Semiempirical calculations show that the intermediate formed by reaction between peroxydisulfate anion and the phenolate ion (the Elbs oxidation) is the species resulting from reaction of the tautomeric carbanion rather than the one resulting from attack by the oxyanion. This is confirmed by synthesis of the latter intermediate by reaction between Caro's acid dianion (peroxymonosulfate) and some nitro-substituted fluorobenzenes. This intermediate rearranges preferentially to give the phenol ortho-sulfate rather than the para-sulfate characteristic of the Elbs oxidation. This reaction of an arylperoxysulfate to give a phenol ortho-sulfate is a new rearrangement. © 2002 Elsevier Science Ltd. All rights reserved.