Abstract Wet molybdate sulfuric acid (= dioxo [bis (sulfato-κO)] molybdenum; MSA), a new solid acid, can be used in combination with sodium nitrite (NaNO 2) to transform a variety of secondary amines to the corresponding N-nitroso compounds under mild, heterogeneous conditions (Table). The process has several advantages: the reagents are inexpensive and non-hazardous, the reaction is clean, fast, and high-yielding, and MSA can be readily ...