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
Diffusion of Cl-through a cationexchange membrane was measured using WI-. Although the results combined with earlier permeability data do not permit calculation of all thermodynamic friction coefficients, it is difficult to explain the membrane behaviour on the basis of a pore model. An approximation proposed by Spiegler is not supported by the experiments.
Using the formalism of irreversible thermodynamics, general conditions are derived for osmotic salt and solvent permeation. It is found that in many types of low charged membranes abnormal osmosis may occur; for the more selective ion exchangers, however, solvent flow is usually directed towards the concentrated phase, whereas electrolyte flux may be parallel or opposed to the activity gradient, regardless of the nature of the membrane. Application of the theoretical results in a particular system requires membrane composition data and leads to a set of “friction coefficients” rik. Determination of all rik values even in a simple system like sodium chloride, water and membrane requires an extensive set of experimental data. Though the complete set has not yet been obtained, rik values could be estimated from data on osmosis, transference, conductivity and diffusion. The friction between co‐ion and membrane appears to have a predominant effect on dialysis efficiency.
Transport through a polyelectrolyte membrane in aqueous binary electrolyte solutions is described by six constants, either six permeabilities Lik (with i, k = 1, 2, 3, including i = k) or friction coefficients fik (with i, k = 1, 2, 3, 4; i ≠ k). In a porous, selective membrane the friction of the co‐ion with the polymer matrix can be neglected, whereas the molecular friction coefficient of small ions and solvent approaches its free solution value. The required experimental information reduces to three independent measurements, for which electro‐osmosis, conductivity and co‐ion diffusion may be taken. A check on the fik values thus calculated is provided by expressing the ratio of electric transference numbers in friction quantities and comparing with experiment. The proposed device does not involve concentration averages; it is shown to be compatible with experimental data.
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