Dehydroacetic Acid

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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C₈H₈O₄168.15

Keto form: 2H-Pyran-2,4(3H)-dione, 3-acetyl-6-methyl-;

3-Acetyl-6-methyl-2H-pyran-2,4(3H)-dione CAS RN®: 520-45-6.

Enol form: 2H-Pyran-2-one, 3-acetyl-4-hydroxy-6-methyl-;

3-Acetyl-4-hydroxy-6-methyl-2H-pyran-2-one CAS RN®: 771-03-9.

1 DEFINITION

Dehydroacetic Acid contains NLT 98.0% and NMT 100.5% of dehydroacetic acid (C₈H₈O₄), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

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

3 ASSAY

Procedure

Sample: 500 mg

Blank: 75 mL of neutralized alcohol

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.1 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Transfer the Sample into a 250-mL conical flask, dissolve it in 75 mL of neutralized alcohol, and add phenolphthalein TS. Titrate with Titrant to a pink endpoint that persists for NLT 30 s. Perform a blank determination.

Calculate the percentage of dehydroacetic acid (C₈H₈O₄) in the Sample taken:

Result ={[(V_S − V_B ) × N × F]/W} × 100

V_S = Titrant volume consumed by the Sample (mL)

V_B = Titrant volume consumed by the Blank (mL)

N = actual normality of the Titrant (mEq/mL)

F = equivalency factor, 168.2 mg/mEq

W = Sample weight (mg)

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

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

5 SPECIFIC TESTS

Melting Range or Temperature, Class I 〈741〉: 109°–111°

Loss on Drying 〈731〉

Analysis: Dry a sample at 80° for 4 h.

Acceptance criteria: NMT 1.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers. No storage requirements specified.

USP Reference Standards 〈11〉

USP Dehydroacetic Acid RS