Bechamp reduction of DNS to DAS using H.sub.2 SO.sub.4 and trace of HOAc

摘要

A process for preparing bis-diaminostilbene dilsulfonic acid from bis- dinitrostilbene disulfonic acid by an improved Bechamp reduction process is disclosed. The process involves reduction with metallic iron in an acidic medium consisting of 0.033 to 0.27% of acetic acid and 0.38 to 0. 76% of sulfuric acid in water at an oxidation- reduction potential (iron/thalamide electrode) in the range 140 to 270 millivolts.