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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Maragh, Paul T.,; Dasgupta, Tara, P
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Article Title
Kinetics and mechanisms of the formation and reactivity of m-hydroxo-m-sulfito-bis[bis(1,2-diaminoethane) chromium (III)]
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Journal Title
Journal of the Chemical Society. Dalton Transactions
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Reprint Status
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Date of Publication
1993
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Issue ID
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Page(s)
2401-2406
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Notes
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Abstract
The kinetics of formation of [(en)2Cr(m-OH)(m-SO3)Cr(en)2]3+ cation from [(en)2Cr(m-OH2Cr(en)2]4+ (en=1,2-diaminoethane) in aqueous buffered sulfite solution has been studied spectrophotometrically. This formation consisted of two steps; first a rapid uptake of SO2 by the ring-cleaved mono-m- hydroxo species [(OH) (en)2Cr(m-OH)Cr (en)2(OH)]3+ to form a terminal O-bonded sulfito intermediate. This reaction was studied at 600 nm in the ranges 3.78 pH 5.47, 20 q 30C and 0.03 [S]r 0.05 mol dm-3([S]r=[SO2]+[HSO3-]+[SO2-3]. The rate constant for uptake of SO2 at 25C was found to be (8.7 0.1) x 107 dm3 mol-1 s-1 with DH = 6.5 0.9 kJ mol-1 and DS = -71 2 J K-1 mol-1. The second step in which the sulfito intermediate undergoes a ring closure to form the (m-OH) (m-SO3) complex with the elimination of H2O (or OH-) was studied in the ranges 2.46 pH 4.46, 19.9 q 29.9C and 0.03 [S]r 0.05 mol dm-3, and the rate constant for this process, k3, was found to be 0.68 s-1 at 25.2C with DH = 28 1 kJ mol-1 and DS = -155 3 J K-1 mol-1. The rate constant for ring closure with the loss of OH- was found to be 0.15 s-1 at 25.2C with DH =66 7 kJ mol-1. The (m- OH) (m-SO3) complex decomposes in acid to give free sulfite with a rate constant of (7.8 0.1) x 10-5 s-1 at 25C which is independent of [H+] over the range 0.01-1.0 mol dm-3 HC104. It undergoes additional sulfite uptake (k = 3.01 x 10-4 s-1, 25C, DH = 91 8 kJ mol-1, DS = -8.7 29.6 J K-1 mol-1) to form a possible disulfito product. The reaction was found to be independent of [S]r but dependent on [H+] over the ranges 2.11 pH 7.28, 0.03 [S]r [S]r 0.05 mol dm-3 and 20 q 30C....
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