XII alcohols phenols ethers

1. ALCOHOLS, PHENOLS, ETHERS Mr. Pranav A. Galgale

2. Chemical Reactions of alcohols and Phenols Alcohol acts as Electrophile Nucleophile Attraction towards positive charge Attraction towards negative charge 1. Alcohols as nucleophiles R – O C H + 2. Alcohols as electrophiles C + R – O – H + R – CH2 –O – H + H+ R – CH2 –O H H + Br - R – CH2 – BrR – CH2 – O H H + + The bond between C – O is broken when alcohols react as nucleophiles. R – O C H++ Protonated alcohols The bond between O H is broken when alcohols react as nucleophiles.

3. Reactions are classified into two types Reaction involving cleavage of O – H bond Reaction involving cleavage of C – O bond Acidity of alcohol 1. Reaction with metals: Alcohols and phenols react with active metals such as sodium, potassium and aluminium to yield corresponding alkoxides and hydrogen. 2 R – O – H + 2Na 2 R – O – Na + H2 Which is characteristics of acids Alcohols and phenols are Brönsted acids i.e., they can donate a proton to a stronger base (B:). R – O – H B:+ B – H R – O+ BaseAcid Conjugate Acid Conjugate Base Base + H+ = Conjugate acid Acid – H+ = Conjugate base

4. Acidity of alcohols The acidic character of alcohols is due to the polar nature of O–H bond R – groups (i.e.) alky group is electron donating group (EDG). So it shows +I effect. e. g. –CH3, –C2H5 R – O – H d- d+ polar nature due to partial separation of charges R CHOH R R CH2OH R C – OH R R Primary alcohol Secondary alcohol Tertiary alcohol So, as R – group increases; polarity of alcohols decreases and as polarity decreases acidity of alcohol decreases 1o > 2o > 3o Acidity decrease

5. Alcohols are, however, weaker acids than water. This can be explained by the reaction of water with an alkoxide. R – O H – O – H+ Base Acid Conjugate Acid Conjugate Base R – O – H + : O – H – Here water acts as acid This reaction shows that water is a better proton donor (i.e.,stronger acid) than alcohol. Alcohols act as Bronsted bases as well. It is due to the presence of lone electron pairs on oxygen, which makes them proton acceptors. (Protonated alcohols)

6. Acidity of phenols 1. phenols react with active metals such as sodium, potassium and aluminium to yield corresponding phenoxides and hydrogen. OH 2Na+ O Na+ H2+ 2. phenols react phenols react with aqueous sodium hydroxide to form sodium phenoxides. OH + NaOH O Na+ H2O+

7. The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon of benzene ring which acts as an electron withdrawing group. 1. Due to resonance, oxygen of –OH group gets positive charge. So, phenols are more acidic than alcohols 50 % s characters In phenol ‘C’ to which –OH is attached is sp2 hybridised which is more electronegative than sp3 hybridised ‘C’ in alcohols This increases the polarity of O–H bond 2. We know that, sp hybridised carbon sp2 hybridised carbon sp3 hybridised carbon Electronegativity decreases because ‘s’ characters of hybrid orbitals decrease 33.33% s characters 25% s characters Due to all these reasons phenol is more acidic than alcohol phenol is more acidic than alcohol….. Why??? > >

8. O O + O + O + Resonance structures of phenoxide ion OH OH + OH + OH + OH Resonance structures of phenol O -

9. If electron withdrawing groups (EWG) are present on phenol ring (e.g. – NO2, –CN, –CHO) ; acidic strength of phenol increases. Because EWG favour formation of phenoxide ion. If electron donating groups (EDG) are present on phenol ring (e.g. alkyl groups) ; acidic strength of phenol decrease. Because these groups do not favour formation of phenoxide ion. Same you can apply for alcohols as well.

10. Do it yourself…..

11. Esterification Alcohols and phenols heated with carboxylic acid, acid chlorides and acid anhydrides to form esters in presence of H2SO4 R – OH + R’ COOH H+ R COOR’ + H2O OH + R’COOH H+ O – C – R’ + H2O || O H+ R COOR’ + H2O R’ C – O O R’ C – O R – OH + Also represented as (R’CO)2O OH + R’COCl Pyridine used in this reaction neutralises HCl so equilibrium shifts towards RHS O – C – R’ + HCl || O The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin. H+ COOH CH3COOH COOCH3 + COOH (CH3CO)2O+ OH Aspirin Aspirin has analgesic, anti inflammatory & anti pyretic properties IMPORTANT pyridine OH – is removed from acid H+ is removed from acid

