Etidronic acid, Hydroxy Ethylidene Diphosphonic Acid, HEDP, HEDP, HEDPA, 2809-21-4

Etidronic acid, Hydroxy Ethylidene Diphosphonic Acid, HEDP, HEDP, HEDPA, 2809-21-4

Chemical Identity

• Name: 1-Hydroxyethylidene-1,1-diphosphonic acid

• Synonyms: HEDP, HEDPA, Etidronic acid, Hydroxyethylidene diphosphonic acid

• CAS No: 2809-21-4

• EINECS No: 220-552-8

• Molecular Formula: C₂H₈O₇P₂

• Molecular Weight: 206.03 g/mol

• InChIKey: DBVJJBKOTRCVKF-UHFFFAOYSA-N

Physical and Chemical Properties

• Density (60% solution): 1.45 g/cm³

• Melting Point: 198–199 °C

• Boiling Point (Predicted): 578.8 °C

• pKa values: 1.35, 2.87, 7.03, 11.3 (at 25 °C)

• pH (1% solution, 25 °C): 1.3–1.8

• Solubility: Fully soluble in water, miscible with methanol and ethanol

• Appearance: Colorless to light yellow liquid or white crystalline powder

• Stability: Stable under light and heat; incompatible with strong oxidizing agents

Production Methods

1. Phosphorous Acid + Acetic Anhydride

2H3PO3+(CH3CO)2O→C2H8O7P2(HEDP)+CH3COOH

By-product: Acetic Acid

2. Glacial Acetic Acid + Phosphorus Trichloride + Water

CH3COOH+2PCl3+5H2O→C2H8O7P2(HEDP)+6HCl

By-product: Hydrochloric Acid

Applications

• Water Treatment: Scale and corrosion inhibitor, prevents CaCO₃ precipitation.

• Power Plants: Used in cooling towers and boilers for scale/corrosion control.

• Metal Processing: Forms complexes with Cu, Zn, Fe ions; dissolves oxides.

• Electroplating: Non-cyanide complexing agent, especially for copper plating.

• Detergents & Cosmetics: Peroxide stabilizer, used in soaps and shampoos.

• Swimming Pools: Prevents stains and scale, stable in chlorine environments.

• Oil & Gas: Additive in acidizing solutions to prevent sludge and deposits.

Storage and Packaging

• Packaging: 200 L plastic drums, 1000–1450 Kg IBC tanks, 25 Kg bags (powder form).

• Storage Conditions: Keep in a cool, dry, shaded place; avoid direct sunlight.

• Shelf Life: Approximately 10 months under proper conditions.

• Note: Powder form preferred in cold climates to avoid freezing of liquid solution.

Safety and Toxicity

• Risk Codes: R22 (Harmful if swallowed), R37/38 (Irritating to respiratory system and skin), R41 (Risk of serious eye damage).

• LD₅₀ (oral, mouse): ~1800 mg/kg.

• UN No: 3265 (Corrosive liquid, acidic, organic).

• WGK (Germany): 2 (water hazard class).

• Precautions: Use gloves, goggles, and protective clothing; rinse immediately with water in case of contact.

Industrial Advantages

• High thermal stability (up to 250 °C) and tolerance to alkaline conditions.

• Excellent chlorine resistance, making it suitable for pool and municipal water treatment.

• Synergistic effects when combined with other inhibitors (zinc salts, polycarboxylates, molybdates).

•  

Sectoral applications and typical dosage ranges:

1. Water Treatment & Energy Sector

• Applications: Cooling towers, boilers, heat exchangers, power plants.

• Function: Scale inhibitor and corrosion inhibitor.

• Dosage:

  • 2–10 mg/L → scale inhibition.

  • 10–50 mg/L → corrosion inhibition.

• Advantages: Stable up to 250 °C, effective under high pH conditions, synergistic with zinc salts and polycarboxylates.

2. Municipal & Potable Water Systems

• Applications: Municipal water treatment plants, drinking water additives.

• Function: Prevents precipitation of iron and manganese oxides, stabilizes chlorine.

• Dosage: 1–10 mg/L.

• Note: Approved in some countries as a drinking water additive.

3. Swimming Pools

• Applications: Pool water treatment.

• Function: Prevents stains and scale, maintains chlorine stability.

• Dosage: 5–15 mg/L.

• Advantages: Resistant to chlorine degradation, long-lasting effect.

4. Metal Processing & Electroplating

• Applications: Non-cyanide electroplating (especially copper plating).

• Function: Complexing agent, surface activator.

• Dosage:

  • 100–120 mL/L (60% solution) in plating bath.

  • 15–20 g/L copper sulfate used together.

  • Pre-treatment: immersion in 1–2% HEDP solution before plating.

5. Detergents & Cosmetics

• Applications: Industrial detergents, soaps, shampoos, personal care products.

• Function: Peroxide stabilizer, chelating agent for Ca²⁺, Fe²⁺, Cu²⁺, Zn²⁺.

• Dosage: 1000–2000 mg/L in detergent formulations.

• Advantages: Improves product stability and prevents discoloration.

6. Textile & Dye Industry

• Applications: Textile auxiliaries, dye fixation processes.

• Function: Peroxide stabilizer, chelating agent.

• Dosage: 10–50 mg/L in process water.

• Advantages: Stable under high temperature and alkaline conditions.

7. Oil & Gas Industry

• Applications: Acidizing solutions in oil and gas wells.

• Function: Prevents sludge and scale formation.

• Dosage: 50–200 mg/L depending on process conditions.

• Advantages: Effective under high pressure and temperature.

8. Electronics & Specialty Chemicals

• Applications: Cleaning agents in electronics manufacturing.

• Function: High-purity chelating agent for metal ions.

• Dosage: 5–20 mg/L depending on application.

• Advantages: Ensures surface cleanliness and prevents ion contamination.

Summary Table