Quick Search



HEDP = 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid

EC / List no.: 220-552-8
CAS no.: 2809-21-4
Mol. formula: C2H8O7P2

HEDP is a colourless to pale yellow clear liquid. 
HEDP is widely used as a sequestrant, chelating and deposit control agent, and provides excellent control of calcium and other metal salts (including iron and manganese) by acting as a strong crystal modifying agent and threshold inhibitor.

HEDP is a 60% active aqueous solution and is part of the Bisphosphonic Acid Group. 
HEDP is highly water soluble and stable under harsh conditions, which makes it ideal for water treatment. 
The main uses in the water treatment industry are, reverse osmosis formulation, cooling water treatment, boiler water treatment, swimming pools, scale and corrosion inhibitor.

1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP) acid with its CAS number 2809-21-4​  is a cost effective scale inhibitor used in various industrial applications such as industrial water treatment and detergents.

Additionally 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP) shows a good stability in presence of chlorine as well as corrosion inhibition properties in presence of zinc and other phosphates and can also be used as chelating agent in the textile industry.

Applications of HEDP
• Cooling water systems / industrial water treatment
• Industrial detergents
• Swimming pools
• Metal surface treatment as a corrosion inhibitor for steel
• Stabilizer in H2O2 solutions
• Sequestering agent in textile auxiliaries

The phosphonate HEDP (also known as etidronic acid) is an excellent water hardness stabilizer and chelating agent that can be found in both household and industrial applications. 
These properties allow the chemical to produce exceptional results in the production of detergent and the treatment of cooling water.

Structure of HEDP
HEDP has the chemical formula C2H8O7P2 and belongs to the phosphonate family, which can be further classified into chelating agents, scale inhibitors, stabilizers and corrosion inhibitors. 

Phosphonates are salts and organic compounds of phosphoric acids. 
As salts, phosphonates can exist in both the primary (M' H2PO3) and secondary (M'2H PO3) forms.

Phosphonates have the general structure R-PO(OH)2. 
They differ from esters of phosphoric acids by having a direct bond between the phosphorous and carbon atom. 
This means they can be more easily hydrolyzed and are soluble in water most of the time.

HEDP (1-Hydroxyethylidene-1, 1-diphosphonic acid) is also sold under the name etidronic acid.

Chemical identifiers:

Item number: 210108
CAS Number: 2809-21-4
EINECS: 220-552-8
Commodity code: 28351000
Hazard identification number: 80 
UN number: 3265
Index number: 015-157-00-0

Properties of HEDP
HEDP is a colorless liquid with a characteristic odor. 
Besides the liquid form, by request, we can also supply HEDP as dust-free solid granules.

The substance has a boiling point of around 100 degrees Celsius and is not explosive.

The liquid is fully soluble in water and is considered a very good limescale inhibitor, water hardness stabilizer and chelating agent, particularly for trivalent metal ions (such as ferric ions, Fe3+) and simple metal ions (such as iron, zinc and copper).

HEDP is used as chelating agent (especially for metal ions such as Fe, Cu and Zn), corrosion inhibitor and stabilizing agent (water hardness, peroxides) in the detergents industry, water treatment, metallurgy and dyeing industry.

HEDP in the detergent industry
HEDP (short for 1-Hydroxyethylidene-1,1-diphosphonic acid) has been used as an additive in the industrial production of detergent for a long time.

The main reason is that HEDP can function as a chelating agent, scale inhibitor and dispersant and possesses excellent hydrolytic and thermal stability.

The phosphonate is therefore an essential ingredient in many detergents. 
In addition to its ability to stabilize water hardness and facilitate the dispersion of dirt particles, the chemical is able to remove stains and has antimicrobial and bleaching properties.

HEDP is thus able to perform numerous functions in detergents and has superseded the highly controversial EDTA, a chemical that has a bad reputation due to its environmental impact.

Use of HEDP in water treatment
HEDP is also commonly used in industrial water treatment. 
HEDP is able to prevent the formation of insoluble sulfate and carbonate deposits. 
This makes HEDP an ideal chemical for reducing encrustations on fabric, which is why manufacturers generally like to use it as a chelating agent in detergents.

Due to its exceptional dispersion properties, HEDP is also effective against contaminants. 
The chemical is an ideal limescale and corrosion inhibitor and becomes especially effective in a solution containing other inhibitors.

