116 Scientific Proceedings^ Royal Dublin Society, 



IV. — Action of Nitric Acid at loio Concentrations. 



(a) In Acetic Acid Solutions. — (1) Two grams of diphenylurethane were dis- 

 solved in fifty grams of glacial acetic acid, and four molecular proportions of fuming 

 nitric acid were added. The solution, which had a light greenish colour, was 

 allowed to remain for ten weeks at the laboratory temperature, and was then 

 poured into water. The solid which separated was filtered and recrystallised 

 from alcohol. The colourless crystals thus obtained melted at 72° C, and proved 

 to be diphenylurethane. As the weiglit of the solid recovered was almost two 

 grams, little, if any, reaction can have occurred between the nitric acid and the 

 diphenylurethane. 



(2) Three similar solutions containing respectively one, two, and three molecular 

 amounts of nitric acid to two grams of diphenylurethane in glacial acetic acid 

 were prepared and allowed to remain at the room temperature for ten weeks. At 

 the end of that time the diphenylurethane'was in each case recovered unchanged. 



It is evident, therefore, that at the ordinary temperature any niti'ation of 

 diphenylurethane by means of nitric acid in an acetic acid solution which may 

 occur must be a very slow one. 



(b) In Carbon Tetrachloride Solutions. — (1) Two grams of diphenylurethane 

 were dissolved in fifty grams of carbon tetrachloride, and 0'7 c.c. of fuming nitric acid 

 (two molecular amounts) was added. After a few days the solution had a lemon- 

 yellow colour, and the slight upper layer was brown. At the end of five weeks the 

 carbon tetrachloride was evaporated, and the residue, which consisted of a colour- 

 less solid intermixed with a small quantity of oil, was dissolved in hot alcohol. 

 The solid which separated from the alcohol on cooling proved to be unchanged 

 diphenylurethane, melting at 72° C. The small amount of oil which was simul- 

 taneously formed was insufficient for further examination. 



(2) In a second experiment three molecular quantities of nitric acid were 

 added to a solution, similar to the last, of two grains of diphenylurethane in 

 carbon tetrachloride. As in the last experiment, the solution was yellow, and the 

 upper layer was brown, in colour. After three weeks crystals began to separate, 

 and at the end of another week the carbon tetrachloride was evaporated. The 

 oily, crystalline solid which remained was washed with ether and alcohol. It 

 consisted of colourless crystals which melted at 68° C, and proved to be identical 

 with 4-nitro-diphenylurethane. 



(3) In another experiment four molecular quantities of nitric acid were added 

 to the solution, which in this case rapidly acquired a deep yellow colour, and on 

 standing overnight a brown oil separated. After the first four weeks yellowish- 

 white crystals formed. When the mixture had remained ten weeks in all at the 

 laboratory temperature, the solid was filtered, washed with a little carbon tetra- 

 chloride, dried, and recrystallised from alcohol, from which it separated in the form 

 of yellow crystals, which melted at 133°-I34:° C, and proved to be identical with 

 4'10-dinitro-diphenylurethane. 



When the carbon tetrachloride was evaporated from the filtrate from the 

 crystals just mentioned, a brown oil remained. As this oil did not crystallise, it 

 was decomposed by heating on the water-bath with alcoholic potash for about an 

 hour. The mixture was diluted with water, and the solid which separated was 

 filtered and dried. When heated with chloroform part of the solid dissolved -, 

 the solution was filtered while hot, and from it 4-10-dinitro-diphenylamine, 

 melting at 214° C, was deposited on cooling. The portion which remained 

 undissolved was crystallised from benzene, from which it separated in the form 

 of red crystals, melting at 219° C, and which were identical with 2-10-dinitro- 

 diphenylaniine. 



