Resorcinol

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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» Resorcinol contains not less than 99.0 percent and not more than 100.5 percent of C₆H₆O₂, calculated on the dried basis.

Packaging and storage—Preserve in well-closed, light-resistant containers.

USP Reference standards 〈11〉—

USP Resorcinol RS

1 Identification—

Change to read:

A: ▲ Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K ▲ (CN 1-May-2020) —

[Note—If necessary to recrystallize, dissolve in dehydrated alcohol.]

B:

Dissolve 100 mg in 2 mL of 1 N sodium hydroxide, add 1 drop of chloroform, and heat the mixture: an intense crimson color is produced.

Then add a slight excess of hydrochloric acid: the color changes to pale yellow.

C:

To 10 mL of a solution (1 in 100) add 1 drop of ferric chloride TS: a blue-violet color is produced, and it fades slowly.

Melting range 〈741〉

Between 109° and 111°.

Loss on drying 〈731〉

Dry it over silica gel for 4 hours: it loses not more than 1.0% of its weight.

Residue on ignition 〈281〉

Not more than 0.05%.

Phenol—

Heat gently a solution (1 in 20): the odor of phenol is not perceptible.

Catechol—

To 10 mL of a solution (1 in 20) previously mixed with 2 drops of 1 N acetic acid add 0.5 mL of lead acetate TS: no turbidity is produced.

Ordinary impurities 〈466〉—

Test solution: methanol.

Standard solution: methanol.

Eluant: a mixture of hexanes and ethyl acetate (70:30).

Visualization: 17 and then 1.

Application volume: 10 µL.

Limits: not more than 1.0%.

2 Assay—

Dissolve about 1.5 g of Resorcinol, accurately weighed, in water to make 500.0 mL. Transfer to an iodine flask 25.0 mL of the resulting solution, add 50.0 mL of 0.1 N bromine VS, dilute with 50 mL of water, add 5 mL of hydrochloric acid, and at once insert the stopper in the flask. Shake for 1 minute, allow to stand for 2 minutes, and add 10 mL of potassium iodide TS while slightly loosening the stopper. Shake thoroughly, allow to stand for 5 minutes, remove the stopper, and rinse it and the neck of the flask with 20 mL of water into the flask. Titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding starch TS as the endpoint is approached. Perform a blank determination.

From the volume of 0.1 N sodium thiosulfate VS used, calculate the volume, in mL, of 0.1 N bromine VS consumed by the resorcinol.

Each mL of 0.1 N bromine is equivalent to 1.835 mg of C₆H₆O₂.