Studies On The Reduction Of Azobenzene Compounds By Sulfur-catalyzed CO/H₂O System

Hydroazobenzenes were often used in the fields of dyes and pharmaceuticals as fine chemicals and intermediates in organic synthesis.In recent years,many researchers had been explored the synthesis method and made a lot of progresses.The various synthesis methods had advantages and disadvantages.In the 1960s,it was discovered that sulfur could catalyze CO/H₂O system for carbonylation reduction.The catalyst in this reduction system could be separated well after the reaction was completed,and the reaction conditions were relatively mild,and it had the characteristics of reaction-controlled phase transfer.Inspired by the catalytic reduction system of Se/CO/H₂O,the symmetric azobenzenes were used as the raw material,selenium was the initiator of the catalytic cycle,and this paper explored the reaction of sulfur catalytic CO/H₂O system for reduction of azobenzenes in atmospheric pressure.Because sulfur was cheaper than selenium,and the hydrogen sulfide produced during the reaction was less toxic than hydrogen selenide.In this system,azobenzenes could be directly reduced to hydrogenated azobenzenes and the good yield was obtained.The catalyst showed high catalytic activity in the reaction process.The reaction had no by-product formation.In the experiment process,the single variable control method was used to investigate the amount of catalyst used,the type and amount of cocatalyst,the type and amount of solvent,water amount,temperature and time.We found the optimized reaction conditions of the experiment:substrate:5.5 mmol,catalyst:5%sulfur and 0.5%selenium,cocatalyst:25%anhydrous sodium acetate,solvent:40 mL of N,N-dimethylforma-mide,water:2 mL,temperature:85?,pressure:atmospheric pressure,reaction time:2 h.A series of derivatives of azoben-zenes were reduced in the S/CO/H₂O system with high yield.The mechanism of the reaction was discussed and explained on the basis of previous studies.