Methods of Preparation of Ether Preparation and Properties
→ Laboratory Method : In this method, diethyl ether is prepared by Williamson’s continuous etheration process.
→ Ethanol is taken in excess with cone. sulphuric acid and recaction is carried out at 413 K.
→ Method : Accordiñg to figure 11.1, ethyl alcohol is taken in distillation flask (2 volume) conc. H2SO4 (1 volume) is added slowly in it.
→ Flask is heated on sandbath at 413 K temperature and diethyl ether start to form which is collected in a receiver kept in ice mixture. When ethanol is added in distillation flask with the help of dropping funned ether is prepared in continuous form.
→ Purification : Diethyl ether obtained by this method contains impurities of ethanol, water and suiphar dioxide.
→ Impure ether is taken in a separating funnel, then dii. NaOH is added and solution is stirred due to which impurity of sulphur dioxide is removed. Lower layer of NaOH solution is removed and ether is stirred gentaly with water and conc. solution of CaCl2.
- By this impurity of ethanol is removed. Surface of ether is again dried with fused CaCl2.
- Pure Ether is obtained by fractional distillation at 306-308 K temperature.
- In the above method, during reaction H9S04 is also formed with ether as product. Hence, initial amount of conc.
- H2SO4 should be enough to convert ethanol into ether and reaction should continuously go on. But this does not happen due to following reasons:
- Wate. comes out when ether forms from ethanol. This dilutes the conc. H2SO4.
- Some part of conc. H2SO4 is used in the oxidation of alcohol and H2SO4 itself reduced to sulphur dioxide.
- Hence, H2SO4 should be replaced during whole process.
- Industrial Method : Apparatus is shown in figure 11.2. Ethanol is mixed drop by drop in conc. sulphuric acid.
- The mixture is heated by passing steam in the coils. Temperature is kept constant at 413 K.
- The vapour mixture which comes out is a mixture of ethanol vapour, ether vapour and acid fumes.
- The mixture is passed from the botom of a chamber. In this chamber from above dii.
- NaOH solution falls down. Here acid fumes are separated from vapour mixture.
- When remaining vapour mixture is passed through fractional column, ethanol and water are condensed in it.
- Due to low boiling point of ether it is released from the upper part and then condensed and collected in a receiver.
Other Methods of Ether
→ When vapours of ethanol are passed over heated catalyst like alumina or aluminium phosphate at about 523 K temperature, ether forms.
→ Vapours of ether are dried with the help of fused CaCl2. If temperature of reaction increases to about 653 K, then ethene is formed in place of ether.
→ Williamson’s Synthesis : When alkyl halide is treated with sodium or potassium alkoxide, formation of ether takes place. It is a nucleophilic substitution reaction. This reaction can be used to prepare simple and mixed both types of ethers.
→ Foe example If we want to prepare ethyl tert-butyl ether, then reaction of ethyl bromide should be carried out with sodium tert-butoxide.
→ However, if we use tert-butyl bromide and sodium ethoxide as reactants then in the presence of strong base sodium ethoxide tert-butyl bromide undergo elimination reaction to form 2-methyl propene.