THE KANSAS UNIVERSITY 

 SCIENCE BULLETIN. '"'^^^" 



Vol. XIII.] July, 1922. [Xo. 10. 



On the Preparation of the Aryl Isothiocyanates. 



BY F. B. DAINS, R. Q. BREWSTER, C. P. OLAXDER. 



THE aromatic mustard oils, RNCS, which have been the sub- 

 ject of many investigations on account of their reactivity, have 

 been prepared by a number of different methods. The most com- 

 mon one involves the synthesis of the disubstituted thioureas from 

 the amines and the subsequent splitting of the thioureas into aryl 

 isothiocyanates and the amine or some derivative. Thus thiocar- 

 banilide, when boiled with concentrated hydrochloric acid, 20 per 

 cent sulphuric acid or concentrated phosphoric acid gave phenyl 

 mustard oil and varying amounts of aniline and triphen^'l guanidine. 



The yield of mustard oil, based on the aniline used, in general is 

 far from satisfactory on account of losses incurred in the prepara- 

 tion of the thiourea and the subsequent splitting with acid.^ 



An interesting modification in the preparation of these compounds 

 depends upon the action of acetic anhydride or an acid chloride such 

 as acetyl chloride upon the thiourea.- The acetyl derivative of the 

 thiourea, which is first formed, readily breaks down into the mustard 

 oil and an acyl-aryl amide, 



RNHCSNCOCH3R = RXCS + RXHCOCH3. 



While the above methods are of general applicability, it is evi- 

 dent that only one-half of the original amine can be converted into 

 the isothiocyanate, and that it necessitates the synthesis of the sub- 

 stituted thiourea. 



Fortunately, however, H. S. Fry's^ interesting method for the 

 preparation of the diaryl thiocarbamides has made readily acces- 

 sible various thioureas that were difficult to obtain by the older 

 ; methods. 



^— 1. J. 1858, 394. Z. 1869, 359. Ber. 15, 986 (1882). 

 L , 2. J. Chem. Soc, 59, 400 (1891). J. Am. Chem. Soc, 22, 188 (1900). 

 3. J. A. Chem. Soc, 35, 1539 (1903). 



(3) 



