5-Sulfosalicylic acid (also known as 2-hydroxy-5-sulfobenzoic acid) is an organic compound that integrates both a sulfonic acid group ($-\text{SO}_3\text{H}$) and a carboxylic acid group ($-\text{COOH}$) onto a phenol ring. Commercial grade is most commonly encountered in its dihydrate form ($\text{C}_7\text{H}_6\text{O}_6\text{S} \cdot 2\text{H}_2\text{O}$).
Key Chemical & Physical Properties
| Property |
Anhydrous Form |
Dihydrate Form (Most Common) |
| Chemical Formula |
$\text{C}_7\text{H}_6\text{O}_6\text{S}$ |
$\text{C}_7\text{H}_6\text{O}_6\text{S} \cdot 2\text{H}_2\text{O}$ |
| CAS Registry Number |
97-05-2 |
5965-83-3 |
| Molar Mass |
$218.18\text{ g/mol}$ |
$254.21\text{ g/mol}$ |
| Appearance |
White crystalline powder |
White to off-white needle-like crystals or crystalline powder |
| Melting Point |
$\sim120^\circ\text{C}$ (decomposes) |
$105 - 110^\circ\text{C}$ |
| Solubility in Water |
Highly soluble |
Freely soluble in water, alcohol, and acetone |
| Light Sensitivity |
Light sensitive (store away from sunlight) |
Light sensitive |
Primary Applications
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Urinary Protein Testing: Widely used in clinical diagnostics to detect protein (albumin) in urine via turbidimetric precipitation.
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Complexometric Indicator / Reagent: Used in analytical chemistry to form intense pink/red complexes with iron(III) ($\text{Fe}^{3+}$) ions, enabling colorimetric determination and titration of iron.
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Anodizing & Metal Finishing: Serves as an additive in aluminum anodizing electrolyte baths to produce hard, corrosion-resistant coatings.
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Chemical Intermediate: Used as a precursor in organic synthesis for the preparation of specialized dyes, surfactants, and pharmaceutical intermediates.
Safety & Handling
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Corrosive & Irritant: Causes severe skin burns and eye irritation; harmful if swallowed.
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Handling: Store in tightly closed containers in a cool, dark place away from strong light and oxidizing agents.
Trade & Identification Details