Electrophilic aromatic substitution. Part 24. The nitration of isopropylbenzene, 2- and 4-isopropyltoluene, 1-chloro-4-isopropylbenzene, 4-isopropylanisole, and 2-bromotoluene: nitrodeisopropylation

Abstract

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_i^Pri(ipso-Wheland intermediate) is nitrodeisopropylation. From 4-isopropyltoluene W_i^Pri is also nitrodeisopropylated, but some 1,2-nitro-migration may occur. From the same compound W_i^Me 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 W_i^Pri. 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.