PRACTICAL ORGANIC AND BlO-CHEMISTRV 



(5) Sandmeyer's Reactions. 



On adding a solution of cuprous chloride in hydrochloric acid, 

 or ,, cuprous bromide in hydrobromic acid, 

 or ,, ,, ,, cuprous cyanide in potassium cyanide, 

 to a solution of diazobenzene chloride and warming, nitrogen is 

 evolved and chlorobenzene, bromobenzene or cyanobenzene (phenyl- 

 cyanide) is formed : 



C 6 H 5 N 2 C1 + CuCN = C 6 H 5 CN + N 2 + CuCl. 



In practice these reactions are carried out by mixing aniline with a slight 

 excess of hydrochloric acid, cooling in ice and adding the calculated quantity 

 of sodium nitrite solution, as shown by testing with potassium iodide-starch 

 paper. The aqueous solution is warmed, or potassium iodide is added, or it 

 is poured into the solution of the cuprous salt and warmed. The product 

 can generally be isolated by steam distillation. 



Phenylhydrazine. C 6 H 5 . NH . NH 2 . 



Phenylhydrazine is obtained by reducing diazonium chloride with 

 stannous chloride : 



C 6 H 5 . N 2 . Cl + 2H 2 = C 6 H 6 NH . NH 2 . HC1. 



Its constitution is proved by its conversion into aniline and 

 ammonia by reduction with zinc and hydrochloric acid : 



C 6 H B NH . NH 2 + H 2 = C 6 H 5 NH 2 + NH 3 . 



Preparation. 



A molecular proportion of aniline (9*3 gm.) is dissolved in about 10 times 

 the calculated quantity of concentrated hydrochloric acid (200 c.c.), thoroughly 

 cooled in ice and diazotised by adding the calculated quantity of sodium 

 nitrite (6*9 gm.). As soon as excess of nitrite is present, as indicated by 

 starch-iodide paper, rather more than the calculated quantity of stannous 

 chloride (45 gm.) dissolved in the proper amount of concentrated hydrochloric 

 acid (100 c.c.) is slowly added. Phenylhydrazine hydrochloride separates out. 

 It is filtered off by suction and washed with concentrated hydrochloric acid. 

 It is dissolved in water and decomposed with excess of caustic soda ; the oil 

 is extracted with ether, the ethereal solution dried with solid potash, the ether 

 distilled off and the base distilled in vacua. 



Properties. 



Phenylhydrazine consists of colourless prisms which melt at 23 

 and boil at 241 with slight decomposition. It dissolves slightly in 

 cold water and easily in alcohol and ether. As a strong base it forms 

 salts with acids ; the hydrochloride crystallises in needles and is 

 easily soluble in warm water. 



Reactions. 



(1) Phenylhydrazine and its salts reduce Fehling's solution. 



(2) It is converted into benzene on heating its solutions with 

 copper sulphate or ferric chloride. 



(3) It combines with aldehydes, ketones and carbohydrates to 

 form hydrazones and osazones. The hydrazone is decomposed by con- 

 centrated hydrochloric acid, and on reduction gives an amine and aniline. 



