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Dr Nahed Elsayed

Learning ObjectivesLearning Objectives

Chapter seven discusses the following topics and by the end of this chapter the Chapter seven discusses the following topics and by the end of this chapter the students will:students will:

Know the Know the structure of ethersstructure of ethers Know the different methods of naming ethersKnow the different methods of naming ethers Know the physical properties of ethersKnow the physical properties of ethers Know the different methods used in preparation of ethers Know the different methods used in preparation of ethers Know the reactions of opened ethers with HX Know the reactions of opened ethers with HX Know the different methods used in synthesis of epoxides Know the different methods used in synthesis of epoxides Know the reactions of epoxides with different nucleophiles such as HKnow the reactions of epoxides with different nucleophiles such as H22O, ROH, O, ROH,

HX, Grignard and organolithium eagents HX, Grignard and organolithium eagents

Structure Of EthersStructure Of EthersEther: is a class of is a class of organic compounds that contain an ether linkage — an that contain an ether linkage — an oxygen atom connected to two connected to two alkyl or or aryl groups via σ bonds. thus groups via σ bonds. thus Ethers feature C-O-C linkage — of general formula R–O–R or Ar–O–Ar or Ethers feature C-O-C linkage — of general formula R–O–R or Ar–O–Ar or Ar–O–RAr–O–R

Nomenclature Of Ethers Nomenclature Of Ethers Common names Common names The common names of ethers are derived by naming the alkyl groups The common names of ethers are derived by naming the alkyl groups bonded to the oxygen then listing them in alphabetical order followed by bonded to the oxygen then listing them in alphabetical order followed by the word "ether". the word "ether". IUPAC names IUPAC names The ether functional group does not have a characteristic IUPAC The ether functional group does not have a characteristic IUPAC nomenclature suffix, so it is necessary to designate the smaller alkyl nomenclature suffix, so it is necessary to designate the smaller alkyl group as an alkoxy substituent of a parent compound (alkane , or alkene, group as an alkoxy substituent of a parent compound (alkane , or alkene, or alkyne,or alcohol,----) or alkyne,or alcohol,----)

H O H R O H R O R

water alcohol ether

Alkyl group Alkyl group Name Name Alkoxy Alkoxy Group Name Group Name

CHCH33–– MethylMethyl CHCH33O–O– MethoxyMethoxy

CHCH33CHCH22–– EthylEthyl CHCH33CHCH22O– O– EthoxyEthoxy

(CH(CH33))22CH–CH– IsopropylIsopropyl (CH(CH33))22CHO– CHO– IsopropoxyIsopropoxy

(CH(CH33))33C–C– tert-Butyltert-Butyl (CH(CH33))33CO– CO– tert-Butoxytert-Butoxy

CC66HH55–– PhenylPhenyl CC66HH55O– O– PhenoxyPhenoxy

The common alkoxy substituents are given names derived from their The common alkoxy substituents are given names derived from their

alkyl componentalkyl component

Common Dimethyl ether Diethyl ether Divinyl ether Diphenyl etherCommon Dimethyl ether Diethyl ether Divinyl ether Diphenyl etherIUPACIUPAC Methoxy methane Ethoxy ethane Phenoxy benzeneMethoxy methane Ethoxy ethane Phenoxy benzene

Common Hexyl methyl ether Ethyl methyl ether Ethyl vinyl ether Methyl Phenyl ether Common Hexyl methyl ether Ethyl methyl ether Ethyl vinyl ether Methyl Phenyl ether (anisole)(anisole)IUPAC Methoxy hexane Methoxy ethane Ethoxy ethene Methoxy benzeneIUPAC Methoxy hexane Methoxy ethane Ethoxy ethene Methoxy benzene

IUPAC 3-Methoxyhexane 5-Ethoxy-2-heptene Propenyloxy benzeneIUPAC 3-Methoxyhexane 5-Ethoxy-2-heptene Propenyloxy benzene

O

O OH3C O CH3

CH3O

O OH3C O C6H13

OCH3

H3C CH3

O

CH3

H3CCH3

OCH3

Physical Properties of EtherPhysical properties of ethers

Boiling Points

The boiling points of ethers are lower than those of alcohols

having the same molecular weights.

Solubility in water

compound Formula MW Bp (°C)

Ethanol CH3-CH2-OH 46 78

Dimethyl ether CH3-O-CH3 46 -25

Propane CH3-CH2-CH3 44 -42

Ethers are much less soluble in water than alcohols. (Because they don’t have –OH group, So they are not hydrogen bond donors).More water-soluble than hydrocarbons of similar molecular weight (Because they are polar)..

