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The regioselectivity in the nitrosation of seven N-methyl-N'-substituted phenylureas (CH3NHCONHC6H4-G; G = H, p-CH3, m-CH3, m-CH3O, p-F, m-F, m-Br) was examined using NaNO2 and 4 different acids (diluted HCl, HCOOH, CH3COOH, CF3COOH). In all cases, the two regioisomeric products, N-nitroso-N-methyl-N'-substituted phenylureas (A) and N'-nitroso-N-methyl-N'-substituted phenylureas (B) were observed to be formed as major products and product ratios were determined by the integration of their methyl peaks in 1H-NMR. Electron donating substitutent(G) on phenyl of the ureas generally led to increase the ratio of B to A. The data have revealed that the relative sensitivity of the nitrosonium species (HONO, HCOONO, CH3COONO, CF3COONO) toward the change of electron density on nitrogen with phenyl substitutents are 1.00 : 0.93 : 0.78 : > ∼ 0.7.
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