Neutral and alkaline solutions in water of the nitrophenyl phosphates are very stable in the dark. These compounds. however, and the meta derivative in particular were found to undergo a remarkable rapid hydrolysis when exposed to visible or ultra-violet light. The reaction velocity is independent of the hydrogen ion concentration at pH's between 3 and 12 but increases strongly at higher pH's. Nitrophenol and phosphoric acid could be traced as the products of this photochemical reaction. The reaction proved to be zero order; the rate did not change upon varying of the temperature from 25" to 40" C. The nitrophenyl sulphates s h m an analogous behaviour but for the fact that the increase of reaction rate at higher pH's does not occur and that the difference in the rate of photochemical reaction between the meta compound on the one hand and the ortho and para derivatives on the other hand are even greater than with the phosphates. The experimental evidence points to a purely photochemical (non sensitized) reaction, the nature of which is tentatively discussed. W e wish to report a remarkable example of the promotion of a very simple (ionic) reaction by light. During investigations into the reactivity of nitrophenyl phosphates towards water, alcohols, amines and other nucleophilic reagents it was observed that hydrolysis of such esters was very strongly promoted by light.In the dark hydrolysis could hardly be demonstrated even after Iong periods of time in an alkaline medium at room temperature. This was to be expected on the strength of the presence of the negative charge due to the ionized phosphate group. In diffuse daylight, however, hydrolysis becomes noticeable in a period of one or two hours, the solutions turning yellow as nitrophenolate ions are formed. The presence of free inorganic phosphate could be demonstrated. The three isomers -ortho, rneta-and para-nitrophenyl phosphate -show the phenomenon which is most pronounced with the mefa derivative.Closer investigations with solutions of the latter compound revealed that the rate of this light-accelerated hydrolysis decreases at pH values
The synthesis of L2Pd-ethylene complexes (L = triphenylphosphine, tricyclohexylphosphine, or tri-otolyl phosphite) and of L2Pd (L == tricyclohexylphosphine) is reported ; these easily accessible compounds may serve as starting materials in oxidative addition reactions.
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