MERCAPTANS AND SULPHIDES 79 



Alkyl Sulphides. 



Ethyl sulphide, C 2 H 5 . S . C 2 H 5 , is another product of the putrefaction of 

 proteins, being derived from cystine (p. 143). 



Preparation. 



Sulphides are obtained : 



(1) By the action of phosphorus pentasulphide upon ethers : 



5 (C 2 H 5 ) 2 + P 2 S 5 = 5(C 2 H 5 ) 2 S + P 2 5 . 



(2) By the action of potassium sulphide on an alkyl halide or alkyl 



potassium sulphate : 



2 C H 5 I + K 2 S = 2KI + (C H 5 ) 2 S 

 2C 2 H 5 KSO 4 + K 2 S = 2K 2 SO 4 + (C 2 H 5 ) a S. 



Properties. 



The sulphides are colourless, neutral liquids with very unpleasant smell ; 

 ethyl sulphide boils at 91. 



They resemble the ethers in being comparatively stable compounds. On 

 oxidation with nitric acid, they are converted into sulphones which are stable 

 crystalline compounds : 



(C 2 H 5 ) 2 S + 2 = (C 2 H 6 ) 2 S0 2 . 



Alkyi Bisulphides. 



Bisulphides are formed when mercaptans are exposed to the air : 



2 C 2 H 5 SH + O = H 2 + C 2 H 5 . S S . C 2 H 5 , 

 or by the action of iodine upon sodium mercaptides : 



2 C 2 H 5 S . Na + I 2 = 2NaI + C 2 H 5 . S S . C 2 H 5 . 



