Crotamiton

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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C₁₃H₁₇NO        203.28

2-Butenamide, N-ethyl-N-(2-methylphenyl)-.

N-Ethyl-o-crotonotoluidide CAS RN®: 483-63-6; UNII: D6S404XD0H.

Crotamiton is a mixture of cis and trans isomers containing not less than 97.0 percent and not more than 103.0 percent of C₁₃H₁₇NO.

1 Packaging and storage

Preserve in tight, light-resistant containers.

USP REFERENCE STANDARDS (11)-

USP Crotamiton RS

2 Identification

Change to read:

A: Spectroscopic Identification Tests (197), Infrared Spectroscopy: 197F (CN 1-May-2020)

Change to read:

B: Spectroscopic Identification Tests (197), Ultraviolet-Visible Spectroscopy: 197U (CN 1-May-2020)

Solution: 20 µg per mL.

Medium: cyclohexane.

C: To about 10 mL of a saturated solution in water add a few drops of potassium permanganate TS: a brown color is produced, and a brown precipitate is formed on standing.

SPECIFIC GRAVITY (841): between 1.008 and 1.011 at 20°.

REFRACTIVE INDEX (831): between 1.540 and 1.543 at 20°.

RESIDUE ON IGNITION (281): not more than 0.1%.

3 Bound halogen

Place 4 drops in a 3-mm (ID) test tube, and add calcium oxide to a height of 1 cm. Heat the tube in a flame, starting from the top, until the reaction is complete, then ignite for a short time. Transfer the contents to a beaker containing 10 mL of water, acidify with nitric acid, and filter. To the filtrate add 0.2 mL of silver nitrate solution (1 in 60): any opalescence obtained is not more than that obtained from a blank solution treated in the same manner.

4 Assay

Transfer about 50 mg of Crotamiton, accurately weighed, to a 100-mL volumetric flask, add cyclohexane to volume, and mix. Transfer 10.0 mL of this solution to a 250-mL volumetric flask, dilute with cyclohexane to volume, and mix. Determine the absorbance of this solution and of a solution of USP Crotamiton RS in the same medium having a known concentration of about 20 µg per mL in 1-cm cells at the wavelength of maximum absorbance at about 242 nm, with a suitable spectrophotometer, using cyclohexane as the blank. Calculate the quantity, in mg, of C₁₃H₁₇NO in the Crotamiton taken by the formula:

2.5C(A_u/A_s)

in which C is the concentration, in µg per mL, of USP Crotamiton RS in the Standard solution; and A_u and A_s are the absorbances of the assay solution and the Standard solution, respectively.