The oxidation kinetics and reaction time mechanisms of some small molecules, thiosulfate, sulfite, and dimethylamine, have been studied in reaction with several transition metal chelates. The rate data were tested for correlation with the Marcus theory for outer sphere electron transfer.
The reaction of thiosulfate with a series of (Os (LL)$\sb3$) $\sp{3+}$ complexes (where LL = phen; bpy; 4,7-(Me)$\sb2$phen; 5,6-(Me)$\sb2$phen; and 5-Cl phen) was found to proceed by a simple bimolecular reaction, first order in both (S$\sb2$O$\sb3\sp{2-}$) and (Os (III)). The second order rate constants for these reactions were 1.12 $\times$ 10$\sp2$, 1.30 $\times$ 10$\sp2$, 2.74, 63.0, and 1.47 $\times$ 10$\sp4$ M$\sp{-1}$ s$\sp{-1}$ respectively. The reduction potential for the redox couple S$\sb2$O$\sb3\sp{-/2-}$ was calcuated at 1.30 V. A linear free energy relationship was found; the slope of the plot of log k$\sb{12}$ vs. log K$\sb{\rm eq}$ was 0.48, in excellent agreement with the Marcus LFER prediction of 0.50. This is the first good evidence for an outer sphere electron transfer mechanism for the oxidation of thiosulfate.
An analytical method to analyze the polythionates was developed using ion-pair chromatography with conductivity detection and tetraalkylammonium salts for separation. The technique was rapid and sensitive, Tri-, tetra-, and pentathionate were separated along with thiosulfate in less than 15 minutes with detection limits in the sub ppm range for most species.
The reaction of sulfite by (Ru (NH$\sb3)\sb4$phen) $\sp{3+}$ has also been studied, along with the reverse reaction of Ru (II) with the sulfite radical generated by pulse radiolysis. The forward reaction exhibited evidence of sulfite radical attack of the phen ring system, the first time this has been observed. The second order rate constant for the forward reaction was 1.00 $\times$ 10$\sp5$ M$\sp{-1}$ s$\sp{-1}$, and the reverse reaction had a rate constant of 1.92 $\times$ 10$\sp8$ M$\sp{-1}$ s$\sp{-1}$. The results did not agree with the Marcus prediction. The other reaction studied was the oxidation of dimethylamine with IrCl$\sb6\sp{2-}$. A range for the rate constant from 300 to 900 M$\sp{-1}$ s$\sp{-1}$ was found. The self exchange rate constant of dimethylamine was calculated as 400 M$\sp{-1}$ s$\sp{-1}$ assuming an outer-sphere mechanism.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16178 |
| Date | January 1988 |
| Creators | Rabin, Steven Barry |
| Contributors | Stanbury, David M. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 219 p., application/pdf |
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