Research On The Selective Reduction Of DNS To DSD-acid In Fe/H₂O/CO₂ System

4.4'-diaminostilbene-2.2'-disulfonic acid (DSD-acid) is an important intermediate in fine chemicals. It is commonly used in the production of fluorescent whitening agents (FBs). direct dyes and reactive dyes.DSD-acid is mostly prepared from 4.4'-dinitrostilbene-2.2'-disulfonic acid (DNS) via selective reduction. Several factors (the molar ratio of iron to DNS, the reaction temperature, the stirring rate, the reaction time, the CO2 pressure and the concentration of the solution) were studied in the paper, the optimal conditions were shown as follows:DNS 2.5 mmol, iron 20 mmol, the deionic water 30ml. the constant pressure of CO2 0.1 MPa, the reaction temperature 20℃, the reaction time 1 hour, the stirring rate 1100 rpm. Under the optimal conditions, the conversion of DNS and the yield of DSD-acid could reach up to 100% and 99%, respectively.The iron mud was then reduced by hydrogen to reductive iron which could be recycled in Fe/H2O/CO2 system. The results showed that the iron could be recycled for five times without obvious loss of activity, and it provided a new way to eliminate the pollution of the iron mud.The reduction activity of the reductive iron which is newly reduced by hydrogen from iron oxide is also investigated in this paper. Under the optimal conditions of DNS 2.5 mmol. reductive iron 15 mmol, the deionic water 25 ml. the constant pressure of CO2 0.1 MPa, the reaction temperature 20℃, the reaction time 1 hour, the stirring rate 1100 rpm, the conversion of DNS and the yield of DSD-acid could reach up to 100% and 99%. respectively. The result showed that the reduction activity of the reductive iron is higher than the common iron.