Kinetics and mechanism of replacement of sulphite in the pentacyano(sulphito)ferrate(II) ion by cyanide ion
- 1 January 1974
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 3,p. 344-346
- https://doi.org/10.1039/dt9740000344
Abstract
The kinetics of replacement of sulphite by cyanide ion in Na5[Fe(CN)5SO3] in aqueous solution follow the rate law –dln[Fe(CN)5SO3 5–]/dt=k1k2[CN–]/(k–1[SO3 2–]+k2[CN–]), which is consistent with reactions (i) and (ii). [Fe(CN)5SO3]5– [graphic omitted] [Fe(CN)5]3–+ SO3 2–(i), [Fe(CN)5]3–+ CN– [graphic omitted] [Fe(CN)6]4–(ii) At 43 °C, pH 10·80, and 1M ionic strength k1=(9·50 ± 0·21)× 10–4 s–1. The [Fe(CN)5]3– intermediate is sufficiently long-lived to exhibit selective reactivity toward different reagents as shown by the competition factor k2/k–1= 8·76 ± 0·53. The kinetic data are considered as evidence for a limiting SN1 mechanism. The competition factor has been interpreted in terms of free-energy changes resulting from desolvation processes of the competitors.Keywords
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