Phosphonic acid

Editor-In-Chief: Henry A. Hoff

Overview
In inorganic chemistry, phosphonic acid is a phosphorus oxoacid with a formula of H3PO3, more commonly known as phosphorous acid. It exists in solution as two tautomers, the major one being HP(O) (OH)2 and the minor one P(OH)3. The former is sometimes termed phosphonic acid, with the latter designated as phosphorous acid. Sometimes confusingly, both these names are also used to refer to H3PO3 in general, i.e. both tautomers.

In organic chemistry, a phosphonic acid is a compound with the general formula RP(O)(OH)2.

An example of an organic phosphonic acid is Foscarnet.

An oligophosphonic acid refers to a few molecules of phosphonic acid condensed into a molecule with the loss of water.

A general formula for such oligophosphonic acids is (HPO)nOn-1(OH)2, where n = 2, 3, 4, etc., oligo-. A polyphosphonic acid can have dozens of such phosphonic acid units condensed in a row with the loss of H2O for each unit added on.

An example that incorporates triphosphonic acid: ethane-1,1,2-triphosphonic acid. In some phosphonic anhydrides (RPO2)3, R can be tBu, 2-methylphenyl, 2,4,6-trimethylphenyl.