2,5-Dihydroxybenzoic acid, alias 5-hydroxysalicylic acid, commonly known as DBH, also known as gentisic acid, is a polyhydroxycarboxylic acid, which is a secondary product of salicylic acid after renal metabolism. 2,5-Dihydroxybenzoic acid is Chemicalbook white needle crystal, soluble in hot water, ethanol and ether, insoluble in chloroform, benzene and carbon disulfide. When heated for a long time above 150 °C, it will decompose into carbon dioxide and hydroquinone, which is unstable in the air and turns blue in the presence of ferric chloride. 2,5-Dihydroxybenzoic acid is a hydroquinone compound, which is prone to oxidation reaction and is often used as an antioxidant excipient in the pharmaceutical industry. 2,5-Dihydroxybenzoic acid is also an antipyretic analgesic and an important pharmaceutical intermediate. 2,5-Dihydroxybenzoic acid is also a commonly used matrix in matrix-assisted laser desorption ionization mass spectrometry, and its application is very wide. White needle crystals. Melting point 204.5-205 ℃. Soluble in water, ethanol and ether, insoluble in chloroform, benzene and carbon disulfide. When heated for a long time above 150°C, it will decompose into carbon dioxide and hydroquinone, which is unstable in the air. It turns blue in the presence of ferric chloride.