Лако-красочные материалы — производство

The moist filter cake of sodium 2-nitrochlorobenzene-4-sulfonate (page 106) is dissolved in 400 cc. boiling water; the solution is filtered to remove any undissolved residue. To the filtrate is added 300 grams of crystalline neutral sodium sulfite (Na2S03 * 7H20), taking care that the resulting solution is not alkaline to phenolphthalein. (If it is, hydrochlo­ric acid is added carefully just to the point of disappearance of the alka­line reaction.) The solution is now boiled under reflux for 2 hours, during which it becomes an intense yellow in color. The hot solution is then treated with 100 grams of solid salt, and when the latter is completely dissolved, the solution is allowed to stand overnight in the ice chest. The resulting thick paste is filtered with suction, and the filter cake is well pressed out and washed with cold saturated salt solution until the wash­ings are only weakly yellow in color. Pure sodium nitrobenzene-2,5-di — sulfonate may be obtained by crystallization from aqueous alcohol, but the product obtained above is usable in the next reduction step without further purification.