of anhydrous zinc chloride at 300°C or (NH 4 )2 SO 3 / NH 3 at 150°C to form aniline. (c) Nitration : Phenol reacts with dilute nitric acid at 5-10°C to form ortho and para nitro phenols, but the yield is poor due to oxidation of phenolic group. The – OH group is activating group, hence nitration is possible with dilute nitric acid. OH NO2 HNO3(dil. )(510°C) + oNitrophenol 60 This conversion of phenol into aniline is called Bucherer reaction. C 6 H 5 OH NH 3 C 6 H 5 NH 2 H 2 O ZnCl 2 300 o C 5 C 6 H 5 OH P2 S 5 5 C 6 H 5 SH P2 O 5 Thiophenol which gets oxidised to o- and p- nitrophenol with dilute nitric acid. OH NO HONO (05°C) (a) Halogenation : Phenol reacts with bromine in carbon disulphide (or CHCl 3 ) at low temperature to OH U OH Br (CS2 ) + D YG + Br2 oBromophenol OH Br Br + 3HBr Br 2, 4, 6Tribromophenol white precipitate ST pNitrosopheno l OH NO2 + NO2 o- p- Nitrophenol However, when phenol is treated with concentrated HNO3 in presence of concentrated H 2 SO 4 , 2,4,6-trinitrophenol (Picric acid) is formed. OH OH O2N OH OH SO3H (H2SO4 ) oHydroxybenzene sulphonic acid + SO3H pHydroxybenzene sulphonic acid At low temperature (25°C), the ortho-isomer is the major product, whereas at 100°C, it gives mainly the para-isomer. NO2 HNO3 (conc.) H2SO4(conc.) (b) Sulphonation : Phenol reacts with conc. H 2 SO 4 readily to form mixture of ortho and para hydroxy benzene sulphonic acids. NO [O] HNO3 (Dil.) U Phenol forms a with excess of bromine water yielding 2, 4, 6-tribromophenol. OH oNitrosophenol Br + 3Br2 + OH pBromophenol OH OH OH ID (iii) Reactions of benzene nucleus : The –OH group is ortho and para directing. It activates the benzene nucleus. It is believed that the mechanism of the above reaction involves the formation of o- and p- nitroso phenol with nitrous acid, HNO 2 (NaNO 2 HCl) at 0-5°C, E3 (g) Action of P2S5 : By heating phenol with phosphorus penta sulphide, thiophenols are formed. OH NO2 pNitrophenol Aniline form mixture of ortho and para bromophenol. OH OH NO2 6To get better yield of2, 4, picric acid, first Trinitrophenol sulphonation of phenol is made (picric and then acid) nitrated. Presence of SO 3 H group prevents oxidation of phenol. (d) Friedel-Craft’s reaction : Phenol when treated with methyl chloride in presence of anhydrous aluminium chloride, p-cresol is the main product. A very OH smallOH amount of o-cresol is alsoOH formed. CH3 + CH3Cl AlCl + 3 CH3 p-Cresol (major product) o-cresol (minor) Alcohol, Phenol and Ethers RX and AlCl 3 give poor yields because 1209 AlCl 3 coordinates with O. So Ring alkylation takes place as follows, C6 H 5 OH AlCl 3 C6 H 5 OAlCl 2 HCl 60 Thus to carry out successful Friedel-Craft’s reaction with phenol it is necessary to use a large amount of AlCl 3. The Ring alkylation takes place as follows : OH / \ OH CH (CH 3 )2 OH OH COCH3 anhydrous AlCl3 Acetyl chloride + CH3COCl COCH3 orth Para o hydroxy acetophenone ONa AlCl 3 HCl HC N ClCH NH OH U (e) Kolbe-Schmidt reaction (Carbonation) : (g) Gattermann’s reaction : Phenol, when treated with liquid hydrogen cyanide and hydrochloric acid gas in presence of anhydrous aluminium chloride yields mainly p-hydroxy benzaldehyde (Formylation). ID + E3 CH 3 CH CH 2 H SO 4 C6 H 5 OH 2 o - and p - C6 H 4 or HF ( CH ) CH OH 3 2 D YG COONa 1306 140°C atm AlCl 3HCl H2 O –NH3 CH = NH Sodium salicylate OH COOC6H5 Salol OCOCH3 U COOH H+ H2 