78 PRACTICAL ORGANIC AND BIO-CHEMISTRY 

 MERCAPTANS AND SULPHIDES. 



The sulphur compounds corresponding to the alcohols, i.e. thio-alcohols,. 

 are known as mercaptans ; the sulphur compounds corresponding to the ethers, 

 i.e. thio-ethers, are known as sulphides, or alkyl sulphides. Bisulphides are 

 also known. 



CH 3 . SH C 2 H 5 . S . C 2 H 5 C 2 H 5 . S S . C 2 H 6 



Methyl mercaptan. Ethyl sulphide. Ethyl disulphide. 



Mercaptans. 



Methyl mercaptan is a product of the putrefaction of proteins. It occurs 

 in the urine after a diet of asparagus and gives it the peculiar unpleasant 

 odour. 



Preparation. 



Mercaptans are prepared : 



(1) By heating the alcohol with phosphorus pentasulphide : 



5 CH 3 OH + P 2 S 5 = 5 CH 3 SH + P 2 5 . 



(2) By heating the alkyl halide or alkyl potassium sulphate with potas- 



sium hydrosulphide : 



CH 3 I + KSH = CH 3 SH + KI 

 C 2 H 5 O . SO 2 . ONa + KSH = C 2 H 6 SH + NaKSO 4 . 



About 2-5 c.c. of a saturated solution of sodium ethyl sulphate are made 

 alkaline with sodium hydroxide and an equal volume of sodium hydrosulphide 

 (33 P er cent.) is added. On warming ethyl mercaptan is formed which is- 

 recognised by its garlic-like unpleasant odour. 



Properties. 



Methyl mercaptan is a gas, ethyl mercaptan is a colourless liquid boiling 

 at 36. The other mercaptans are also liquids which are insoluble in water 

 and have a disgusting smell. 



Like the alcohols they react with sodium with evolution of hydrogen : 



2CH 3 SH + Na 2 = 2CH 3 SNa + H 2 . 



The mercaptans react with mercuric oxide forming crystalline com- 

 pounds : 



2 C 2 H 6 SH + HgO = (C 2 H 8 . S) 2 Hg + H 2 O. 



These compounds are termed mercaptides, the name of the group being; 

 derived from the mercury compounds. On oxidation with nitric acid the 

 mercaptans yield sulphonic acids : 



CH 3 SH + 30 = CH 3 . SO 3 H. 



The sulphonic acids are isomeric with alkyl hydrogen sulphites. The 

 latter compounds are esters and are hydrolysed by alkali ; the sulphonic acids 

 are stable. In the sulphonic acids the sulphur atom is joined to carbon, in 

 the sulphites it is joined to oxygen : 



o CH - 



\OH 



Methyl sulphonic acid. Methyl hydrogen sulphite. 