12. + R – O – H Step 2 Attack of alcohol on carbonyl carbon R’ – C – O – H || O H++ R’ – C – O – H | O | – H R – O – H + Step 1 Protonation R’ – C – O – H | O | – H R – O – H + H+ R’ – C – O – H | O | – HH – R – O – H + + Step 3 Protonation R’ – C – O – H | R – O + Step 4 Dehydration and deprotonation – H2O – H+ Step 5 Deprotonation R’ – C – O | R – O + – R’ – C O | R – O –– Role of H2SO4 – 1. Protonation 2. Dehydration Mechanism R’ – C – O – H | O – H +

13. Reactions involving braking of C – O bond 1.Reactions with HX CH3OH HCl+ ZnCl2 CH3Cl + H2O CH3CH2OH HBr+ CH3CH2Br + H2O 2.Reactions with PX3 and PX5 3R – O – H + PCl3 3R – Cl + H3PO3 R – O – H + PCl5 R – Cl + POCl3 + HCl

14. 3.Reactions with SOCl2 (Darzen’s method) R – O – H + SOCl2 R – Cl + SO2 + HCl R – Cl + SO2 + HCl N Follows SNi mechanism Follows SN2 mechanism Without pyridine

15. 4. Dehydration of alcohols 1o alcohols – Conc. H2SO4 at 443 K 2o alcohols – 85% H3PO4 at 440 K 3o alcohols – 20% H3PO4 at 358 K Ease of reaction: 1o alcohols < 2o alcohols < 3o alcohols Ease of reaction increases Conc. H2SO4 443 K CH2 = CH2 + H2O CH3 – CH – CH3 | OH 85% H3PO4 440 K CH2 = CH – CH3 + H2O CH3 – C – CH3 | OH | CH3 20% H3PO4 358K CH3 – C = CH2 + H2O | CH3 CH2 – CH2 | H | OH ab Because in this reaction carbocation formation takes place Tertiary carbocation is most stable that’s why tertiary alcohols can undergo dehydration easily

16. Mechanism CH3 – CH – CH3 + H + | O – H CH3 – CH – CH3 | O HH + CH3 – CH – CH3 | O HH + CH3 – CH – CH2 + | H Step 1: Protonation Step 2: Dehydration (formation of carbocation) Step 3: Deprotonation CH3 – CH – CH3 + - H2O CH3 – CH = CH2 + H+ Here H+ (acid) used in step 1 forms again in step 3 To shift equilibrium to RHS alknene is removed

17. 5. Oxidation H – C – O – H | | In oxidation these two bonds break C = O [O] Following oxidation agents are used, 1. KMnO4 / OH – followed by hydrolysis 2. KMnO4 / H+ 3. K2Cr2O7 / H+ 4. Conc. HNO3 Strong oxidising agents Alcohols directly converted into carboxylic acid PCC (Pyridinium chloro chromate) N H + Cl - + CrO3 CrO3 Mild oxidising agents Specifically oxidise 1o Alcohols into aldehydes 2o alcohols into ketones R – CH2 – OH PCC R – CHO CH – OH R R CrO3 C = O R R Tertiary alcohols do not oxidise easily. If vigorous oxidation is carried out they undergo elimination i.e. they form alkenes.

18. When the vapours of a primary or a secondary alcohol are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde or a ketone is formed while tertiary alcohols undergo dehydration. 6. Dehydrogenation reaction CH3 – CH2 – OH Cu 573K CH3 – CHO CH – OH CH3 CH3 Cu 573K C = O CH3 CH3 CH3 – C – CH3 | OH | CH3 Cu 573K CH3 – C = CH2 + H2O | CH3

19. Reactions of phenols 1. Electrophilic aromatic substitution The –OH group attached to the benzene ring. Due to this p electrons delocalise on ortho and para position. So, electron density at ortho and para position increases. Therefore, phenols show electrophilic substitution reaction. –OH group directs the incoming group to ortho and para positions in the ring. OH a. Nitration O H O d+ d- d- N = O H – O N OO d+ d- OH N OO d- Intermolecular H – Bonding Intramolecular H – Bonding Steam volatile Steam on – volatile So, both ortho and para products are separated by steam distillation Dilute HNO3 OH NO2 OH NO2 o – Nitrophenol p – Nitrophenol +