O + ClCH = NH Rearrangem ent Sodium phenyl carbonate OH OH OH OCOONa + CO2 OH (h) Mercuration OH OH OH HgOCOCH3 + (CH3COO)2Hg + o-Hydroxy phenyl mercuric acetate COOH HgOCOCH3 CH3COCl ST Salicylic acid Aspiri n COOCH3 OH + 3H2 Oil of winter used, salicylic acid (predominating product) is formed. OH ONa H H+2 O Salicylaldehy de CHO NaOH CHCl3 NaOH(aq. ) Ni 150200°C Phenol (C6H5OH ) (iv) Miscellaneous reactions CHCl2 Cyclohexanol (C6H11,OH) (used as a good solvent) (a) Coupling reactions : Phenol couples with benzene diazonium chloride in presence of an alkaline solution to form a red dye (p-hydroxy azobenzene). N = NCl + OH OH OH CH3OH (f) Reimer-Tiemann reaction : green Phenol, on refluxing with chloroform and sodium hydroxide (aq.) followed by acid hydrolysis yields salicylaldehyde (o-hydroxy benzaldehyde) and a very small amount of p-hydroxy benzaldehyde. However, when carbon tetrachloride is CHO p-Hydroxy phenyl mercuric acetate (i) Hydrogenation OH CHO p-Hydroxy benzaldehyd e Benzene diazonium chloride OH NaO –HCl H Phenol N=N pHydroxyazobenzene OH 1210 Alcohol, Phenol and Ethers (phenolphthalein) used as an indicator. O O || || C – OH C deep green or blue colour which changes to red on dilution with water. When made alkaline with NaOH original green or blue colour is restored. This reaction is known as Liebermann’s nitroso reaction and is used as a test of phenol. 60 Phenol couples with phthalic anhydride in presence of concentrated H 2 SO 4 to form a dye, (c) Liebermann’s nitroso reaction : When phenol is reacted with NaNO 2 and concentrated H 2 SO 4 , it gives a O || Phthalic O anhydride Phthalic acid H O OH Phenol (2 molecules) N D YG O C OH OH Quinoxi m NaO –H2O H OH NO H H2SO 4H2O OH Indo phenol (Red) U C O Sod. Salt of indophenol (blue) (d) Oxidation : Phenol turns pink or red or brown on exposure to air and light due to slow oxidation. The colour is probably due to the formation of quinone and phenoquinone. O Conc. H2SO (–4 H2O) N OH + H ID O || OH pNitrosophenol H OH NO E3 C || O HONO OH C – OH C6H5OH or OH O2 by air or CrO3 O O C6H5OH pbenzoquinone O - - - HO OH - - - O Phenoquinone (pink) OH O Phenolphthale in [O CrO]2Cl U (b) Condensation with formaldehyde : Phenol condenses with formaldehyde (excess) in presence of sodium hydroxide or acid (H ) for about a week to Phenol O pbenzoquinone ST form a polymer known as bakelite (a resin). OH + CH2O OH OH CH2OH NaO H + o-hydroxy benzyl alcohol But on oxidation with potassium persulphate in alkaline solution, phenol forms 1, 4-dihydroxy benzene (Quinol). This is known as Elbs persulphate oxidation. OH CH2OH Pheno l Condensation with HCHO continues give CH2 CH2 CH2 CH2 Polymer Bakelite (a resin) OH Quinol OH CH2 OH K2S2O8 in alkaline solution p-hydroxy benzyl alcohol OH + H2O 2 (4) Uses : Phenol is extensively used in industry. The important applications of phenol are Alcohol, Phenol and Ethers (i) As an antiseptic in soaps, lotions and ointments. A powerful antiseptic is “Dettol” which is a phenol derivative (2, 4-dichloro-3, 5-dimethyl phenol). (ii) In the manufacture of azo dyes, phenolphthalein, etc. (iii) In the preparation of picric acid used as an explosive and for dyeing silk and wool. (iv) In the manufacture of cyclohexanol required for the production of nylon and used as a solvent for rubber and lacquers. (v) As a preservative for ink. (vi) In the