It is prepared by treatment of 2-hydroxybenzoic acid (I) with phosphorous pentachloride. The reaction involves a first stage in which (I) is converted by PCl5 to the corresponding acyl chloride (II) upon release of phosphorous oxychloride, which reacts immediately with the free phenolic group of (II), giving rise to the acid trichloride (III). In a second stage, (III) is hydrolyzed with enough water to give the 2-phosphonoxybenzoic acid (IV). The reaction is carried out in a one-step process, which involves chlorination, phosphonation and hydrolysis, the isolation of the intermediate (III) being unnecessary. The final product is recovered from the reaction mixture by precipitation with a suitable inert organic solvent and is submitted to further purification.

It is prepared by treatment of 2-hydroxybenzoic acid (I) with phosphorous pentachloride. The reaction involves a first stage in which (I) is converted by PCl5 to the corresponding acyl chloride (II) upon release of phosphorous oxychloride, which reacts immediately with the free phenolic group of (II), giving rise to the acid trichloride (III). In a second stage, (III) is hydrolyzed with enough water to give the 2-phosphonoxybenzoic acid (IV). The reaction is carried out in a one-step process, which involves chlorination, phosphonation and hydrolysis, the isolation of the intermediate (III) being unnecessary. The final product is recovered from the reaction mixture by precipitation with a suitable inert organic solvent and is submitted to further purification.