Oxygen Atom Transfer The Reactions Themselves

However, interesting a case this makes for the examination of mechanism, the point must first be established that it represents a reaction worth conducting, and second that it can be carried out on a laboratory scale to give a useful amount of product. With a suitable rhenium catalyst, nearly quantitative conversions have been realized within a reasonable time. A total of 15 substrates were studied, such that the insensitivity to functional groups, steric and electronic variables were established. All the substrates examined gave essentially complete conversion to product on a scale of 1 g of PyO, irrespective of a wide range of functional groups present (26). 

Several other reactions of this general type are catalyzed by 1 and its relatives, 

Much of the kinetic data have been obtained with the specific components written in Eq. (4), after which determinations were extended to the generalized compounds RC5H4NO and PR3 to characterize the specific electronic and steric effects of substituents. It was easy to demonstrate that the reaction went to completion by applying 1H- and 31P-NMR spectroscopies. Indeed, the reaction took place so rapidly with the concentrations used (44 mM of each reagent and ImM of catalyst 1) that product formation was complete before the first NMR spectrum could be recorded. 

It therefore became more convenient to monitor the reaction progress with UV/Visible spectrophotometry, because all the pyridine N-oxides have strong absorption bands near 330 nm, with e 103Lmol 1cm 1. Two approaches for the analysis of the kinetic data were used. In the first but much less precise method, the initial reaction rates were calculated from the objective method of fitting the experimental values of [PyOL to this function (30)  

The initial rate is given by the numerical value of m1 from polynomial fitting. The rate proved to be a function of three concentration variables, [1], [PyO] and [PPh3]. Values of the rate were determined in series with two variables maintained constant and the third varied. This led to this tentative rate equation  

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