1hydroxyethylidene11diphosphonic

1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) is an organic polyphosphonic acid used primarily as a chelating agent and scale inhibitor in water treatment and cleaning formulations. It belongs to the phosphonate family and is commonly marketed in its sodium salt forms to improve water solubility and ease of handling.

Structure and properties: HEDP features a hydroxyethylidene core with two phosphonic acid groups, which gives it a strong ability to bind metal ions such as calcium and magnesium. This chelating action helps prevent precipitation of insoluble salts and reduces scale formation. The compound is highly water-soluble and exists in multiple protonation states depending on pH, allowing it to function effectively across a broad pH range in various formulations.

Applications: In industrial water systems, HEDP acts as a scale inhibitor and, in combination with other additives, can provide corrosion control by keeping hardness ions in solution. It is widely used in cooling towers, boilers, and other closed-loop systems. In consumer and industrial detergents, cleaners, and paper and pulp processing, HEDP serves as a sequestrant that binds metal ions to enhance cleaning efficiency and protect equipment. It is also encountered in some cosmetics and personal care products as a chelating agent.

Safety and handling: HEDP should be handled with standard chemical precautions. It can irritate skin and eyes on contact and should be used with appropriate gloves and eye protection. It is typically stored in sealed containers, away from incompatible materials, and handled in well-ventilated areas according to the supplier’s safety data sheet.