Because of these properties, HEDP is frequently added as a treatment chemical to cooling water systems, carbon water systems, industrial boilers and desalination plants.

Other applications of HEDP
HEDP has likewise many uses in the construction materials industry. 
Apart from its ability to liquefy certain materials, modify their rheology and delay the curing process, HEDP is also an additive that can remove corrosion from metal surfaces and prevent subsequent rust formation.

Moreover, the paper and textile industries use the compound as a chelating agent to bind heavy metals as well as for demineralization and as a stablizier in bleaching applications.

In the cosmetics industry, HEDP can be found in hair dyes and bleaches as a stabilizing agent. 
The compound also has a significant influence on the cleansing effects of soap, shampoo and body wash. 
On top of that, it is added to sunscreens to improve the dispersion of white pigments.

Due to its unique compatibility with other chemicals, HEDP is extremely versatile and plays a crucial role in both the industry and our everyday lives.

HEDP is as a member of the family of drugs known as bisphosphonates, etidronate differs from endogenous pyrophosphate in its resistance to enzymatic hydrolysis. 
This agent adsorbs to hydroxyapatite cells and reduces the number of osteoclasts, thereby inhibiting abnormal bone resorption. 
Etidronate may also directly stimulate bone formation by osteoblasts.

HEDP  is a 1,1-bis(phosphonic acid) that is (ethane-1,1-diyl)bis(phosphonic acid) having a hydroxy substituent at the 1-position. 
HEDP inhibits the formation, growth, and dissolution of hydroxyapatite crystals by chemisorption to calcium phosphate surfaces. 
HEDP has a role as a bone density conservation agent, a chelator and an antineoplastic agent. 
HEDP is a conjugate acid of an etidronic acid(2-).

Etidronic acid is a first generation bisphosphonate similar to [clodronic acid] and [tiludronic acid]. 
These drugs were developed to mimic the action of pyrophosphate, a regulator of calcification and decalcification.
 Etidronate’s use has decreased over the years in favor of the third generation, nitrogen containing bisphosphonate [zoledronic acid], [ibandronic acid], [minodronic acid], and [risedronic acid]. 
Etidronic acid was granted FDA approval on 1 September 1977.

Industry Uses
• Corrosion inhibitors and anti-scaling agents
• Finishing agents
• Intermediates
• Plating agents and surface treating agents
• Processing aids, not otherwise listed
• Solvents (for cleaning and degreasing)
• Surface active agents
• used in detergent manufacture

Consumer Uses
• Automotive care products
• Building/construction materials - wood and engineered wood products
• Cleaning and furnishing care products
• Fabric, textile, and leather products not covered elsewhere
• Lubricants and greases
• Metal products not covered elsewhere
• Water treatment products

Household Products
• Auto Products
• Commercial / Institutional
• Home Maintenance
• Inside the Home
• Landscaping/Yard
• Personal Care
• Pet Care

General Manufacturing Information
Industry Processing Sectors
• PAll other basic inorganic chemical manufacturing
• PAll other basic organic chemical manufacturing
• PAll other chemical product and preparation manufacturing
• Fabricated metal product manufacturing
• Machinery manufacturing
• Miscellaneous manufacturing
• Oil and gas drilling, extraction, and support activities
• Paper manufacturing
• Petroleum lubricating oil and grease manufacturing
• Plastics product manufacturing
• Rubber product manufacturing
• Soap, cleaning compound, and toilet preparation manufacturing
• Textiles, apparel, and leather manufacturing
• Utilities
• Wholesale and retail trade
• Wood product manufacturing

HEDP also known as etidronic acid which shows multifunctional properties that includes scale inhibition and corrosion inhibition. 
HEDP is very good complexing agent for metal ions like Fe, Cu, and Zn. 
HEDP shows good chemical stability under high pH value. 
Furthermore, it is difficult to hydrolyze and decompose under ordinary light and heat conditions.

HEDP is used in several end use applications that include detergents, water treatment, oilfield, textile, paper and personal care. 
Furthermore, it can be used for formulating RO membrane antiscalants, thermal desalination antiscalants, formulation for treating sterilizers etc. 
HEDP can be used directly also for such applications as single or in combination with a suitable dispersant.

