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Chapter 10 Structure and Synthesis of Alcohols

Organic Chemistry , 6 th Edition L. G. Wade, Jr. Chapter 10 Structure and Synthesis of Alcohols. Structure of Alcohols. Hydroxyl (-OH) functional group Oxygen is sp 3 hybridized. Classification. Primary: carbon with –OH is bonded to one other carbon.

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Chapter 10 Structure and Synthesis of Alcohols

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  1. Organic Chemistry, 6th EditionL. G. Wade, Jr. Chapter 10Structure and Synthesis of Alcohols

  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. 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

  5. Unsaturated Alcohols • Hydroxyl group takes precedence. Assign that carbon the lowest number. • Use alkene or alkyne name. 4-penten-2-ol pent-4-ene-2-ol Chapter 10

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

  7. Hydroxy Substituent • When -OH is part of a higher priority class of compound, it is named as hydroxy. • Example: 4-hydroxybutanoic acid Chapter 10

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

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

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

  11. 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 3-chlorophenol para-cresol meta-chlorophenol Chapter 10

  12. 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

  13. => Boiling Points Chapter 10

  14. Solubility decreases as the size of the alkyl group increases. Solubility in Water Chapter 10

  15. 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

  16. 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

  17. 2-Propanol • “Rubbing alcohol” • Catalytic hydration of propene Chapter 10

  18. 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

  19. Table of Ka Values => Chapter 10

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

  21. 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 0.0 a Chapter 10

  22. 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

  23. 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

  24. 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

  25. Some Grignard Reagents Chapter 10

  26. 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

  27. 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

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

  29. Synthesis of 2º Alcohols Grignard + aldehyde yields a secondary alcohol. Chapter 10

  30. Synthesis of 3º Alcohols Grignard + ketone yields a tertiary alcohol. Chapter 10

  31. 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

  32. Grignard + Acid Chloride (1) • Grignard attacks the carbonyl. • Chloride ion leaves. Chapter 10

  33. Grignard and Ester • Grignard attacks the carbonyl. • Alkoxide ion leaves! ? ! Chapter 10

  34. 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

  35. 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

  36. 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

  37. 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

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

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

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

  41. End of Chapter 10 Chapter 10

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