1)1) Dehydration of alcohols:Dehydration of alcohols: The dehydration of alcohols takes place in the presence of acid catalysts (H2SO4, H3PO4) under controlled temperature. The general reaction for ether formation is

Preparation of Preparation of EthersEthers

R O H H O R R O R+H

+

heat+ H2O

Examples

CH3 O H CH3 O CH3

CH3CH2 O H CH3CH2 O CH2CH3

H+

heat+ H2O2

H+

heat+ H2O2

methyl alcohol

ethyl alcohol

methyl ether

ethyl ether

(100 %)

(88 %)

Preparation of EthersPreparation of Ethers

2)2)The Williamson synthesThe Williamson synthesThis method is usually used for preparation of unsymmetricalThis method is usually used for preparation of unsymmetrical ethersethers

R O R X R O R......

Na+

+

sodium alkoxide alkyl halide

+ NaX

ether

O R X O R......

Na+

+

sodium phenoxidealkyl halide

+ NaX

ether

OH

NaOH

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OH O

CH3CH2 Br

OCH2CH3

Na

Na+

+ NaBr

cyclohexanol ethoxycyclohexane sodium

cyclohexyloxide

OH1) Na

2) CH3-I

OCH3

3,3-dimethyl-2-pentanol 2-ethoxy-3,3-dimethypentane

Examples

The alkoxide is commonly made by adding Na or K to the alcohol

Reactions Of EthersReactions Of Ethers

Cleavage of ethers by hot concentrated acids

General equation:R O R H X R OH R X+heat

(concentrated)

+

The acids most often used in this reaction are HI, HBr, and HCl

Specific example

CH3CH2 O CH2CH3 H I CH3CH2OH CH3CH2I+heat

(concentrated)

+

Ethers are quite stable compounds.

Ethers react only under strongly acidic condition.

When ethers are heated in concentrated acid solutions,

the ether linkage is broken

CH3CH2 O CH2CH3 + 2HBr

(conc, excess)

heat2 CH3CH2Br + H2O

If an excess of acid is present, the alcohol initially

produced

is converted to alkyl halide thus the net products will be

2 moles of alkyl halide.

For example

R O R H X R X+ 2 + H2O2

Epoxides are cyclic ethers in which the ether oxygen is part

of a three-membered ring. C C

O

an epoxide

The simplest and most important epoxide is ethylene oxide.

O

ethylene oxide 12

Cyclic EthersCyclic Ethers

O O O

O

O

1,4-DioxaneOxiraneFuranTetrahydrofuranEthylene Oxide (epoxide)

In cyclic ethers (heterocyclic), one or more carbons are replaced

with oxygen.

Peroxyacid Epoxidation

Peroxyacids (sometimes called peracids) are used to

convert alkenes to epoxides. If the reaction takes place in

aqueous acid, the epoxide opens to a glycol. Because of

its desirable solubility properties, meta-

chloroperoxybenzoic acid (MCPBA) is often used for these

epoxidations.R-C-O-O-H

O O

R-C-O-H

O

+ +

O

Cl

C-O-O-H

O

MCPBA

CH2Cl2

epoxycyclohexanecyclohexene

MCPBA :

Example

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Epoxides are much more reactive than common dialkyl ether

this is due to the strain in the three-membered ring, which is

relieved when the epoxide ring is opened after a reaction has

taken place.

Examples of ring-opening reactions of ethylene oxide

that form commercially important products are:

1- Epoxides open in acidic solutions to form glycols.

H3OCH CH

O

R CH CH R

OH

OH

R R

+

2- Epoxides open in acidic alcohol solutions to form alkoxy alcohols

3- When an epoxide reacts with a hydrohalic acid ( HCl,

HBr, or HI), a halide ion attacks the protonated epoxide

to give halo alcohol .

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H X CH CH

O

R CH CH R

OH

X

R R+

CH3 OH CH CH

O

R CH CH R

OH

O

R R

CH3+

+.. H3O

4 -Reactions of Epoxides with Grignard and Organolithium Reagents to give longer alcohols

R' MgX CH CH

O

R CH CH R

R'

OH

R' Li

R R+1) ether

2) H3O+

or

5- Ring opening of epoxides with amines

CH3NH2 + R CH CH R

OH3O+

R CH CH R

NHCH3

OH

Exercise 1

Give a correct name for each of the following

compounds.CH2

CH3 O CH2CH2CH3

CH2=CHCH2 O CH2CH=CH2

O CH2CH3

CH3CHCH2CH3

O CH3

CH3CH2CHCH=CH2

O CH2CH3

OCH3

O CH3

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Exercice 2

Propose a Williamson synthesis of 3-butoxy-1,1-

dimethylcyclohexane from 3,3-dimethylcyclohexanol and

butanol

Questions?