BENZENE SERIES. AROMATIC COMPOUNDS. 591 



A solution of pyrrol in alcohol, treated with iodine in the presence 

 of oxidizing agents, such as ferric chloride, deposits after some time 

 crystals of tctra-iodo pyrrol. This compound is official under the 

 name of iodol, iodolum, C 4 I 4 NH = 566.17. It is a pale-yellow, crys- 

 talline powder, almost insoluble in water, soluble in 9 parts of alcohol, 

 1 to 2 parts of ether, and 15 parts of fatty oils; it is, when pure, 

 tasteless and odorless, and contains of iodine 88.97 per cent. 



Antipyrine, Antipyrina, C U H 12 N 2 O = 186.75 (Phenyl-dimethyl- 

 isopyrazolon). When phenyl-hydrazine is heated with diacetic ether, 

 CH 3 CO.CH 2 .COOC 2 H 5 , a substance is formed known as phenyl- 

 methyl-isopyrazolon. 



In this compound a second hydrogen atom may be replaced by 

 methyl, when phenyl-dimethyl-isopyrazolon is formed, which is the 

 substance to which the name antipyrine has been given. 



Antipyrine is a white, crystalline, odorless powder, having a slightly bitter 

 taste; it fuses at 113 C. (235 F.), is soluble in less than its own weight of 

 water, in 1 part of alcohol, in 1 part of chloroform, but only in 50 parts of 

 ether. 



The structure of antipyrine and its relation to pyrrol and isopyrazoltm inay 

 be shown by the constitutional formulas: 



HC CH HC CH HC CH 2 



H S JH I JH HH. 



NH NH NH 



Pyrrol. Pyrazol. Pyrazolin. 



HC CH 2 HC=:CH CH 3 C= 



i!r co HN co 



co 



NC 6 H 5 



Pyrazolon. Isopyrazolon. Phenyl-dimethyl- 



isopyrazolon. 



Analytical reactions : 



1. 0.2 gramme of antipyrine dissolves in 2 c.c. of nitric acid with- 

 out change of color. On heating slightly the liquid assumes a yellow, 

 then an intense red color. 



2. 12 c.c. of a 1 per cent, solution of antipyrine treated with 0.1 

 gramme of potassium nitrite solution yield a colorless solution, which 

 turns intensely green on the addition of 1 c.c. of dilute sulphuric acid. 

 In a more concentrated solution green crystals of isonitroso-antipyrine 

 form on standing. 



