1 1435-1436 2014-2015 Ethers and Epoxides 1. Learning Objectives Chapter seven discusses the...

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1435-14362014-2015

Ethers and EpoxidesEthers and Epoxides

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Learning ObjectivesLearning ObjectivesChapter 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 structure of ethersKnow the structure 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


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Structure Of EthersStructure Of EthersEther: is a class of is a class of organic compounds in which an in which an oxygen atom connected to two connected to two organic groups (organic groups (alkyl or or aryl""benzene ringbenzene ring") by σ bonds. thus Ethers are ") by σ bonds. thus Ethers are compounds of general formula R–O–R or Ar–O–Ar or Ar–O–Rcompounds of general formula R–O–R or Ar–O–Ar or Ar–O–R

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

H O H R O H R O R

water alcohol ether


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http://en.wikipedia.org/wiki/Organic_compound

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Atom

http://en.wikipedia.org/wiki/Alkyl

http://en.wikipedia.org/wiki/Aryl

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

CHCH33–– MethylMethyl CHCH33OO–– MethoxyMethoxy

CHCH33CHCH22–– EthylEthyl CHCH33CHCH22OO–– EthoxyEthoxy

(CH(CH33))22CHCH–– IsopropylIsopropyl (CH(CH33))22CHOCHO–– IsopropoxyIsopropoxy

(CH(CH33))33CC–– tert-Butyltert-Butyl (CH(CH33))33COCO–– tert-Butoxytert-Butoxy

CC66HH55–– PhenylPhenyl CC66HH55OO–– PhenoxyPhenoxy

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

alkyl componentalkyl component


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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


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Physical Properties of Ether

1) Boiling Points

The boiling points of ethers are lower than those of alcohols having the same molecular

weights.

2) Solubility in water 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).

compound Formula MW Bp (°C)

ethanol CH3-CH2-OH 46 78

Dimethyl ether CH3-O-CH3 46 -25

propane CH3-CH2-CH3 44 -42


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1)1) Dehydration of alcohols:Dehydration of alcohols: (only Symmetric ether)(only Symmetric ether)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 EthersPreparation of Ethers

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 %)

symmetric ether


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Preparation of EthersPreparation of Ethers

2)2)The Williamson synthesThe Williamson synthesThis method is usually used for preparation of unsymmetrical ethersThis method is usually used for preparation of unsymmetrical ethers

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 ONa

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OH O

CH3CH2 Br

OCH2CH3

Na

Na+

+ NaBr

cyclohexanol ethoxycyclohexane sodium

cyclohexyloxide

Examples

The alkoxide is commonly made by adding Na or K to the alcoholThe phenoxide is commonly made by adding NaOH to the phenol

3)3)Alkoxide from alcoholAlkoxide from alcohol

OH OCH3

1) Na

2) CH3I

2-Methoxy-3,3-dimethylpentane3,3-dimethyl-2-pentanol


Reactions Of EthersReactions Of EthersCleavage of ethers by hot concentrated acids

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

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)

+


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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


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

oxygen.

Epoxides are cyclic ethers in which the ether oxygen is part of a three-

membered ring.

The simplest and most important epoxide is ethylene oxide.

Cyclic Ethers-Epoxides:Cyclic Ethers-Epoxides:


O O O

O

O

1,4-DioxaneOxiraneFuranTetrahydrofuranEthylene Oxide (epoxide)

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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, because

of 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(cleavage carbon-oxygen bond) of

ethylene oxide that form commercially important products are:

1- Acid –Catalyzed ring opening of epoxides in water to form glycols.

H3OCH CH

O

R CH CH R

OH

OH

R R

+


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2- Acid –Catalyzed ring opening of epoxides in alcohol to form alkoxy alcohols

3- Acid –Catalyzed ring opening of epoxides 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- Ring opening 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

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Exercise 1

Give a correct name for each of the following compounds.

CH2CH3 O CH2CH2CH3

CH2=CHCH2 O CH2CH=CH2

O CH2CH3

CH3CHCH2CH3

O CH3

CH3CH2CHCH=CH2

O CH2CH3

OCH3

O CH3

Exercice 2

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

from 3,3-dimethylcyclohexanol and butanol


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Exercise 3

Predict the products of the following reactions.

CH3OH

O

O

O

CH3MgBr

O

O O

LiAlH4

(a) Di-n-butyl etherconc, HBr

heat

(b)

(c) HBr

(e)

(f)

MCPA

CH2Cl2

CH3OH

CH3O

(g)

H2O

(d)H3O

+

(e)H2O


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Thank You for your kind attention !Thank You for your kind attention !

Questions?

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