manufacture of phenol-formaldehyde plastics such as bakelite. (vii) In the manufacture of drugs like aspirin, salol, phenacetin, etc. (viii) For causterising wounds caused by the bite of mad dogs. (ix) As a starting material for the manufacture of nylon and artificial tannins. (x) In the preparation of disinfectants, fungicides and bactericides. (i) Aqueous solution of phenol gives a violet colouration with a drop of ferric chloride. (ii) Aqueous solution of phenol gives a white precipitate of 2, 4, 6-tribromophenol with bromine water. (iii) Phenol gives Liebermann’s nitroso reaction. Phenol in conc. sulphuric acid NaNO 2 Red Excess of water Blue colour 60 colour NaOH (Excess) (iv) Phenol combines with phthalic anhydride in presence of conc. H 2 SO 4 to form phenolphthalein which E3 gives pink colour with alkali, and used as an indicator. (v) With ammonia and sodium hypochlorite, phenol gives blue colour. ID (5) Tests of phenol 1211 Table : 26.2 Difference between phenol and alcohol Phenol (C6H5OH) U Property Typical phenolic odour Nature, reaction with alkali Acidic, dissolves in hydroxide forming phenoxide. D YG Odour Alcohol (C2H5OH) Pleasant alcoholic odour sodium sodium to Neutral, no reaction with alkalies. Reaction with neutral FeCl3 Gives violet colouration due formation of complex compound. Reaction with halogen acids No reaction with halogen acids. Forms ethyl halides. Oxidation Pink or brown formation of phenoquinone. Undergoes oxidation to give acetaldehyde and acetic acid. colour due to quinone and No reaction. Forms polymer (bakelite). No reaction. Liebermann’s nitroso reaction Positive. Does not show. Coupling with benzene diazonium chloride Forms azo dye. Does not form any dye. Reaction with PCl5 Mainly forms triphenyl phosphate. Forms ethyl chloride Iodoform test Does not show. Positive. ST U Reaction with HCHO Derivatives of phenol NITROPHENOLS Cl (1) Preparation OH OH OH NO 2 120 C NO 2 o - and p - nitropheno l OH + o-isomer (steam volatile) OH NaOH C 6 H 4 C6 H 4 o - and p - chloro nitrobenze ne NO2 Dil. HNO3 (ii) C6 H 4 (iii) C6 H 5 NO 2 Solid KOH Nitrobenze ne NO2 p-isomer (non-volatile) heat NO 2 o - and p - nitropheno l 1212 Alcohol, Phenol and Ethers (iv) NO2 NH2 NH4HS or NO2 Na2S NaNO2/HCl 0-5°C NO2 mDinitrobenzen e m-Nitroaniline N2Cl (ii) From phenol through disulphonic acid OH OH OH OH H2 O NO2 m-Nitrobenzene diazonium chloride m-Nitrophenol Phenol Isomer ortho m.pt. (C) 45 meta 97 para 114 NO2 NO2 SO3H Picric acid Phenol disulphonic acid E3 (2) Properties : o-Nitrophenol is a yellow coloured crystalline compound, while m- and p-isomers are colourless crystalline compounds. O2N HNO3 60 NO2 SO3H H2SO4 OH (iii) O2N O2N 6 NO2 NO2 TNB Picric acid They are stronger acids than phenol. The order is (2) Properties : It is a yellow crystalline solid, melting points 122°C. it is insoluble in cold water but soluble in hot water and in ether. It is bitter in taste. Due to the presence of three electronegative nitro groups, it is a stronger acid than phenol and its properties are comparable to the carboxylic acid. It neutralises alkalies and decomposes carbonates with evolution of carbon dioxide. U : NO2 Ke3Fe(CN) ID The lowest melting point of o-isomer is due to intramolecular hydrogen bonding whereas meta and para isomers possess intermolecular hydrogen bonding and thus, they have higher melting points. NO2 + [O] p-isomer > o-isomer > m-isomer > phenol / C6 H 4 \ D YG When reduced, they form corresponding aminophenols. o- and p-Nitrophenols react with bromine water to form 2, 4, 6-tribromophenol by replacement of nitro group. OH Br OH Br Br2 NO 2 o - or p - isomer Br 2,4,6 Tribromophenol Dry picric acid as well as its potassium or ammonium salts explode violently when detonated. It reacts with PCl 5 to form picryl chloride which on shakingOH with NH 3 yields Cl picramide. NO2 O2N O2N NO2 O2N U H2O (1) Preparation : It is obtained when phenol is treated with conc. HNO 3. However, the yield is very ST NO2 NH3 PCl5 Picric acid (2, 4, 6-trinitrophenol) NH2 NO2 NO2 Picryl chloride poor. It is prepared on an industrial scale : NO2 Picramide (i) From chlorobenzene Cl When distilled with a paste of bleaching powder, it gets decomposed and yields chloropicrin, CCl 3 NO 2 , Cl NO2 HNO3 H2SO4 Chlorobenze ne Aq. Na2CO3 NO2 2, 4Dinitrochlorobenzene OH OH NO2 O2N NO2 HNO3 H2SO4 NO2 NO2 Picric acid (2, 4, 6Trinitrophenol) as one of the products and is thus employed for the manufacture of tear gas. It forms yellow, orange or red coloured molecular compounds called picrates with aromatic hydrocarbons, amines and phenols which are used for characterisation of these compounds. Picrates are explosive in nature and explode violently when heated. These are prepared carefully. O O OH || C O+ OH C Con H2SO4 (– H2O) C OH || OH C || || Phthalic Alizar O Alcohol, Phenol and Ethers 1213 O (3) Uses : It is used as a yellow dye for silk and wool, as an explosive and as an antiseptic in treatment of burns. Catechol (1, 2-Dihydroxy benzene) anhydride in (3) Uses : It finds use as photographic developer, in the manufacture of alizarin and adrenaline hormone and as an antioxidant (inhibitor in auto oxidation) for preserving gasoline. Resorcinol (1, 3-Dihydroxy benzene) (1) Preparation (1) Preparation : It is prepared by alkali fusion of 1,3, benzene disulphonic acid (Industrial method). OH Cl OH NaOH SO3H + CO2 + NaCl ; NaOH Catecho l Cl OH ONa H+/H2 O NaOH 200°C, Cu2+ OK OH SO3K OK OH 2HCl + 3KOH o-phenol sulphonic (iii) acid CHO OH (2) Properties : It is a colourless crystalline solid, melting points 105°C. it is soluble in water. It is affected on exposure to air and light. It acts as a reducing agent as it reduces Tollen’s reagent in cold and Fehling’s solution on heating. With silver oxide it is oxidised to o-benzoquinone. OH OH O + 2Ag + H2O U + Ag2O oBenzoquinone ST It forms insoluble lead salt (white ppt.) when treated with lead acetate solution and gives green colour with FeCl 3 which changes to red on adding solution. It forms alizarin dye stuff when a crystalline OH Br Br + 3Br2 + 3HBr OH OH Br On nitration, it forms 2, 4, 6-trinitro-1, 3dihydroxybenzene. OH OH O2N NO2 HNO3 H2SO4 OH Resorcinol O OH Na 2 CO 3 Tollen’s reagent on warming. U D YG Catechol OH (2) Properties : It is a colourless crystalline solid, melting points 110°C. it is affected on exposure by air and light. It is soluble in water, alcohol and ether. It shows tautomerism. Its aqueous solution gives violet colour with FeCl 3. It reduces Fehling’s solution and + HCOONa + H2O OH ONa With bromine water, it gives precipitate, 2, 4, 6-tribromoresorcinol. Catechol + H2O2 + NaOH OH Salicylaldehy de SO3H OH E3 ONa (ii) OH HCl Fuse ID COOH Cl OH ONa 60 (i)OH OH NO2 Styphnic acid It condenses