Pyrofosforzuur

Pyrofosforzuur, also known as pyrophosphoric acid or diphosphoric acid, is an inorganic acid with the formula H4P2O7. It is the condensation product of two phosphoric acid molecules, formed by the removal of a water molecule: 2 H3PO4 → H4P2O7 + H2O. In aqueous solution it behaves as a polyprotic acid and hydrolyzes readily to phosphoric acid (H3PO4).

Preparation and occurrence

Pyrofosforzuur is typically prepared by dehydration of phosphoric acid using strong dehydrating agents such as phosphorus pentoxide (P2O5) or concentrated sulfuric acid, or by controlled heating of phosphoric acid. It does not occur freely in nature and is mainly obtained in laboratory or industrial settings for use as a reagent.

Properties

The compound forms colorless, hygroscopic crystals and is highly polar and acidic. In solution it exists in multiple protonated forms, reflecting its polyprotic character. Pyrofosforzuur is a strong dehydrating agent and rapidly hydrolyzes in water to yield phosphoric acid.

Reactions and applications

Pyrofosforzuur readily forms esters with alcohols and amines to give diphosphate (pyrophosphate) esters. It is used as a dehydrating agent in organic synthesis and as a source of pyrophosphate for preparing phosphate esters and related compounds. Its salts, known as pyrophosphates (for example disodium pyrophosphate), are widely used as buffering agents and food additives, including as leavening agents in baking.

Safety

Pyrofosforzuur is corrosive and should be handled with appropriate protective equipment. It reacts with water and bases with heat release and can cause severe irritation to skin and eyes.