1. 1 Jerry Poteat Science Department Georgia Perimeter College © John Wiley and Sons, Inc. Version 1.0 Chapter 22 Alcohols, Ethers, Phenols, and Thiols Hein * Pattison * Arena * Best

2. 2 Chapter Outline 22.1 Functional Groups 22.2 Classification of Alcohols 22.3 Naming Alcohols 22.4 Physical Properties of Alcohols 22.5 Chemical Properties of Alcohols 22.6 Common Alcohols 22.7 Phenols

3. 3 Chapter Outline 22.8 Properties of Phenols 22.9 Production of Phenol 22.10 Ethers 22.11 Structures and Properties of Ethers 22.12 Preparation of Ethers 22.13 Thiols

4. 4 22.1 Functional Groups

5. 5 A functional group is a group of atoms ( or atom) in an organic compound that has specific behavorial characteristics. For example the hydroxyl (–OH ) group is the characteristic functional group for alcohols and phenols. What is a functional group ?

6. 6 Alcohols, ethers, and phenols are organic compounds that are structural derivatives of water.

7. 7 22.2 Classification of Alcohols

8. 8 Alcohols are classified by the number of R groups (i.e. carbon atoms) attached to the hydroxyl carbon as shown here.

9. 9 Figure 22.1 Models illustrating the structure of methanol and ethanol.

10. 10

11. 11 Alcohols with more than one –OH group are known as polyhydroxy alcohols. These include diols, triols, and carbohydrates like glucose.

12. 12 The -OH group of an alcohol like 2-butanol can be written as a single-line formula by enclosing the ­OH in parentheses.

13. 13 22.3 Naming Alcohols

14. 14 IUPAC Rules for Naming Alcohols 1.Name the longest continuous carbon chain containing the hydroxyl group. 2. Drop an –e from the corresponding alkane parent name and add the suffix –o1.

15. 15 IUPAC Rules for Naming Alcohols 3. Carbon chains with three or more carbon atoms are numbered so the -OH group carbon atom is assigned the lowest possible number. This number is given as a prefix in the name. 4. Attached groups are named and numbered as stated previously.

16. 16 Other Examples of Naming Alcohols

17. 17 22.4 Physical Properties of Alcohols

18. 18 Physical Properties of Alcohols Alcohols contain the polar hydroxyl group (–OH). The –OH group can undergo hydrogen bonding which affects the solubility and boiling point of alcohols.

19. 19 Hydrogen Bonding and Boiling Point Hydrogen bonding between alcohol molecules explains the increase in boiling points of alcohols compared to alkanes.

20. 20 Hydrogen Bonding and Solubility Hydrogen bonding between alcohol and water molecules is the reason for the increased solubility of alcohols.

21. 21 Effect of Hydroxyl Groups on Boiling Points Table 22.2 shows that the boiling point (b.p.) of an alcohol is much higher than the parent alkane due to the effects of hydrogen bonding.

22. 22 Effect of Hydroxyl Groups on Boiling Points Increasing the number of –OH groups in a molecule increases the boiling point and solubility of the molecule. Notice in Table 22.3 that the b.p. of 1,2-ethanediol is 100  C higher than the b.p. of 1-propanol because of an additional -OH group.

23. 23 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 OH 1-hexanol (solubility = 0.6g/100g H 2 O) Effect of Hydroxyl Groups on Solubility The effect of added –OH groups on solubility can be more significant for a carbohydrate like glucose. Note the difference in solubility of hexanol (only one –OH group) and glucose ( five –OH groups). D-glucose (solubility = 95g/10g H 2 O)

24. 24 A branched-chain alcohol will have a lower boiling point than the corresponding straight-chain alcohol. For example 2-butanol is branched and has a b.p. of 91.5  C versus 118  C for 1-butanol. Effect of Branching on Boiling Point CH 3 CH 2 CH 2 CH 2 OH 1-butanol

25. 25 General Solubility of Alcohols Alcohols with three carbon atoms or less are infinitely soluble in water while those with four or more carbon atoms have limited solubility in water. However, all hydrocarbons are insoluble in water.

