Aspects of the reactivities of co-ordinated malonate, oxalate and carbonate

by David Barrett Rands

Institution: University of Auckland
Year: 1972
Record ID: 1585132
Full text PDF: http://hdl.handle.net/2292/2116


The acid catalysed aquation of potassium trismalonatochromium(III) and potassium bismalonatodiaquochromium(III) have been studied. Almost linear plots of log kobs against the Hammett acidity function were interpreted as being due to an A-1 mechanism operating. Two kinetically different types of co-ordinated oxygen were found in a study of the oxygen exchange between the trisoxalatocobalt(III) anion and 0-18 enriched water. The carbonyl, or outer, oxygen atoms are thought to exchange by an A-2 bimolecular mechanism, while the carboxyl, or inner, oxygen atoms are thought to exchange indirectly by co-ordination of enriched oxalate groups to the cobalt centre during the anation reaction of the bisoxalatodiaquocobalt(III) ion. Finally, oxygen exchange reactions between 0-18 enriched water and various carbonato-ammine cobalt(III) complexes were studied, and it was found that generally the three oxygen atoms of the co-ordinated carbonate exchanged at equal rates, an exception being in the case of the carbonatobis(o-phenanthroline)Co(III) ion where the outer, carbonyl, oxygen exchanged faster than the inner, metal-bound, oxygen atoms. The first of these two groups has been interpreted in terms of a fast, reversible one ended dissociation process occurring, which is much faster than oxygen exchange, and the latter case in terms of a rate determining one ended dissociation step.