Homogeneous permanganate oxidation in non-aqueous organic soution. A stable organomanganese intermediate in the oxidation of endo-dicyclopentadiene
✍ Scribed by Toshio Ogino
- Publisher
- Elsevier Science
- Year
- 1980
- Tongue
- French
- Weight
- 227 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
The absorption spectrwn of a stable organomanganese iratemediate in the homogeneously catalyaed pemangamzte oxkkrtion of endo-d~cyctopentadiene in a non-aqueous system W8 directly determined. The formation and the decompositim of the intermediate mre monitored by folZoting the changes of ab8orbances. It is generally accepted that cyclic manganese(V) esters are formed in the initial step of the reactions of permanganate ion with olefins. 2,3 The lifetime of these intermediates is transient in aqueous solutions and the spectrophotometric detections have been accomplished by stopped-flow techniques.495 A longer-lived manganese(V) ester is known in the oxidation of thymine as the only one example of stable intermediate.6 This letter describes the first direct spectrophotometric detection of a stable organomanganese intermediate in non-aqueous organic solution. Permanganate ion solubilized in CH2C12 by use of equimolar amount of triethylbenzylamnonium chloride oxidizes 1 to give a homogeneous dark brown solution which gives varying proportions of the diol (2) and the dialdehyde (2) upon treatments with aqueous solutions.' The ratio p:? is pH dependent and 2 predominates with alkaline conditions. OH: 1. KMn04-TEBACl, CH2C12 2. H20 *zm and/or @ OHC 2 When a 2-fold excess of _l_ was used, MnOi was consumed in few minutes and the absorption spectrum of the reaction mixture was determined 5 minutes after the reaction was complete.7 The spectrum exhibits a strong absorption maximum at 275 nm (e=BOOO)' and a long shoulder in the visible region (Fig. 1). It is of interest to note that the spectrum in the visible region resembles that of the organomanganese(V) intermediate in the oxidation reaction of crotonate anion by aqueous MnO4 solution.' The latter spectrum was determined via monitoring the spectrum changes at 28 wave lengths by stopped-flow techniques and analyzing the kinetic data. When the reaction mixture was allowed to stand at O"C, the absorption intensity decreased gradually with the formation of precipitates of Mn02, and after 24 hours, the solution became completely colorless (Fig. 1). The change is of first order and the lifetime was found to be ca. 3.2 hours. The product of this anhydrous decomposition of the intermediate was identified as a mixture of the diol (2) and the dialdehyde (2) in ca. 1:l ratio. However, the dialdehyde was found to be a mixture of stereoisomers at formyl groups, suggesting the occurrence of a basic species