An Alternative Method for the Selective Synthesis of Ortho-nitro Anilines Using Bismuth Nitrate Pentahydrate

Nitroaromatic compounds are important scaffolds used for the synthesis of a variety of compounds, such as explosives, herbicides, dyes, perfumes and pharmaceuticals. Bismuth nitrate pentahydrate is a widely used reagent in organic synthesis; however, its utility as a nitrating agent for anilines is underexplored.

The aim of this work is to propose and find the proper reaction conditions of an alternative nitrating agent constituted by a mixture of bismuth nitrate / acetic anhydride in DCM with a series of substituted anilines under mild reflux.

Several anilines having both activating and deactivating substituents in the ortho, meta and para positions were the substrate for the nitration reaction. Experimental conditions were performed in "one-pot" conditions before product purification.

Bi(NO₃)₃•5H₂O demonstrated to be effective and somehow regioselective when it came to the nitration of anilines in the ortho position. Although other products were also identified under these conditions, in most cases, the ortho derivative was the major or even the only product obtained with moderate to high yields in the range of 50% - 96%.

Bi(NO₃)₃•5H₂O is an efficient and safe nitrating agent since the use of concentrated and corrosive acids like sulfuric and nitric is avoided; furthermore, bismuth nitrate is low-priced and no special care nor equipment is required.