with phthalic anhydride and forms OH fluorescein. OH O O=C H C= O+ H O OH OH Conc. H2SO4 – 2H2O O=C O C condensed with phthalic anhydride in the presence of sulphuric acid. O OH || C || OH O+ O C Con H2SO4 (–H2O) C C || || O Phthalic anhydride O Alizarin Phthalic anhydride OH OH OH Fluorescei n Resorcinol (2 moles) With nitrous dinitrosoresorcinol acid, OH OH it forms 2, O NO NOH OH O HNO2 OH NO NOH OH 4- 1214 Alcohol, Phenol and Ethers Trihydric Phenols : Three trihydroxy isomeric derivatives of benzene are Pyrogallol (1, 2, 3), hydroxy quinol (1, 2, 4) and phloroglucinol (1, 3, 5). OH HOOC (3) Uses Dienol form OH Diketo form O (1, O2N NO2 Aniline ID OH O H2N U ST It acts as a powerful reducing agent as it is easily oxidised to p-benzoquinone. It reduces Tollen’s reagent and Fehling’s solution. OH Quinol [O] FeCl3 HO NH2 OH O O pBenzoquinone Due to this property, it is used as photographic developer. (3) Uses : It is used as an antiseptic, developer in photography, in the preparation of quinhydrone electrode and as an antioxidant. +CO2+3NH4Cl OH Phlorogluci nol OH OH OH + ½ O2 OH (2) Properties : It is a colourless crystalline solid, melting points 170°C. it is soluble in water. It also shows tautomerism. It gives blue colour with FeCl 3 HO NH2 Hydroxyquinol is prepared by the alkaline fusion of hydroquinone in air. Quino l solution. NO2 COOH Fe/H2 [H O ] 4 Fe/HCl [H] 2, 4, 6-trinitro toluene U D YG [O MnO2]/H2SO NO2 H2O/H+ 100°C Quinol O O2N KMnO4 [O] (p-Benzoquinone is obtained by oxidation of aniline) NH2 Pyrogallol OH COOH NO2 4-Dihydroxy (1) Preparation : It is formed by reduction of pbenzoquinone with sulphurous acid (H 2 SO 3 H 2 O SO 2 ). O O+SO2+2H2O HO OH+H2SO4 H2SO3+H2O + CO2 E3 quinol Gallic acid CH3 (ii) It is also used in the treatment of eczema. 2, 4, 6-trinitroresorcinol is used as an explosive. or OH Phloroglucinol is obtained from trinitrotoluene (TNT) by following sequence of reactions. (i) It is used as antiseptic and for making dyes. Hydroquinone benzene) OH hea 220° t C 60 Resorcinol behaves as a tautomeric compound. This is shown by the fact that it forms a dioxime and a bisulphite derivative. OH O Pyrogallol is obtained by heating aqueous solution of gallic acid at 220°C. OH OH NaOH Fus e OH OH Quinol Hydroxy Quinol The three isomers are colourless crystalline compounds. All are soluble in water and their aqueous solutions give characteristic colour with FeCl 3 (Red, brown or bluish violet). Alkaline solutions absorb oxygen rapidly from air. Uses of pyrogallol (i) As a developer in photography. (ii) As a hair dye. (iii) In treatment of skin diseases like eczema. (iv) For absorbing unreacted oxygen in gas analysis. Ether Alcohol, Phenol and Ethers Ethers are anhydride of alcohols, they may be obtained by elimination of a water molecule from two alcohol molecules. R OH HO R R O R H 2 O Ether (1) From alkyl halides (i) Williamson’s synthesis It is a nucleophilic substitution reaction and proceed through S N 2 mechanism. RONa RX RO R NaX In this reaction alcohol must be present in excess. When this reaction is carried out between different alcohols then there is a mixture of different ethers is obtained. (b) With Al2O3 at 250° C : 3 2 ROH 2 R O R H 2O Al O C 2 H 5 OC 2 H 5 NaBr Ethoxy etha ne halide BF to undergo elimination is 3 o 2 o 1o. (c) For better yield alkyl halide should be primary and