Etidronic acid (1-hydroxyethylidene-1,1-diphosphonic acid o HEDP) is a phosphonate derived from phosphorus.
The name defines the structure of the molecule:
- Ethyldronic is derived from 'ethane', an alkane that indicates the presence of two carbon atoms in the molecule. The 'Hydron' part is derived from 'hydrogen,' referring to the hydrogen atoms in the molecule.
- Acid. This term refers to a substance that can donate a proton or accept a pair of electrons in reactions.
The synthesis of ethyldronic acid typically involves the reaction of phosphorous acid (H3PO3) with acetic anhydride at elevated temperatures. The synthesis process takes place in several stages:
- Preparation of materials. Phosphorous acid is commercially available. Acetic anhydride or acetyl chloride, which are used as the acetylating agent, are also commercially available.
- Acetylation. Phosphorous acid is reacted with acetic anhydride or acetyl chloride at elevated temperatures and in anhydrous conditions to prevent hydrolysis of the acetylating agent. The reaction can be represented as follows:
2H3PO3 (phosphorous acid) + (CH3CO)2O (acetic anhydride) -> C2H8O7P2 (ethyldronic acid) + CH3COOH (acetic acid)
- Purification. The crude ethyldronic acid product may contain unreacted phosphorous acid and acetic anhydride as well as acetic acid produced as a by-product and therefore must be purified to remove these impurities through various methods, such as crystallization, filtration or extraction.
- Characterization. The final stage of the synthesis process is the characterization of the product to confirm its identity and purity. This can be done through various methods, such as infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), and mass spectrometry (MS).
It appears in the form of a white powder.
What it is for and where
Ethyldronic acid is a type of bisphosphonate, a class of drugs that prevent bone density loss. In the context of cosmetics and personal care products, it is used as a chelating agent, helping to prevent the breakage of the product and to maintain its clarity and its color, also preventing the growth of microbes.
In water and detergent treatment, ethyldronic acid helps bind and neutralize metal ions to prevent them from contributing to water hardness or causing discoloration. It is also used in industrial environments to prevent fouling and corrosion.
Dentistry
Prior to obturation, the intracanal medicament should be removed. Medicament residues can reduce root canal permeability by promoting the formation of calcium carbonate particles and interfering with sealing ability of root canal sealers (1).
The aim of this study was to compare the efficiency of irrigation protocols (EDTA, citric acid, and etidronate) in Ca(OH)2 removal. Inter-group comparison showed that in the coronal-third, etidronate (Group-III) showed highest cleanliness scores, followed by EDTA (2).
In this root canal study, ethidronic acid showed less removal efficacy than SmearClear and MTAd (3).
Orthopedics
Hip fracture is among the most common causes of acute immobilization in elderly patients leading to increased bone resorption, and elderly patients with hip fracture are at high risk for a subsequent hip fracture. Etidronate therapy inhibits bone resorption and improves calcium balance, and such therapy may prevent bone loss and reduce the risk of subsequent hip fracture (4).
Cosmetics
It is a restricted ingredient as III/53 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009.
Chelating agent. It has the function of preventing unstable reactions and improving the bioavailability of chemical components within a product, and removes calcium and magnesium cations that can cause cloudiness in clear liquids.
Other uses
Used as a corrosion inhibitor.
Applications and uses:
- Fertilizers
- Pesticides
- Degreasers
- Detergents
- Antibacterial
Synonyms: Etidronate, HEDP, 1-Hydroxyethylidene-1,1-Bisphosphonate
Although in medicine it is used as synonym of Eidronic Acid, Etidronate is a salt of etidronic acid.
- Molecular formula: C2H8O7P2
- Molecular weight: 206.027
- CAS: 2809-21-4
References__________________________________________________________________
(1) Margelos J, Eliades G, Verdelis C, Palaghias G Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem. J Endod. 1997 Jan; 23(1):43-8.
(2) Chockattu SJ, Deepak BS, Goud KM. Comparison of efficiency of ethylenediaminetetraacetic acid, citric acid, and etidronate in the removal of calcium hydroxide intracanal medicament using scanning electron microscopic analysis: An in-vitro study. J Conserv Dent. 2017 Jan-Feb;20(1):6-11. doi: 10.4103/0972-0707.209079.
(3) Yadav HK, Yadav RK, Chandra A, Tikku AP. A Scanning Electron Microscopic Evaluation of the Effectiveness of Etidronic Acid, SmearClear and MTAD in Removing the Intracanal Smear Layer. J Dent (Shiraz). 2017 Jun;18(2):118-126.
(4) Sato, Yoshihiro MD; Kanoko, Tomohiro MD; Yasuda, Hajime MD; Satoh, Kei MD; Iwamoto, Jun MD Beneficial Effect of Etidronate Therapy in Immobilized Hip Fracture Patients American Journal of Physical Medicine & Rehabilitation: April 2004 - Volume 83 - Issue 4 - p 298-303 doi:10.1097/01.PHM.0000122877.28631.23
Etidronic acid 
