Abstract
Studies of the kinetics and mechanism of the oxidation by periodate in aqueous solution of cis- and trans- cyclo-hexane diols (chapter 2), (+)- and meso- tartaric acids (chapter 3), and mandelic acid (chapter 4) are described in this thesis. Previous work on the periodate oxidation of the cyclo-hexane diols has been extended to various conditions of pH and temperature. As in many oxidations by periodate, these reactions proceed via a cyclic periodate ester. The equilibrium constant for formation of the ester from the trans-diol has been determined over a wide range of conditions, but the equilibrium constant for the cis- diol is smaller, and was only determined at pH 10.06 and 10°C. The UV spectra of the cyclic esters of both diols were obtained, and compared with the spectra of the cyclic esters of other diols. The formation of the cyclic ester is base catalysed; catalysis by pivalate and phosphate in the reaction of the cis- diol was investigated in detail and catalytic constants obtained. Ammonia catalysis of the formation of the cyclic ester from the trans- diol was investigated in detail, and acetate catalysis was detected, but in general the formation of the ester from this diol is fast and its decomposition is the slowest step of the overall reaction. The product of oxidation, hexane-1,6-dial , was identified by n. m. r. All previous work on the kinetics of oxidation of tartaric acid by periodate was confined to the (+)-isomer. The present work consisted of a kinetic study of the oxidation of the (+)- and meso- isomers, in buffered and unbuffered solutions. In general, the meso- isomer is oxidised more rapidly; this is in contrast to the relative rates of oxidation of (+)- and meso-2,3-butanediols. The dependence of rate on pH is complex and could not be explained completely. No kinetic evidence for the formation of an intermediate was found, but the observation of buffer catalysis indicated that formation of a cyclic ester is rate-determining over at least part of the pH range. The kinetics of the oxidation of mandelic acid by periodate were investigated at 40°C and pH range 2-9. At low pH the reaction is second order, but above pH 4 the kinetics become complex, due in part to the oxidation of the first product, benzaldehyde. The stoicheiometry of the reaction was investigated.