alkoxide should be secondary or tertiary. CH 3 3 ROH CH 2 N 2 R O CH 3 N 2 (b) In higher cases, there can be 1, 2-hydride or 1, 2-methyl shift to form more stable carbonium ion. (3) Alkoxy mercuration-demercuration C C R OH Hg[OOCCF3 ]2 alkene U CH 3 (a) This method is very useful for preparing mixed ethers. ID alkyl E3 Ethy l methy l ether of | | | | CH 3 D YG CH 3 CH 3 | | CH 3 C Cl 2 5 CH 3 C Cl , C H ONa | | CH 3 CH 3 CH 3 CH 3 U | | CH 3 C C 2 H 5 O CH 3 C C 2 H 5 OH | CH 2 H || CH 2 ST Aryl halide and sodium alkoxide cannot be used for preparing phenolic ethers because aryl halide are less reactive toward nucleophilic substitution reaction than alkyl halides. (ii) By heating alkyl halide with dry silver oxide heat 2 RX Ag 2 O R O R 2 AgX , 2C2 H 5 Br Ethyl bromide | heat Ag 2 O C2 H 5 OC 2 H 5 2 AgBr Diethyl ether (2) From alcohols (i) By dehydration of alcohols (a) With conc. H2SO4 at 140° C | | | | NaBH 4 C C OR H Ether Ethy l tert. buty l ether (d) Secondary and tertiary alkyl halides readily undergo E2 elimination in the presence of a strong base to form alkenes. | | OR HgOOCCF3 CH 3 Sodium salt of tert. buty l alcohol Mercuric trifluoro acetate | C C C 2 H 5 Br NaO C CH 3 C 2 H 5 O C CH 3 Ethy l brom ide Ether (ii) By the action of diazomethane on alcohols : This reaction is in presence of catalyst, boron trifluoride or HBF4. CH 3 I CH 3 OC 2 H 5 NaI Tendency 140 o C 250 o C (a) Order of reactivity of primary halide is CH 3 X CH 3 CH 2 X CH 3 CH 2CH 2 X. (b) H SO (conc.) 60 General methods of preparation of ethers C 2 H 5 ONa C 2 H 5 Br Sodium ethoxide Ethy l brom ide ROH HOR 24 ROR H 2 O. 2 molecules of alcohol This reaction is mainly applicable for the dehydration of primary alcohols. Secondary and tertiary alcohols form alkenes mainly. General formula is Cn H 2n 2O C 2 H 5 ONa Sodium ethoxide 1215 This is the best method for the preparation of tethers. (4) Reaction of lower halogenated ether with grignard reagent ROCH 2 X XMg R ROCH 2 R MgX 2 Halogenate d ether Grignard reagant Higher ether (i) Higher members can be prepared by the action of grignard reagent on lower halogenated ethers. (ii) Ether form soluble coordinated complexes with grignard reagent. Physical properties (1) Physical state : Methoxy methane and methoxy ethane are gases while other members are volatile liquid with pleasant smell. (2) Dipole moment (D.M.) : Bond angle of ether is due to sp 3 hybridisation of oxygen atom. Since C – O bond is a polar bond, hence ether possess a net dipole moment, even if they are symmetrical. dipole moment of dimethyl ether is 1.3 D and dipole moment of di ethyl ether is 1.18 D. The larger bond angle may be because of greater repulsive interaction between bulkier alkyl groups as compared to smaller H-atoms in water. 1216 Alcohol, Phenol and Ethers (4) Solubility : Solubilities of ethers in water are comparable with those of alcohols. Example : Di ethyl ether and n-butyl alcohol have approximately the same solubility in water. This is because, ether form hydrogen bond with water much in the same way as alcohol do with water. O.......... H Ether With strong oxidising agent like dichromate ethers are oxidised to aldehydes. 