20. With concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol. The product is commonly known as picric acid. The yield of the reaction product is poor. OH concentrated HNO3 OH NO2O2N NO2 Nowadays picric acid is prepared by treating phenol first with concentrated sulphuric acid which converts it to phenol-2,4, 6- triisulphonic acid, and then with concentrated nitric acid to get 2,4,6-trinitrophenol. OH concentrated H2SO4 OH SO3HHO3S SO3H Poor yield concentrated HNO3 OH NO2O2N NO2 Maximum yield

21. Phenol is heated with acyl cholride in presence of anhydrous AlCl3(Lewis acid) to give hydroxy phenyl acetate (para and ortho product). Out of two; para product is major. Friedel Craft’s acylation and alkylation OH Anhydrous AlCl3 + CH3COCl OH + COCH3 OH COCH3 Major Phenol is heated with alkyl cholride in presence of anhydrous AlCl3(Lewis acid) to give p and o alkyl phenol. Out of two; para product is major. OH Anhydrous AlCl3 + CH3Cl OH + CH3 OH CH3 Major

22. b. Halogenation When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2 and at low temperature, monobromophenols are formed. OH Br2 in CS2 273 K OH Br The usual halogenation of benzene takes place in the presence of a Lewis acid, such as FeBr3 which polarises the halogen molecule. In case of phenol, the polarisation of bromine molecule takes place even in the absence of Lewis acid. It is due to the highly activating effect of –OH group attached to the benzene ring. When phenol is treated with bromine water, 2,4,6-tribromophenol is formed as white precipitate. OH 3Br2 Bromine water OH BrBr Br

23. Write the structures of the major products expected from the following reactions: (a) Mononitration of 3-methylphenol (b) Dinitration of 3-methylphenol (c) Mononitration of phenyl methanoate. Do it yourself….. OH CH3 NO2 OH CH3 NO2 (a) (b) OH CH3 NO2 NO2 (c) OCOCH3 NO2

24. 2. Kolbe’s reaction Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product. OH NaOH i. CO2 ii. H+ OH COOH 3. Reimer-Tiemann reaction OH CHCl3 + NaOH O Na+ – O Na+ CH2Cl – O Na+ CHO – NaOH H+ OH CHO Slicyladehyde Slicylic acid

25. OH Zn + ZnO 4. Reduction OH Na2Cr2O7 O O 5. Oxidation Benzoquinone

26. ROH 2Na R’COOH H2SO4 2 R – O – Na + H2 RCOOR’ + H2O 1o alcohols – Conc. H2SO4 at 443 K 2o alcohols – 85% H3PO4 at 440 K 3o alcohols – 20% H3PO4 at 358 K Dehydration C = C Oxidation C = O Cu / 573 K C = O 1o alcohols – Aldehyde 2o alcohols – Ketone 3o alcohols form alkenes HCl ZnCl2 RCl SOCl2 R – Cl + SO2 + HCl KMnO4 / OH – followed by hydrolysis KMnO4 / H+ K2Cr2O7 / H+ Alcohols Carboxylic acids1o alcohols – Aldehyde 2o alcohols – Ketone PCC or CrO3 3o alcohols undergo elimination and form alkenes

27. OH Dilute HNO3 OH NO2 OH NO2 Conc HNO3 OH NO2O2N NO2 Poor yield concentrated H2SO4 OH SO3HHO3S SO3H concentrated HNO3 OH NO2O2N NO2 Maximum yield Br2 in CS2 273 K OH Br 3Br2 Bromine water OH BrBr Br OH Zn + ZnO Reduction OH Na2Cr2O7 O O Oxidation

28. OH NaOH i. CO2 ii. H+ OH COOH O Na+ – Kolbe’s reaction OH CHCl3 + NaOH O Na+ CH2Cl – O Na+ CHO – NaOH H+ Slicyladehyde OH CHO Reimer-Tiemann reaction IMPRTANT NAME REACTIONS OH Anhydrous AlCl3 + CH3COCl OH COCH3 Major OH Anhydrous AlCl3 + CH3Cl OH CH3 Major Friedel Craft’s acylation and alkylation

29. Ethers Ethers are organic compounds in which two alkyl groups attached with oxygen this oxygen is known as ethereal oxygen. Classification of ethers Simple ethers / Symmetrical ethers Mixed ethers / Asymmetrical ethers CH3 – O – CH3 C2H5 – O – C2H5 O CH3 – O – C2H5 CH3 – O – CH CH3 CH3 O CH3

