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Dr. Wolf's CHM 201 & 202 15-1 Chapter 15 Alcohols, Diols, and Thiols.

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Presentation on theme: "Dr. Wolf's CHM 201 & 202 15-1 Chapter 15 Alcohols, Diols, and Thiols."— Presentation transcript:

1 Dr. Wolf's CHM 201 & 202 15-1 Chapter 15 Alcohols, Diols, and Thiols

2 Dr. Wolf's CHM 201 & 202 15-2 Sources of Alcohols

3 Dr. Wolf's CHM 201 & 202 15-3 Methanol is an industrial chemical end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde MethanolMethanol

4 Dr. Wolf's CHM 201 & 202 15-4 Methanol is an industrial chemical end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde prepared by hydrogenation of carbon monoxide CO + 2H 2  CH 3 OH MethanolMethanol

5 Dr. Wolf's CHM 201 & 202 15-5 Ethanol is an industrial chemical Most ethanol comes from fermentation Synthetic ethanol is produced by hydration of ethylene Synthetic ethanol is denatured (made unfit for drinking) by adding methanol, benzene, pyridine, castor oil, gasoline, etc. EthanolEthanol

6 Dr. Wolf's CHM 201 & 202 15-6 Isopropyl alcohol is prepared by hydration of propene. All alcohols with four carbons or fewer are readily available. Most alcohols with five or six carbons are readily available. Other alcohols

7 Dr. Wolf's CHM 201 & 202 15-7 Hydration of alkenes Hydroboration-oxidation of alkenes Hydrolysis of alkyl halides Syntheses using Grignard reagents organolithium reagents Sources of alcohols Reactions discussed in earlier chapters (Table 15.1)

8 Dr. Wolf's CHM 201 & 202 15-8 Reduction of aldehydes and ketones Reduction of carboxylic acids Reduction of esters Reaction of Grignard reagents with epoxides Diols by hydroxylation of alkenes Sources of alcohols New methods in Chapter 15

9 Dr. Wolf's CHM 201 & 202 15-9 Preparation of Alcohols by Reduction of Aldehydes and Ketones

10 Dr. Wolf's CHM 201 & 202 15-10 CRHOH H CRH O Reduction of Aldehydes Gives Primary Alcohols

11 Dr. Wolf's CHM 201 & 202 15-11 Pt, ethanol (92%) Example: Catalytic Hydrogenation CH 3 O CH 2 OH O CH 3 O CH + H2H2H2H2

12 Dr. Wolf's CHM 201 & 202 15-12 CRHOH R' C R R' O Reduction of Ketones Gives Secondary Alcohols

13 Dr. Wolf's CHM 201 & 202 15-13 (93-95%) Example: Catalytic Hydrogenation + H2H2H2H2OPt ethanol HOH

14 Dr. Wolf's CHM 201 & 202 15-14 H:–H:–H:–H:– H:–H:–H:–H:– CRH OHOHOHOH H CRH O CRH OHOHOHOH R' CRR' O Retrosynthetic Analysis

15 Dr. Wolf's CHM 201 & 202 15-15 Sodium borohydride Lithium aluminum hydride Li+ Na+ – B HHHH – Al HHHH Metal Hydride Reducing Agents act as hydride donors

16 Dr. Wolf's CHM 201 & 202 15-16 NaBH 4 (82%) Examples: Sodium Borohydride CH 2 OH O CH O2NO2NO2NO2Nmethanol O2NO2NO2NO2N O HOH(84%) NaBH 4 ethanol Aldehyde Ketone

17 Dr. Wolf's CHM 201 & 202 15-17 Lithium aluminum hydride more reactive than sodium borohydride cannot use water, ethanol, methanol etc. as solvents diethyl ether is most commonly used solvent

18 Dr. Wolf's CHM 201 & 202 15-18 Examples: Lithium Aluminum Hydride (84%) Aldehyde KetoneO CH 3 (CH 2 ) 5 CH CH 3 (CH 2 ) 5 CH 2 OH 1. LiAlH 4 diethyl ether 2. H 2 O O (C 6 H 5 ) 2 CHCCH 3 1. LiAlH 4 diethyl ether 2. H 2 O (86%)OH (C 6 H 5 ) 2 CHCHCH 3