26. 26 22.5 Chemical Properties of Alcohols

27. 27 Acidic and Basic Properties of Alcohols Alcohols can act as weak acids or weak bases due to the nature of the –OH group as shown here.

28. 28 Reactions of Alcohols Protonation to form an oxonium ion Deprotonation to form an alkoxide ion Oxidation to form aldehydes, ketones, or carboxylic acids Dehydration to form alkenes and ethers Esterification to form esters Alcohols undergo many reactions including these five:

29. 29 Protonation Alcohols form oxonium ions in the presence of a strong acid.

30. 30 Alcohols form alkoxide ions in the presence of strong bases or an alkali metal. Deprotonation The order of reactivity of ROH with alkali metals is 1  > 2  > 3 .

31. 31 Alcohols are oxidized to form aldehydes, ketones, or carboxylic acids. [O] is the general symbol for oxidizing agents with some common oxidizing agents being KMnO 4, K 2 Cr 2 O 7, and O 2. Oxidation

32. 32 The oxidation state of carbon is determined by the functional group as shown here and in Table 22.4. Oxidation States of Carbon

33. 33 The oxidation of ethanol is used in the breath analyzer test. Application of an Oxidation Reaction The orange color of K 2 Cr 2 O 7 in the picture on the left partially changes to green in the picture on the right when it reacts with ethanol (CH 3 CH 2 OH) from the balloon.

34. 34 Ethanol is toxic because it is oxidized to ethanal which can cause cirrhosis of the liver. Oxidation: Biochemistry of Ethanol Ethanal in turn is oxidized to acetic acid which can contribute to obesity if ethanol is consumed in excess.

35. 35 Alcohols are dehydrated to form alkenes. Dehydration

36. 36 Some alcohols give two possible alkenes when dehydrated as shown here. Dehydration : Saytzeff’s Rule

37. 37 Dehydration : Saytzeff’s Rule The observation that two alkene isomers are possible in some cases is known as Saytzeff’s rule which states…… …the more highly substituted alkene isomer is the major product formed when two alkene isomers are possible.

38. 38 Preparation of Ethers by Intramolecular Dehydration Ethers can be prepared by splitting out water from two molecules of an primary alcohol. This type of reaction is known as a condensation reaction.

39. 39 Alcohols react with carboxylic acids to form esters in a reaction know as esterification. Esterificaiton

40. 40 Utility of the Hydroxyl Functional Group The –OH functional group is a valuable intermediate because it is a “ gateway’ functional group to the synthesis of the functional groups listed in Figure 22.2. Figure 22.2 Hydroxyl group reactions

41. 41 Utility of the Hydroxyl Functional Group The –OH is an integral part in the degradation of fats to ketones in the body as shown here and in the next slide.

42. 42 Utility of the Hydroxyl Functional Group alkene

43. 43 22.6 Common Alcohols

44. 44 Synthesis of Alcohols 1.Hydrolysis of an ester 2. Alkaline hydrolysis of an alkyl halide (1° and 2° alcohols only) 3. Catalytic reduction of aldehydes and ketones. There are three general methods for making an alcohol:

45. 45 Hydrolysis of an Ester An ester can be hydrolyzed to an alcohol and a carboxylic acid.

46. 46 Hydrolysis of RX (only 1  or 2  ROHs can be prepared) A 1  or 2  alkyl halide (RX) can be hydrolyzed to an alcohol and a salt. (general reaction)

47. 47 Catalytic Reduction of Aldehydes and Ketones These reactions are covered in more detail in Chapter 23.

48. 48 Preparation of Methanol Methanol is a common industrial solvent prepared by the high-pressure catalytic hydrogenation of carbon monoxide.

