1-Hydroxyethylidene-1,1-diphosphonic acid
[CAS# 2809-21-4]

Identification

• Classification: API >> Water, electrolyte and acid-base balance regulator >> Electrolyte balance regulator
• Name: 1-Hydroxyethylidene-1,1-diphosphonic acid
• Synonyms: 1-Hydroxyethane-1,1-diphosphonic acid; 1-Hydroxyethylidenedi(phosphonic acid); Dequest 2010; Etidronic acid; HEDP
• Molecular Formula: C₂H₈O₇P₂
• Molecular Weight: 206.03
• CAS Registry Number: 2809-21-4
• EC Number: 220-552-8
• SMILES: CC(O)(P(=O)(O)O)P(=O)(O)O

Properties

• Solubility: 1.5 g/L (water 20 °C)
• Density: 1.45 (60% aq.)
• Melting point: 199 °C

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Risk Statements: H290-H302-H314-H318-H413
• Safety Statements: P234-P260-P264-P264+P265-P270-P273-P280-P301+P317-P301+P330+P331-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P321-P330-P363-P390-P405-P406-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413
Skin corrosion	Skin Corr.	1C	H314
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Skin corrosion	Skin Corr.	1B	H314
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H332
Skin corrosion	Skin Corr.	1A	H314
Acute toxicity	Acute Tox.	4	H312

• Transport Information: UN 3265

Discovery and Applications

1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP), also known as ethomid, was first synthesized in the mid-20th century as part of an exploration of various applications for organic phosphonates. Its discovery marked a significant advancement in controlling scale and managing metal ions in a variety of systems. HEDP's unique properties stem from its structure, where a hydroxyethylidene group is bonded to two phosphonic acid groups, providing a high affinity for metal ions and effective scale inhibition. HEDP has the molecular formula C2H8O7P2 and is available as a colorless to pale yellow liquid or crystalline solid. Its phosphonic acid groups bind tightly to metal ions, forming a stable complex. This chelation prevents metal salt precipitation and scale formation, making HEDP very effective in maintaining system cleanliness and efficiency.

The most important application of HEDP is in water treatment systems. It acts as a scale remover and corrosion inhibitor by sequestering metal ions, such as calcium and magnesium, preventing scale deposits from forming on pipes and equipment. This property is critical in cooling towers, boilers, and reverse osmosis systems, where scale buildup can lead to inefficient operation and equipment damage.

HEDP is widely used in detergents and household cleaning products for its ability to chelate metal ions and enhance the effectiveness of detergents. By stabilizing metal ions, HEDP improves the ability of detergents to remove stains and prevents soil from redepositing on fabrics and surfaces. It is also used in industrial cleaners to control metal ion interference during the cleaning process.

In the cosmetics and personal care industry, HEDP is used as a stabilizer in peroxide formulations. It helps maintain the stability and effectiveness of products such as hair bleaches and dental care products, ensuring consistent performance over time.

HEDP is used in agriculture as a stabilizer for micronutrient solutions and fertilizers. Its chelating ability ensures that plants receive essential nutrients to promote growth and yield. It also helps control scale in irrigation systems, maintaining efficiency and reducing maintenance costs.

In addition to water treatment and cleaning, HEDP is used in a variety of industrial applications, including paper and pulp processing, textiles, and oilfield production. Its anti-scaling and chelating properties help manage process efficiencies and prevent interruptions to operations due to scale and metal ion buildup.

While HEDP is very effective, its environmental impact is a concern. It is biodegradable, but its persistence and bioaccumulation potential require careful management in drainage systems. Regulations often require specific treatment procedures to mitigate any adverse effects on the aquatic environment.

References

2024. Rickets and Osteomalacia: Vitamin D-Sensitive and -Resistant States. Endotext.
DOI: NBK278975

2000. Evaluation of toxicity and efficacy of 186Re-hydroxyethylidene diphosphonate in patients with painful bone metastases of prostate or breast cancer. Journal of Nuclear Medicine, 41(4).
DOI: 41/4/641

1998. Functional improvement in a patient with cerebral calcinosis using a bisphosphonate. Movement Disorders, 13(1).
DOI: 10.1002/mds.870130123