Propylthiouracil

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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C₇H₁₀N₂OS 170.23

4(1H)-Pyrimidinone, 2,3-dihydro-6-propyl-2-thioxo-;

6-Propyl-2-thiouracil  CAS RN^®: 51-52-5; UNII: 721M9407IY.

1 DEFINITION

Propylthiouracil contains NLT 98.0% and NMT 100.5% of propylthiouracil (C₇H₁₀N₂OS), calculated on the dried basis.

IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197A or (USP 1-May-2022) 197K

2 ASSAY

2.1 Procedure

Sample: 300 mg

Analysis: Transfer the Sample to a 500-mL conical flask, and add 30 mL of water. Add from a buret 30 mL of 0.1 N sodium hydroxide VS, heat to boiling, and agitate until the solution is complete. Wash down any particles on the wall of the flask with a few milliliters of water, add 50 mL of 0.1 N silver nitrate while mixing, and boil gently for 7 min. Cool to room temperature and continue to titrate with 0.1 N sodium hydroxide VS, determining the endpoint potentiometrically using a glass-calomel electrode system. Each milliliter of 0.1 N sodium hydroxide is equivalent to 8.512 mg of propylthiouracil (C₇H₁₀N₂OS).

Acceptance criteria: 98.0%–100.5% on the dried basis

3 IMPURITIES

3.1 Residue on Ignition 〈281〉: NMT 0.1%

Delete the following:

3.2 Selenium 〈291〉

Sample: 200 mg

Acceptance criteria: 0.003% (USP 1-May-2022)

3.3 Ordinary Impurities 〈466〉

Solvent: Methanol

Application volume: 10 µL

Eluant: Toluene, ethyl acetate, and formic acid (50:45:5) in a nonequilibrated chamber

Visualization: 1

Acceptance criteria: Meets the requirements

4 SPECIFIC TESTS

Melting Range or Temperature 〈741〉: 218°–221°

Loss on Drying 〈731〉

Analysis: Dry at 105° for 2 h.

Acceptance criteria: NMT 0.5%

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed, light-resistant containers.

USP Reference Standards 〈11〉

USP Propylthiouracil RS