Ethylenediaminetetraacetic acid

Structural formula
General
Surname	Ethylenediaminetetraacetic acid
other names	Ethylenedinitrilotetraacetic acid; Ethylenediaminetetraethanoic acid; Edetic acid ( INN ); Titriplex ® ll; Idranal ® II; Chelaplex II; EDTA; EDTA ( INCI ) ; EDTAH 4 ;
Molecular formula	C 10 H 16 N 2 O 8
Brief description	colorless solid
External identifiers / databases
EC number	200-449-4
ECHA InfoCard	100,000,409
PubChem	6049
ChemSpider	5826
DrugBank	DB00974
Wikidata	Q408032
Drug information
ATC code	V03 AB03
properties
Molar mass	292.24 g mol −1
Physical state	firmly
density	1.46 g cm −3 (20 ° C)
Melting point	245 ° C (decomposition)
solubility	practically insoluble in water (0.5 g l −1 at 20 ° C); easily in ethanol and diethyl ether ;
safety instructions
	Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
H and P phrases	H: 319-332-373
	P: 280-304 + 340-312-305 + 351 + 338-337 + 313
Toxicological data	4500 mg kg −1 ( LD 50 , rat , oral )
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Ethylenediaminetetraacetic acid or ethylenediaminetetraacetate , the tetraanion of ethylenediaminetetraacetic acid, is a hexadentate complexing agent and forms particularly stable 1: 1 chelate complexes with cations with a charge number of at least +2. The abbreviation EDTA stands for the German name E Thylen d iamin t etra a acetate as well as the English name E thylene d iamine t etraacetic a cid. Gerold Schwarzenbach did pioneering work on EDTA in the 1940s at the University of Zurich . The first synthesis of EDTA was carried out by Ferdinand Münz at IG Farben in 1935 , who also patented a process for this purpose.

properties

EDTA metal ion chelate complex

In addition to the two free electron pairs of the nitrogen atoms , the ethylenediaminetetraacetic acid anion can also provide four carboxy groups for a complex compound, i.e. it can bind 6-fold to a cation . It is thus able to form very stable complexes even with those cations which, such as calcium , have an extremely low tendency to form complexes. Complexes of this type are also known as chelate complexes , from the Greek chele , crab claws. EDTA forms particularly stable complexes with Cu ²⁺ , Ni ²⁺ , Fe ³⁺ and Co ²⁺ . At an acidic pH value , EDTA exists in various acid forms that are less dissociated . The acid therefore dissolves slowly, especially at low pH , while the salts dissolve very quickly in water. EDTA is not soluble in fats . The p K _S values are sorted by source 0.26, 0.96, 2.60, 2.76 (for deprotonation of the four carboxyl groups) or 0, 1.5, 2, 2.66 (for the deprotonation of four carboxyl groups) and 6.16, 10.24 (for the deprotonation of the two amino groups ).

synthesis

Through the Strecker synthesis of formaldehyde and hydrocyanic acid with ethylenediamine via the tetranitrile and subsequent alkaline hydrolysis.

use

EDTA is one of the most commonly used complexing agents. In 1999 around 35,000 tons were used in Europe and 50,000 tons in the USA.

In addition to the free acid, its salts are also often used:

Disodium ethylenediamine tetraacetate (Na ₂ H ₂ EDTA, sodium edetate , INS 386)
Tetrasodium ethylenediamine tetraacetate (Na ₄ EDTA)
Calcium disodium ethylenediamine tetraacetate (CaNa ₂ EDTA, E 385 )

The main uses of EDTA and their salts are

Detergents : EDTA is contained in many washing and cleaning agents for binding Ca ²⁺ and Mg ²⁺ ions (softening) (but it should not be confused with the TAED used there).
Industrial cleaning: complexing of divalent cations such as Ca ²⁺ and Mg ²⁺ as well as some heavy metal ions
Photo industry: Fe ^III -EDTA is an important component (oxidizing agent for metallic silver) in color development.
Paper industry: For complexing Fe ³⁺ and Mn ²⁺ ions, which decompose the hydrogen peroxide in chlorine-free bleaching
Agrochemicals: Fe ^III -, Cu ^II - and Zn ^II -EDTA are used as fertilizer, especially on calcareous soils (see also hydroponic fertilizers # complexing agents )
Preservative: EDTA complexes divalent metal cations, which are essential for the function of many enzymes. This prevents bacteria from multiplying in contact lens care products, among other things.

