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Chapter 10 Structure and Synthesis of Alcohols

Organic Chemistry , 5 th Edition L. G. Wade, Jr. Chapter 10 Structure and Synthesis of Alcohols. Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2003, Prentice Hall. Structure of Alcohols. Hydroxyl (OH) functional group

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Chapter 10 Structure and Synthesis of Alcohols

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  1. Organic Chemistry, 5th EditionL. G. Wade, Jr. Chapter 10Structure and Synthesis of Alcohols Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2003,Prentice Hall

  2. Structure of Alcohols • Hydroxyl (OH) functional group • Oxygen is sp3 hybridized. => Chapter 10

  3. Classification • Primary: carbon with –OH is bonded to one other carbon. • Secondary: carbon with –OH is bonded to two other carbons. • Tertiary: carbon with –OH is bonded to three other carbons. • Aromatic (phenol): -OH is bonded to a benzene ring.=> Chapter 10

  4. => Classify these: Chapter 10

  5. IUPAC Nomenclature • Find the longest carbon chain containing the carbon with the -OH group. • Drop the -e from the alkane name, add -ol. • Number the chain, starting from the end closest to the -OH group. • Number and name all substituents. => Chapter 10

  6. Name these: 2-methyl-1-propanol 2-butanol 2-methyl-2-propanol 3-bromo-3-methylcyclohexanol => Chapter 10

  7. Unsaturated Alcohols • Hydroxyl group takes precedence. Assign that carbon the lowest number. • Use alkene or alkyne name. 4-penten-2-ol (old) pent-4-ene-2-ol (1997 revision of IUPAC rules) => Chapter 10

  8. Acids Esters Aldehydes Ketones Alcohols Amines Alkenes Alkynes Alkanes Ethers Halides => Naming Priority Chapter 10

  9. Hydroxy Substituent • When -OH is part of a higher priority class of compound, it is named as hydroxy. • Example: also known as GHB => 4-hydroxybutanoic acid Chapter 10

  10. Common Names • Alcohol can be named as alkyl alcohol. • Useful only for small alkyl groups. • Examples: isobutyl alcohol sec-butyl alcohol => Chapter 10

  11. Naming Diols • Two numbers are needed to locate the two -OH groups. • Use -diol as suffix instead of -ol. 1,6-hexanediol => Chapter 10

  12. Glycols • 1, 2 diols (vicinal diols) are called glycols. • Common names for glycols use the name of the alkene from which they were made. 1,2-ethanediol 1,2-propanediol propylene glycol => ethylene glycol Chapter 10

  13. Naming Phenols • -OH group is assumed to be on carbon 1. • For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4. • Methyl phenols are cresols. 4-methylphenol para-cresol => 3-chlorophenol meta-chlorophenol Chapter 10

  14. Physical Properties • Unusually high boiling points due to hydrogen bonding between molecules. • Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases. => Chapter 10

  15. => Boiling Points Chapter 10

  16. Solubility decreases as the size of the alkyl group increases. => Solubility in Water Chapter 10

  17. Methanol • “Wood alcohol” • Industrial production from synthesis gas • Common industrial solvent • Fuel at Indianapolis 500 • Fire can be extinguished with water • High octane rating • Low emissions • But, lower energy content • Invisible flame => Chapter 10

  18. Ethanol • Fermentation of sugar and starches in grains • 12-15% alcohol, then yeast cells die. • Distillation produces “hard” liquors • Azeotrope: 95% ethanol, constant boiling • Denatured alcohol used as solvent • Gasahol: 10% ethanol in gasoline • Toxic dose: 200 mL ethanol, 100 mL methanol => Chapter 10

  19. => 2-Propanol • “Rubbing alcohol” • Catalytic hydration of propene Chapter 10

  20. Acidity of Alcohols • pKa range: 15.5-18.0 (water: 15.7) • Acidity decreases as alkyl group increases. • Halogens increase the acidity. • Phenol is 100 million times more acidic than cyclohexanol! => Chapter 10

  21. Table of Ka Values => Chapter 10

  22. => Formation of Alkoxide Ions React methanol and ethanol with sodium metal (redox reaction). React less acidic alcohols with more reactive potassium. Chapter 10

  23. Formation of Phenoxide Ion Phenol reacts with hydroxide ions to form phenoxide ions - no redox is necessary. O O H O H + + H O H p K = 1 5 . 7 a p K = 1 0 a => Chapter 10

  24. Synthesis (Review) • Nucleophilic substitution of OH- on alkyl halide • Hydration of alkenes • water in acid solution (not very effective) • oxymercuration - demercuration • hydroboration - oxidation => Chapter 10

