4 THE UNIVERSITY SCIENCE BULLETIN. 



A second general method for the synthesis of the mustard oils is 

 based upon the intermediate formation of the salt of a substituted 

 dithiocarbamic acid, RNHCSSMe. This is illustrated by the Hof- 

 mann^ syntheses of alkyl isothiocyanates, which involve the desul- 

 phurization of the salt RNHCSSNH3R with mercuric chloride, silver 

 nitrate, etc. 



In the aromatic series compounds of the type RNHCSSNH3R 

 cannot, as a rule, be isolated, but instead lose hydrogen sulphide and 

 go over to the ordinary thiourea, RNHCSNHR. On the other 

 hand, the aryl amines react with carbon bisulphide and ammonia 

 and give almost quantitatively the corresponding ammonium salts, 

 RNHCSSNH4. This should afford a convenient source of mustard 

 oils, provided some simple means could be devised for removing a 

 mole of NH.SH. 



METHODS FOR SUCH ELIMINATION. 



Andreasch^ and others have shown that the ammonium dithio- 

 carbamates react with ethyl chloroformate with the formation of 

 aryl isothiocyanates, RNCS. The yields, however, are varying and 

 the products are apt to be contaminated with the corresponding 

 oxygen ureas. The method involves, too, the use of the expensive 

 ethyl chloroformate. 



In a paper published in 1891, LosanitscM described a number of 

 salts of phenyl dithiocarbamic acid and obtained from the am- 

 monium dithiocarbamate, in water solution, the corresponding col- 

 ored salts of copper, nickel, cobalt, iron, mercury and manganese. 

 The statement was made "that the best method for the prepara- 

 tion of phenyl mustard oil is to treat a solution of ammonium 

 phenyl dithiocarbamate with copper sulphate and distill with steam. 

 The yield of mustard oil is theoretical." No confirmatory data, 

 however, were given for this statement. Later Heller and Bauer'^ 

 found that lead carbonate reacted with the ammonium aryl dithio- 

 carbamates, yielding mixtures of the aryl isothiocyanates and mono- 

 aryl thioureas. 



Since considerable amounts of the aryl isothiocyanates were 

 needed in another investigation in this laboratory, it seemed ad- 

 visable to follow up this observation of Losanitsch and ascertain 



4. Ber. 1, 170 (1868). Ber. 8, 108 (1875). Ann. 371, 201 (1909). 



5. Monat. 27, 1211 (1906). Monat. 30, 701 (1909). Monat. 33, 363 (1912). Am. Ch. 

 J. 24, 432 (1902). Ber. 35, 3368 (1902). Ber. 36, 3520 (1903). Ber. 40, 2198 (1912). 



6. Ber. 24, 3021 (1891). 



7. J. Prak. Ch. (2) 65, 365 (1902). 



