Kinetics of thallium(III)[and mercury(II)]-catalysed aquations of the chloropenta-amminecobalt(III) and cis- and trans-dichlorobis(ethylenediamine)cobalt(III) complexes
- 1 January 1971
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A
- p. 118-122
- https://doi.org/10.1039/j19710000118
Abstract
The thallium(III)-catalysed aquations of Co(NH3)5Cl2+ and cis- and trans-Co(en)2Cl2 +(first chloride) show a first-order dependence on [TlIII] over a wide range. There is no evidence in the case of the cis-complex for the formation of a stable binuclear adduct as in the corresponding mercury(II)-catalysed aquation. Enthalpies of activation are 3·5–6·1 kcal mol–1 less and entropies of activation 4–5 e.u. less than those observed for the uncatalysed reactions. Rate constants for the aquation of Co(NH3)5Cl2+ remain essentially unchanged as the [H+] is decreased from 2·0M to 0·3M(the amount of TlOH2+ increases from 4 to 21%) and TlOH2+ appears to be about as effective a catalyst as Tl3+. In each case Hg2+ is more effective than Tl3+ and with Co(NH3)5Cl2+(at 35°) HgCl+(0·59 | mol–1 s–1)∼ Hg2+(0·55) > Tl3+(0·034) > TlCl2+(0·012). The charge on the catalyst appears to be important in the determination of this order of effectiveness.Keywords
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