Fosfonihapporyhmä

Fosfonihapporyhmä (phosphonic acid group) is a functional group characterized by a phosphorus atom bonded to two hydroxyl groups and a substituent such as carbon. The simplest member is phosphonic acid, written as H3PO2, and the group is generally represented by the formula –PO(OH)2. The group differs from phosphoric acid, which contains three hydroxyl groups, in that it has only two OH groups directly attached to the phosphorus. In organic chemistry it is introduced by reactions that convert phosphites to phosphonic acids or by direct substitution on a phosphorus center.

The phosphonic acid group has a strong acidity, with a pKa around 1.1 to 1.5, and its ability to form stable complexes with metal ions makes it useful in catalysis and chelation chemistry. It is a key motif in pharmaceuticals, notably in the antibiotic fosfomycin and in a variety of kinase inhibitors. The group is also employed in the synthesis of organophosphorus pesticides, herbicides, and polymer cross‑linkers. Reactions of compounds containing fosfonihapporyhmä include alkylation, acylation, and condensation reactions that produce a wide array of organic and inorganic materials.

Common methods for synthesizing phosphonic acids involve the Michaelis–Arbuzov reaction, which converts alkyl halides and phosphite esters into phosphonates, the Pudovik reaction for adding phosphites to carbonyl compounds, and the Hirao coupling for forming organophosphorus bonds. Because phosphonic acids are corrosive and can be persistent in the environment, handling requires caution and proper safety protocols.