19 Dr. Wolf's CHM 201 & 202 15-19 neither NaBH 4 or LiAlH 4 reduces isolated double bonds HOH O 1. LiAlH 4 diethyl ether 2. H 2 O (90%) SelectivitySelectivity

20 Dr. Wolf's CHM 201 & 202 15-20 Preparation of Alcohols By Reduction of Carboxylic Acids and Esters

21 Dr. Wolf's CHM 201 & 202 15-21 lithium aluminum hydride is only effective reducing agent Reduction of Carboxylic Acids Gives Primary Alcohols CRHOH H C R HO O

22 Dr. Wolf's CHM 201 & 202 15-22 Example: Reduction of a Carboxylic Acid 1. LiAlH 4 diethyl ether 2. H 2 O COH O CH 2 OH (78%)

23 Dr. Wolf's CHM 201 & 202 15-23 Lithium aluminum hydride preferred for laboratory reductions Sodium borohydride reduction is too slow to be useful Catalytic hydrogenolysis used in industry but conditions difficult or dangerous to duplicate in the laboratory (special catalyst, high temperature, high pressure Reduction of Esters Gives Primary Alcohols (Also Chapter 19)

24 Dr. Wolf's CHM 201 & 202 15-24 Example: Reduction of an Ester 1. LiAlH 4 diethyl ether 2. H 2 O (90%)O COCH 2 CH 3 CH 3 CH 2 OH CH 2 OH +

25 Dr. Wolf's CHM 201 & 202 15-25 Preparation of Alcohols From Epoxides

26 Dr. Wolf's CHM 201 & 202 15-26 Reaction of Grignard Reagents with Epoxides CH 2 OMgX H3O+H3O+H3O+H3O+ H2CH2CH2CH2C O RMgXR RCH 2 CH 2 OH

27 Dr. Wolf's CHM 201 & 202 15-27 CH 3 (CH 2 ) 4 CH 2 MgBr H2CH2CH2CH2C CH 2 O + 1. diethyl ether 2. H 3 O + CH 3 (CH 2 ) 4 CH 2 CH 2 CH 2 OH (71%) ExampleExample

28 Dr. Wolf's CHM 201 & 202 15-28 Preparation of Diols

29 Dr. Wolf's CHM 201 & 202 15-29 Diols are prepared by... reactions used to prepare alcohols hydroxylation of alkenes

30 Dr. Wolf's CHM 201 & 202 15-30 OO HCCH 2 CHCH 2 CH CH 3 H 2 (100 atm) Ni, 125°C HOCH 2 CH 2 CHCH 2 CH 2 OH CH 3 3-Methyl-1,5-pentanediol (81-83%) Example: reduction of a dialdehyde

31 Dr. Wolf's CHM 201 & 202 15-31 vicinal diols have hydroxyl groups on adjacent carbons ethylene glycol (HOCH 2 CH 2 OH) is most familiar example Hydroxylation of Alkenes Gives Vicinal Diols

32 Dr. Wolf's CHM 201 & 202 15-32 syn addition of —OH groups to each carbon of double bond Osmium Tetraoxide is Key Reagent C C HOHOHOHO OHOHOHOH C C O O Os OO C C

33 Dr. Wolf's CHM 201 & 202 15-33 (CH 3 ) 3 COOH OsO 4 (cat) tert-Butyl alcohol HO – ExampleExample (73%) CH 2 CH 3 (CH 2 ) 7 CH CH 3 (CH 2 ) 7 CHCH 2 OH OH

34 Dr. Wolf's CHM 201 & 202 15-34 (CH 3 ) 3 COOH OsO 4 (cat) tert-Butyl alcohol HO – ExampleExample (62%)HH HH OH HO

35 Dr. Wolf's CHM 201 & 202 15-35 Reactions of Alcohols: A Review and a Preview

36 Dr. Wolf's CHM 201 & 202 15-36 Table 15.2 Review of Reactions of Alcohols reaction with hydrogen halides reaction with thionyl chloride reaction with phosphorous tribromide acid-catalyzed dehydration conversion to p-toluenesulfonate esters

37 Dr. Wolf's CHM 201 & 202 15-37 New Reactions of Alcohols in This Chapter conversion to ethers esterification esters of inorganic acids oxidation cleavage of vicinal diols