30. Classification of ethers Aliphatic ethers Aromatic ethers Cyclic ethers C2H5 – O – C3H7 CH3 – O – C4H9 O CH2 – O CH3 Oxirane Oxetane O CH2 CH2 H2C H2C CH2 O Benzyl phenyl ether Methyl phenyl ether

31. Nomenclature of ethers CH3 – O – CH3 C2H5 – O – C2H5 C2H5 – O – CH3 Dimethyl ether Common name IUPAC name Methoxymethane Diethyl ether Ethoxyethane Ethyl methyl ether Methoxyethane Methyl isopropyl ether 2 – methoxypropaneCH3 – O – CH CH3 CH3 1 2 3 CH3 – O – C – CH3 CH3 CH3 1 2 3 tertbutyl methyl ether 2–methyl–2–methoxypropane

32. O CH3 O C2H5 O CH3 – CH – O – CH – CH3 CH3CH3 1 2 3 1 23 CH3 – CH – CH2 – CH2 – O – CH3 OH 1 2 3 4 methyl phenyl ether Anisol Methoxybenzene Phenetole Ethoxybenzene Diphenyl ether Phenoxybenzene 2 – (2–propoxy)propane-------- -------- 2 – methoxybutan–2–ol Common name IUPAC name

33. – O – CH – CH2 – CH3 CH3 1 2 3 4 O C2H5 NO2 1 2 2 – cylcopropoxybutane 1– ethoxy–2–nitrocylcohexane -------- -------- Common name IUPAC name

34. Structure of functional group O C C 111.7o Two Sp3 hybridised orbital with lone pair of electrons Bond angle greater than usual tetrahedral angle (109.5o)because stearic hindrance of two alkyl groups. Sp3 hybridisation

35. Methods of preparation of ethers 1. By dehydration of alcohols Ethanol protic acids (H2SO4, H3PO4) At 443 K Intermolecular dehydration (Substitution) Intramolecular dehydration (Alkenes are formed) (Elimination) protic acids (H2SO4, H3PO4) At 413 K Intermolecular dehydration (Ethers are formed) (Substitution) CH3 – CH2 – OH H2SO4 443 K H2SO4 413 K CH2 = CH2 CH3 – CH2 – O – CH2 – CH2

36. Mechanism Intermolecular dehydration of alcohols follows SN2 mechanism CH3 – CH2 – O – H + H+ CH3 – CH2 – O H H + CH3 – CH2 – O H H + +CH3 – CH2 – O – H CH3 – CH2 – O – CH2 – CH3 | H + CH3 – CH2 – O – CH2 – CH3 | H + CH3 – CH2 – O – CH2 – CH3 First molecule of alcohol Second molecule The reaction follows SN1 pathway when the alcohol is secondary or tertiary However, in case of secondary and tertiary alcohols there is competition between substitution reaction and elimination reaction. In this elimination reaction dominates over the substitution. This method is inappropriate because asymmetrical ethers cannot be prepared by this process

37. It is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium alkoxide. 2. Williamson synthesis R – X R’ – O Na – + + R’ – O – R + NaX Ethers containing secondary or tertiary alkyl groups may also be prepared by this method. This reaction follows SN2 mechanism CH3 CH3 – C – O Na | | CH3 +– + CH3 – Br CH3 CH3 – C – O – CH3 | | CH3 + NaBr 1. Better results are obtained if the alkyl halide is primary. 2. In case of secondary and tertiary alkyl halides, elimination competes over substitution. 3. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. Alexander William Williamson

38. CH3 – C = CH2 | CH3 + NaBr + CH3OHCH3 – O Na +– CH3 CH3 – C – Br | | CH3 + Phenols are also converted to ethers by this method. In this, phenol is used as the phenoxide ion. OH NaOH O Na – + R’– X O – R’

39. Due to this polar nature ethers have higher boiling point than alkanes of comparable masses. But they have lower boiling points than alcohols because absence of intermolecular H – bonding Physical properties of ethers O C C | | d+ d- The C-O bonds in ethers are polar and thus, ethers have a net dipole moment. But they are weakly polar than alcohols 1. Boiling point 2. Solubility in water Ethers form intermolecular H – bonding with water just like alcohols so, they are soluble in water. O R R d- O HH O H Hd+ d+ d+

40. Chemical reactions of ethers Ethers are the least reactive of the functional groups. The cleavage of C-O bond in ethers takes place under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules. 1. Cleavage of C–O bond in ethers R – O – R + HX RX + R – OH R – O – R H + X – Similarly, phenols also can be formed by this method. O – R + HX OH + R – OH

