Lecture 16 - Alcohols, Phenols

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Transcript of Lecture 16 - Alcohols, Phenols

General

Organic ChemistryTwo 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 MethanolMethanol is an industrial chemical

end uses: solvent, antifreeze, fuel principal use: preparation of formaldehyde prepared by hydrogenation of carbon monoxideCO + 2H2 CH3OH CO + 2H2 CH3OH

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 alcohols Other 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 of alcohols Sources of alcohols Reactions discussed in earlier chapters

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

Sources of alcohols Sources of 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 of Aldehydes Gives Primary Alcohols Reduction of Aldehydes Gives Primary Alcohols

R C H O H

R C H OH

Example: Catalytic Hydrogenation Example: Catalytic Hydrogenation O CH3O CH + H2

Pt, ethanol

CH3O

CH2OH (92%)

Reduction of Ketones Gives Secondary Alcohols Reduction of Ketones Gives Secondary Alcohols

R C R' O H

R C R' OH

Example: Catalytic Hydrogenation Example: Catalytic Hydrogenation

O + H2 Pt ethanol

H

OH

(93-95%)

Metal Hydride Reducing Agents Metal Hydride Reducing Agents H + Na H B H Sodium borohydride H Li + H H Al H Lithium aluminum hydride H

act as hydride donors

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

(84%)

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

Examples: Lithium Aluminum Hydride Examples: Lithium Aluminum Hydride Aldehyde O CH3(CH2)5CH Ketone O (C6H5)2CHCCH3 1. LiAlH4 diethyl ether 2. H2O OH (C6H5)2CHCHCH3 (84%) 1. LiAlH4 diethyl ether 2. H2O

CH3(CH2)5CH2OH (86%)

Preparation of Diols

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

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

HCCH2CHCH2CH CH3

Hydroxylation of Alkenes Hydroxylation of Alkenes Gives Vicinal Diols Gives Vicinal Diolsvicinal diols have hydroxyl groups on adjacent carbons ethylene glycol (HOCH2CH2OH) is most familiar example

Just for general knowledge, will not be tested on

Osmium Tetraoxide is Key Reagent Osmium Tetraoxide is Key Reagent syn addition of OH groups to each carbon of double bond C C C O OsJust for general knowledge, will not be tested on

C HO C O O

C OH

O

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 of Reactions of Alcohols Review of Reactions of Alcoholsreaction with hydrogen halides acid-catalyzed dehydration

New Reactions of Alcohols in This New Reactions of Alcohols in This Chapter Chapterconversion to ethers esterification esters of inorganic acids oxidation cleavage of vicinal diols

Conversion of Alcohols to Ethers

Conversion of Alcohols to Ethers Conversion of Alcohols to EthersRCH2O H H+ RCH2O CH2R + H OH CH2R OH

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

Example Example2CH3CH2CH2CH2OH

H2SO4, 130CCH3CH2CH2CH2OCH2CH2CH2CH3 (60%)

Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl EtherStep 1: CH3CH2O

H H

OSO2OH

+ CH3CH2O

H +

OSO2OH

H Just for general knowledge, will not be tested on

Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl EtherStep 2: H CH3CH2 CH3CH2O +O

CH3CH2 + CH3CH2O H

H + O H

+

H

HJust for general knowledge, will not be tested on

Mechanism of Formation of Diethyl Ether Mechanism of Formation of Diethyl EtherStep 3: CH3CH2 + CH3CH2O H OSO OH 2

CH3CH2 CH3CH2O

+ OSO2OH

H

Just for general knowledge, will not be tested on

Ethers

Nomenclature of Ethers, Epoxides

Functional Class IUPAC Names of Ethers Functional Class IUPAC Names of Ethersname the groups attached to oxygen in alphabetical order as separate words; "ether" is last word

CH3OCH2 CH3 ethyl methyl ether CH3CH2OCH2 CH3 diethyl ether CH3CH2OCH2CH2CH2Cl 3-chloropropyl ethyl ether

Functional Class IUPAC Names of Sulfides Functional Class IUPAC Names of Sulfidesanalogous 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 of Cyclic Ethers Names of Cyclic EthersO 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 of Cyclic Sulfides Names of Cyclic SulfidesS Thiirane S Thietane

S Thiolane

S ThianeJust 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 angles at oxygen are sensitive Bond angles at oxygen are sensitive to steric effects to steric effectsO H 105 H O CH3 108.5 H

O CH3 112

O CH3 (CH3)3C 132 C(CH3)3

An oxygen atom affects geometry in much the An oxygen atom affects geometry in much the same way as a CH2 group same way as a CH2 group

most stable conformation of diethyl ether resembles pentane

Physical Properties of Ethers

Ethers resemble alkanes more than alcohols Ethers resemble alkanes more than alcohols with respect to boiling point with respect to boiling pointboiling point 36C O 35CIntermolecular hydrogen bonding possible in alcohols; not possible in alkanes or ethers.

OH 117C

Ethers resemble alcohols more than alkanes Ethers resemble alcohols more than alkanes with respect to solubility in water with respect to solubility in watersolubility in water (g/100 mL) very small O 7.5Hydrogen bonding to water possible for ethers and alcohols; not possible for alkanes.

OH

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