Phosphate ions, reaction with hydrogen

DFP is stable and in the absence of moisture can be stored for considerable periods without decomposition. Hydrolysis in neutral aqueous solution occurs slowly. The reaction is catalyzed by both acid and base. At pH>7, hydrolysis is proportional to the hydroxide ion concentration and at high pH is extremely rapid. The product is always diisopropyl phosphoric acid (equation 38), except under more forcing conditions which eventually produce phosphate (and propan-2-ol). The hydrolysis is strongly catalyzed by the addition of a-effect nucleophiles such as hypochlorite, peroxide, hydroxylamine, hydroxamic acid and their substituted derivatives . Under basic conditions, such nucleophiles (HOX) are present as the anion and are responsible for the rapid initial displacement of fluoride ion from DFP to give intermediate 36 shown in equation 39. Displacement of OX by hydroxide ion regenerates the catalytic OX anion. The reaction with hydrogen... 

As a third and final example of a chain reaction, we shall consider a net reaction that produces sulfate and hydrogen phosphate ions.7 The scheme is more intricate than the earlier ones. It starts with the homolytic dissociation of S2Ojj- as one of two parallel initiation steps, and utilizes SO -, HO, and HPO - as intermediates. The scheme suggested is shown here, and one can easily allow for the products that are identical save for protonation ... 

The close similarity between the structures of the amine phosphate and the final product of the reaction of the amine phosphate with metal (Zn2+) is shown in Fig. 7.24. The amine phosphate consists of a hydrogen-bonded network with water molecules and resembles the loosely hydrogen-bonded structures involved in the synthesis of aluminosilicates. The mechanism of formation of the initial ladder phosphate can be understood in terms of the displacement of the water molecules from the amine phosphate by the Zn2+ ions. 

In phosphorus removal, the phosphorus must be in the phosphate form and, because the reaction occurs in water, the phosphate ion originates a series of reactions with the hydrogen ion. The series is as follows ... 

Hydrolysis of meperidine hydrochloride in dilute hydrochloric acid is a specific hydronium ion catalyzed reaction which is first order with respect to hydrogen ion concentration. A positive, primary salt effect was noted in dilute acid solution. The hydrolysis of the protonated form of meperidine hydrochloride was found to be first order with respect to meperidine hydrochloride over a wide range of hydrogen ion concentration (pH 1-7) A catalytic effect with respect to meperidine hydrolysis was exhibited by di-hydrogen phosphate ion, the only phosphate ion studied in the investigation, and the possibility of similar effects with respect to other buffer systems should be recognized. The rate of hydrolysis was found to be very slow in the pH range of 3.5 to 5 with maximum stability at pH U.01. The calculated half-life for meperidine hydrochloride at pH U.9 is 23.8 years at 25 °C. 

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