Preparation and Synthesis of Alcohols: Sources, Methods, and Reactions, Study notes of Organic Chemistry

Download Preparation and Synthesis of Alcohols: Sources, Methods, and Reactions and more Study notes Organic Chemistry in PDF only on Docsity! 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 prepared by hydrogenation of carbon monoxide CO + 2H2 Æ CH3OH Methanol 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. Ethanol 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 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) 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 15.2 Preparation of Alcohols by Reduction of Aldehydes and Ketones Examples: Lithium Aluminum Hydride Aldehyde Ketone O CH3(CH2)5CH 1. LiAlH4 diethyl ether 2. H2O O (C6H5)2CHCCH3 1. LiAlH4 diethyl ether 2. H2O (84%) CH3(CH2)5CH2OH (86%) OH (C6H5)2CHCHCH3 neither NaBH4 or LiAlH4 reduces carbon-carbon double bonds O H OH 1. LiAlH4 diethyl ether 2. H2O (90%) Selectivity 15.3 Preparation of Alcohols By Reduction of Carboxylic Acids and Esters lithium aluminum hydride is only effective reducing agent Reduction of Carboxylic Acids Gives Primary Alcohols C R H OH H C R HO O Example: Reduction of a Carboxylic Acid 1. LiAlH4 diethyl ether 2. H2O COH O CH2OH (78%) 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 Example: Reduction of an Ester 1. LiAlH4 diethyl ether 2. H2O (90%) O COCH2CH3 CH3CH2OH CH2OH + 15.4 Preparation of Alcohols From Epoxides Reaction of Grignard Reagents with Epoxides H2C CH2 O R MgX CH2 CH2 OMgX R H3O+ RCH2CH2OH CH3(CH2)4CH2MgBr H2C CH2 O + 1. diethyl ether 2. H3O+ CH3(CH2)4CH2CH2CH2OH (71%) Example 15.5 Preparation of Diols Diols are prepared by... reactions used to prepare alcohols hydroxylation of alkenes 15.7 Conversion of Alcohols to Ethers RCH2O H CH2R OH H+ RCH2O CH2R H OH+ Conversion of Alcohols to Ethers acid-catalyzed referred to as a "condensation" equilibrium; most favorable for primary alcohols Example 2CH3CH2CH2CH2OH H2SO4, 130°C CH3CH2CH2CH2OCH2CH2CH2CH3 (60%) Figure 15.3 Mechanism of Formation of Diethyl Ether Step 1: CH3CH2O •• •• H H OSO2OH CH3CH2O •• H OSO2OH H + –+ Figure 15.3 Mechanism of Formation of Diethyl Ether Step 2: CH3CH2 •• H H +O CH3CH2O •• •• H ++ CH3CH2 CH3CH2O •• H •• H H O•• Figure 15.3 Mechanism of Formation of Diethyl Ether Step 3: + CH3CH2 CH3CH2O •• H •• OCH2CH3 •• H + CH3CH2 CH3CH2O •• •• OCH2CH3 •• H H + Intramolecular Analog HOCH2CH2CH2CH2CH2OH H2SO4 130° O (76%) via: O H +O H H •• •• •• reaction normally works well only for 5- and 6-membered rings 15.8 Esterification condensation Fischer esterification acid catalyzed reversible Esterification ROH H2O+ H+ +R'COH O R'COR O Example of Fischer Esterification H2O+ CH3OH+COH O COCH3 O H2SO4 0.1 mol 0.6 mol 70% yield based on benzoic acid high yields not reversible when carried out in presence of pyridine Reaction of Alcohols with Acyl Chlorides ROH HCl+ +R'CCl O R'COR O pyridine + CClO2N OCH3CH2 CH3 OH (63%) NO2 CH3CH2 CH3 OC O Example