The Bromination of Salicylate Anions. Evidence for the Participation of the Ortho Carboxylate Group

Article abstract of DOI:10.1021/jo00223a011

Salicylate monoanions show reduced selectivity toward bromine in aqueous solution when compared to similarly substituted phenols.In particular, 5-substituted salicylate ions show ρ⁺ = -2.69 whereas for para-substituted phenols ρ⁺ = -5.21.From this and other evidence it is argued that bromine attack on such ions may involve proton transfer from the hydroxyl group to the o-carboxylate to which it is hydrogen bonded. 5-Methylsalicyclic acid (8a) forms, in part, an unstable cyclohexadienone (13) resulting from ipso bromine attack.The breakdown of 13 shows intramolecular catalysis by the o-COOH group, which has an effective molarity of 58 M.The microscopic reverse reaction of bromine on the anion 8a must, therefore, involve the o-CO2^- group, as suggested above.Implications with respect to the activating effect of hydroxyl groups on cation-forming reactions are discussed.