Hydroxyethylidene diphosphonic acid (HEDP) is also used as corrosion and scale inhibition in circulating cooling water systems, low-pressure boilers and in oil field applications such as electric power, refineries, chemical industry, fertilizer and metallurgy etc. 
Hydroxyethylidene diphosphonic acid (HEDP) is widely used in detergent application as chelant. Aquapharm also supply etidronic acid for peroxide stabilizer, electroplating chelating agent and dye-fixing agent.

Specifications of hydroxyethylidene diphosphonic acid (HEDP)
Parameter: Product details
Appearance: Clear Colourless to Pale yellow aqueous solution
Physical State: Aqueous Solution
Active Content: 60% (as Acid)
Specific Gravity @ 25C : 1.44
pH of 1% Solution @ 25C: <2
Freezing Point C: -25
Chloride as Cl-: <0.01%
Iron (Fe) PPM: <10

HEDP is an organophosphoric acid corrosion inhibitor. 
HEDP can chelate with Fe, Cu, and Zn ions to form stable chelating compounds. 
HEDP can dissolve the oxidized materials on these metals’ surfaces. 
HEDP shows excellent scale and corrosion inhibition effects under temperature 250℃. 
HEDP has good chemical stability under high pH value, hard to be hydrolysed, and hard to be decomposed under ordinary light and heat conditions. 
Its acid/alkali and chlorine oxidation tolerance are better than that of other organophosphoric acids (salt). 
HEDP can react with metal ions in water system to form hexa-element chelating complex, with calcium ion in particular. Therefore, HEDP has good anti-scale and visible threshold effects. 
When built together with other water treatment chemicals, it shows good synergistic effects.

HEDP acts as human protein tyrosine phosphatase inhibitor. 
HEDP is also useful for photographic applications. 
HEDP finds application to strengthen bone, osteoporosis treatment and to treat Paget's disease of bone. 
In addition, it is used in corrosion inhibition in circulating cool water systems, oil fields and low-pressure boilers with electric power, the chemical industry, metallurgy and fertilizers. 
HEDP is also utilized for formulating reverse osmosis and thermal desalination anti-scaling agents. Furthermore, it is used in detergents, water treatment, cosmetics and pharmaceuticals.

Manufacturing Process    
Phosphorous acid was premixed with acetic acid to form a 50 wt % solution of phosphorous acid dissolved in acetic acid. 
The acids were mixed on a molar basis of 1.36:1, acetic acid to phosphorous acid, and this corresponded on a mol percentage basis to 57.6% acetic acid and 42.4% phosphorous acid. 
Acetic anhydride was continuously metered into a stream of the phosphorous acid-acetic acid mixture to form the reaction solution. 
The acetic anhydride was metered into the acid mixture at a mol ratio of 1.33 mols of acetic anhydride per mol of phosphorous acid. 
The metering rates were 18.5 lb/hr of the phosphorous acid/acetic acid premixed solution and 15.1 lb/hr acetic anhydride. 
The reaction solution was continuously passed through a heat exchanger where it was heated to 190°F then it was continuously fed into a two stage back-mix reaction zone where due to the heat of reaction the temperature rose to 275°F. 
The average residence in the reaction zone was 27 min. 
The reaction zone consisted of two back-mix reactors each having a capacity of 7.5 pounds of the reaction solution. 
A stream of reaction solution was continuously with drawn from the second reactor and continuously mixed with a stream of water which was being metered at a rate of 2 lb/hr. 
This amount of water corresponded to 18% excess over the theoretical amount necessary to hydrolyze all of the acetyl-containing compounds in the reaction solution to free acids. 
The hydrolyzed solution was continuously passed through a heat exchanger and cooled to room temperature after which the solution was continuously passed to a crystallizer where, with agitation, the ethane-1-hydroxy-1,1-diphosphonic acid crystallized. 
The slurry was then filtered and the crystals were recovered and dried. Analysis of the product showed a conversion rate of phosphorous acid to ethane-1-hydroxy-1,1- diphosphonic acid of 86%. 
Sodium hydroxide may be used to give the disodium salt.

About this substance
Helpful information
This substance is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, at ≥ 10 000 to < 100 000 tonnes per annum.