41. Ethers with two different alkyl groups are also cleaved in the same manner. R – O – R’ + HX RX + R’ – OH The order of reactivity of hydrogen halides is as follows: HI > HBr > HCl. Mechanism CH3 – O – C2H5 + H – I CH3 – O – C2H5 H | + + I – Oxonium ion CH3 – O – C2H5 H | + I + – CH3 O – C2H5 H |+ I CH3 – I + C2H5 – OH

42. If HI is used in excess the molecule of alcohol also get converted into alkyl iodide + H – I + I – CH3 – CH2 – O H H + I + – CH3 – CH2 – I + H2O CH3 – CH2 – O H H + CH3 – CH2 – O – H If aromatic ethers are used, then phenols get formed. Phenols cannot be attacked by I- again because C – O bond in phenol cannot be broken easily as this bond is strong bond. This bond is strong because, 1. it shows partial double bond character because of resonance 2. Due to higher electronegativity of sp2 hybridised carbon.

43. However, when one of the alkyl group is a tertiary group, the halide formed is a tertiary halide. CH3 CH3 – C – O – CH3 | | CH3 + HI CH3 CH3 – C – I | | CH3 CH3 – OH + But in case of aromatic ethers, always phenol gets formed because C – O bond cannot be broken easily as it shows partial double bond characters.

44. The alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol. 2. Electrophilic substitution O – R O – R + O – R + O – R + O – R

45. a. Halogenation: Anisole undergoes bromination withbromine in ethanoic acid even in the absence of iron (III) bromide catalyst. It is due to the activation of benzene ring by the methoxy group. Para isomer is obtained in 90% yield. O – CH3 Br2 Bromine water + O – CH3 Br O – CH3 Br p – bromoanisol Major o – bromoanisol Minor

46. Phenol is heated with acyl cholride in presence of anhydrous AlCl3(Lewis acid) to give (para and ortho product). Out of two; para product is major. b. Friedel Craft’s acylation and alkylation O CH3 Anhydrous AlCl3 + CH3COCl O CH3 + COCH3 O CH3 COCH3 Major Phenol is heated with alkyl cholride in presence of anhydrous AlCl3(Lewis acid) to give p and o productsl. Out of two; para product is major. OH + CH3Cl O CH3 + CH3 O CH3 CH3 Major 4 – methoxyacetophenone 2 – methoxyacetophenone Anhydrous AlCl3 CS2 4 – methoxytoulene 2– methoxytoulene

47. O CH3 c. Nitration H2SO4 + HNO3 O CH3 NO2 O CH3 NO2 o– Nitroanisol Minor p – Nitroanisol Major +

48. Some Commercially Important Alcohols Methanol, CH3OH, also known as ‘wood spirit’, was produced by destructive distillation of wood. Today, most of the methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of ZnO – Cr2O3 catalyst. CO + 2H2 ZnO + CrO3 200 – 300 atm 573 – 673 K CH3 OH Methanol is a colourless liquid and boils at 337 K. It is highly poisonous in nature. Ingestion of even small quantities of methanol can cause blindness and large quantities causes even death. Methanol is used as a solvent in paints, varnishes and chiefly for making formaldehyde. 1. Methanol

49. Ethanol, C2H5OH, is obtained commercially by fermentation, the oldest method is from sugars. The sugar in molasses, sugarcane or fruits such as grapes is converted to glucose and fructose, (both of which have the formula C6H12O6), in the presence of an enzyme, invertase. Glucose and fructose undergo fermentation in the presence of another enzyme, zymase, which is found in yeast. 2. Ethanol C12H22O11 + H2O Invertase C6H12O6 + C6H12O6 C6H12O6 Zymase 2C2H5OH + 2CO2

50. Wine making grapes are the source of sugars and yeast As grapes ripen, the quantity of sugar increases and yeast grows on the outer skin. When grapes are crushed, sugar and the enzyme come in contact and fermentation starts Fermentation takes place in anaerobic conditions i.e. in absence of air. Carbon dioxide is released during fermentation The action of zymase is inhibited once the percentage of alcohol formed exceeds 14 percent. If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid which in turn destroys the taste of alcoholic drinks.

51. Ethanol is a colourless liquid with boiling point 351 K. It is used as a solvent in paint industry and in the preparation of a number of carbon compounds. The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid). It is known as denaturation of alcohol. Properties of ethanol

XII alcohols phenols ethers

XII alcohols phenols ethers

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