Gallic Acid: Properties, Uses & FAQs for Researchers

Gallic acid is a naturally occurring trihydroxybenzoic acid found widely in plants, valued in research for its potent antioxidant, antimicrobial, and anti-inflammatory properties.

Chemical Name

3,4,5-Trihydroxybenzoic acid

Molecular Formula

C₇H₆O₅

Molecular Weight

170.12 g/mol

CAS Number

149-91-7

Appearance

White to light tan crystalline powder

Solubility

Soluble in water, ethanol, and methanol; sparingly soluble in diethyl ether

SKU

G421763

What Is Gallic Acid?

Gallic acid (3,4,5-trihydroxybenzoic acid, CAS 149-91-7) is a naturally occurring polyphenolic compound belonging to the hydroxybenzoic acid subclass of phenolic acids. It is found in a wide variety of plants, including gallnuts, sumac, witch hazel, tea leaves, oak bark, and numerous fruits. In plant metabolism, gallic acid serves as a key biosynthetic precursor to hydrolyzable tannins such as gallotannins and ellagitannins.

Structurally, gallic acid features a benzene ring with three hydroxyl groups at the 3, 4, and 5 positions and a carboxylic acid group at the 1 position. This arrangement confers excellent electron-donating capacity, underpinning its strong free-radical scavenging activity. Gallic acid is commercially available as the anhydrous form or as the monohydrate; researchers should confirm the form when preparing molar solutions.

Chemical Properties and Stability

Gallic acid is a white to light tan crystalline powder with a molecular weight of 170.12 g/mol (anhydrous). Key physicochemical properties relevant to laboratory use include:

• Melting point: approximately 250–253 °C (with decomposition)
• pKa: The carboxylic acid group has a pKa of approximately 4.4; the phenolic hydroxyl groups have higher pKa values, making gallic acid predominantly anionic at physiological pH.
• Solubility: Freely soluble in hot water and ethanol; moderately soluble in cold water; sparingly soluble in diethyl ether; practically insoluble in most non-polar solvents.
• Stability: Gallic acid is susceptible to oxidation, particularly in alkaline conditions or upon prolonged exposure to light and air. Solutions should be prepared fresh or stored under inert atmosphere. Solid material should be stored in a cool, dry, dark place, tightly sealed.

Because of its phenolic nature, gallic acid can undergo autoxidation in aqueous solution, forming colored oxidation products. Antioxidant assays using gallic acid as a standard should account for this sensitivity.

Key Research Applications

Gallic acid is a versatile research reagent employed across multiple scientific disciplines:

• Antioxidant assays: Gallic acid is widely used as the reference standard in total phenolic content determination via the Folin–Ciocalteu method, with results expressed as gallic acid equivalents (GAE). It is also employed in DPPH, ABTS, and FRAP radical-scavenging assays.
• Antimicrobial research: Studies have demonstrated activity of gallic acid against a range of Gram-positive and Gram-negative bacteria, as well as certain fungi, supporting its use in research into natural preservatives and adjunctive antimicrobial agents.
• Anti-inflammatory and anticancer studies: Gallic acid modulates multiple signaling pathways including NF-κB and MAPK cascades. It is frequently used as a tool compound in cell-based assays investigating apoptosis, cell cycle arrest, and pro-inflammatory cytokine suppression.
• Tannin chemistry and food science: As a structural unit of hydrolyzable tannins, gallic acid is used in studies of tannin hydrolysis, astringency, and protein-polyphenol interactions.
• Synthesis and materials science: Gallic acid serves as a building block for the synthesis of propyl gallate (an approved food antioxidant), epigallocatechin gallate (EGCG) analogs, and metal-organic frameworks (MOFs) owing to its multidentate chelating capability.

Storage, Handling, and Safety

Storage: Store gallic acid in a tightly sealed container away from light, heat, and moisture. Recommended storage temperature is 2–8 °C or room temperature in a cool, dry environment, depending on the supplier's specification. Avoid alkaline conditions. Keep away from strong oxidizing agents.

Handling: Standard laboratory precautions apply. Wear appropriate personal protective equipment (PPE) including gloves, safety glasses, and a lab coat. Avoid inhalation of dust. Work in a well-ventilated area or fume hood when handling bulk quantities.

