76 PRACTICAL ORGANIC AND BIO-CHEMISTRY. 



ETHERS. 



Preparation. 



Ethers are prepared either by distilling alcohols with concentrated 

 sulphuric acid or by the action of sodium ethoxide upon an alkyl 

 halide : 



/ C 2 H 5 OH + H 2 SO 4 = C 2 H 5 HSO 4 + H 2 O 

 \C,H S OH + C 2 H 6 HS0 4 = C 2 H 5 OC 2 H 5 + H 2 S0 4 

 CH 3 ONa + CH 3 I = CH 3 OCH 3 + Nal. 



If in the first preparation a different alcohol be used in the second 

 reaction, and if in the second preparation the alkoxideand halide con- 

 tain different radicles, mixed ethers are formed, e.g. 



CH 8 .O.C 2 H 6 . 



ETHYL ETHER. 



Preparation. 



Ethyl ether is generally prepared by distilling ethyl alcohol with 

 sulphuric acid hence its name of sulphuric ether. According to the 

 equation the sulphuric acid is combined and again liberated so that it 

 should be possible to convert an unlimited quantity of alcohol into- 

 ether, but bye-products are formed which interfere with the reaction. 

 The process is known as the continuous process. 



A distilling flask of about 500 c.c. capacity is fitted with a tap funnel and 

 a thermometer, the bulb of which reaches nearly to the bottom of the flask. 

 The neck of the flask is connected to a long condenser and the receiver is 

 cooled by standing in ice water. A mixture of no c.c. of absolute alcohol 

 and 80 c.c. of concentrated sulphuric acid is placed in the flask and heated to 

 140-145. At this temperature ether is formed and absolute alcohol is 

 dropped in from the tap funnel at the same rate as the liquid distils. The 

 preparation is continued until about twice the volume of alcohol originally 

 mixed with the sulphuric acid has been added. The distillate consists of 

 ether, alcohol, water and sulphurous acid. It is put into a separating funnel 

 and shaken with dilute caustic soda. The alkaline layer is withdrawn and 

 the upper layer of ether shaken with saturated salt solution, which is also 

 withdrawn. The ether is put into a distilling flask, which is loosely corked, and 

 dried by being allowed to stand in contact with calcium chloride for 12- 

 24 hours. The flask is connected with a condenser and the ether distilled 

 off from a water-bath (b p. 35). 



Purification of Ethyl Ether. 



The ether obtained above contains traces of alcohol and water. These 

 can only be removed by treatment with metallic sodium. The ether is placed 

 in a flask, provided with a calcium chloride tube to prevent access of moisture 

 and to allow the escape of hydrogen, and several slices of sodium are added. 

 When no further effervescence is observed the ether is decanted into a dis- 

 tilling flask and distilled from a water-bath. Pure ether of constant boiling- 

 point 35 is collected. 



