METHOD FOR DECIDING END POINT IN DISTILLATION OF ARSENIC TRICHLORIDE

摘要

PURPOSE:To effectively perform distillation of arsenic trichloride by deciding the end point of distillation by means of AsCl3/HCl contained in a distillate in case of distilling and purifying a produced soln. obtained by adding excess concd. hydrochloric acid and concd. sulfuric acid to arsenic oxide. CONSTITUTION:About 1.3-1.5 equivalent concd. hydrochloric acid for arsenic oxide (preferably arsenious acid) is stirred at room temp. and arsenic oxide is added thereto. As it is, about 1.1l preferably 1.5-2.0l concd. sulfuric acid for 1kg arsenic oxide is slowly added in equal velocity and the mixture is distilled and purified in decompression after stirring sufficiently it. During this distillation, the distillate is received in a graduated receiver and the volume of an upper layer (HCl) and a lower layer (AsCl3) of the distilled soln. is read with the passage of time at intervals and a point of time wherein AsCl3/HCl volume ratio is attained to <=2.5 preferably 2.0-2.2 is made the end point of distillation. Thereby effective distillation can be performed without distilling unnecessarily HCl having about >=10 times latent heat of evaporation in comparison with AsCl3.