This substance is used by consumers, in articles, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Consumer Uses
This substance is used in the following products: water softeners, washing & cleaning products, air care products, polishes and waxes, coating products, fertilisers and cosmetics and personal care products.
Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Article service life
Release to the environment of this substance can occur from industrial use: in the production of articles and in processing aids at industrial sites. Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners), outdoor use resulting in inclusion into or onto a materials (e.g. binding agent in paints and coatings or adhesives) and indoor use in long-life materials with low release rate (e.g. flooring, furniture, toys, construction materials, curtains, foot-wear, leather products, paper and cardboard products, electronic equipment). This substance can be found in complex articles, with no release intended: machinery, mechanical appliances and electrical/electronic products (e.g. computers, cameras, lamps, refrigerators, washing machines) and vehicles. This substance can be found in products with material based on: stone, plaster, cement, glass or ceramic (e.g. dishes, pots/pans, food storage containers, construction and isolation material), metal (e.g. cutlery, pots, toys, jewellery), wood (e.g. floors, furniture, toys), fabrics, textiles and apparel (e.g. clothing, mattress, curtains or carpets, textile toys) and paper (e.g. tissues, feminine hygiene products, nappies, books, magazines, wallpaper).

Widespread uses by professional workers
This substance is used in the following products: water softeners, coating products, washing & cleaning products, air care products, polishes and waxes, fertilisers and cosmetics and personal care products.
This substance is used in the following areas: building & construction work and agriculture, forestry and fishing.
Release to the environment of this substance can occur from industrial use: in the production of articles.
Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Formulation or re-packing
This substance is used in the following products: pH regulators and water treatment products, water softeners, water treatment chemicals and washing & cleaning products.
Release to the environment of this substance can occur from industrial use: formulation of mixtures, formulation in materials, manufacturing of the substance and in processing aids at industrial sites.
Uses at industrial sites
This substance is used in the following products: water softeners, pH regulators and water treatment products, water treatment chemicals, washing & cleaning products and coating products.
This substance is used in the following areas: municipal supply (e.g. electricity, steam, gas, water) and sewage treatment, mining and formulation of mixtures and/or re-packaging.
This substance is used for the manufacture of: pulp, paper and paper products, textile, leather or fur, metals, fabricated metal products, machinery and vehicles, furniture and chemicals.
Release to the environment of this substance can occur from industrial use: in processing aids at industrial sites, in the production of articles and as processing aid.
Other release to the environment of this substance is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners).
Release to the environment of this substance can occur from industrial use: manufacturing of the substance, formulation of mixtures and in processing aids at industrial sites.

(1-hydroxy-1-phosphono-ethyl)phosphonic acid
(1-hydroxy-1-phosphonoethyl)phosphonic acid
(1-hydroxyethan-1,1-diyl)bis(phosphonic acid)
(1-Hydroxyethane-1,1-diyl)bis(phosphonic acid)
(1-hydroxyethane-1,1-diyl)bis(phosphonic acid)
(1-hydroxyethylidene)bis-phosphonic acid,
1-hydroxy ethylidene -1,1-diphosphonic acid
1-hydroxy ethylidene-1,1-diphosphonic acid
1-Hydroxyethane-1,1-diphosphonic acid
1-hydroxyethane-1,1-diphosphonic acid
1-Hydroxyethane-1,1-diphosphonic Acid (HEDP)
1-hydroxyethane-1,1-diyl)bis(phosphonic acid
1-hydroxyethylene (bis-Phosphonic acid)
1-Hydroxyethylidene- 1,1-diphosphonic acid
1-Hydroxyethylidene-1, 1-Diphosphonic Acid
1-Hydroxyethylidene-1,1-diphosphonic aci
1-Hydroxyethylidene-1,1-diphosphonic acid
1-hydroxyethylidene-1,1-diphosphonic acid
Editronic Acid
Etidronic Acid
Etidronic acid
etidronic acid
Etidronic acid
Phosphonic acid, (1-hydroxyethylidene)bis-
Phosphonic acid, (1-hydroxyethylidene)di
phosphonic acid,(1-hydroxyethylidene)bis-

