Anethole

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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C₁₀H₁₂O   148.20

Benzene, 1-methoxy-4-(1-propenyl)-, (E)-;

(E)-p-Propenylanisole CAS RN: 4180-23-8.

Synthetic CAS RN: 104-46-1.

1 DEFINITION

Anethole is obtained from Anise Oil and other sources, or it is prepared synthetically. It contains NLT 98.0% and NMT 102.0% of (E)-1-methoxy (ERR 1-Nov-2022)-4-(1-propenyl) benzene (or trans-anethole) (C₁₀H₁₂O).

2 IDENTIFICATION

A. SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197F

B. CHROMATOGRAPHIC IDENTITY

Analysis: Proceed as directed in the Assay for trans-Anethole.

Acceptance criteria: The retention time of the major peak, excluding the internal standard peak, of the Sample solution corresponds to the anethole peak of the Standard solution.

3 ASSAY

ASSAY FOR trans-ANETHOLE

Internal standard solution: 2 mg/mL of USP Menthol RS (internal standard) in hexanes

Standard solution: 2 mg/mL of USP Anethole RS in Internal standard solution (use a freshly prepared solution)

Sample solution: 2 mg/mL of Anethole in Internal standard solution (use a freshly prepared solution)

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.53-mm x 30-m capillary; bonded with a 1.0-µm layer of phase G16

Temperatures

Injection port: 250°

Detector: 250°

Column: 125° (isothermally)

Carrier gas: Helium

Flow rate: 10 mL/min

Injection volume: 1.0 µL

Injection type: Split injection; split ratio of 10:1

Run time: 30 min

System suitability

Sample: Standard solution

[NOTE-The relative retention times for menthol and trans-anethole are about 0.5 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 15 between menthol and trans-anethole

Tailing factor: 0.8-2.0 for menthol and trans-anethole peaks

Relative standard deviation: NMT 2.0% for the peak response ratio of trans-anethole to the internal standard

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of trans-anethole (C₁₀H₁₂O) in the portion of Anethole taken:

Result = (R_u/R_s) × (C_s/C_u) × 100

R_u= peak response ratio of trans-anethole to the internal standard (peak response of trans-anethole/peak response of the internal standard) from the Sample solution

R_s= peak response ratio of trans-anethole to the internal standard (peak response of trans-anethole/peak response of the internal standard) from the Standard solution

C_s=concentration of USP Anethole RS in the Standard solution (mg/mL) C_{S} = 1

C_u= concentration of Anethole in the Sample solution (mg/mL)

Acceptance criteria: 98.0%-102.0%

4 IMPURITIES

LIMIT OF CIS-ANETHOLE, P-ANISALDEHYDE, AND OTHER VOLATILE IMPURITIES

Internal standard solution: 0.01 mg/mL of USP Menthol RS (internal standard) in hexanes

System suitability solution: 4 mg/mL of USP Anethole RS in Internal standard solution after exposure to UV light for 1 h

Standard solution: 0.01 mg/mL of USP Anethole RS and 0.01 mg/mL of USP p-Anisaldehyde RS in Internal standard solution (use a freshly prepared solution)

Sample solution: 2 mg/mL of Anethole in Internal standard solution (use a freshly prepared solution)

Chromatographic system: Proceed as directed in the Assay, except use a Run time of 60 min.

System suitability

Samples: System suitability solution and Standard solution

[NOTE-See Table 1 for the relative retention times.]

Table 1

Suitability requirements

Resolution: NLT 5 between cis-anethole and trans-anethole, System suitability solution

Relative standard deviation: NMT 5.0% for the peak response ratio of trans-anethole to the internal standard and NMT 5.0% for the peak response ratio of p-anisaldehyde to the internal standard, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of p-anisaldehyde in the portion of Anethole taken:

Result = (R_u1/R_s1) x (C_s1/C_u) × 100

R_u1= peak response ratio of p-anisaldehyde to the internal standard (peak response of p-anisaldehyde/peak response of the internal standard) from the Sample solution

R_s1= peak response ratio of p-anisaldehyde to the internal standard (peak response of p-anisaldehyde/peak response of the internal standard) from the Standard solution

C_S1 = concentration of USP p-Anisaldehyde RS in the Standard solution (mg/mL)

C_u = concentration of Anethole in the Sample solution (mg/mL)

Calculate the percentage of cis-anethole or any other unspecified volatile impurity in the portion of Anethole taken:

Result = (R_u2/R_s2) × (C_s2/C_u) × 100

R_u2 = peak response ratio of cis-anethole or any other unspecied impurity to the internal standard (peak response of cis-anethole or any other unspecied impurity/peak response of the internal standard) from the Sample solution

R_s2 = peak response ratio of trans-anethole to the internal standard (peak response of trans-anethole/peak response of the internal standard) from the Standard solution

C_s2 = concentration of USP Anethole RS in the Standard solution (mg/mL)

C_u = concentration of Anethole in the Sample solution (mg/mL)

Acceptance criteria: Disregard peaks that are less than 0.05% for any unspecified impurities and any peaks due to solvent.

Total impurities including cis-anethole, p-anisaldehyde, and all other unspecified impurities: NMT 2.0%

LIMIT OF PHENOLS

Sample: 1 mL

Analysis: Shake the Sample with 20 mL of water, and allow the liquids to separate. Pass the water layer through a filter paper previously moistened with water, and to 10 mL of the filtrate add 3 drops of ferric chloride TS.

Acceptance criteria: No purple or purplish color is produced.

5 SPECIFIC TESTS

SPECIFIC GRAVITY (841): 0.983-0.988

DISTILLING RANGE, Method I (721): 231°-237", a correction factor of 0.063°/mm being applied as necessary

OPTICAL ROTATION, Angular Rotation (781A): -0.15° to +0.15°

REFRACTIVE INDEX (831): 1.557-1.561

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight, light-resistant containers.

LABELING: Label to indicate whether it is of natural sources or is prepared synthetically.

USP REFERENCE STANDARDS (11)

USP Anethole RS

USP p-Anisaldehyde RS

USP Menthol RS