Kojic acid CAS：501-30-4

Kojic acid appears as colorless, prismatic or needle-shaped crystals. It is readily soluble in water, ethanol and acetone, slightly soluble in diethyl ether, ethyl acetate, chloroform and pyridine, and insoluble in most other organic solvents. It can be crystallized using acetone or ethyl acetate, and can also be purified by vacuum sublimation at 150–200°C. Its melting point is recorded in literature as 151–154°C. 5,7-diethyl kojic acid and its derivatives show characteristic absorption maxima at 315 nm and 255 nm respectively. Kojic acid is sensitive to light and heat. When a 0.5% aqueous solution is heated at 100°C for 3 hours or exposed to sunlight for 5 hours under different pH conditions, it turns yellow to brown at pH 5–7, while remaining relatively stable at pH 4. It reacts with ferric chloride to produce a distinct red color, which can be used for quantitative analysis. In addition, kojic acid can reduce Fehling’s reagent and ammoniacal silver nitrate solution. Its molecular structure contains a hydroxyl group adjacent to the carbonyl group, allowing it to form salts with various metals. The other hydroxyl groups can further react to form ether and ester derivatives.