38 Dr. Wolf's CHM 201 & 202 15-38 Conversion of Alcohols to Ethers

39 Dr. Wolf's CHM 201 & 202 15-39 RCH 2 O H CH 2 R OH H+H+H+H+ RCH 2 O CH 2 R HOH+ Conversion of Alcohols to Ethers acid-catalyzed referred to as a "condensation" equilibrium; most favorable for primary alcohols

40 Dr. Wolf's CHM 201 & 202 15-40 ExampleExample 2CH 3 CH 2 CH 2 CH 2 OH H 2 SO 4, 130°C CH 3 CH 2 CH 2 CH 2 OCH 2 CH 2 CH 2 CH 3 (60%)

41 Dr. Wolf's CHM 201 & 202 15-41 Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl Ether Step 1: CH 3 CH 2 O H H OSO 2 OH CH 3 CH 2 O H OSO 2 OH H + – +

42 Dr. Wolf's CHM 201 & 202 15-42 Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl Ether Step 2: CH 3 CH 2 HH+ O CH 3 CH 2 O H + + CH 3 CH 2 CH 3 CH 2 O H HHO

43 Dr. Wolf's CHM 201 & 202 15-43 Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl Ether Step 3: + + CH 3 CH 2 CH 3 CH 2 O H OSO 2 OH – H OSO 2 OH CH 3 CH 2 CH 3 CH 2 O

44 Dr. Wolf's CHM 201 & 202 15-44 reaction normally works well only for 5- and 6-membered rings Intramolecular Analog HOCH 2 CH 2 CH 2 CH 2 CH 2 OH H 2 SO 4 130° O (76%)

45 Dr. Wolf's CHM 201 & 202 15-45 Intramolecular Analog HOCH 2 CH 2 CH 2 CH 2 CH 2 OH H 2 SO 4 130° O (76%) via: O H + O H H

46 Dr. Wolf's CHM 201 & 202 15-46 Esterification (more on esters and other acid derivatives in later chapters)

47 Dr. Wolf's CHM 201 & 202 15-47 a condensation reaction called Fischer esterification acid catalyzed reversible EsterificationEsterification ROH H2OH2OH2OH2O + H+H+H+H+ + R'COHO R'COR O

48 Dr. Wolf's CHM 201 & 202 15-48 Example of Fischer Esterification H2OH2OH2OH2O + CH 3 OH + COHO COCH 3 O H 2 SO 4 0.1 mol 0.6 mol (i.e. excess) 70% yield based on benzoic acid

49 Dr. Wolf's CHM 201 & 202 15-49 high yields not reversible when carried out in presence of pyridine Reaction of Alcohols with Acyl Chlorides ROH HCl ++ R'CClO R'COR O

50 Dr. Wolf's CHM 201 & 202 15-50 pyridine + CCl O2NO2NO2NO2NO CH 3 CH 2 CH 3 OHOHOHOH (63%) NO 2 CH 3 CH 2 CH 3 OCOCOCOC O ExampleExample

51 Dr. Wolf's CHM 201 & 202 15-51 analogous to reaction with acyl chlorides Reaction of Alcohols with Acid Anhydrides ROH ++ R'COR O O R'COCR'O R'COHO

52 Dr. Wolf's CHM 201 & 202 15-52 pyridine (83%) + C 6 H 5 CH 2 CH 2 OH O F 3 CCOCCF 3 O C 6 H 5 CH 2 CH 2 OCCF 3 OExampleExample

53 Dr. Wolf's CHM 201 & 202 15-53 Esters of Inorganic Acids

54 Dr. Wolf's CHM 201 & 202 15-54 Esters of Inorganic Acids ROH + HOEWG ROEWG + H 2 O EWG is an electron-withdrawing group HONO 2 (HO) 2 SO 2 (HO) 3 P O+–

55 Dr. Wolf's CHM 201 & 202 15-55 Esters of Inorganic Acids ROH + HOEWG ROEWG + H 2 O EWG is an electron-withdrawing group HONO 2 (HO) 2 SO 2 (HO) 3 P O+– CH 3 OH + HONO 2 CH 3 ONO 2 + H 2 O (66-80%)

56 Dr. Wolf's CHM 201 & 202 15-56 Oxidation of Alcohols

57 Dr. Wolf's CHM 201 & 202 15-57 Primary alcohols Secondary alcohols from H 2 O Oxidation of Alcohols RCH 2 OH ORCHORCOHORCR' RCHR'OH

