CAS 123-31-9 corresponds to Hydroquinone, also known as p-benzoquinone or 1,4-benzenediol. It is an aromatic dihydroxy compound with strong reducing properties, widely used in developers, antioxidants, dye intermediates, and skin whitening ingredients.

Basic Information
- Chinese name: Hydroquinone
- English name: Hydroquinone
- CAS No.: 123-31-9
- Molecular formula: C₆H₆O₂
- Molecular weight: 110.11 g/mol
- IUPAC Name: Benzene-1,4-diol
Appearance: White needle-like crystals (easily oxidized to light red or brown upon exposure to light)
- Melting point: approximately 172°C; boiling point: approximately 287°C (partial decomposition)
- Solubility: Soluble in hot water, ethanol, and ether; sparingly soluble in cold water and benzene

Key Features and Applications
1. Chemical properties: Strong reducing power, easily oxidized to benzochinone in air; weak acidity (pKa≈9.9); reacts violently with strong oxidizing agents.
2. Core Applications:
– Photography industry: Black-and-white film developers, color film stabilizers
– Chemical materials: rubber aging inhibitors, plastic antioxidants, dye intermediates (anthraquinone/azo)
– Pharmaceutical and Cosmetic: Topical whitening agents (inhibit melanin, typically 2%-5% concentration), hair dye components
– Others: Corrosion inhibitors for water treatment, monomer polymerization inhibitors

Safety Warning
Toxicity: Moderate oral toxicity (rat LD₅₀ ≈ 320-370 mg/kg); can be absorbed through the skin, causing poisoning and gray-blue syndrome; irritates the eyes and respiratory tract.
- Carcinogenicity: Classified as Group 2B by IARC (possibly carcinogenic to humans), prolonged exposure may lead to liver and kidney damage.
- Protection: Must be stored in a lightproof, sealed container, kept away from fire sources/oxidizers; wear goggles, anti-toxic gloves, and protective clothing during handling; rinse immediately with plenty of water upon contact.

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Hydroquinone CAS 123-31-9
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