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Rate-acidity profiles have been obtained for the nitrosation of anisole, 2,6-dimethylanisole (DMA), and 2,6-dimethylphenol (DMP) in aqueous sulphuric acid. The phenol is more reactive than the corresponding anisole, and D M A has a more shallow profile than anisole. A deuterium kinetic isotope effect (k,/k,) of 4.0 for [4-2H]anisole indicates that the product of nitrosation of anisole in 46.5% sulphuric acid (p-nitrosophenol) is formed by slow proton loss from the Wheland intermediate. Intense colours were associated with the nitrosation of these compounds when nitrous acid was in excess.The kinetics of nitrous acid-catalysed nitration of anisole were studied in 43.0 and 47.0% sulphuric acid; the product isp-nitrophenol. Nitrosation followed by oxidation by NV was the major pathway at these acidities. The other pathway has a kinetic form given by k, = k,[N~~'][NV], consistent with a process where oxidation by NV is rate-limiting. Product studies show that p-nitrophenol is formed at lower acidities and 0 -and p-nitroanisole at higher acidities. A mechanism is suggested involving a radical cation species, which would predominate at higher acidities and account for the k, pathway at lower acid it ies.The nitrous acid-catalysed nitration of D M A gives 2,6-dimethyl-4-nitroanisole in higher yield as the acidity increases.