Phosphonous

Phosphonous is a term used in chemistry to describe compounds containing the phosphonous acid group. This functional group has the general formula R-P(OH)2, where R is an organic substituent. Phosphonous acids are a type of organophosphorus compound and are related to phosphinic acids (R2P(OH)) and phosphonic acids (R3P(OH)).

The central phosphorus atom in a phosphonous acid is bonded to one organic group, two hydroxyl groups, and one lone pair of electrons. This arrangement gives the phosphorus atom a pyramidal geometry. Phosphonous acids are typically less stable than their phosphinic and phosphonic acid counterparts and can undergo oxidation or disproportionation reactions.

The synthesis of phosphonous acids can be achieved through various methods, often involving the reaction of organometallic reagents with phosphorus trihalides followed by hydrolysis. For example, a Grignard reagent can react with phosphorus trichloride to form an organodichlorophosphine, which upon hydrolysis yields the phosphonous acid.

Phosphonous acids and their derivatives can exhibit a range of chemical properties depending on the nature of the organic substituent. They can act as acids, releasing protons from the hydroxyl groups. The phosphorus atom can also participate in coordination chemistry. While less extensively studied than phosphonic acids, phosphonous acid derivatives find applications in areas such as catalysis and as intermediates in the synthesis of other organophosphorus compounds.