In alkaline aqueous media octacyanohmgstate(V) ions are reduced to [W(CN)(8
)](4-) ions by vanillin which is oxidised mainly to bisvanillin. The reacti
on proceed in three stages. In the first stage which was studied by stopped
-flow technique the initial reaction is first-order in both [W(CN)(8)](3-)
and [van(-)] and is catalysed by alkali-metal cations. The rate of reaction
increases in the series of alkali metal ions in the order Na+ < K+ < Cs+.
The apparent activation parameters, DeltaH(#) are equal to 20.7 +/- 1.4 (Na
+) and 14.9 +/- 1.1 (K+) kJ mol(-1) and DeltaS(#) are equal to -174 +/- 20
(Na+) and -188 +/- 25 (K+) J mol(-1) K-1. The mechanism of the first stage
is discussed.