2[O ] CH 3 CH 2 OCH 2 CH 3 2CH 3 CHO H 2 O Acetaldehyde The presence of peroxide can be indicated by the formation of blood red colour complex in the following reaction. SCN Peroxide Fe 2 Fe 3 [Fe (SCN )n ]3 n Blood red colour (n 1 to 6 ) O H........... O Water R R Ether Solubility of ether in water decreases with the size of alkyl groups. R R R | | | H O- - - H O- - - H O- - hy drogenbo nding in alcohols R O R No hy drogen bond in ether (6) Density : Ethers are lighter than water. (ii) Oxidation with K2Cr2O7 / H R R CH 2 O CH R (a) Oxidation of ether can only be possible if any one of the alkyl groups of ether has hydrogen on carbon. (b) -carbon having two hydrogens converts in carboxylic group and -carbon having only one hydrogen converts into keto group. ID (5) Hydrogen bonding : There is no hydrogen directly attach (bonded) to oxygen in ethers, so ethers do not show any intermolecular hydrogen bonding. K 2 Cr2 O7 CH 3 COOH CH 3 CH 2 COOH H D YG ( -Monochloro diethyl ether ) CH 3 CH 2 OCH 2 CH 3 CH 3 CHClOCHClC H 3 Cl 2 Diethyl ether dark ( , -Dichlorodiethyl ether ) C 2 H 5 OC 2 H 5 10 Cl 2 C 2 Cl 5 OC 2 Cl 5 10 HCl Cl 2 light (Perchlorodiethyl ether ) CH 3 CH 3 O || CH 3 COOH CH 3 C CH 3 K 2 Cr2 O7 (i) Halogenation : dark / CH 3 CH 2 O CH (1) Reaction due to alkyl group Cl 2 CH 3 CH 2 OCH 2 CH 3 CH 3 CHClOCH 2 CH 3 CH 3 CH 2 O CH 2 CH 2 CH 3 U Chemical properties : Ethers are quite stable compounds. These are not easily attacked by alkalies, dilute mineral acids, active metals, reducing agents or oxidising agents under ordinary conditions. Diethyl ether acid, E3 R R Formation of peroxide can be prevented by adding small amount of Cu 2 O to ether. 60 (3) Boiling points : Boiling points of ethers are much lower than those of isomeric alcohols, but closer to alkanes having comparable mass. This is due to the absence of hydrogen bonding in ethers. H / (iii) Salt formation : Due to lone pair of electrons on oxygen atom. Ether behaves as Lewis base and form stable oxonium salt with strong inorganic acids at low temperature. H | C 2 H 5 OC 2 H 5 HCl (C 2 H 5 )2 O Cl or.. (ii) Burning : Ethers are highly inflammable. They burn like alkanes. U Diethy l oxonium chloride [(C 2 H 5 )2 O H ] Cl ST C 2 H 5 O C 2 H 5 6O2 4 CO 2 5 H 2 O (2) Reaction due to ethernal oxygen.. C 2 H 5 OC 2 H 5 H 2 SO 4 (C 2 H 5 )2 O HSO 4 | (i) Peroxide formation : H Diethy l oxonium hy drogen sulphate.... C 2 H 5 O C 2 H 5 O : (C 2 H 5 )2 O O..... (a) The boiling point of peroxide is higher than that of ether. It is left as residue in the distillation of ether and may cause explosion. Therefore ether may never be evaporated to dryness. (b) Absolute ether can be prepared by distillation of ordinary ether from conc. H 2 SO 4 and subsequent storing over metallic sodium. or [(C 2 H 5 )2 O H ] HSO 4 The oxonium salts are soluble in acid solution and ethers can be recovered from the oxonium salts by treatment with water. (C2 H 5 )2 O Cl 2 (C2 H 5 )2 O HCl H O | H Diethy l ether Oxonium salt The formation of oxonium salt is similar to the formation of ammonium salts from ammonia and acids. Alcohol, Phenol and Ethers Ether is removed from alkyl halides by shaking with conc. H 2 SO 4. Ethers can be distinguished from alkanes with the help of this reaction. (iv) Reaction with Lewis acids : Being Lewis bases, ethers form complexes with Lewis acids such as BF3 , AlCl 3 , FeCl 3 , etc. These complexes are called The silver iodide thus form can be detected and estimated. This is the basis of Zeisel method for the detection and estimation of alkoxy group in