Safety classification: Gallic acid is generally regarded as having low acute toxicity at typical laboratory working concentrations. It is not currently classified as a controlled substance. However, researchers should consult the current Safety Data Sheet (SDS) provided with the product for up-to-date hazard classifications, first-aid measures, and disposal guidelines.

Disposal: Dispose of gallic acid and its solutions in accordance with local institutional and governmental regulations for phenolic waste.

Ordering and Product Information

Aladdin Scientific offers gallic acid under SKU G421763. Researchers requiring a related reference standard may also consult SKU G131992 as noted in the product cross-reference.

When ordering, please confirm:

• The required form (anhydrous vs. monohydrate) and purity grade suitable for your assay.
• Pack size and quantity appropriate for your experimental throughput.
• Any applicable certificate of analysis (CoA) requirements, including HPLC purity data.

For bulk inquiries, custom purity grades, or technical support, contact Aladdin Scientific's customer service team. Current pricing, availability, and promotional offers can be viewed on the product page or by contacting your regional Aladdin representative.

Frequently asked questions

What is gallic acid used for in the laboratory?

Gallic acid is primarily used as the reference standard for total phenolic content assays (Folin–Ciocalteu method, reported as gallic acid equivalents), as well as in DPPH, ABTS, and FRAP antioxidant assays. It is also employed as a tool compound in antimicrobial, anti-inflammatory, and anticancer cell-based studies, and as a synthetic building block for propyl gallate and other polyphenol derivatives.

How should gallic acid solutions be prepared and stored?

Gallic acid dissolves readily in ethanol and methanol, and is moderately soluble in water. For aqueous solutions, gentle warming or the addition of a small volume of ethanol as co-solvent can improve dissolution. Because gallic acid is prone to oxidative degradation, aqueous solutions should be prepared fresh, protected from light, and used promptly. If storage is necessary, keep solutions under an inert atmosphere (e.g., nitrogen) at low temperature and discard if discoloration occurs.

What is the difference between gallic acid anhydrous and gallic acid monohydrate?

Gallic acid monohydrate contains one molecule of water per molecule of gallic acid, giving a molecular weight of approximately 188.14 g/mol, compared to 170.12 g/mol for the anhydrous form. When preparing molar or weight-per-volume solutions, researchers must use the correct molecular weight for the form in hand. The anhydrous form (CAS 149-91-7) is more common for high-precision analytical work. Always verify the form stated on the certificate of analysis before use.

Is gallic acid the same as tannic acid?

No. Gallic acid (MW 170.12 g/mol) is a simple monomeric phenolic acid, whereas tannic acid is a complex mixture of polygalloyl glucose esters (hydrolyzable tannins) with much higher molecular weights (typically around 1,700 g/mol). Gallic acid is a hydrolysis product of tannic acid. The two reagents are not interchangeable; researchers should select the appropriate compound based on their specific experimental requirements.

What purity grade of gallic acid is appropriate for antioxidant assays?

For quantitative antioxidant assays such as the Folin–Ciocalteu total phenolic method, DPPH, or FRAP, a purity of ≥98% (HPLC) is generally recommended to ensure accurate standard curves. Confirm the purity and form (anhydrous vs. monohydrate) on the certificate of analysis supplied with each lot. Contact Aladdin Scientific for CoA details for SKU G421763.

References

1. Singleton, V. L., Orthofer, R., & Lamuela-Raventós, R. M. (1999). Analysis of total phenols and other oxidation substrates and antioxidants by means of folin-ciocalteu reagent. Methods in Enzymology, 299, 152–178. doi:10.1016/S0076-6879(99)99017-1
2. Kahkonen, M. P., Hopia, A. I., Vuorela, H. J., et al. (1999). Antioxidant activity of plant extracts containing phenolic compounds. Journal of Agricultural and Food Chemistry, 47(10), 3954–3962. doi:10.1021/jf990146l
3. Badhani, B., Sharma, N., & Kakkar, R. (2015). Gallic acid: a versatile antioxidant with promising therapeutic and industrial applications. RSC Advances, 5(35), 27540–27557. doi:10.1039/C4RA13881H

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