hydroquinones

Hydroquinone, also known as 1,4-benzenediol, is an aromatic organic compound with two hydroxyl groups in para positions on a benzene ring. Its molecular formula is C6H6O2, and it exists as a white crystalline solid. It is moderately soluble in water and more soluble in many organic solvents, and it participates readily in redox reactions, being easily oxidized to benzoquinone.

Production and occurrence: Hydroquinone is manufactured commercially on a large scale by several routes, typically via reduction of p-benzoquinone or related quinones. Small quantities occur naturally in some plants as metabolic byproducts or intermediates.

Uses: It has a history of use as a photographic developing agent and as an antioxidant and stabilizer in rubber and certain polymers. In organic synthesis it serves as a reducing agent. In cosmetics and dermatology, hydroquinone is used in some jurisdictions as a skin-lightening agent by inhibiting tyrosinase and melanin production, but its use is restricted or banned in many regions due to safety concerns.

Safety and regulation: Hydroquinone can cause skin irritation and sensitization; prolonged or repeated exposure may be associated with ochronosis, a hyperpigmentation disorder. Its safety profile has prompted reviews for carcinogenic potential. Many regulatory authorities restrict or prohibit its use in cosmetic products, and environmental considerations note toxicity to aquatic life. Proper handling and disposal are advised in industrial applications.