Electrophilic aromatic substitution. Part 29. The kinetics and products of the solvolyses in aqueous sulphuric acids of 2-cyano-3,4-dimethyl-4-nitrocyclohexa-2,5-dienyl acetate: the non-occurrence of an intramolecular 1,3-migration of the nitro-group in the solvolytic reactions of the diene. The kinetics and products of nitration of 2,3-and 3,4-dimethylbenzonitrile
The kinetics in 61.8–79.5% H2SO4 and the products formed in 61.8–84.3% H2SO4 for the solvolyses of the above-named diene have been determined. The reactions are interpreted as involving concurrent elimination of nitrous acid and AAL1 generation of the same ipso-intermediate as arises in the nitration of 2,3-dimethylbenzonitrile. This intermediate reacts by intermolecular rearrangement (as is proved by the isolation from the solvolyses of 2,3-dimethylbenzonitrile and the trapping of nitronium ion by reaction with 4-fluorophenol), by nucleophilic capture by water, and by 1,2-intramolecular rearrangement to 2,3-dimethyl-4-nitrobenzonitrile. The results permit the partitioning of the overall solvolytic rate coefficient and the demonstration that the derived coefficient for the reaction competing with the elimination depends on acidity as would be expected for an AAL1 reaction. The elimination of nitrous acid is also acid-catalysed and may not be a simple E1 reaction. The solvolytic reactions of the diene do not lead to a 1,3-intramolecular rearrangement of the nitro-group and the observed 1,3-rearrangement of the diene to give 2,3-dimethyl-5-nitrobenzonitrile under non-solvolytic conditions appears to be a thermal reaction of the diene molecule. By combining the solvolysis results with those for the nitration of 2,3-dimethylbenzonitrile in 70.4–82.5% H2SO4 it is shown that the major primary consequence of the nitration is ipso-attack and that it is possible to determine the positional reactivities in the nitrile.