Monobenzone

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

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

DOWNLOAD PDF HERE

C₁₃H₁₂O₂ 200.24

Phenol, 4-(phenylmethoxy)-;

p-(Benzyloxy)phenol   CAS RN®: 103-16-2; UNII: 9L2KA76MG5.

1 DEFINITION

Monobenzone contains NLT 98.0% and NMT 102.0% of monobenzone (C₁₃H₁₂O₂), calculated on the dried basis.

2 IDENTIFICATION

2.1 A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K

Change to read:

2.2 B. Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U

Analytical wavelength: 292 nm

Standard solution: 10 µg/mL of USP Monobenzone RS in methanol

Sample solution: 10 µg/mL in methanol

Acceptance criteria: Absorptivities of the Standard solution and Sample solution, calculated on the dried basis, do not differ by more than 3.0%.

Delete the following:

2.3 C. Melting Range or Temperature 〈741〉, Class I

Sample: Transfer 500 mg of Monobenzone, previously dried, to a 150-mL flask fitted with a reflux condenser, using a suitable glass joint. Add 5 mL of pyridine and 3 mL of acetic anhydride. Reflux for 10 min, and cool. Add 100 mL of water and 6 mL of acetone to the flask, and insert a stopper. Cool the contents of the flask in a refrigerator for 1 h, collect the precipitate in a sintered-glass crucible, and wash the precipitate with water until no odor of pyridine remains. Dry the precipitate for 16 h in a vacuum desiccator over phosphorus pentoxide.

Acceptance criteria: The monobenzone acetate so obtained melts between 110° and 113°.

3 ASSAY

3.1 Procedure

Standard solution: 40 µg/mL of USP Monobenzone RS in methanol

Sample solution: 40 µg/mL of Monobenzone in methanol

Spectrometric conditions

• Mode: UV
• Analytical wavelength: Maximum absorbance at about 292 nm
• Blank: Methanol

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of monobenzone (C₁₃H₁₂O₂) in the portion of Monobenzone taken:

Result = (Aᵤ/Aₛ) × (Cₛ/Cᵤ) × 100

Aᵤ = absorbance of the Sample solution

Aₛ = absorbance of the Standard solution

Cₛ = concentration of USP Monobenzone RS in the Standard solution (µg/mL)

Cᵤ = concentration of the Sample solution (µg/mL)

Acceptance criteria: 98.0%–102.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.5%

5 SPECIFIC TESTS

Delete the following:

5.1 Melting Range or Temperature 〈741〉, Class I: 117°–120°

5.2 Loss on Drying 〈731〉

Analysis: Dry at 105° for 3 h.

Acceptance criteria: NMT 1.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers, and avoid exposure to temperatures above 30°.

USP Reference Standards 〈11〉

USP Monobenzone RS