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15.8 Esterification (more on esters and other acid derivatives in later chapters)

15.8 Esterification (more on esters and other acid derivatives in later chapters). Dr. Wolf's CHM 201 & 202. 15-46. a condensation reaction called Fischer esterification acid catalyzed reversible. O. O. R'COH. R'C OR. Esterification. H +. +. +. RO H. H 2 O.

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15.8 Esterification (more on esters and other acid derivatives in later chapters)

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  1. 15.8Esterification(more on esters and other acid derivatives in later chapters) Dr. Wolf's CHM 201 & 202 15-46

  2. a condensation reaction called Fischer esterification acid catalyzed reversible O O R'COH R'COR Esterification H+ + + ROH H2O Dr. Wolf's CHM 201 & 202 15-47

  3. 70% yield based on benzoic acid O + COH CH3OH H2SO4 O COCH3 Example of Fischer Esterification 0.1 mol 0.6 mol (i.e. excess) + H2O Dr. Wolf's CHM 201 & 202 15-48

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

  5. CH3CH2 O O2N OH CCl CH3 CH3CH2 O NO2 OC CH3 Example + pyridine (63%) Dr. Wolf's CHM 201 & 202 15-50

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

  7. O O + C6H5CH2CH2OH F3CCOCCF3 O C6H5CH2CH2OCCF3 Example pyridine (83%) Dr. Wolf's CHM 201 & 202 15-52

  8. 15.9Esters of Inorganic Acids Dr. Wolf's CHM 201 & 202 15-53

  9. + (HO)3P O Esters of Inorganic Acids ROH + HOEWG ROEWG + H2O EWG is an electron-withdrawing group – HONO2 (HO)2SO2 Dr. Wolf's CHM 201 & 202 15-54

  10. + (HO)3P O Esters of Inorganic Acids ROH + HOEWG ROEWG + H2O EWG is an electron-withdrawing group – HONO2 (HO)2SO2 CH3OH + HONO2 CH3ONO2 + H2O (66-80%) Dr. Wolf's CHM 201 & 202 15-55

  11. 15.10Oxidation of Alcohols Dr. Wolf's CHM 201 & 202 15-56

  12. O O O OH RCHR' Oxidation of Alcohols Primary alcohols RCH2OH RCH RCOH Secondary alcohols from H2O RCR' Dr. Wolf's CHM 201 & 202 15-57

  13. Aqueous solution Mn(VII) Cr(VI) KMnO4 H2CrO4 H2Cr2O7 Typical Oxidizing Agents Dr. Wolf's CHM 201 & 202 15-58

  14. O Aqueous Cr(VI) FCH2CH2CH2CH2OH H2SO4 K2Cr2O7 H2O FCH2CH2CH2COH (74%) Dr. Wolf's CHM 201 & 202 15-59

  15. H OH O O Aqueous Cr(VI) FCH2CH2CH2CH2OH H2SO4 K2Cr2O7 H2SO4 H2O Na2Cr2O7 H2O FCH2CH2CH2COH (74%) (85%) Dr. Wolf's CHM 201 & 202 15-60

  16. All are used in CH2Cl2 Pyridinium dichromate (PDC) (C5H5NH+)2 Cr2O72– Pyridinium chlorochromate (PCC) C5H5NH+ ClCrO3– Nonaqueous Sources of Cr(VI) Dr. Wolf's CHM 201 & 202 15-61

  17. N + H O CH3(CH2)5CH Example: Oxidation of a primary alcohol with PCC(pyridinium chlorochromate) ClCrO3– PCC CH3(CH2)5CH2OH CH2Cl2 (78%) Dr. Wolf's CHM 201 & 202 15-62

  18. (CH3)3C CH2OH O (CH3)3C CH Example: Oxidation of a primary alcohol with PDC(pryidinium dichromate) PDC CH2Cl2 (94%) Dr. Wolf's CHM 201 & 202 15-63

  19. involves formation and elimination of a chromate ester O O O O Mechanism H H C C HOCrOH CrOH OH O Dr. Wolf's CHM 201 & 202 15-64

  20. involves formation and elimination of a chromate ester •• O •• O O O O C O Mechanism H H H H C C HOCrOH CrOH OH O Dr. Wolf's CHM 201 & 202 15-65

  21. 15.11Biological Oxidation of Alcohols Dr. Wolf's CHM 201 & 202 15-66

  22. + NAD (a coenzyme) + H O NAD CH3CH H Enzyme-catalyzed + CH3CH2OH alcohol dehydrogenase + + Dr. Wolf's CHM 201 & 202 15-67

