Silica sulfuric acid/NaNO2 as a novel heterogeneous system for the chemoselective N-nitrosation of secondary amines under mild conditions

Neat chlorosulfonic acid reacts with silica gel to give silica sulfuric acid in which sulfuric acid is immobilized on the surface of silica gel via a covalent bond. A combination of silica sulfuric acid and sodium nitrite in the presence of wet SiO2 was used as an effective nitrosating agent for the nitrosation of secondary amines to their corresponding nitroso derivatives under mild and heterogeneous conditions in excellent yields.