Lecture 16 - Alcohols, Phenols

General

Organic Chemistry Two credits Second Semester 2009

King Saud bin Abdulaziz University for Health Science

Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition

Instructor: Rabih O. Al-Kaysi, PhD.

Lecture 16

Chapter 10

Alcohols, Ethers and Phenols

Sources of Alcohols

Methanol Methanol Methanol is an industrial chemical

end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde

Methanol Methanol Methanol is an industrial chemical

end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde prepared by hydrogenation of carbon monoxide CO CO ++ 2H 2H22→ → CH CH3OH 3OH

Ethanol Ethanol 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.

Other Otheralcohols alcohols 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.

Sources Sourcesof ofalcohols alcohols Reactions discussed in earlier chapters

Hydration of alkenes Hydroboration-oxidation of alkenes Hydrolysis of alkyl halides Syntheses using Grignard reagents organolithium reagents

Sources Sourcesof ofalcohols alcohols New methods in Chapter

Reduction of aldehydes and ketones Reduction of carboxylic acids Reduction of esters Reaction of Grignard reagents with epoxides Diols by hydroxylation of alkenes

Preparation of Alcohols by Reduction of Aldehydes and Ketones

Reduction Reductionof ofAldehydes AldehydesGives GivesPrimary PrimaryAlcohols Alcohols

R

R C H

O

H

C H

OH

Example: Example: Catalytic CatalyticHydrogenation Hydrogenation O CH3O

CH

+

H2

Pt, ethanol

CH3O

CH2OH (92%)

Reduction Reductionof ofKetones KetonesGives GivesSecondary SecondaryAlcohols Alcohols

R

R C R'

O

H

C R'

OH

Example: Example: Catalytic CatalyticHydrogenation Hydrogenation

H

O +

H2

OH

Pt ethanol (93-95%)

Metal MetalHydride HydrideReducing ReducingAgents Agents H

H + Na H

–

B

H

Li

+

Al

H

H

H Sodium borohydride

H

–

Lithium aluminum hydride

act as hydride donors

Examples: Examples: Sodium SodiumBorohydride Borohydride Aldehyde O2N O

O2N NaBH4 CH2OH

CH methanol

(82%)

Ketone O

NaBH4 ethanol

H OH

(84%)

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

Examples: Examples: Lithium LithiumAluminum AluminumHydride Hydride Aldehyde O CH3(CH2)5CH

1. LiAlH4 diethyl ether 2. H2O

CH3(CH2)5CH2OH (86%)

Ketone O (C6H5)2CHCCH3

1. LiAlH4 diethyl ether 2. H2O

OH (C6H5)2CHCHCH3 (84%)

Preparation of Diols

Diols Diolsare areprepared preparedby... by... reactions used to prepare alcohols hydroxylation of alkenes

Example: Example: reduction reductionof ofaadialdehyde dialdehyde O

O

HCCH2CHCH2CH CH3

H2 (100 atm) Ni, 125°C HOCH2CH2CHCH2CH2OH CH3 3-Methyl-1,5-pentanediol (81-83%)

Hydroxylation Hydroxylationof ofAlkenes Alkenes Gives GivesVicinal VicinalDiols Diols vicinal diols have hydroxyl groups on adjacent carbons ethylene glycol (HOCH2CH2OH) is most familiar example

Just for general knowledge, will not be tested on

Osmium OsmiumTetraoxide TetraoxideisisKey KeyReagent Reagent syn addition of —OH groups to each carbon of double bond C

C

C

HO C

C OH

C O

O Os O

O

Just for general knowledge, will not be tested on

Just for general knowledge, will not be tested on

Example Example CH3(CH2)7CH

CH2

(CH3)3COOH OsO4 (cat) tert-Butyl alcohol HO– CH3(CH2)7CHCH2OH OH (73%)

Reactions of Alcohols

Review Reviewof ofReactions Reactionsof ofAlcohols Alcohols reaction with hydrogen halides acid-catalyzed dehydration

