Abstract Efficient N‐nitrosation of amines, amides, and ureas, and also S‐nitrosation of thiols were performed with dinitrogentetroxide impregnated on activated charcoal (N2O4/charcoal) in CH2Cl2 at room temperature. High selectivity was observed for N‐nitrosation of dialkyl amines, N‐alkylamides and N‐alkylureas. Dealkylation and N‐nitrosation of trialkylamines were also performed by this reagent