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|Title:||Kinetics and mechanism of heterogeneous cadmium sulphide and homogeneous manganese(II) catalysed oxidation of sulphur(IV) by dioxygen in acetate buffered medium|
|Authors:||Manoj, S V|
Gupta, K S
and Mn(II) catalysed autoxidation of aqueous sulphur(IV) has been studied in
detail. The CdS catalysed reaction obeys rate law (i), with k3
= 1.17×10-12 mol L-1s-1|
-d [S(IV)] /dt = k3 [S(IV)]2 [H+]-2 + k4 [CdS] [S(IV)]2 [H+]-1 .....(i)
and k4 = 4.5 × 10-7 L2.mol-2 g-1 s-1 at 30°C in acetate buffered medium. For manganese(II) catalysed reaction, the overall rate law is given by Eq. (ii) with ke =2×10-4 L mol-1s-1 and kf = 6.9×10-2 L2 mol-2 s-1
Robs = Ro + ke [Mn(II)] [S(IV)] [H+]-1 + kf [Mn(II)] [S(IV)]2 [H+]-1 ....(ii)
at 30°C in acetate buffered medium. Ro term represents the uncatalysed and /or trace metal ion catalysed rate. Ethanol strongly inhibits both the reactions indicating the operation of a radical chain mechanism. A study of the effect of ethanol shows that whereas the non-transition metal oxide catalysed sulphur(IV) autoxidation is severely inhibited, the transition metal oxide catalysed autoxidation is inhibited only slightly. This has been interpretated in terms of the operation of a radical chain mechanism in the case of former and a non-radical mechanism in the case of the latter.
|Appears in Collections:||IJC-A Vol.39A(05) [May 2000]|
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