  25. Glycols (Review) • Syn hydroxylation of alkenes • osmium tetroxide, hydrogen peroxide • cold, dilute, basic potassium permanganate • Anti hydroxylation of alkenes • peroxyacids, hydrolysis => Chapter 10

  26. Organometallic Reagents • Carbon is bonded to a metal (Mg or Li). • Carbon is nucleophilic (partially negative). • It will attack a partially positive carbon. • C - X • C = O • A new carbon-carbon bond forms. => Chapter 10

  27. Grignard Reagents • Formula R-Mg-X (reacts like R:-+MgX) • Stabilized by anhydrous ether • Iodides most reactive • May be formed from any halide • primary • secondary • tertiary • vinyl • aryl => Chapter 10

  28. => Some Grignard Reagents Chapter 10

  29. Organolithium Reagents • Formula R-Li (reacts like R:-+Li) • Can be produced from alkyl, vinyl, or aryl halides, just like Grignard reagents. • Ether not necessary, wide variety of solvents can be used. => Chapter 10

  30. => Reaction with Carbonyl • R:- attacks the partially positive carbon in the carbonyl. • The intermediate is an alkoxide ion. • Addition of water or dilute acid protonates the alkoxide to produce an alcohol. Chapter 10

  31. => Synthesis of 1° Alcohols Grignard + formaldehyde yields a primary alcohol with one additional carbon. Chapter 10

  32. => Synthesis of 2º Alcohols Grignard + aldehyde yields a secondary alcohol. Chapter 10

  33. => Synthesis of 3º Alcohols Grignard + ketone yields a tertiary alcohol. Chapter 10

  34. => How would you synthesize… Chapter 10

  35. Grignard Reactions with Acid Chlorides and Esters • Use two moles of Grignard reagent. • The product is a tertiary alcohol with two identical alkyl groups. • Reaction with one mole of Grignard reagent produces a ketone intermediate, which reacts with the second mole of Grignard reagent. => Chapter 10

  36. Grignard + Acid Chloride (1) • Grignard attacks the carbonyl. • Chloride ion leaves. Ketone intermediate => Chapter 10

  37. Grignard and Ester (1) • Grignard attacks the carbonyl. • Alkoxide ion leaves! ? ! Ketone intermediate => Chapter 10

  38. => Second step of reaction • Second mole of Grignard reacts with the ketone intermediate to form an alkoxide ion. • Alkoxide ion is protonated with dilute acid. Chapter 10

  39. => How would you synthesize... Using an acid chloride or ester. Chapter 10

  40. => Grignard Reagent + Ethylene Oxide • Epoxides are unusually reactive ethers. • Product is a 1º alcohol with 2 additional carbons. Chapter 10

  41. Limitations of Grignard • No water or other acidic protons like O-H, N-H, S-H, or -C—C-H. Grignard reagent is destroyed, becomes an alkane. • No other electrophilic multiple bonds, like C=N, C—N, S=O, or N=O. => Chapter 10

  42. Reduction of Carbonyl • Reduction of aldehyde yields 1º alcohol. • Reduction of ketone yields 2º alcohol. • Reagents: • Sodium borohydride, NaBH4 • Lithium aluminum hydride, LiAlH4 • Raney nickel => Chapter 10

  43. => Sodium Borohydride • Hydride ion, H-, attacks the carbonyl carbon, forming an alkoxide ion. • Then the alkoxide ion is protonated by dilute acid. • Only reacts with carbonyl of aldehyde or ketone, not with carbonyls of esters or carboxylic acids. Chapter 10

  44. => Lithium Aluminum Hydride • Stronger reducing agent than sodium borohydride, but dangerous to work with. • Converts esters and acids to 1º alcohols. Chapter 10

  45. Comparison of Reducing Agents • LiAlH4 is stronger. • LiAlH4 reduces more stable compounds which are resistant to reduction. => Chapter 10

  46. => Catalytic Hydrogenation • Add H2 with Raney nickel catalyst. • Also reduces any C=C bonds. Chapter 10

  47. Thiols (Mercaptans) • Sulfur analogues of alcohols, -SH. • Named by adding -thiol to alkane name. • The -SH group is called mercapto. • Complex with heavy metals: Hg, As, Au. • More acidic than alcohols, react with NaOH to form thiolate ion. • Stinks! => Chapter 10

  48. => Thiol Synthesis Use a large excess of sodium hydrosulfide with unhindered alkyl halide to prevent dialkylation to R-S-R. Chapter 10

  49. => Thiol Oxidation • Easily oxidized to disulfides, an important feature of protein structure. • Vigorous oxidation with KMnO4, HNO3, or NaOCl, produces sulfonic acids. Chapter 10

  50. End of Chapter 10 Chapter 10

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