1-Hydroxyethane-1,1-diphosphonic acid; 
1-Hydroxyethylidene-1,1-diphosphonic acid; 
1-hydroxyethylidenedi(phosphonic acid); 
Etidronic Acid; 
1-Hydroxyethylidene-1,1-bis-(phosphonic acid); 
Ethane-1-hydroxy-1,1-diphosphonic acid; 
Oxyethylidenediphosphonic acid
Etidronic acid
1-Hydroxyethylidene-1,1-diphosphonic acid
Acetodiphosphonic acid
Hydroxyethanediphosphonic acid
Turpinal SL
Oxyethylidenediphosphonic acid
Dequest 2015
Dequest Z 010
Acido etidronico
Ferrofos 510
Acide etidronique
1-Hydroxyethane-1,1-diphosphonic acid
Phosphonic acid, (1-hydroxyethylidene)bis-
Diphosphonate (base)
(1-Hydroxyethane-1,1-diyl)diphosphonic acid
1-Hydroxyethanediphosphonic acid
Dequest 2010
Ethane-1-hydroxy-1,1-diphosphonic acid
(Hydroxyethylidene)diphosphonic acid
(1-Hydroxyethylene)diphosphonic acid
Acide etidronique [INN-French]
Acido etidronico [INN-Spanish]
Acidum etidronicum [INN-Latin]
(1-Hydroxyethylidene)diphosphonic acid
1,1,1-Ethanetriol diphosphonate
1-Hydroxyethane-1,1-bisphosphonic acid
(1-Hydroxyethylidene)bis(phosphonic acid)
Acidum etidronicum
(1-Hydroxyethylidene)bisphosphonic acid
(1-hydroxyethane-1,1-diyl)bis(phosphonic acid)
Hydroxyethane-1,1-diphosphonic acid
(1-Hydroxyethylidene)diphoshonic acid
(1-hydroxy-1-phosphonoethyl)phosphonic acid
Phosphonic acid, (1-hydroxyethylidene)di-
ethane-1-hydroxy-1,1-bisphosphonic acid
2809-21-4 (freeacid)
1-hydroxyethane 1,1-diphosphonic acid
(1-hydroxyethan-1,1-diyl)bis(phosphonic acid)
(1-Hydroxy-1,1-ethanediyl)bis(phosphonic acid)
Phosphonic acid, P,P'-(1-hydroxyethylidene)bis-
Etidronic acid [USAN:INN:BAN]
Phosphonic acid, 1-hydroxy-1,1-ethanediyl ester
Etidronic acid (USAN/INN)
(1-hydroxy-1-phosphono-ethyl)phosphonic acid
1-hydroxy ethylidene
Etidronate (Didronel)
0-02-00-00171 (Beilstein Handbook Reference)
Etidronic acid 60% aqueous solution
Etidronic acid, 60% aqueous solution
(1-hydroxy-ethylidene)diphosphonic acid
1-hydroxyethane-1,1-diyldiphosphonic acid
1-hydroxy ethylidene-1,1-diphosphonic acid
(1-Hydroxy-1-phosphono-ethyl)-phosphonic acid
(1-Hydroxyethylidene)bisphosphonic acid monohydrate
1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (Powder)
(1-Hydroxyethane-1,1-diyl)diphosphonic acid monohydrate
1-Hydroxyethylidenediphosphonic acid 60% aqueous solution
1-Hydroxyethane-1,1,-diphosphonic acid 60% aqueous solution
(1-Hydroxyethylidene)biphosphonic acid
Hydroxyethylidene Diphosphonic acid (HEDP)
1-Hydroxyethylidene-1,1-bis-(phosphonic acid)
1-Hydroxyethane-1,1-diphosphonic Acid (ca. 60% in Water, ca. 4.2mol/L)
1-hydroxyethylidenebis(phosphoric acid)
1-Hydroxyethylidene-1,1-diphosphonic aci
hydroxy ethylidene diphosphoric acid
1-hydroxy ethylene-1,1'-diphosphonic acid
1-Hydroxyethane-1,1,-diphosphonic acid, 1-Hydroxyethylidenediphosphonic acid
Hydroxyethane diphosphonic acid,1-
Phosphonic acid, P,P'-(1-hydroxyethylidene)bis-
Etidronic Acid Monohydrate (1 g)
1-diphosphonic acid
1-Hydroxyethylidene-1,1-Diphosphonic Acid/HEDP Powder
(1-Hydroxyethane-1,1-diyl)diphosphonic acid
1-Hydroxyethylidene-1,1-diphosphonic Acid Etidronic Acid
Etidronate (Didronel)
Etidronic acid,60% in water
1-Hydroxyethane-1,1-diphosphonic acid, 60 wt.% solution in H2O
Etidronic acid Monohydrate (HEDP),


  • Share !