metals, which reduce it, and it will attack quartz. Pyrophosphoric acid is also produced:
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but this conversion is slow at room temphoerature.
The acid is tribasic: at 25°, pK1 = 2.15, pK2=7.1, pK3≈12.4. The pure acid and its crystalline hydrates have tetrahedral PO4 groups connected by hydrogen bonds. Hydrogen bonding persists in the concentrated solutions and is responsible for the syrupy nature. For solutions of concentration less than ~50%, the phosphate anions are hydrogen-bonded the liquid water rather to than to other phosphate anions.
Phosphates and the polymerized phosphate anions (for which the free acids are unknown) are discussed on page 117. Large numbers of phosphate esters can be made by the reaction
OPCIJ + 3ROH = + 3HCl
or by oxidation of trialkylphosphites. Phosphate esters such as tributylphosphate are used in the extraction
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Desters.which are strongly acidic. are completely In the antomc form at normal (and physiological) pH's: Thev are thus relatively resistant to nucleophilic attack by' either OH or H and this IS why enzymic catalysis is indispensible to achieve useful rates of reaction. Relatively little has been firmly established as yet concernmg the mechanisms of most phosphate ester hydrolyses, especially the many enzynuc ones. Two important possibilities are the following. I. One-step nucleophllic displacement (SN 2) With inversion: