Structure of ether
Classification of Acyclic ethers:
IUPAC Nomenclature of ether "Alkoxy Alkane"
|3||Methoxy benzene (Anisole)|
|4||3-Ethoxy-1, 1-dimethyl cyclohexane|
Method of Preparation of Ether:
(1) Williamson synthesis-
RX + R - OR'
e.g. (i) n-PrOH
(ii) MeOH Me
(iii) t-BuOH t-Bu t-Butyl ethyl ether
(This reaction produces a poor yield of ether because of the bulkiness of t-BuO-)
2. Williamson's Continuous Etherification process or by Dehydration of Alcohols-
(i) ROH + RO +
ROR + H3O+
This is an acid-base reaction in which the alcohol accepts a proton from the sulfuric acid.
Another molecule of the alcohol acts as a nucleophile and attacks the protonated alcohol in an reaction.
Another acid-base reaction converts the protonated ether to an ether by transferring a proton to a molecule of water (or to another molecule of the alcohol).
Only one combination of alkylhalide and alkoxide is appropriate for the preparation of each of the following ethers by Willianson ether synthesis. What is the correct combination in each case ?
3. From alkenes:
(a) By addition of alcohols in alkenes:
When alcohol is added to alkenes in presence of acid, we get ethers.
(II) Carbocation alcohol
e.g. (I) = CH2 + (H2SO4) Me3
(II) Me3 + EtOH Me3COEt
(b) Alkoxymercuration - demercuration:
(i) RCH=CH2 +R'OH RCH(OR')CH3
(ii) CH2=CHCH3 +CH3CH(OH)CH 3
(iii) CH3CH=CHCH3 +CH3CH(OH)CH 2CH3
Reactions of ethers:
1. With HX-
e.g. (i) CH3CH2CH2CH3 2CH3-CH2Br
2. Reaction with sulphuric acid-
Ethers dissolve in concentrated solutions of strong inorganic acids to from oxonium salts, i.e. ether behave as Bronsted Lowry bases.
R2O H2SO4 R-OH
When heated with dilute H2SO4
R2O H2SO4 2ROH
e.g. C2H5OC2H5 +H2SO4 C2H5OH +C2H5OHSO4 C2H5OH+ H2SO4
3. Autoxidation of ethers :
When ethers are stored in the presence of atmospheric oxygen, they slowly oxidize to produce hydroperoxides and dialkyl peroxides, both of which are explosive. Such a spontaneous oxidation by atmospheric oxygen is called an autoxidation.
4. Reaction with acid chlorides and anhydrides:
Reagent : ZnCl2, AlCl3 etc.
General reaction: (i) R-O-R +R-CO-Cl R-Cl +RCOOR
RCOCl +AlCl3 RCO + AlCl4-
RCO RCOOR' + R"Cl + AlCl3
C2H5OC2H5 + CH3COCl C2H5Cl + CH3COOC2H5
(ii) R2O + 2CH3COOR
e.g. C2H5OC2H5 + (CH3CO)2O 2CH3COOC2H5
5. Reaction with carbon monoxide :
Ether react with CO at 125-180oC and at a pressure of 500 atm, in the presence of BF3 plus a little water.
R2O + CO RCOOR
6. Reaction with halogens :
When treated with chlorine or Br, ether undergoes substitution, the extent of which depends on the conditions.
CH3CH2OCH2CH3 CH3CHClOCH2CH3 CH3CHClOCHClCH3
In presence of light,
The reaction proceeds by a free-radical mechanism, and α-substitution occurs readily because of resonance stabilization of the intermediate radical.