Abstract
In Section 1 of this work, an investigation of the equilibria between monomeric periodate species has been carried out using relaxation techniques. Rate and equilibrium parameters of the system are reported. In acid solutions, equilibria between orthoperiodic acid, its monoanion, and metaperiodate monoanion are significant, and evidence is offered to suggest that the hydration-dehydration processes involve pentaco-ordinated periodate species as steady-state intermediates. In alkaline solution it has been established that both hydrated and dehydrated forms contribute to periodate dianions, whereas the dehydrated mesoperiodate trianion predominates over the orthoperiodate trianion. It is proposed that the mechanisms of the hydration and dehydration processes are intimately associated with water of solvation. In Section 2, several aspects of the oxidation of vicinal diols by periodate are discussed. Evidence is presented to show that formation of the monoester intermediate of reaction is by nucleophilic attack of a hydroxyl oxygen at iodine, and cyclisation is buffer catalysed. It is proposed that the hydroxyl oxygen possessing the larger electron density due to diol substituent groups is responsible for the formation of the monoester. Inductive and stereochemical aspects of the reaction are discussed with data for several diols, particularly cis & trans isomers of the cyclohexane-1,2-diols and butane-2,3-diols.