Austin, Rupert Philip; (1993) Novel oxidation reduction reactions in trifluoromethanesulphonic acid. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes three apparently disparate chemical processes. However, all are linked by the fact that they each formally involve unusual oxidation reduction reactions made possible not by the oxidative power of the trifluoromethanesulphonic acid solvent, but rather by its high acidity. 1,3-Dimethyl-2-chlorobenzene has been found to undergo an unusual reaction with 1,4-dinitrobenzene in trifluoromethanesulphonic acid at 70 °C. The principle products of the reaction after quenching with water are 4,4',4"-trichloro-3,5,3',5',3",5"-hexamethyltriphenylmethanol and 1,4-diaminobenzene. The reaction was shown to occur also with many aromatic nitro compounds in place of the 1,4-dinitrobenzene, but not with nitromethane. The overall mechanism of the reaction is discussed in terms of a complex sequence of oxidation reduction reactions, along with a number of forward and reverse benzylation reactions. Kinetic and acidity dependence studies were used to show that it is the O-protonated form of the aromatic nitro compound that facilitates the oxidation reduction processes, and protonated aromatic nitro compounds are proposed to have previously unknown oxidative properties. In light of the work described above, the mechanism of cyclisation of 2-alkylnitrobenzenes to give 3-alkylanthianils in trifluoromethanesulphonic acid has been reassessed. This reaction has also been shown to be initiated by protonation of the nitro group, and the mechanism is discussed in terms of a rate-determining intramolecular hydrogen shift from the benzylic carbon atom to an oxygen atom of the protonated nitro group, followed by several rapid steps. 2-Nitrobenzyl alcohol, 2-nitro benzylchloride, and 2-nitrosobenzaldehyde have been found to react with trifluoromethanesulphonic acid to give 4-amino-3-carboxyphenyltriflate in good yield. The mechanism is discussed, and a cyclic nitrenium ion intermediate is proposed. This work also led to a brief study of the Bamberger rearrangement of N-phenylhydroxylamine in trifluoromethanesulphonic acid.

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