ORGANIC CHEMISTRY CHM 207

1. ORGANIC CHEMISTRY CHM 207 CHAPTER 6: HYDROXYL COMPOUNDS (ALCOHOLS AND PHENOL) NOR AKMALAZURA JANI

2. SUBTOPICS • Nomenclature of alcohols, phenols. • Classification of alcohols. • Physical properties of alcohols: - Physical state - Boiling points - Solubility of alcohols in water • Acidity of alcohols and phenols • Reactions of alcohols: - Reaction with sodium - Oxidation - Esterification - Halogenation and haloform reactions - Dehydration - Formation of ether (Williamson ether synthesis)

3. Reactions of phenols: - Reaction with sodium - Esterification - Halogenation of the ring - Nitration of the ring • Tests to distinguish classes of alcohols: i) Lucas test ii) Oxidation • Haloform test to identify methyl alcohol group - Iodoform - Bromoform • Uses of alcohols and phenols.

4. ALCOHOLS • Alcohols: Organic compounds containing hydroxyl (-OH) functional groups. • Phenols: Compounds with hydroxyl group bonded directly to an aromatic (benzene) ring.

5. NOMENCLATURE OF ALCOHOLS

6. IUPAC RULES Select the longest continuous chain of carbon atoms containing the hydroxyl group. Number the carbon atoms in this chain so that the one bonded to the –OH group has the lowest possible number. Form the parent alcohol name by replacing the final –e of the corresponding alkane name by –ol. When isomers are possible, locate the position of the –OH by placing the number (hyphenated) of the carbon atom to which the –OH is bonded immediately before the parent alcohol name. Name each alkyl branch chain (or other group) and designate its position by number.

7. This is the longest continuous chain that contains an hydroxyl group. Select this chain as the parent compound.

8. 4 3 2 1 This end of the chain is closest to the OH. Begin numbering here.

9. 4 3 2 1 3-methyl-2-butanol

10. This is the longest continuous chain that contains an hydroxyl group. Select this chain as the parent compound.

11. 5 4 3 2 1 This end of the chain is closest to the OH. Begin numbering here.

12. 5 4 3 3 2 2 1 3-methyl-2-pentanol

13. NOMENCLATURE OF CYCLIC ALCOHOLS • Using the prefix cyclo- • The hydroxyl group is assumed to be on C1.

14. NOMENCLATURE OF ALCOHOLS CONTAINING TWO DIFFERENT FUNCTIONAL GROUPS • Alcohol containing double and triple bonds: - use the –ol suffix after the alkene or alkyne name. • The alcohol functional group takes precedence over double and triple bonds, so the chain is numbered in order to give the lowest possible number to the carbon atom bonded to the hydroxyl group. • The position of the –OH group is given by putting its number before the –ol suffix. • Numbers for the multiple bonds were once given early in the name.

15. EXAMPLE 1) Longest carbon chain that contains –OH group - 5 carbon 2) Position of –OH group - Carbon-2 3) Position of C=C - Carbon-4 COMPLETE NAME = 4-penten-2-ol

16. Some consideration: - OH functional group is named as a hydroxy substituent when it appears on a structure with a higher priority functional group such as acids, esters, aldehydes and ketones. - Examples:

17. MAIN GROUPS Acids Esters Aldehydes Ketones Alcohols Amines Alkenes Alkynes Alkanes Ethers Halides decreasing priority

18. NOMENCLATURE OF DIOLS • Alcohols with two –OH groups are called diols or glycols. • Naming of diols is like other alcohols except that the suffix diol is used and two numbers are needed to tell where the two hydroxyl groups are located.

19. NOMENCLATURE OF PHENOLS • The terms ortho (1,2-disubstituted), meta (1,3-disubstituted) and para (1,4-disubstituted) are often used in the common names.

20. Phenols may be monohydric, dihydric or trihydric according to the number of hydroxyl groups present in the benzene ring.

