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Gallic acid monohydrate
1. Basic Information
Name: Gallic acid monohydrate
Alias: 3,4,5-Trihydroxybenzoic acid monohydrate
CAS No.: 5995-86-8
Molecular Formula: C?H?O?·H?O
Molecular Weight: 188.13
Category: Natural polyphenol raw material, antioxidant, analytical reagent, pharmaceutical intermediate, food additive, cosmetic antioxidant
2. Physical and Chemical Properties
Physical Properties
- Appearance: White or off-white crystalline needle powder
- Odor: Odorless, slight astringent taste
- Solubility: Soluble in hot water, ethanol, methanol, acetone; slightly soluble in cold water; insoluble in benzene, chloroform, petroleum ether
- Melting Point: 220–225 ℃ (decomposes, loses crystal water at ~120 ℃)
- Density (predicted): 1.68 g/cm3
- Hygroscopy: Slightly hygroscopic under high humidity
- Aqueous property: Weakly acidic aqueous solution, pH≈3.0–4.0; easy to oxidize and turn dark in alkaline environment
Chemical Properties
- Molecular structure: Benzoic acid with three ortho/para phenolic hydroxyl groups, contains one crystal water; polyhydroxy aromatic structure with strong reducing activity
- Strong reducibility: Phenolic hydroxyl groups easily oxidized by air, light, metal ions; aqueous solution gradually turns gray-brown when exposed to air
- Color reaction with iron ions: Forms dark blue-black complex with Fe3?, used for qualitative detection of ferric ions
- Esterification reaction: Carboxyl group can react with alcohols to synthesize propyl gallate, octyl gallate and other oil-soluble antioxidants
- Thermal stability: Stable below 100 ℃; loses crystal water above 120 ℃; high temperature above melting point decarboxylates to produce pyrogallol
- Photostability: Light-sensitive; UV irradiation accelerates phenolic oxidation, powder darkens
- Compatibility: Compatible with acidic systems, vitamin C; incompatible with strong alkali, heavy metal salts, strong oxidants
3. Main Application Fields
1. Food Antioxidant Intermediate (Core Application)
Synthetic raw material for gallate series food antioxidants (propyl gallate, dodecyl gallate), prevent oil rancidity
2. Pharmaceutical Raw Material
Antioxidant and anti-inflammatory auxiliary for oral and external preparations; raw material for hemostatic, antibacterial drugs
3. Cosmetic Raw Material
Natural antioxidant, inhibits melanin formation, used in whitening, anti-aging skin care products
4. Analytical Chemistry Reagent
Detection reagent for ferric ion, gold, cerium and other metal ions; standard for polyphenol content determination
5. Tannery & Ink Industry
Mordant for leather dyeing, raw material for iron gall ink
4. Quality Specification Table
| Test Item | Standard Specification |
| CAS Number | 5995-86-8 |
| Molecular Formula | C?H?O?·H?O |
| Appearance | Uniform white crystal without brown discoloration |
| HPLC Purity | Pharma/Food Grade ≥99.0% |
| Crystal Water Content | 9.0% ~ 10.0% |
| Loss on Drying (105℃) | 9.0% ~ 10.0% |
| Residue on Ignition | ≤0.10% |
| Heavy Metals (Pb) | ≤10 ppm |
| Iron (Fe) | ≤10 ppm |
| Packaging | 1kg/5kg light-proof aluminum foil bag, 25kg PE lined fiber drum |
| Storage Condition | Hermetically sealed cool dry warehouse below 25 ℃, full light shielding, isolate alkaline substances and oxidants |
| Transportation Requirement | Light-sensitive polyphenol crystal, moisture-proof sealed packaging |
| Shelf Life | 24 months under nitrogen vacuum sealed storage |
Safety Warning
Mild irritant polyphenol crystalline powder. Dust irritates eyes and respiratory mucosa; contact with alkaline substances easily oxidizes and stains skin. All operations carried out in ventilated fume hood with dust mask, splash-proof goggles and nitrile gloves. Avoid mixing with strong alkali and iron/copper salts. Waste liquid diluted and neutralized before discharge; solid waste belongs to general plant extract fine chemical waste.
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