Hydroquinone
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
C6H6O2 110.11
1,4-Benzenediol.
Hydroquinone CAS RN®: 123-31-9; UNII: XV74C1N1AE.
Hydroquinone contains not less than 99.0 percent and not more than 100.5 percent of C6H6O2, calculated on the anhydrous basis.
Packaging and storage-Preserve in tight, light-resistant containers.
USP REFERENCE STANDARDS (11)-
USP Hydroquinone RS
Identification-
Change to read:
A: Spectroscopic Identification Tests (197), Infrared Spectroscopy: 197K (CN 1-May-2020).
B: Prepare a solution of it in methanol containing approximately 1 mg per mL, and prepare a similar solution of USP Hydroquinone RS. Apply 5 µL of each solution to a suitable thin-layer chromatographic plate (see Chromatography (621)) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of equal volumes of methanol and chloroform until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Heat on a hot plate or under a lamp until spots appear: the R
value of the principal spot obtained from the solution under test corresponds to that obtained from the Standard solution.
C: A 1 in 40,000 solution in methanol exhibits an absorbance maximum at 293 ± 2 nm.
MELTING RANGE (741): between 172° and 174°.
WATER DETERMINATION, Method I (921): not more than 0.5%.
RESIDUE ON IGNITION (281): not more than 0.5%.
Assay-Dissolve about 250 mg of Hydroquinone, accurately weighed, in a mixture of 100 mL of water and 10 mL of 0.1 N sulfuric acid, add 3 drops of diphenylamine TS, and titrate with 0.1 N ceric sulfate VS until a red-violet endpoint is reached. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N ceric sulfate is equivalent to 5.506 mg of C6H6O2.
