ETHER

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H O H R O H R O R

water alcohol ether

Structure and nomenclature of ethers

Ethers are compounds of formula R -O-R', where R and R' may be

alkyl groups or aryl groups.

Common names (Alkyl Alkyl Ether Names)

Common names of ethers are formed by naming the two alkyl

groups on oxygen and adding the word ether. Under the current

system, the alkyl groups should be named in alphabetical order.

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H3C-O-CH3 H3C-CH2-O-CH2-CH3

H2C=CH-O-CH=CH2

Common Dimethyl ether Diethyl ether Divinyl ether

IUPAC Methoxy methane

Ethoxy ethane

H3C-O-C6H13 H3C-O-CH2-CH3 H3C-O-CH=CH2

Common Hexyl methyl ether

Ethyl methyl ether Methyl vinyl ether

IUPAC Methoxy hexane

mehoxy ethane Methoxy ethene

Examples

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Common: Diphenyl etherIUPAC : Phenoxy benzene

Common: Methyl Phenyl ether (anisole)IUPAC : Methoxy benzene

CH3CH3

OCH3

CH3CH3

O

CH3

OCH3

3-Methoxyhexane 5-Ethoxy-2-heptene 1-Phenoxy-1-propene

Examples

Physical Properties of EtherBoiling Points

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

same molecular weights.

Solubility in water Ethers are much less soluble in water than alcohols.More water-soluble than hydrocarbons of similar molecular weight.

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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Preparation of ehers

Ethers by 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:

R O H H O R R O R+H

+

heat+ H2O

Examples

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2 CH3HO H2SO4, 140 C CH3OH3C + H2O

methyl alcohol methyl ether

2 CH2CH3HO H2SO4, 140 C CH2CH3OH3CH2C + H2O

ethyl alcohol ethyl ether

(100%)

(88%)

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The Williamson synthesis of ethers

O- Na+RROR + NaX

sodium alkoxide ether

+ R X

O- Na+ROR + NaX

sodium phenoxide ether

+ R X

alkyl halide

alkyl halide

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

Examples

OH O

CH3CH2 Br

OCH2CH3

Na

Na+

+ NaBr

cyclohexanol ethoxycyclohexane sodium

cyclohexyloxide

8

OH1) Na

2) CH3-I

OCH3

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

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3,3-dimethyl-2-pentanol 2-Methoxy-3,3-dimethypentane

Cleavage of ethers by hot concentrated acids

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)

+

Specific example

CH3CH2 O CH2CH3 H I CH3CH2OH CH3CH2I+heat

(concentrated)

+

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

9

Reaction of Ether

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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 into an alkyl halide by the reaction.

For example

R O R H X R X+ 2 + H2O2

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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

11

Cyclic EthersEpoxide

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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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Their reactivity 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

+

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

3- When an epoxide reacts with a hydrohalic acid ( HCl,HBr, or HI), a

halide ion attacks the protonated epoxide.

4- Reactions of Epoxides with Grignard and Organolithium Reagents

15

H X CH CH

O

R CH CH R

OH

X

R R+

R' MgX CH CH

O

R CH CH R

R'

OH

R' Li

R R+1) ether

2) H3O+

or

CH3 OH CH CH

O

R CH CH R

OH

O

R R

CH3+

+.. H3O

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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

16

Exercise 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.

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O

O

O

O

O

di-n-butyl ethera]

b]

c]

d]

e]

f]

g]

conc,HBr

heat

CH3OH

H3O+

CH3MgBr

HBr

CH3O-

CH3OH

MCPA

CH2Cl2

H3O