Cyclic two-stage nitration process for preparing 4-chloro-3,5- dinitrobenzotrifluoride from 4-chlorobenzotrifluoride

摘要

In accordance with the present invention, there is provided herein a cyclic, two-stage process for dinitrating 4- chlorobenzotrifluoride to form 4-chloro-3,5-dinitrobenzotrifluoride in high yield. The process commences with a mononitration stage wherein 4- chlorobenzotrifluoride is substantially completely converted to 4-chloro- 3-nitrobenzotrifluoride (the "monoitro" compound) in the presence of a nitric acid, sulfur trioxide and sulfuric acid mixture. The used acid mixture then is diluted with water to form an aqueous used acid layer in which the solubility of the mononitro compound is negligible and a mononitro layer. The aqueous used acid layer then is separated from the mononitro layer and discarded. The mononitro compound thereafter is further nitrated in a dinitration stage in the presence of a fresh nitric acid, sulfur trioxide and sulfuric acid mixture. The fresh acid mixture contains an excess of nitric acid sufficient to carry out both nitrations using the partially spent acid mixture of the dinitration stage as the acid mixture for the mononitration stage. The reaction product of the dinitration stage is the desired dinitro compound and a partially spent acid mixture, which contains some dinitro compound dissolved therein. The dinitro layer then is separated from the partially spent acid layer and recovered and the acid layer is recycled back to the mononitration stage.