Electronic effects in the N-nitrosation of N-benzylpivalamides

A series of N-4-R-benzylpivalamides (R = MeO, Me, H, CF3, and NO2) was nitrosated using a standardized solution of N2O4 in CDCl3 at -40 degreesC. The reactions, which produced the corresponding N-4-R-benzyl-N-nitrosopivalamides, were followed by H-1 NMR spectroscopy. The rate of nitrosation was found to vary in a systematic way with the nature of the 4-R-group on the aromatic ring. Thus, electron-releasing groups increased the rate of the reaction, whereas electron-withdrawing ones decelerated N-nitrosation. In a similar fashion, the nitrosations were accelerated in polar solvents but were slower in solvents of low polarity. The sensitivities of N-nitrosation to these intra- and intermolecular electronic effects are compared to those from a previous study examining the dependence of the kinetics of nitrosoamide thermolyses on the same factors.