| Boiling Point | 285°C (lit.) |
| Melting Point | 172–175°C (lit.) |
| Color | White |
| Linear Formula | C6H4-1,4-(OH)2 |
| Formula Weight | 110.11 |
| Physical Form | Crystal-powder |
| Chemical Name or Material | Hydroquinone |
| UN Number | 3077 |
| Molecular Weight | 110.11 g/mol |
| SMILES String | Oc1ccc(O)cc1 |
| Solubility | 50 mg/mL (water), clear |
| CAS Number | 123-31-9 |
| EC Number | 204-617-8 |
| NACRES | NA.77 |
| PubChem Substance ID | 57654278 |
| MDL Number | MFCD00002339 |
| InChI | 1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H |
| InChI Key | QIGBRXMKCJKVMJ-UHFFFAOYSA-N |
| Beilstein/REAXYS Number | 605970 |
| Quality Level | 200 |
| Reference Grade | ReagentPlus®, ≥99% |
| Biological Source | Synthetic |
Hydroquinone is a simple aromatic diol — a benzene ring with two hydroxyl groups in the para position — that also occurs naturally in coffee, tea, and wine at low levels. Its readily reversible oxidation to benzoquinone makes it an effective reducing agent, which is the chemistry behind its long-standing role as a photographic developing agent and polymerization inhibitor, while its ability to inhibit melanogenesis has driven its use (under regulatory controls) in dermatological and cosmetic skin-lightening formulations.
Hydroquinone’s largest historical industrial use is as a photographic developing agent, exploiting its reducing chemistry to convert exposed silver halide to metallic silver. It’s also a standard polymerization inhibitor, added to reactive monomers (like acrylates and styrene) during manufacturing and storage to prevent premature polymerization. In regulated cosmetic and dermatological contexts, it’s used topically to inhibit melanogenesis for treating hyperpigmentation conditions such as melasma and lentigines. In research, it’s used as a reagent for sodium-bisulfite DNA conversion and in Timm’s histochemical staining.
Sigma Aldrich’s GHS classification includes suspected carcinogenicity and mutagenicity warnings — please ensure this reaches your EHS/compliance team.
