4571-14-6Relevant academic research and scientific papers
"Ipso" aromatic nitration in the gas phase
Attina,Cacace,Ricci
, p. 4424 - 4429 (2007/10/03)
Nitration of selected dialkylbenzenes, including o- and p-cymene, p-rerf-butyltoluene, p-diisopropylbenzene, and p-di-rert-butylbenzene, by protonated methyl nitrate, (CH3OH-NO2)+, has been investigated in the gas phase in the pressure range from 10~8 to 720 Torr by Fourier transform ion cyclotron resonance (FT-ICR) and collisional activated dissociation (CAD) mass spectrometry and by the radiolytic technique. The results provide the first demonstration of gas-phase electrophilic aromatic nitrodealkylation and a quantitative evaluation of its efficiency relative to the competing nitration process. Dealkylation occurs exclusively following attack of the nitrating cation at the "ipso" position, which promotes intramolecular migration of the alkyl substituent to the nitro group, yielding O-alkylated or O-protonated ions. The positional selectivity of the nitration, and the relative rate of the "ipso" attack by (CH3OH-NO2)+ are discussed, especially as regards the role of the intrinsic steric requirements of the alkyl group, which in the gas phase is unaffected by the many complicating factors, e.g., solvation, ion pairing, etc., operative in solution. The results are compared with those concerning condensed-phase nitrodealkylation and the related nitrodesilylation reaction.
Electrophilic aromatic substitution. Part 24. The nitration of isopropylbenzene, 2- and 4-isopropyltoluene, 1-chloro-4-isopropylbenzene, 4-isopropylanisole, and 2-bromotoluene: Nitrodeisopropylation
Manglik, Ajay K.,Moodie, Roy B.,Schofield, Kenneth,Tobin, Geoffrey D.,Coombes, Robert G.,Hadjigeorgiou, Panicos
, p. 1606 - 1616 (2007/10/02)
The kinetics and products of nitration in aqueous sulphuric acid of the title compounds have been studied. 4-Isopropyl-phenol and -anisole are nitrated at or near the encounter rate. In 65-79% H2SO4 2-isopropyltoluene suffers ca. 25% ipso-attack; the only fate of W iPri (ipso-Wheland intermediate) is nitrodeisopropylation. From 4-isopropyltoluene WiPri is also nitrodeisopropylated, but some 1,2-nitro-migration may occur. From the same compound WiMe may be captured by water, rearrange, or give 4-methylacetophenone; a mechanism is proposed for the formation of the last compound. Nitrodeisopropylation occurs without the assistance of water. With 4-isopropylanisole, demethoxylation and nitrodeisopropylation are consequences of the formation of WiPri. The results are consistent with increasing attack at C-4 with increasing acidity, loss of isopropyl without assistance from water, and decomposition of the unobserved intermediate, 4-isopropyl-4-nitrocyclohexa-2,5-dienone, by two processes. One, acid-catalysed process gives 4-nitrophenol and possibly 4-isopropyl-2-nitrophenol. The other, probably radical, process gives 4-isopropyl-2-nitrophenol. In contrast to 4-bromotoluene, 2-bromotoluene is not nitrodebrominated.
