Effects of Cerium(III) Salts on Stability of Palladium(II) Salts in Acetic Acid

Abstract

Effects of cerium(III) salts on the reduction of palladium(II) salts with acetic acid, formic acid, acetaldehyde and ethylene have been studied. The decomposition of palladium(II) acetate was pseudo-first-order with respect to palladium(II) concentration (Fig.1) and accelerated upon addition of lithium acetate (Fig.2). This reaction was markedly inhibited by addition of cerous acetate even in the presence of large excess of lithium acetate (Fig.3). Similar effects were observed in the case of the reduction with formic acid, acetaldehyde and ethylene (Fig.4, 6). Apparent activation energies of the reactions with formic acid and ethylene increased in the presence of cerium(III) acetate (Fig.5, 7).
Addition of acetates of Ca(II), Ba(II), Zn(II), Cd(II), Co(II) and Mn(II) also inhibited the reduction of palladium(II) salts (Table 1, 2, 3). The magnitude of these effects was correlated with the electronegativity of the metals (Fig.9), and also with the wave length of the absorption bands of the equimolecular complexes of palladium(II) acetate and metal acetate (Fig.10).
This inhibiting effect was significantly reduced by the addition of lithium chloride for all metal acetates except cerium(III) acetate (Table 3).
It was suggested that effects of cerium(III) acetate were due to the stabilization of Pd(II) species by the formation of Pd(II)-Ce(III) complex.