49. 49 Methanol: Properties and Applications Methanol is primarily used as a feedstock to produce the intermediate formaldehyde. It is also used as an industrial solvent and as a denaturant for ethanol. Methanol has a b.p. of 65  C making it a highly flammable liquid. Methanol is poisonous and can cause blindness or death when taken internally.

50. 50 Preparation of Ethanol Ethanol can be prepared by fermentation or by the acid-catalyzed addition of water to ethylene. Fermentation Hydration

51. 51 Pure ethanol has a b.p. of 78  C and is very hygroscopic. 100% ethanol takes up water very quickly until a stable concentration of 95.6% ethanol is reached. Ethanol can act in the body as a food, drug, or a poison depending on the quantity consumed. Ethanol: Properties and Applications

52. 52 Ethanol is used commercially as an intermediate in the manufacture of other chemicals such as acetic acid. It is also used as a solvent for many organic substances, as a compounding ingredient for pharmaceuticals, perfumes, flavorings, etc., and as a major component in alcoholic beverages. Ethanol: Applications

53. 53 2-propanol is a secondary alcohol prepared from propene. Commercial uses include the manufacture of chemicals like acetone, as an industrial solvent, and in rubbing-alcohol formulations. 2-Propanol (Isopropyl Alcohol)

54. 54 Ethylene Glycol is a diol obtained from petroleum or prepared by from ethylene oxide. Commercial uses include the manufacture of Dacron polyester fiber and Mylar film, explosives, antifreeze, as a solvent for paints, plastics, and ink applications. Ethylene Glycol (1,2-Ethanediol)

55. 55 Glycerol (1,2,3-Propanetriol) Glycerol (i.e. glycerine) is a polyhydroxy alcohol. It is a desirable commercial chemical because of its attraction for water which is due to the polarity of its hydroxyl groups. Commercial uses include the manufacture of polymers and explosives ( see reaction below), as an emollinet in cosmetics, as a humectant in tobacco products, and as a sweetner.

56. 56 22.7 Phenols

57. 57 Phenols Phenols are organic compounds that have a hydroxy group attached to an aromatic ring.

58. 58 Naming Phenols Derivatives of phenols are named using the general methods for naming aromatic compounds as shown here.

59. 59 Common Phenols Some phenols are known by common names as shown here.

60. 60 Phenols as Flavoring Agents These phenols are often used as flavoring agents.

61. 61 Phenols as Antioxidants BHT is an antioxidant preservative for food while urushiols are the active ingredients in poison ivy and poison oak.

62. 62 Phenols as Disinfectants These phenol isomers are effective disinfectants

63. 63 Phenols as a Natural Drug and Indicator ( a common lab pH indicator) Phenols occur naturally in plants like marijuana and some phenols are used as pH indicators.

64. 64 Phenols as Hormones (a hormone) Adrenalin is a phenol that is a hormone.

65. 65 22.8 Properties of Phenols

66. 66 Properties of Phenol Phenol is a weak acid with a melting point of 41  C. The table below is a comparison of the pH of phenol with the pH of water and acetic acid. Water Phenol (0.1M) Acetic acid (0.1M) 7.0 5.5 2.87 Substance pH

67. 67 Properties of Phenols Phenols will react with a strong base like NaOH but not with weaker bases like NaHCO 3.

68. 68 Properties of Phenols Alcohols however do not react with either NaOH or NaHCO 3.

69. 69 Properties of Phenols The toxicity of phenols to microorganisms make them excellent antiseptics.

70. 70 22.9 Production of Phenols

71. 71 Production of Phenol Phenol is obtained from coal tar but it is also produced synthetically by the process shown below. Phenol is used to manufacture phenol-formaldehyde resins and plastics.

72. 72 22.10 Ethers

73. 73 Ethers Ethers are organic compounds that have the general formula ROR` where both R groups can be the same or different.

