ONIUM IONS .20. AMBIDENT REACTIVITY OF THE NITRONIUM ION - NITRATION VS OXIDATION OF HETEROORGANIC (S, SE, P, AS, SB) COMPOUNDS - PREPARATION AND NMR SPECTROSCOPIC (C-13,N-15,P-31) STUDY OF NITRO AND NITRITO ONIUM IONS

The reaction of nitronium salts with sulfides, selenides, phosphines, arsines, and stibines has been investigated. Nitronium hexafluorophosphate (tetrafluoroborate) reacts rapidly at 78 °C with diaryl, aryl alkyl, and dialkyl sulfides, affording sulfoxides as the major products. Selenides, phosphines, arsines, and stibines react equally readily, giving the corresponding oxygenated products. In the case of diphenyl sulfide, less than 5% of competing ring C-nitro products were obtained. These observations suggest the intermediacy of nitrito onium ions (˂X+-ONO) being in equilibrium with the related nitro onium ions (˂X+-NO2). The present study represents the first demonstration of the ambident reactivity of the nitronium ion in solution chemistry (i.e., competing attack on oxygen vs. nitrogen of N02 +). The equilibrium was confirmed by carrying out trans nitrosation of N, N-dimethylaniline in the presence of these onium salts. 13C, 15N, and 31P NMR studies of the onium salts are also reported, showing that nitro onium salts are irreversibly transformed into nitrito onium salts either upon raising the temperature or during prolonged reaction times. © 1979, American Chemical Society. All rights reserved.