The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3-96.4% sulfuric acid a t 25' and in 65.0-90.4% sulfuric acid a t 75.5' by spectrophotometric methods. The pK, of azoxybenzene in aqueous sulfuric acid has also been determined. I t is found thathlthough azoxybenzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (11) a s the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.
A facile synthesis of 4,6-dideoxy-3-O-methyl-D-xylo-hexose (D-chalcose) is described, which involves the preparation of methyl 4,6-dichloro-4,6-dideoxy-3-O-methyl-D-galactopyranoside (2) by a reaction with sulfuryl chloride, and its reduction to the dideoxy sugar by hydrogenation over Raney nickel.
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