Purifying Pararosanilin for Use in Colorless Schiff Reagent

Pararosanilin hydrochloride or pararosanilin base was purified by suspending 20 g. of the dye in 400 ml. of water, acidifying with 50 ml. of 2N HCl and adding 4—5 g. of decolorizing charcoal. The mixture was then heated to boiling and boiled for 2 minutes. The entire mixture was transferred to a large, covered, fluted filter, and the filtrate allowed to stand overnight while the pararosanilin hydrochloride precipitated. The pararosanilin hydrochloride was filtered off, resuspended in 100 ml. of ether-alcohol (10:1) and shaken for 3 to 5 min. The ether-alcohol suspension was filtered and the pararosanilin hydrochloride washed repeatedly on the filter with ether until the ether wash was no longer colored. It was then washed several times with distilled water (total volume 400 ml.), dried in vacuuo over concentrated sulfuric acid, ground to a fine powder and stored in a dark brown bottle.