3,4-dihydroxybenzoic acid is a kind of organic acid with white to light brown aciculary crystals, which naturally exists in the leaves of Pteridophyllaceae aconitum, the leaves of Holly, salvia miltiorrhiza, hibiscus and other plants as well as traditional Chinese medicine, and has a variety of active substances of traditional Chinese medicine. The substance is a water-soluble phenolic acid that dissolves in water, ethanol and ether, and releases carbon dioxide when it breaks down in boiling water. Aqueous solution of 3,4-dihydroxybenzoic acid changes color and turns dark red when it meets sodium bicarbonate, and green when it meets ferric chloride.
There are many synthetic processes for 3,4-dihydroxybenzoic acid. For example, vanillin can be used as raw material, and 3,4-dihydroxybenzoic acid can be obtained by alkali fusion oxidation demethylation and acidification. 3,4-dihydroxybenzoic acid can also be obtained by oxidizing piperol with potassium permanganate and hydrolyzing it with aluminum chloride. Because 3,4-dihydroxybenzoic acid has good antibacterial effect on dysentery bacillus, typhoid bacillus, Escherichia coli, Pseudomonas aeruginosa, bacillus subtilis, alkali producing bacillus, staphylococcus aureus and other bacteria, it has been widely used in the medical field.