Green Synthesis Of O-nitro-p-toluidine

The synthesis of 2-nitro-4-toluidine (red base GL, GL for abbreviation) was studied. GL was prepared from 4-toluidine via acetylation, nitration and hydrolysis. Three steps of acetylation, nitration and hydrolysis were combined in one reactor. As one nitrating method, fuming nitric acid was used as the nitrating agent. As another nitrating method, the mixed acid instead of fuming nitric was used as the nitrating agent. Then the nitrating process was improved: HNO₃/Nb₂O₅ was used as the novel nitrating agent, 1, 2-dichloroethane was used as the solvent and three steps of acetylation, nitration and hydrolysis were combined in one reactor. The temperature and time of acetylation, nitration and alkaline hydrolysis was 80℃, 1h, 40℃, 1h, 95℃, 1.5h respectively. After nitrating reaction, excessive acid was eliminated. For yield and purity of GL, Mb₂O₅ roasting temperature, roasting time as well as Mb₂O₅ recycling use was inspected. The optimal conditions were obtained: the 4-toluidine and an acetic anhydride mole of ratio was 1:1.15, the 4-toluidine and a fuming nitric acid mole of ratio was 1 : 2.3. Under the optimal conditions, the yield of GL was 90.5% and the purity was 99.41%.By filtration Mb₂O₅ was easily separated from the product. After drying at 300℃for 2h, Mb₂O₅ could be reused in the nitration step. Nitration with mixture of nitric acid and Mb₂O₅ meet the requirements of clean production. Repeated use of Mb₂O₅ in the nitration for 4 times had no decrease of the product yield.