3,4-dihydroxybenzoic acid, a needle-like crystal soluble in hot water, ethanol, and ether, varies in appearance from white to light brown, depending on its purity. 3,4-dihydroxybenzoic acid not only breaks down in boiling water, but also releases carbon dioxide. 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 of 3,4-dihydroxybenzoic acid. For example, 3,4-dihydroxybenzoic acid can be obtained from vanillin by alkali fusion oxidation demethylation followed by acidification. If piperanol is used as raw material, 3,4-dihydroxybenzoic acid can be synthesized, oxidized with potassium permanganate and hydrolyzed with aluminum trichloride to get 3,4-dihydroxybenzoic acid. Because 3,4-dihydroxybenzoic acid has good antibacterial effect on shigella, Typhoid, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, alkali producing bacillus, staphylococcus aureus and other bacteria, it has a wide range of applications in the medical field.