New NewReactions Reactionsof ofAlcohols AlcoholsininThis This Chapter Chapter conversion to ethers esterification esters of inorganic acids oxidation cleavage of vicinal diols

Conversion of Alcohols to Ethers

Conversion Conversionof ofAlcohols Alcoholsto toEthers Ethers RCH2O

CH2R

H

OH H+

RCH2O

CH2R

+

H

OH

acid-catalyzed referred to as a "condensation" equilibrium; most favorable for primary alcohols

Example Example 2CH3CH2CH2CH2OH

H2SO4, 130°C CH3CH2CH2CH2OCH2CH2CH2CH3 (60%)

Mechanism Mechanismof ofFormation Formationof ofDiethyl DiethylEther Ether Step 1: •• • CH3CH2O •

H

OSO2OH

H

+ CH3CH2O ••

H +

– OSO2OH

H knowledge, will not be tested on Just for general

Mechanism Mechanismof ofFormation Formationof ofDiethyl DiethylEther Ether Step 2: H CH3CH2

•• +O

+

H •• • CH3CH2O •

CH3CH2 +• CH3CH2O •

H + •• O •• H

H H

Just for general knowledge, will not be tested on

Mechanism Mechanismof ofFormation Formationof ofDiethyl DiethylEther Ether Step 3: CH3CH2

CH3CH2

+• CH3CH2O •

CH3CH2O •• H

+

••

•• •• OSO 2OH – ••

H

••

OSO2OH ••

Just for general knowledge, will not be tested on

Ethers

Nomenclature of Ethers, Epoxides

Functional FunctionalClass ClassIUPAC IUPACNames Namesof ofEthers Ethers name the groups attached to oxygen in alphabetical order as separate words; "ether" is last word

CH3OCH2 CH3 ethyl methyl ether

CH3CH2OCH2CH2CH2Cl 3-chloropropyl ethyl ether

CH3CH2OCH2 CH3 diethyl ether

Functional FunctionalClass ClassIUPAC IUPACNames Namesof ofSulfides Sulfides analogous to ethers, but replace “ether” as last word in the name by “sulfide.” CH3SCH2 CH3 ethyl methyl sulfide CH3CH2SCH2 CH3 diethyl sulfide

SCH3 cyclopentyl methyl sulfide

Names Namesof ofCyclic CyclicEthers Ethers O Oxirane (Ethylene oxide)

O Oxetane

O Oxolane (tetrahydrofuran) O

O O 1,4-Dioxane Oxane (tetrahydropyran) Just for general knowledge, will not be tested on

Names Namesof ofCyclic CyclicSulfides Sulfides S

S

Thiirane

Thietane

S Thiolane

S Thiane Just for general knowledge, will not be tested on

Structure and Bonding in Ethers and Epoxides bent geometry at oxygen analogous to water and alcohols, i.e. sp3 hybidization

Bond Bondangles anglesat atoxygen oxygenare aresensitive sensitive to tosteric stericeffects effects O

O H

H

CH3

105°

O CH3 112°

H 108.5°

O CH3

C(CH3)3

(CH3)3C 132°

An Anoxygen oxygenatom atomaffects affectsgeometry geometryin inmuch muchthe the same sameway wayas asaaCH CH22group group

most stable conformation of diethyl ether resembles pentane

Physical Properties of Ethers

Ethers Ethersresemble resemblealkanes alkanesmore morethan thanalcohols alcohols with withrespect respectto toboiling boilingpoint point boiling point 36°C O

35°C

OH 117°C

Intermolecular hydrogen bonding possible in alcohols; not possible in alkanes or ethers.

Ethers Ethersresemble resemblealcohols alcoholsmore morethan thanalkanes alkanes with withrespect respectto tosolubility solubilityin inwater water solubility in water (g/100 mL) very small 7.5

O

OH

9

Hydrogen bonding to water possible for ethers and alcohols; not possible for alkanes.