  23. nicotinamide adenine dinucleotide (oxidized form) _ _ O O O O H P P O O O O O NH2 HO N + C OH N HO HO N O NH2 Figure 15.3 Structure of NAD+ Dr. Wolf's CHM 201 & 202 15-68

  24. O H CNH2 + H + N R Enzyme-catalyzed + CH3CH2OH + Dr. Wolf's CHM 201 & 202 15-69

  25. O O CNH2 CH3CH Enzyme-catalyzed H H •• N R Dr. Wolf's CHM 201 & 202 15-70

  26. 15.12Oxidative Cleavage of Vicinal Diols Dr. Wolf's CHM 201 & 202 15-71

  27. HIO4 C C C O O HO OH Cleavage of Vicinal Diols by Periodic Acid + C Dr. Wolf's CHM 201 & 202 15-72

  28. CH3 CH CCH3 HO OH O O CH CH3CCH3 Cleavage of Vicinal Diols by Periodic Acid HIO4 + (83%) Dr. Wolf's CHM 201 & 202 15-73

  29. OH O O HCCH2CH2CH2CH OH Cyclic Diols are Cleaved HIO4 Dr. Wolf's CHM 201 & 202 15-74

  30. 15.13Preparation of Thiols Dr. Wolf's CHM 201 & 202 15-75

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

  32. 1) analogous to alcohols, but suffix is -thiol rather than -ol 2) final -e of alkane name is retained, not dropped as with alcohols CH3CHCH2CH2SH CH3 Nomenclature of Thiols 3-Methyl-1-butanethiol Dr. Wolf's CHM 201 & 202 15-77

  33. 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 Dr. Wolf's CHM 201 & 202 15-82

  34. Thiols are less polar than alcohols Methanol Methanethiol bp: 65°C bp: 6°C

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

  36. C6H5S H Cl H (75%) C6H5SNa SN2 KSH Br SH SN2 (67%) RS– and HS – are weakly basic and good nucleophiles

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

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

  39. O O Example: sulfide-disulfide redox pair SH HSCH2CH2CH(CH2)4COH O2, FeCl3 S S a-Lipoic acid (78%) (CH2)4COH Dr. Wolf's CHM 201 & 202 15-86

  40. 15.14Spectroscopic Analysis of Alcohols Dr. Wolf's CHM 201 & 202 15-87

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

  42. OH 3500 3000 2500 2000 1500 1000 500 Figure 15.4: Infrared Spectrum of Cyclohexanol C—H O—H C—O Wave number, cm-1 Dr. Wolf's CHM 201 & 202 15-89

  43. chemical shift of O—H proton is variable; depends on temperature and concentration O—H proton can be identified by adding D2O; signal for O—H disappears (converted to O—D) 1H NMR H H C O d 3.3-4 ppm d 0.5-5 ppm Dr. Wolf's CHM 201 & 202 15-90

  44. CH2CH2OH 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0 Figure 15.5 (page 607) Chemical shift (d, ppm) Dr. Wolf's CHM 201 & 202 15-91

  45. chemical shift of C—OH is d 60-75 ppm C—O is about 35-50 ppm less shielded than C—H 13C NMR CH3CH2CH2CH3 CH3CH2CH2CH2OH d 13 ppm d 61.4 ppm Dr. Wolf's CHM 201 & 202 15-92

  46. UV-VIS Unless there are other chromophores in themolecule, alcohols are transparent aboveabout 200 nm; lmax for methanol, for example, is 177 nm. Dr. Wolf's CHM 201 & 202 15-93

  47. molecular ion peak is usually small a peak corresponding to loss of H2Ofrom the molecular ion (M - 18) isusually present peak corresponding to loss of analkyl group to give an oxygen-stabilized carbocation is usuallyprominent Mass Spectrometry of Alcohols Dr. Wolf's CHM 201 & 202 15-94

  48. molecular ion peak is usually small a peak corresponding to loss of H2Ofrom the molecular ion (M - 18) isusually present peak corresponding to loss of analkyl group to give an oxygen-stabilized carbocation is usuallyprominent •• R CH2 OH •• •+ R CH2 OH •• • R Mass Spectrometry of Alcohols + CH2 OH •• Dr. Wolf's CHM 201 & 202 15-95

  49. End of Chapter 15

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