58 Dr. Wolf's CHM 201 & 202 15-58 Aqueous solution Mn(VII) Cr(VI) KMnO 4 H 2 CrO 4 KMnO 4 H 2 CrO 4 H 2 Cr 2 O 7 Typical Oxidizing Agents

59 Dr. Wolf's CHM 201 & 202 15-59 Aqueous Cr(VI) FCH 2 CH 2 CH 2 CH 2 OH K 2 Cr 2 O 7 H 2 SO 4 H2OH2OH2OH2O FCH 2 CH 2 CH 2 COH (74%)O

60 Dr. Wolf's CHM 201 & 202 15-60 Aqueous Cr(VI) FCH 2 CH 2 CH 2 CH 2 OH K 2 Cr 2 O 7 H 2 SO 4 H2OH2OH2OH2O FCH 2 CH 2 CH 2 COH (74%)O Na 2 Cr 2 O 7 H 2 SO 4 H2OH2OH2OH2O (85%)HOH O

61 Dr. Wolf's CHM 201 & 202 15-61 All are used in CH 2 Cl 2 Pyridinium dichromate (PDC) (C 5 H 5 NH + ) 2 Cr 2 O 7 2– Pyridinium chlorochromate (PCC) C 5 H 5 NH + ClCrO 3 – Nonaqueous Sources of Cr(VI)

62 Dr. Wolf's CHM 201 & 202 15-62 Example: Oxidation of a primary alcohol with PCC (pyridinium chlorochromate) CH 3 (CH 2 ) 5 CH 2 OH PCC CH 2 Cl 2 O CH 3 (CH 2 ) 5 CH (78%) ClCrO 3 – N H +

63 Dr. Wolf's CHM 201 & 202 15-63 PDC CH 2 Cl 2 O(94%) CH 2 OH (CH 3 ) 3 C CH Example: Oxidation of a primary alcohol with PDC (pryidinium dichromate)

64 Dr. Wolf's CHM 201 & 202 15-64 MechanismMechanism involves formation and elimination of a chromate ester C OHOHOHOH HOCrOH OO C O H HOO CrOH

65 Dr. Wolf's CHM 201 & 202 15-65 MechanismMechanism involves formation and elimination of a chromate ester C OHOHOHOH HOCrOH OO C O H HOO CrOH O CO H H

66 Dr. Wolf's CHM 201 & 202 15-66 Biological Oxidation of Alcohols

67 Dr. Wolf's CHM 201 & 202 15-67 alcoholdehydrogenase Enzyme-catalyzedEnzyme-catalyzed CH 3 CH 2 OH + NAD (a coenzyme) ++ ++H NADH CH 3 CH O

68 Dr. Wolf's CHM 201 & 202 15-68 nicotinamide adenine dinucleotide (oxidized form) HO HO O O N N NH 2 P O P O O HO OH H C O N O O OO + __ Figure 15.3 Structure of NAD +

69 Dr. Wolf's CHM 201 & 202 15-69 Enzyme-catalyzedEnzyme-catalyzed CH 3 CH 2 OH + N H CNH 2 O+ R +H +

70 Dr. Wolf's CHM 201 & 202 15-70 Enzyme-catalyzedEnzyme-catalyzed N H CNH 2 OR CH 3 CH OH

71 Dr. Wolf's CHM 201 & 202 15-71 Oxidative Cleavage of Vicinal Diols

72 Dr. Wolf's CHM 201 & 202 15-72 Cleavage of Vicinal Diols by Periodic Acid CC HO OH HIO 4 C O O C +

73 Dr. Wolf's CHM 201 & 202 15-73 Cleavage of Vicinal Diols by Periodic Acid HIO 4 CH CCH 3 CH 3 OHHO CH 3 CCH 3 OCHO+ (83%)

74 Dr. Wolf's CHM 201 & 202 15-74 Cyclic Diols are Cleaved HIO 4 OHOH O HCCH 2 CH 2 CH 2 CH O

75 Dr. Wolf's CHM 201 & 202 15-75 Preparation of Thiols

76 Dr. Wolf's CHM 201 & 202 15-76 Nomenclature of Thiols 1) analogous to alcohols, but suffix is -thiol rather than -ol 2) final -e of alkane name is retained, not dropped as with alcohols

