21 ноября, 2015 
Pokraskin Aniline
(Toluidine, Xylidine, m-Nitroaniline)
A mixture of 9.3 grams (0.1 mole) of aniline in 30 cc. hot water is stirred with a glass rod while 25 cc. concentrated hydrochloric acid is added in a thin stream. The solution is allowed to cool to about 40°C.,
and enough ice is added to lower the temperature to 0°, leaving a little ice still unmelted. A 20 per cent solution[54] of sodium nitrite containing 7 grams of pure NaN02 is then added rapidly with good stirring. This nitrite solution, standardized with pure sulfanilic acid (see Analytical Section), should be kept in stock. The diazotization is complete when a drop of the reaction mixture gives an immediate test with both starch — iodide and Congo red. All diazotizations should be followed with these two reagents. The diazotization requires about 2 minutes (30 minutes in large scale operations), the final temperature is about 70°, and the total volume is about 250 cc.
When p-toluidine and the chloroanilines are used, some precipitation of the hydrochlorides occurs when the mixtures are cooled in ice. The precipitates disappear rapidly during diazotization.
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