Solid acid catalysts for fluorotoluene nitration using nitric acid

Green Chemistry Pub Date: 2003-10-24 DOI: 10.1039/B307146D

Abstract

Fluorotoluenes have been nitrated regioselectively in the liquid phase under mild conditions using solid acid catalysts. Excellent yields were obtained with 70% nitric acid as nitrating agent. Nitration of 2-fluorotoluene at 90 °C showed 55% conversion with 90% selectivity for 2-fluoro-5-nitrotoluene whereas 3-fluorotoluene showed more than 79% conversion even at 60 °C with 67% selectivity for 3-fluoro-6-nitrotoluene and 30% selectivity for 3-fluoro-4-nitrotoluene. In the case of 4-fluorotoluene, side chain nitration was observed instead of ring nitration with 53% conversion and 59% selectivity for 4-fluoro-α-nitrotoluene. Among the different catalysts studied for fluorotoluene nitration, Fe/Mo/SiO2, MoO3/SiO2 and H-beta showed higher conversion and selectivity in all three isomers due to higher acidity. A recycling study of catalyst H-beta for nitration of 3-fluorotoluene showed no significant loss in conversion as well as selectivity even after 5 recycles indicating the high stability of the catalyst. Compared to the conventional process, fluorotoluene nitration over solid acid catalysts is a highly regioselective, clean and environmentally friendly process with a simpler work up procedure.

Graphical abstract: Solid acid catalysts for fluorotoluene nitration using nitric acid
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