21. CLASSIFICATION • According to the type of carbinol carbon atom (C bonded to the –OH group). • Classes: i) Primary alcohol - -OH group attached to a primary carbon atom ii) Secondary alcohol - -OH group attached to a secondary carbon atom iii) Tertiary alcohol - -OH group attached to a tertiary carbon atom

22. TYPE STRUCTURE EXAMPLES • Primary (1°) • Secondary (2°) • Tertiary (3°)

23. Polyhydroxy Alcohols • Alcohols that contain more than one OH group attached to different carbons are called polyhydroxy alcohols. • Monohydroxy: one OH group per molecule. • Dihydroxy: two OH groups per molecule. • Trihydroxy: three OH groups per molecule.

25. PHYSICAL PROPERTIES • PHYSICAL STATES OF ALCOHOLS - simple aliphatic alcohols and lower aromatic alcohols (such as phenylmethanol, C6H5CH2OH) → liquids at room temperature. - highly branched alcohols and alcohols with twelve or more carbon atoms → solids.

26. BOILING POINTS - The boiling points of alcohols are higher than those of alkanes and chloroalkanes of similar relative molecular mass. - For example: C2H5OH CH3CH2CH3 CH3Cl Relative molecular mass: 46 44 50.5 Boiling point: 78°C -42°C -24°C - Reason: intermolecular hydrogen bonds exist between the –OH groups in the alcohol molecules. δ- δ+ δ- δ+ δ- δ- hydrogen bonding hydrogen bonding - Branched chain alcohols boils at a lower temperature (more volatile) than the straight chain alcohols with the same number of carbon atoms.

27. SOLUBILITY OF ALCOHOLS IN WATER i) alcohols with short carbon chains (such as methanol, ethanol, and propanol) dissolve in water. - when alcohols dissolve in water, hydrogen bonds are formed between the –OH group of the alcohol molecule and the –OH group of the water molecule. ii) the solubility of alcohols in water decreases sharply with the increasing length of the carbon chain. Higher alcohols are insoluble in water. - alcohol contains a polar end (-OH group) called ‘hydrophilic’ and a non-polar end (the alkyl group) called ‘hydrophobic’. - the water solubility decreases as the alkyl group becomes larger.

28. iii) alcohols with more than one hydroxyl group (polyhydroxy alcohols) are more soluble than monohydroxy alcohols with the same number of carbon atoms. This is because they can form more hydrogen bonds with water molecule. iv) branched hydrocarbon increases the solubility of alcohol in water. - reason: branched hydrocarbon cause the hydrophobic region becomes compact. * Phenol is unusually soluble (9.3%) because of its compact shape and the particularly strong hydrogen bonds formed between phenolic –OH groups and water molecules.

29. ACIDITY OF ALCOHOLS AND PHENOLS • Alcohol is weakly acidic. • In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O-). R-OH + H2O R-O- + H3O+ Ka = ~ 10-16 to 10-18 alkoxide ion Example CH3CH2-OH + H2O CH3CH2-O- + H3O+ • The acid-dissociation constant, Ka, of an alcohol is defined by the equilibrium Ka R-OH + H2O R-O- + H3O+ * More smaller the pKa value, the alcohol is more acidic Ka = [H3O+] [RO-] [ROH] pKa = - log (Ka)

30. Acidity OF PHENOLS • Phenol is a stronger acid than alcohols and water. R-OH + H2O R-O- + H3O+Ka = ~ 10-16 to 10-18 alcohol alkoxide ion Ka = 1.2 x 10-10 H2O + H2O HO- + H3O+Ka = 1.8 x 10-16 hydroxide ion

31. Phenol is more acidic than alcohols by considering the resonance effect. i) The alkoxide ion (RO-) - the negative charge is confined to the oxygen and is not spread over the alkyl group. - this makes the RO- ion less stable and more susceptible to attack by positive ions such as H+ ions.

32. ii) The phenoxide ion - one of the lone pairs of electrons on the oxygen atom is delocalised into the benzene ring. - the phenoxide ion is more stable than the alkoxide ion because the negative charge is not confined to the oxygen atom but delocalised into the benzene ring. - the phenoxide ion is resonance stabilised by the benzene ring and this decreases the tendency for the phenoxide ion to react with H3O+.