77 Dr. Wolf's CHM 201 & 202 15-77 Nomenclature of Thiols 1) analogous to alcohols, but suffix is -thiol rather than -ol 2) final -e of alkane name is retained, not dropped as with alcohols CH 3 CHCH 2 CH 2 SH CH 3 3-Methyl-1-butanethiol

78 Dr. Wolf's CHM 201 & 202 15-82 1. low molecular weight thiols have foul odors 2. hydrogen bonding is much weaker in thiols than in alcohols 3. thiols are stronger acids than alcohols 4. thiols are more easily oxidized than alcohols; oxidation takes place at sulfur Properties of Thiols

79 Thiols are less polar than alcohols MethanolMethanethiol bp: 65°C bp: 6°C

80 Dr. Wolf's CHM 201 & 202 15-83 have pK a s of about 10; can be deprotonated in aqueous base stronger acid (pK a = 10) weaker acid (pK a = 15.7) Thiols are stronger acids than alcohols H RS OHOHOHOH –RS H OHOHOHOH – ++

81 RS – and HS – are weakly basic and good nucleophiles HClH C6H5SC6H5SC6H5SC6H5S C 6 H 5 SNa SN2SN2SN2SN2 (75%) KSH SN2SN2SN2SN2 (67%) BrSH

82 Dr. Wolf's CHM 201 & 202 15-84 Oxidation of thiols take place at sulfur thiol (reduced) disulfide (oxidized) RS H RS SR thiol-disulfide redox pair is important in biochemistry other oxidative processes place 1, 2, or 3 oxygen atoms on sulfur

83 Dr. Wolf's CHM 201 & 202 15-85 Oxidation of thiols take place at sulfur thioldisulfide sulfinic acid sulfonic acid RS H RS SR sulfenic acid RS OH RS OH O –+ RS OH O – 2+ O –

84 Dr. Wolf's CHM 201 & 202 15-86 HSCH 2 CH 2 CH(CH 2 ) 4 COH SHSHSHSH O 2, FeCl 3 (CH 2 ) 4 COH  -Lipoic acid (78%) Example: sulfide-disulfide redox pair O OS S

85 Dr. Wolf's CHM 201 & 202 15-87 Spectroscopic Analysis of Alcohols

86 Dr. Wolf's CHM 201 & 202 15-88 O—H stretching: 3200-3650 cm –1 (broad) C—O stretching: 1025-1200 cm –1 (broad) Infrared Spectroscopy

87 Dr. Wolf's CHM 201 & 202 15-89200035003000250010001500500 Wave number, cm -1 Figure 15.4: Infrared Spectrum of Cyclohexanol O—H C—H C—OOH

88 Dr. Wolf's CHM 201 & 202 15-90 chemical shift of O—H proton is variable; depends on temperature and concentration O—H proton can be identified by adding D 2 O; signal for O—H disappears (converted to O—D) 1 H NMR C O HH  3.3-4 ppm  0.5-5 ppm

89 Dr. Wolf's CHM 201 & 202 15-91 01.02.03.04.05.06.07.08.09.010.0 Chemical shift ( , ppm) Figure 15.5 (page 607) CH2CH2OHCH2CH2OHCH2CH2OHCH2CH2OH

90 Dr. Wolf's CHM 201 & 202 15-92 chemical shift of C—OH is  60-75 ppm C—O is about 35-50 ppm less shielded than C—H 13 C NMR CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 OH  13 ppm  61.4 ppm

91 Dr. Wolf's CHM 201 & 202 15-93 UV-VISUV-VIS Unless there are other chromophores in the molecule, alcohols are transparent above about 200 nm; max for methanol, for example, is 177 nm. max for methanol, for example, is 177 nm.

92 Dr. Wolf's CHM 201 & 202 15-94 molecular ion peak is usually small a peak corresponding to loss of H 2 O from the molecular ion (M - 18) is usually present peak corresponding to loss of an alkyl group to give an oxygen- stabilized carbocation is usually prominent Mass Spectrometry of Alcohols

93 Dr. Wolf's CHM 201 & 202 15-95 molecular ion peak is usually small a peak corresponding to loss of H 2 O from the molecular ion (M - 18) is usually present peak corresponding to loss of an alkyl group to give an oxygen- stabilized carbocation is usually prominent Mass Spectrometry of Alcohols CH 2 R OH R OH+ OH R +

94 End of Chapter 15


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