DAIXS ET AL.: ARYL ISOTHIOCYANATES. 7 



salt. To determine the best conditions for such a decomposition 

 the following experiments were undertaken, using the dry am- 

 monium salt of the aryl dithiocarbamates. 



FERROUS SULPHATE. 



A solution of 60 gms. of the iron salt in the minimum volume 

 of water was added to 40 gms. of the ammonium phenyl dithio- 

 carbamate in 200 cc. of water. A yellowish-brown precipitate 

 formed immediately. The mixture, which had a noticeable odor 

 of the phenyl isothiocyanatc, was allowed to stand for an hour 

 and then distilled with steam, but with the result that only 3 cc. of 

 an impure mustard oil was obtained. 



ZINC SULPHATE. 



On mixing 30 gms. of the ammonium salt in 300 cc. of water 

 with 47 gms. of zinc sulphate in 150 cc. of water a thick, white pre- 

 cipitate of the zinc phenyl dithiocarbamate was formed. This 

 changed on steam distillation to zinc sulphide and gave a 23 per 

 cent yield of the phenyl isothiocyanatc. 



COPPER SULPHATE. 



To a solution of 25 gms. of the ammonium salt in 150 cc. of water 

 was added 34 gms. of copper sulphate in the same volume of water. 

 The odor of mustard oil was very pronounced, and the yellowish- 

 brown copper salt changed readily, on distilling the mixture with 

 steam, to the black copper sulphide. The yield of oil in this case 

 was 71.7 per cent — a very decided increase. 



LEAD NITRATE. 



Using the same concentrations as above, 25 gms. of the ammonium 

 salt and 40 gms. of lead nitrate gave the brown lead salt with a 

 subsequent yield of 77.2 per cent phenyl isothiocyanate — a maxi- 

 mum which has not been exceeded. 



In general it has been found that while both the copper and lead 

 salts are suitable desulphurizing agents, the use of lead nitrate gave 

 the better result in about the above ratio. 



PREP.\RATION OF PHENYL ISOTHIOCYANATE WITHOUT SEPA- 

 RATION OF THE AMMONIUM SALT. 



The data obtained from the preparation of the ammonium salts 

 of the ar^d dithiocarbamates showed that the isolation of this com- 

 pound might be far from quantitative, with the result that the yield 

 of mustard oil based on the amine used would be proportionately 

 lowered. This was proved directly by many experiments, two of 

 which will be described in detail. 