33. EFFECTS OF Acidity • The acidity decreases as the substitution on the alkyl group increase. - Reason: a more highly substituted alkyl group inhibits solvation of the alkoxide ion and drives the dissociation equilibrium to the left. - For example: methanol is more acidic than t-butyl alcohol. • The present of electron-withdrawing atoms enhances the acidity of alcohols. - Reason: the electron withdrawing atom helps to stabilize the alkoxide ion. - For example: 2-chloroethanol is more acidic than ethanol because the electron-withdrawing chlorine atom helps to stabilize the 2-chloroethoxide ion. - alcohol with more than one electron withdrawing atoms are more acidic. For example, 2,2,-dichloroethanol is more acidic than 2-chloroethanol. - Example of electron-withdrawing atom/groups: Halogen atoms and NO2.

34. REACTIONS OF ALCOHOLS • Reaction with sodium • Oxidation • Esterification • Halogenation and haloform reactions • Dehydration • Formation of ether (Williamson ether synthesis)

35. Reaction with sodium • Alcohols reacts with Na at room temperature to form salts (sodium alkoxides) and hydrogen. 2R-O-H + 2Na → 2R-O-Na+ + H2 • For example: CH3CH2OH + Na → CH3CH2O-Na+ + 1/2H2 alcohol sodium ethoxide • Reactivity of alcohols towards the reactions with sodium: CH3 > 1° > 2° > 3°

36. Oxidation 1° alcohol

37. Examples: 1° alcohol

38. 2° alcohol 3° alcohol Example:

39. Esterification • Esterification: - the reaction between an alcohol and a carboxylic acid to form an ester and H2O. H+ = catalyst

40. Esterification also occurs when alcohols react with derivatives of carboxylic acids such as acid chlorides

41. Halogenation and haloform reactions 1) Hydrogen halides (HBr or HCl or HI) R-OH + H-X → R-X + H2O Example: C2H5-OH + H-Br C2H5-Br + H2O • Reactivity of hydrogen halides decreases in order HI > HBr > HCl • Reactivity of alcohols with hydrogen halides: 3° > 2° > 1° H+

42. 2) Phosphorus trihalides, PX3 3R-OH + PX3 3R-X + H3PO3 (PX3 = PCl3 or PBr3 or PI3) Example: (CH3)2CHCH2-OH + PBr3→ (CH3)2CHCH2-Br isobutyl alcohol isobutyl bromide 3) Thionyl chloride (SOCl2) R-OH + SOCl2 → R-Cl + SO2 + HCl Example: CH3(CH2)5CH2-OH + SOCl2 → CH3(CH2)5CH2-Cl + SO2 + HCl 1-heptanol 1-chloroheptane

43. Dehydration • Dehydration of alcohols will formed alkenes and the products will followed Saytzeff rules. conc. H2SO4 R-CH2-CH2-OH R-CH=CH2 + H2O • Saytzeff rule: - A reaction that produces an alkene would favour the formation of an alkene that has the greatest number of substituents attached to the C=C group.

44. Reactivity of alcohols towards dehydration: 3° > 2° > 1° • Reagents for dehydration: i) Concentrated H2SO4 conc. H2SO4 CH3-CH2-OH CH2=CH2 + H2O ii) With phosphoric (v) acid iii) Vapour phase dehydration of alcohols CH3CH2OH CH2=CH2 + H2O Al2O3 heat

45. Formation of ether (Williamson ether synthesis) • Involves the SN2 attack of an alkoxide ion on an unhindered primary alkyl halides. • The alkoxide is made by adding Na, K or NaH to the alcohol. R-O- + R’-X → R-O-R’ + X- alkoxide (R’ must be primary) • The alkyl halides (or tosylate) must be primary, so that a back-side attack is not hindered. • If the alkyl halides is not primary, elimination usually occurs to form alkenes.

47. REACTIONS OF PHENOLS • Reaction with sodium • Esterification • Halogenation of the ring • Nitration of the ring

48. REACTION WITH SODIUM REACTION WITH AQUEOUS SODIUM HYDROXIDE ROH + NaOH no reaction

49. ESTERIFICATION H+

50. HALOGENATION • More reactive towards electrophilic substitution than benzene. • ortho-para director.