Ethylenediaminetetraacetic acid

• Ethylenedinitrilotetraacetic
• Ethylendiamintetraethansäure
• Edetic acid ( INN)
• Titriplex ® II
• Idranal ® II
• Chelaplex II
• EDTA
• EDTAH4

V03AB03

Colorless solid

Fixed

0.86 g · cm -3

245 ° C ( decomposition)

<1.3 Pa ( 20 ° C)

0.26

Poorly in water: 0.5 g · l-1 (25 ° C), slightly soluble in ethanol and diethyl ether

Attention

4500 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

Ethylenediaminetetraacetic acid or ethylene diamine tetraacetate, the tetraanion of ethylenediaminetetraacetic acid, EDTA short, is a hexadentate chelating agents. He is particularly stable 1:1 chelates with cations with a charge number of at least 2. Pioneering work to EDTA made ​​Gerold Schwarzenbach in the 1940s at the University of Zurich.

Properties

The ethylenediaminetetraacetic acid anion, in addition to the two free electron pairs of the nitrogen atom also four carboxy groups of a complex compound made ​​available, which bind 6-fold to a cation. It is able to form very stable complexes with such cations which have an extremely low tendency to form complexes such as calcium. Complexes of this type are also called chelate complexes, from the Greek chele, crab claw. EDTA forms very stable complexes with Cu2 , Ni2 , Fe3 and Co2 . The free acid is poorly soluble, especially at low pH, salts, however, are very well soluble in water. In contrast, it is not soluble in fats.

Synthesis

By the Strecker synthesis from formaldehyde and hydrocyanic acid with ethylenediamine via the tetranitrile and subsequent alkaline hydrolysis.

Use

EDTA is a chelating the most commonly used. In 1999, in Europe around 35,000 tons, 50,000 tons consumed in the United States.

In addition to the free acid in many cases also their salts are used:

• Disodium ethylenediamine tetraacetate ( Na2H2EDTA, disodium edetate, INS 386)
• Tetrasodium ethylenediamine tetraacetate ( Na4EDTA )
• Calcium disodium ethylenediamine tetraacetate ( CaNa2EDTA, E 385)

The most important applications of EDTA and its salts are

• Detergents, EDTA is used in many detergents and cleaning agents for the binding of Ca2 - and Mg2 - containing ions ( softening).
• Industrial cleaning: complexation of divalent cations such as Ca2 and Mg2 and certain heavy metal ions
• Photo Industry: FeIII -EDTA is an important part ( oxidant) in the color development.
• Paper industry: complexation of Fe3 - and Mn2 ions, which disable the hydrogen peroxide in the chlorine-free bleaching
• Agrochemicals: FeIII, CuII, and ZnII - EDTA are used as fertilizer, especially on calcareous soils
• Preservative: EDTA complexed divalent metal cations are essential for the function of many enzymes. The growth of bacteria is prevented among others in contact lens care products.

Other uses of EDTA are:

• Textile industry: stabilization of bleaching baths
• Cosmetics: to avoid as a preservative and to discoloration caused by metals in clear products.
• Medicine: the treatment of metal poisoning. A controversial treatment is chelation therapy, EDTA is injected in order to cleanse the body. In diagnostic medicine is used as calcium EDTA buffer and used for the anticoagulation of blood samples.
• In dentistry, using EDTA solutions in root canal treatment to remove the formed during the preparation of the root canal smear layer and expose the Dentinkanälcheneingänge.
• Calciumdinatriumethylendiamintetraacetat is used as an antioxidant, a stabilizer and a complexing agent. The binding of metal ions, it prevents a color change in food in cans. Oils are prevented for the same reason on rancidity. It's 385 approved only for emulsified sauces, cans and glass jars, low-fat margarine and shellfish in the EU as a food additive called E. In Australia, there has been no approval.
• Calciumdinatriumethylendiamintetraacetat is used in medicine as an anticoagulant additive for blood draws. Furthermore, it is administered as a drug additive against heavy metal poisoning, cardiovascular ailments, rheumatism and arthritis. Other possible medical applications include atherosclerosis and circulatory disorders.

In chemistry or biology EDTA is widely used.

• In analytical chemistry (quantitative analysis) EDTA is used as complexone / Titriplex II standard solution to such as Cu, Pb, Hg, Ca or Mg to determine quantitatively in the Chelatometrie metal ions. Also, the more water-soluble disodium salt ( complexone / Titriplex III) can be used.
• EDTA is one of the constituents of the TAE buffer and TBE, which are, inter alia, on the gel electrophoresis, for example for separation of DNA fragments use.
• Enzyme solutions are often mixed with EDTA to prevent the heavy metal ions caused by inhibition of enzyme activity.
• Plant culture media is added to prevent precipitation of the iron required with the phosphate also required as iron phosphate EDTA.
• In laboratory medicine, blood samples for the study of the blood picture are made anticoagulated with EDTA, because that is necessary for the clotting calcium cation is complexed by EDTA irreversibly.
• In the killing of gram-negative bacteria with lysozyme, EDTA is the permeabilization of the outer membrane added (plastic layer ).
• Nor can inhibit metalloproteases by chelating agents such as EDTA. Due to the chelation of the metal ions from the active site of metalloproteases they lose their catalytic activity.

Biodegradability and Toxicology

EDTA and its metal complexes are not or only poorly biodegradable in wastewater treatment. By increasing the pH and extension of the sludge age, however, a high degree of biological removal of EDTA can be achieved. Of sewage sludge, sediments and soils a variety of micro-organisms has been isolated that can grow with EDTA as the sole carbon and nitrogen source. The metal complexes of EDTA are not or only very slightly toxic to organisms. However, EDTA is also capable of sparingly soluble salts of heavy metals from sediments to solve. When the EDTA then disintegrates, they are released again on the surface.

The toxicity of EDTA for humans is very low, so that EDTA is approved as a food additive. In very high concentrations can especially lead free EDTA by binding of essential metals to disturbances. The measured concentrations of EDTA in the environment are safe for humans.

Environmental behavior

EDTA passes almost exclusively through the waste water into the environment. Since EDTA is degraded very slowly under normal conditions, it can be detected in virtually all water samples at low concentrations. EDTA concentrations in rivers are between 10 and 100 ug / l in lakes 1 to 10 ug / l The groundwater and bank filtrate EDTA can be found in concentrations between 1 and 100 ug / l. At neutral pH values, the adsorption of EDTA on mineral surfaces is low, which leads to a high mobility in the groundwater. Only the FeIII -EDTA complex is rapidly degraded by sunlight. This is the main elimination process for EDTA in the environment. EDTA is only incompletely removed during ozonation or chlorination of drinking water. EDTA is now considered ecologically harmful because free complexing heavy metals released from the sediment and make bioavailable.

The Federal Environment Agency recommends " In terms of precautionary chemicals policy should EDTA and other easily degradable complexing agents such as diethylenetriaminepentaacetic acid ( DTPA) or propylene diamine ( PDTA ) are replaced by materials that are as easily degradable and can be removed in sewage treatment plants ." Possible substitutes include nitrilotriacetic acid ( NTA) and its sodium salts, citrate, gluconate, alanine diacetic acid sodium salt ( ADA), methylglycinediacetic ( MGDA ), etc.

Substitutes

• Nitrilotriacetic acid ( NTA)
• Ethylene glycol bis ( aminoethyl ether )-N, N'-tetraacetic acid (EGTA )
• Ethylenediaminedisuccinic acid (EDDS )
• Citric acid
• Polycarboxylates
• Zeolites, especially zeolite A
• Phosphonates