Hydroquinone

General Notices

C6H6O2 110.11 123-31-9 

Action and use

Depigmenting agent.

Preparation

Tretinoin, Hydrocortisone and Hydroquinone Cream.

DEFINITION

Hydroquinone is 1,4-benzenediol. It contains not less than 99.0% and not more than 100.5% of C6H6O2, calculated with reference to the anhydrous substance.

Characteristics

Fine, white or almost white needles, which darken on exposure to light and air.

Freely soluble in water, in ethanol (96%) and in ether.

Identification

A. The light absorption, Appendix II B, in the range 230 to 350 nm, of a 0.0025% w/v solution in methanol exhibits a maximum at 293 nm.
B. Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions in water, protected from light.
(1) Dissolve the substance being examined in water to produce a solution containing 0.1% w/v of Hydroquinone.
(2) 0.1% w/v of hydroquinone BPCRS.
(3) Equal volumes of solutions (1) and (2).
chromatographic conditions
(a) Use as the coating silica gel.
(b) Use the mobile phase as described below.
(c) Apply 5 µL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, allow it to dry in air and heat until spots appear.
mobile phase

Equal volumes of dichloromethane and methanol.

system suitability

The test is not valid unless the principal spot in the chromatogram obtained with solution (3) appears as a single, compact spot.

confirmation

The principal spot in the chromatogram obtained with solution (1) corresponds to that in the chromatogram obtained with solution (2).

Tests

Melting point

172° to 174°, Appendix V A.

Water

Not more than 0.5%, Appendix IX C, Method I.

Sulfated ash

Not more than 0.5% w/w, Appendix IX A.

Assay

Dissolve 0.25 g in a mixture of 100 mL of water and 10 mL of 0.1m sulfuric acid, add 3 drops of diphenylamine and titrate with 0.1m cerium(iv) sulfate VS until a red-violet colour is reached. Each mL of 0.1m cerium(iv) sulfate VS is equivalent to 5.506 mg of C6H6O2.

Storage

Hydroquinone should be protected from light.