Abstract
The work described in this thesis includes a mechanistic study of the periodic acid / pinacol system. Before any interpretation of the oxidation of pinacol by periodic acid could be made an accurate knowledge of the species present in periodate solutions was essential. Thus the thesis is divided into two parts: PART ONE: A spectrophotometric study of periodates and PART TWO: A kinetic study of the periodate / pinacol reaction. PART ONE: The dimeric periodate ion in solution, the structure of which is probably H[2]I[2]O[10][-4], does not undergo a dehydration or ionisation reaction over the temperature range 1° to 70° and over the pH range 8 to 12. The equilibrium constant for the formation of this ion decreases with increasing temperature and a value for the heat of the dimerisation reaction has been obtained. The possibility of the existence of species such as H[3]I[2]O[10][-3] or HI[2]O[10][-5] in appreciable concentration is considered to be remote. It is proposed that the structure of the periodate trianion is H[2]IO[6][-3] and that of the dianion H[3]IO[6][-2]. The first, second and third ionisation constants of periodic acid were measured spectrophotometrically at various temperatures in the range 1° to 70°. PART TWO: The kinetics of the oxidation of pinacol by periodic acid were investigated over a range of pH at 0° and at 25°. The complex variation of second order rate constant with pH has been quantitatively explained in terms of a mechanism involving the formation of a periodate/diol monoester, and cyclisation to a diester, which decomposes to the products. The occurence of general acid-base catalysis has also been explained.