Salicylic acid the OH group is "ortho" to the carboxyl group. It is also known as 2-hydroxybenzoic acid. It is poorly soluble in water (2 g/L at 20 °C). Aspirin (acetylsalicylic acid or ASA) can be prepared by the esterification of the phenolic hydroxyl group of salicylic acid with the acetyl group from acetic anhydride or acetyl chloride. Salicylic acid can also be prepared using the Kolbe-Schmitt reaction. Salicylic acid is used as a food preservative, a bactericidal and an antiseptic. Sodium salicylate is a useful phosphor in the vacuum ultraviolet spectral range, with nearly flat quantum efficiency for wavelengths between 10
Pyrophosphoric acid it is difficult to recrystallise from the melt. In aqueous solution pyrophosphoric acid like all polyphosphoric acids hydrolyses and eventually an equilibrium is established between phosphoric acid pyrophosphoric acid and polyphosphoric acids. When highly diluted, an aqueous solution of pyrophosphoric acid contains only phosphoric acid. Pyrophosphoric acid is a medium strong inorganic acid. Anions, salts, and esters of pyrophosphoric acid are called pyrophosphates. While pyrophosporic acid is corrosive, it is not known to be otherwise toxic. The name pyrophosphoric acid was given by a "Mr. Clarke of Glasgow" in 1827 who is credited with its discovery following the heating to