The electrical conductance of molten lead(II) 9,10-dihydroxyoctadecanoate and some binary mixtures with lead(II) octadecanoate

Abstract

Data are presented for electrical conductances of molten lead(II) 9,10-dihydroxyoctadecanoate and the system lead(II) octadecanoate–lead(II) 9,10-dihydroxyoctadecanoate. The lead(II) 9,10-dihydroxyoctadecanoate is prepared from 9,10-dihydroxyoctadecanoic acid which in turn is obtained from the oxidation of cis-9-octadecenoic acid by hydrogen peroxide in methanoic acid. For the mole fraction of lead(II) 9,10-dihydroxyoctadecanoate ⩽0.02, the Arrhenius plots for conductance of the mixtures show curvature similar to the behaviour of pure, unsubstituted lead(II) carboxylates, while above this mole fraction the plots display a maximum resembling that of pure lead(II) 9,10-dihydroxyoctadecanoate. Conductances are reproducible with temperature cycling up to the maximum, but show permanent decrease when cycled beyond the maximum for the mole fractions of 9,10-dihydroxyoctadecanoate 0.03. The maximum is interpreted in terms of the current carriers (Pb²⁺ ions) reacting with the dihydroxy groups to form a bridged cyclo-acid. The observed low conductance of pure lead(II) 9,10-dihydroxyoctadecanoate and the decrease in conductance of the mixtures compared with lead(II) octadecanoate is suggested to be due to the relatively small dissociation of the dihydroxy soap. Activation energies for conductance in the low-temperature region show a steady decrease with increasing mole fraction of lead(II) 9,10-dihydroxyoctadecanoate up to a certain composition and then increase. This behaviour is attributed to a change in the microscopic structure of the melt owing to the increasingly dominant role of the substituted hydroxy groups. The activation energy for the pure dihydroxy soap is close to those of other lead(II) soaps, suggesting that the major charge carrier is probably the same, i.e. the Pb²⁺ ion.