| Hydrotalcite-like compounds (HTlcs), whose brucite-like layers are composed of metal cations and anions are in the interlayer gallery, are a kind of solid base catalysts and their general formula are [M1-x2+Mx3+(OH)2]x+(Ax/nn-)·mH2O. M2+and M3+can be replaced by different divalent or trivalent metal ions and An-by other kinds of anions through ion exchange. These HTlcs are widely used in many aspects for their special structure, especially in catalyst. HTlcs with transition metals which have catalytic activity in the brucite-like layers can catalyze different organic reactions. HTlcs containing alkaline species can be used in base catalytic reactions, and those exchanged with ions having large radius or recovered from roasting have larger interlayer spacing and higer surface area, usually leading to greater catalytic activity.4,4’-dinitrostilbene-2,2’-disulfonic acid (DNS) was the intermediate for the preparation of4,4’-diaminostilbene-2,2’-disulfonic acid (DSD), which is an important raw material in dye industry. At present, DNS is prepared by the oxidation of2-methyl-5-nitrobenzene-sulfonic acid (NTS) in alkaline solution catalyzed by transition metal salts like MnSO4. Because of the use of the alkaline solution and the transition metal salts, this production process was environmentally harmful. Introducing both transition metals and alkaline species into the brucite-like layers can prepare the solid base catalysts, which have catalytic activity and stronger alkaline. These solid base catalysts can not only catalyze chemical reaction but also substitute for part of the alkali solution. Furthermore, these solid base catalysts can be easily separated from reaction solution and will contribute to improving the environment.BaFe-containing HTlcs were prepared for the first time and Fe-, CaFe-containing HTlcs were prepared by coprecipitation method, while K/Fe-containing HTlc by immersion process. These four series of HTlcs were used to catalyze the oxidation of NTS to synthetize DNS and the conditions of the reaction were discussed. The best conditions of the reaction are75℃,0.70mol/L NaOH,2%Bao.sMg2.5Al0.8Fe0.4and45mL/min O2. The best hydroxide concentration is0.65～0.75mol/L while the traditional concentration is0.9～1.0mol/L, about25%reduction of hydroxide. |
