Selective nitration of aromatic substrates: reaction of nitrogen dioxide with arylthallium(III) compounds

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Abstract
A method of selectively nitrating aromatic substrates is described in which nitrogen dioxide displaces a thallium(III) substituent electrophilically. High yields of the para-isomer were obtained from alkylbenzenes and a number of other substrates containing ortho–para-directing groups. Similar specificity was observed with xylenes but the process proved only partially successful when applied to mesitylene where, it is postulated, steric interaction between the methyl groups and the bulky thallium substituent inhibits the reaction. Thermodynamic control leading to meta-isomers proved impossible, a low yield of nitroarenes being obtained, the bulk of which originates by direct attack of nitrogen dioxide on regenerated aromatic substrate. Compounds with side-chains which have been reported to direct the incoming thallium substituent to an ortho-site also failed to react and an explanation for this is offered.

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