74. 74 Ethers Ethers have the general formula ROR ’

75. 75 Naming Simple Ethers Name each alkyl group in alphabetical order followed by the word ether as shown here. Use a prefix if both alkyl groups are the same.

76. 76 Naming Ethers Using IUPAC Rules 1.Name the longest continuous carbon chain corresponding to the parent alkane. 2. Name the remaining part as an alkoxy group. For example… …would be named methoxyethane

77. 77 Examples of Naming Alkoxy Groups

78. 78 Examples of Naming Ethers

79. 79 22.11 Structures and Properties of Ethers

80. 80 Structure of Ethers Ethers have a bent shape similar to water and alcohols.

81. 81 Properties of Ethers Ethers are polar enough to dissolve some polar substances ( solubility in water is 7.5g/100g ) but also nonpolar enough to dissolve many organic compounds. The slight solubility of ether in water can be explained by hydrogen bonding as shown here

82. 82

83. 83 Hazards of Using Ethers Ethers are common solvents found in laboratories because they are good solvents for organic compounds. However, ethers can be dangerous because of their highly flammable vapors.

84. 84 Hazards of Using Ethers Ethers also form unstable peroxides when exposed to air as shown in the reaction below. These peroxides can undergo explosive decomposition.

85. 85 22.12 Preparation of Ethers

86. 86 The Williamson Ether Synthesis The Williamson ether synthesis is another method used to prepare ethers. This is a substitution reaction where an alkoxide ion replaces a halide ion in an alkyl halide.

87. 87 The Williamson Ether Synthesis This synthesis is often used to prepare mixed ethers where R  R`.

88. 88 22.13 Thiols

89. 89 Thiols Thiols are organic compounds that contain the –SH group as shown below. Thiols are also called mercaptans. Thiols are named by adding the suffix -thiol to the alkane parent name.

90. 90 Properties of Thiols Thiols have several characteristic properties. (1)Foul odors (2) Lower boiling points than alcohols (3) Readily oxidized to disulfides

91. 91 Foul Odors of Thiols Thiols have strong offensive odors. For example the scent of a skunk is due to thiol components. The strong odor associated with natural gas is due to the additive methanethiol (CH 3 SH).

92. 92 Boiling Points of Thiols Thiols have lower boiling points than alcohols. CH 3 CH 2 OH CH 3 CH 2 SH ethanol ethanethiol ( b.p. is 78  C ) ( b.p. is 36  C ) Thiols boil at lower temperatures because thiols have no hydrogen bonding while alcohols have hydrogen bonding.

93. 93 Oxidation to Disulfides CH 3 SH CH 3 S-SCH 3 A thiol can be readily oxidized to a disulfide. A disulfide is a molecule containing a S-S bond.

94. 94 Biological Role of Thiol Derivatives Thiol derivatives are found in hormones like insulin. The disulfide bond (RS-SR) for example is used to bind proteins to create biologically useful three-dimensional shapes. The thioester group of coenzyme A serves an important role in metabolism.

95. 95 Chapter 22 Summary  Alcohols (ROH) are classified as primary, secondary, or tertiary alcohols.  Alcohols have higher boiling points and higher solubility in water than alkanes due to hydrogen bonding.  Alcohols are “gateway” molecules because they can be protonated, deprotonated, oxidized, dehydrated and esterified.  Alcohols in some cases are dehydrated to form two isomeric alkenes according to Saytzeff’s rule.  Phenols (PhOH) are intermediate in acidity between carboxylic acids and alcohols.

96. 96 Chapter 22 Summary  Phenol derivatives have numerous applications including the use as a disinfectant.  Ethers ( ROR`) have intermediate polarity and serve as solvents for polar and nonpolar compounds.  Ethers can prepared by intramolecular dehydration or by the Williamson ether synthesis.  Thiols (RSH) have lower boiling points than alcohols and have foul odors.  Thiol derivatives like disulfides and thioesters are found in important biological molecules like insulin and coenzyme A.