Continuous mechanochemical nitration of solid aromatics using nitric acid†

Abstract

This manuscript reports continuous flow mechanochemical aromatic nitration of solid aromatic substrates using nitric acid in a vertical single-screw reactor. The substrates include naphthalene, anthracene, salicylic acid, 3-hydroxy-benzaldehyde, 2,6-di-tertbutylphenol, 2,5-di-methylphenol, p-methoxyphenol, p-bromophenol and p-aminophenol. Aromatic nitrations being exothermic, the heat of reaction facilitates achieving the desired temperature. The inertial motion of the screw facilitates mixing within the threads, which aids efficient heat transfer. Temperature control was achieved using a jacket that was used to pass the heating/cooling fluid depending on the substrate. The absence of any solvent significantly expedites the reaction, and control of residence time and temperature facilitates controlled mono-nitration in an efficient manner. In all the cases, the reaction times reduced from several hours to just a few minutes, achieving complete conversion. A case study on the process economics for one such substrate shows significant savings with this approach.