86 MOLECULAR STRUCTURE 



valency : it may often be replaced or supported by methods 

 to be described later, which then show their scientific 

 superiority in the elucidation they give to the notion of 

 valency. 



B. Determination of Constitution from Formation out of, 

 and Conversion into Compounds of known Structure. 



In order to adhere to a definite example in this case 

 too, we will discuss the constitution and isomerism of 

 methyl mustard oil and methyl thiocyanate. The two 

 compounds are known to have the same molecular formula, 

 C 2 H 3 NS, and it was the relations of composition and 

 decomposition that led Hof mann l to choose the appropriate 

 constitutional formulae. 



Formation of methyl mustard oil takes place, amongst 

 other ways, from methylamine (CH 2 NH 2 ) and carbon 

 sulphochloride (C1 2 CS), with separation of hydrochloric 

 acid : 



H 2 CNH 2 + C1 2 CS = aHCl + C 2 H 3 NS (methyl mustard oil); 



decomposition, e. g. under the influence of hydrogen 

 (sodium amalgam and alcohol), to formation of methylamine 

 and methylene sulphide (H 2 CS) : 



C 2 H 3 NS (methyl mustard oil) + 2 H 2 = H 3 CNH*+ H 2 CS. 



% 



For the formation of methyl thiocyanate, on the other 

 hand, we may use methyl sulphide (H 3 CSCH 3 ) and broin- 

 cyanogen (CNBr). The thiocyanate is produced according 

 to the equation 



H,CSCH 3 + BrCN = H 3 CBr + C 2 H 3 NS (methyl thiocyanate) ; 



while decomposition by means of hydrogen leads to separa- 

 tion of methylmercaptan (H 3 CSH) and hydrocyanic acid 

 (HCN) : 



C 2 H 3 NS (methyl thiocyanate) + H, = H 3 CSH + HCN. 



1 Beilstein, Handbuch der organ. Chemie, p. 699. 



