diphosphate

In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates are called diphosphates. The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid. The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new bond, and which mirrors the nomenclature for anhydrides of carboxylic acids. Pyrophosphates are found in ATP and other nucleotide triphosphates, which are important in biochemistry. The term pyrophosphate is also the name of esters formed by the condensation of a phosphorylated biological compound with inorganic phosphate, as for dimethylallyl pyrophosphate. This bond is also referred to as a high-energy phosphate bond.

==Acidity== Pyrophosphoric acid is a tetraprotic acid, with four distinct pKas: , pKa1 = 0.85 , pKa2 = 1.96 , pKa3 = 6.60 , pKa4 = 9.41 The pKas occur in two distinct ranges because deprotonations occur on separate phosphate groups. For comparison, the pKas for phosphoric acid are 2.14, 7.20, and 12.37.