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Chapter 15 Alcohols, Diols, and Thiols

Chapter 15 Alcohols, Diols, and Thiols. 15.1 Sources of Alcohols. Methanol is an industrial chemical end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde. Methanol. Methanol is an industrial chemical end uses: solvent, antifreeze, fuel

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Chapter 15 Alcohols, Diols, and Thiols

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  1. Chapter 15Alcohols, Diols, and Thiols

  2. 15.1Sources of Alcohols

  3. Methanol is an industrial chemical end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde Methanol

  4. Methanol is an industrial chemical end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde prepared by hydrogenation of carbon monoxide Methanol CO + 2H2Æ CH3OH

  5. Ethanol is an industrial chemical Most ethanol comes from fermentation Synthetic ethanol is produced by hydrationof ethylene Synthetic ethanol is denatured (madeunfit for drinking) by adding methanol, benzene,pyridine, castor oil, gasoline, etc. Ethanol

  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. 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. 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. 15.2Preparation of AlcoholsbyReduction of Aldehydes and Ketones

  10. R R H OH C O C H H Reduction of Aldehydes Gives Primary Alcohols

  11. O + CH3O CH H2 CH3O CH2OH Example: Catalytic Hydrogenation Pt, ethanol (92%)

  12. R H OH C R' Reduction of Ketones Gives Secondary Alcohols R C O R'

  13. O Example: Catalytic Hydrogenation H OH Pt + H2 ethanol (93-95%)

  14. R R C O H OH C H H R R H OH C O C R' R' Retrosynthetic Analysis H:– H:–

  15. act as hydride donors H H – + – + H H Li Na H H Al B H H Metal Hydride Reducing Agents Sodiumborohydride Lithiumaluminum hydride

  16. O2N O2N O CH H OH O Examples: Sodium Borohydride Aldehyde NaBH4 CH2OH methanol (82%) Ketone NaBH4 ethanol (84%)

  17. more reactive than sodium borohydride cannot use water, ethanol, methanol etc.as solvents diethyl ether is most commonly used solvent Lithium aluminum hydride

  18. O CH3(CH2)5CH OH O (C6H5)2CHCHCH3 Examples: Lithium Aluminum Hydride Aldehyde 1. LiAlH4diethyl ether CH3(CH2)5CH2OH 2. H2O (86%) Ketone 1. LiAlH4diethyl ether (C6H5)2CHCCH3 2. H2O (84%)

  19. neither NaBH4 or LiAlH4reduces isolateddouble bonds O H OH Selectivity 1. LiAlH4diethyl ether 2. H2O (90%)

  20. 15.3Preparation of Alcohols By Reductionof Carboxylic Acids and Esters

  21. lithium aluminum hydride is only effective reducing agent R H OH C H Reduction of Carboxylic AcidsGives Primary Alcohols R C O HO

  22. O COH CH2OH Example: Reduction of a Carboxylic Acid 1. LiAlH4diethyl ether 2. H2O (78%)

  23. Lithium aluminum hydride preferred forlaboratory reductions Sodium borohydride reduction is too slowto be useful Catalytic hydrogenolysis used in industrybut conditions difficult or dangerous to duplicate in the laboratory (special catalyst, hightemperature, high pressure Reduction of EstersGives Primary Alcohols

  24. O COCH2CH3 1. LiAlH4diethyl ether 2. H2O + CH3CH2OH CH2OH (90%) Example: Reduction of a Carboxylic Acid

  25. 15.4Preparation of Alcohols From Epoxides

  26. R MgX CH2 H2C O Reaction of Grignard Reagentswith Epoxides R CH2 CH2 OMgX H3O+ RCH2CH2OH

  27. Example CH2 H2C CH3(CH2)4CH2MgBr + O 1. diethyl ether 2. H3O+ CH3(CH2)4CH2CH2CH2OH (71%)

  28. 15.5Preparation of Diols

  29. reactions used to prepare alcohols hydroxylation of alkenes Diols are prepared by...

  30. O O HCCH2CHCH2CH CH3 HOCH2CH2CHCH2CH2OH CH3 Example: reduction of a dialdehyde H2 (100 atm) Ni, 125°C 3-Methyl-1,5-pentanediol (81-83%)

  31. vicinal diols have hydroxyl groups on adjacent carbons ethylene glycol (HOCH2CH2OH) is most familiar example Hydroxylation of AlkenesGives Vicinal Diols

  32. syn addition of —OH groups to each carbonof double bond C C C C HO OH C C O O Os O O Osmium Tetraoxide is Key Reagent

  33. CH3(CH2)7CH CH2 (CH3)3COOHOsO4 (cat) tert-Butyl alcoholHO– CH3(CH2)7CHCH2OH OH Example (73%)

  34. H H H H HO OH Example (CH3)3COOHOsO4 (cat) tert-Butyl alcoholHO– (62%)

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