Abstract
The structures of periodate ions in solution were studied by spectrophotometric methods. The presence of a dimer in solutions of high pH was established, and the dimerisation constant measured at 1.0°C and 25.0°C. It is proposed that the structure of the dimer is I[2]O[4-][9], and that of the monomer from which it is derived is HIO[5]. It is confirmed that IO[4-] is the predominant species in neutral solutions. The first and second apparent ionisation constants of ortho-periodic acid were measured using spectrophotometric and potentiometric methods. Previous measurements of the apparent second ionisation constant are in error due to the neglect of the dimerisation of the dianion. The kinetics of the oxidation of phenyl ethane diol by periodate were investigated at 1.0°C over a range of pH and diol concentration. The results, supplemented by spectrophotometric and pH change experiments show that a rapid and reversible formation of a periodate-diol complex occurs. The variation with pH of the rate-constant for the decomposition of the complex to products shows that the only species undergoing decomposition is its mono-anion. The ionisation constants of the complex the equilibrium constants for its formation, and the rate-constant for it decomposition were calculated and compared with the corresponding values for ethane diol. The oxidation of meso-1,2-diphenylethane 1:2 diol by periodate was investigated in an acetate buffer. The effect of buffer concentration and acidity on the rate were also studied. The results show that the formation of a complex is the rate-determining step. The n.m.r. spectra of certain diols and their periodate complexes were obtained. For the diols some conclusions regarding their conformations were made. Spectrophotometric studies show that neither t-butanol nor propane 1:3 diol form periodate complexes in appreciable concentration. Similar studies with glycerol show the presence of one complex at high pH; the equilibrium constant for its formation was measured at 1.0°C.