a compound. (iv) Action of PCl5 heat R O R PCl 5 2 RCl POCl 3. (v) Reaction with acetyl chloride ZnCl 2 CH 3 COCl C 2 H 5 O C 2 H 5 CH 3 COOC 2 H 5.. CH 3 CH 2 CH 3 CH 2 Acetylchloride O BF3 heat Diethyl ether Ethyl acetate 60.. O : BF3 (vi) Reaction with acid anhydride Boron trifluoride etherate (complex) CH 3 CO O OCCH 3 C2 H 5 O C2 H 5 Acetic anhy dride Similarly, diethyl ether reacts with Grignard reagent forming Grignard reagent etherate. Diethy l ether 2 2CH 3 COOC 2 H 5 ZnCl R (CH 3 CH 2 )2 O E3 heat 2(CH 3 CH 2 )2 O RMgX Al 2 O3 C 2 H 5 OC 2 H 5 2CH 2 CH 2 H 2 O Grignard reagent etherate 300 o C Due to the formation of the etherate, Grignard reagents dissolve in ether. That is why Grignard reagents are usually prepared in ethers. However, they cannot be prepared in benzene, because benzene has no lone pair of electrons and therefore, cannot form complexes with them. (viii) Reaction with carbon mono oxide o BF3 / 150 C C 2 H 5 OC 2 H 5 CO C 2 H 5 COOC 2 H 5 ID D YG H 2 SO 4 (a) With dil. H 2 SO 4 : ROR H 2O 2 ROH H 2 SO 4 C2 H 5 OC 2 H 5 H 2 O 2C2 H 5 OH Diethy l ether Ethanol 500 atm. Diethy l ether L i C H 3 H CH 2 CH 2 O CH 2 CH 3 (4) Ring substitution in aromatic ethers : Alkoxy group is ortho and para directing and it directs the incoming groups to ortho and para position. It activates the.. aromatic.. ring towards.... electrophilic.. + + + substitution reaction. :OR :O – R OR OR OR .. C 2 H 5 OC 2 H 5 H 2 SO 4 C 2 H 5 OH C 2 H 5 HSO 4 C 2 H 5 OH H 2 SO 4 C 2 H 5 HSO 4 H 2 O C 2 H 5 OC 2 H 5 2 H 2 SO 4 2 C 2 H 5 HSO 4 H 2 O Ethy l hy drogen sulphate CH 4 CH 2 CH 2 L i O C 2 H 5 (b) With conc. H 2 SO 4 : Diethy l ether Ethy l propionate (ix) Action of bases U (3) Reaction involving cleavage of carbonoxygen bond (i) Hydrolysis Ethy l acetate (vii) Dehydration O(CH 2 CH 3 )2 X Mg There is no reaction in cold. etherates. CH 3 CH 2 CH 3 CH 2 1217 I II :.. IV III V (ii) Action of hydroiodic acid U (a) With cold HI Cold C2 H 5 OC2 H 5 HI C2 H 5 I C2 H 5 OH Diethyl ether Ethyl iodide ST OC2H5 OH + HBr Phenyl ethyl ether Ethyl alcohol + C2H5Br Phenol heat R O R 2 HI RI R I H 2 O B r + Br2 Ethyl bromide (b) With hot HI (iii) Zeisel method : RI AgNO 3 (alc.) AgI RNO 3 III, IV and V show high electron density at ortho and para position. (i) Halogenation : Phenyl alkyl ethers undergo usual halogenation in benzene ring. For example, Bromination of anisole gives ortho and para bromo derivative even in the absence of iron OCH3 catalyst. OCH3 OCH3 (III) bromide CS 2 Anisol e oBromoanisole Br pBromoanisole Para isomer is obtained in 90% yield. (ii) Friedel craft reaction OCH3 OCH3 CH3 AlCl 3 + CH 3 Cl + Methyl chloride Anisol e OCH3 Ortho CH3 Para 1218 Alcohol, Phenol and Ethers CH3OH > C2H5OH > (CH3)2CHOH > (CH3)3C – OH HCOOH > CH3COOH > (CH3)2CH – COOH > (CH3)C – COOH. Pinacol-pinacolone rearrangement : The reaction involves dehydration of diols through the formation of carbocation intermediate which rearranges to more stable compound. OH OH O CH 3 OCH3 COCH3 AlCl 3 + CH 3 COCl + o-Methoxy acetophenon e Anisol e (iii) Nitration OCH3 COCH3 p Methoxy acetophenon e OCH3 OCH3 NO3 Methyl phenyl ether (Anisole) Methyl-2 nitrophenyl ether (oNitroanisole) Ethers are relatively less reactive towards electrophilic substitution reaction. | | | || | CH 3 CH 3 Pinacol H 2O | CH 3 Pinacolone In general, acid strength increases as Cresols
