Melamine-(H2SO4)3/Melamine-(HNO3)3 instead of H2SO4/HNO3: A safe system for the oxidation/nitration reaction

Solid acid reagents are unique acid catalysts/reagents that have become popular over the last two decades. They have proved to be useful to chemists in the laboratory and industry due to the good activation of adsorbed compounds, reaction rate enhancement, selectivity and easier work-up [1]. In continuation of our studies on the application of solid acids and oxidation of heterocyclic compounds [2] and nitration of phenols [3] we found that melamine readily reacts with concentrated sulfuric acid and fuming nitric acid to give melamine-(H2SO4)3 (I) and melamine-(HNO3)3 (II). It is interesting to note that these exothermic reactions are fast, easy and clean not requiring any work-up (Figure 1) Mixture of these new solid acids acts as unique powerful system instead of hazardous H2SO4/HNO3 system for the oxidation of urazoles and dihydropyridines as well as nitration of active aromatic rings under heterogeneous, solvent/metal-free and mild conditions..