Other uses of EDTA are:

Textile industry: stabilization of bleach baths

Cosmetics : as a preservative and to prevent discoloration from metals in clear products.

Medicine: Treatment of metal poisoning. A controversial therapy is chelation therapy , where EDTA is injected to cleanse the body . In diagnostic medicine, EDTA is used as a calcium chelator and is used to anticoagulate blood samples.

In dentistry , EDTA solutions are used in root canal treatments in order to remove the smear layer created during preparation of the root canal and to expose the entrances to the dentinal tubules .

Its calcium-sodium salts are also used:

Calcium disodium ethylenediaminetetraacetate is used as an antioxidant , stabilizer and complexing agent. By binding metal ions, it prevents food in cans from changing color. Oils are prevented from going rancid for the same reason . In the EU it is only approved as a food additive with the designation E 385 for emulsified sauces, canned and glass preserves, semi-fat margarine and shellfish. It is not approved in Australia .
Calcium disodium ethylenediaminetetraacetate is also used in medicine as an anticoagulant additive for drawing blood. Furthermore, it is used as medicaments addition to heavy metal poisoning, heart - circulatory problems , rheumatism and arthritis administered. Further possible medical fields of application are arteriosclerosis and circulatory disorders .

EDTA is widely used in chemistry and biology.

Structural model of EDTA complexing a Cu ²⁺ ion.

In analytical chemistry (quantitative analysis), EDTA is used as a complexon / Titriplex II standard solution to quantitatively determine metal ions such as Cu , Pb , Hg , Ca or Mg in chelatometry . The disodium salt (complexon / Titriplex III), which is more soluble in water, can also be used.

EDTA is one of the components of the TAE and TBE buffers , which are used in gel electrophoresis , for example to separate DNA fragments.

EDTA is often added to enzyme solutions in order to prevent the inhibition of enzyme activity caused by heavy metal ions .

EDTA is added to plant nutrients in order to prevent the required iron from precipitating with the phosphate, which is also required as iron phosphate .

When killing gram-negative bacteria with lysozyme , EDTA is added to permeabilize the outer membrane (plastic layer), sometimes also when cells are disrupted .

Metalloproteases can also be inhibited by chelating agents such as EDTA. As a result of the chelation of the metal ions from the active center of metalloproteases, these lose their catalytic activity.

Biodegradability and toxicology

EDTA and its metal complexes are not or only poorly biodegradable in wastewater treatment. However, by increasing the pH value and extending the age of the sludge, a substantial biological elimination of EDTA can be achieved. A large number of microorganisms that can grow with EDTA as the sole source of C and N have been isolated from sewage sludge , sediments and soils. The metal complexes of EDTA are not or only very slightly toxic to organisms. However, EDTA can also dissolve sparingly soluble heavy metal salts from the sediments. When the EDTA then disintegrates, these 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, free EDTA in particular can lead to disturbances by binding vital metals. The concentrations of EDTA measured in the environment are harmless to humans.

Environmental behavior

EDTA reaches the environment almost exclusively via wastewater. Since EDTA degrades very slowly under normal conditions, it can be detected in practically all water samples in low concentrations. EDTA concentrations in rivers are between 10 and 100 µg / l, in lakes between 1 and 10 µg / l. EDTA can be found in concentrations between 1 and 100 µg / l in groundwater and bank filtrate. At neutral pH values, the adsorption of EDTA on mineral surfaces is low, which leads to high mobility in the groundwater. Only the Fe ^III -EDTA complex is broken down very quickly by sunlight. This is the most important elimination process for EDTA in the environment. EDTA is only incompletely removed during ozonization or chlorination of drinking water. EDTA is now considered ecologically questionable, as free complexing agents release heavy metals from the sediment and make them bioavailable.

The German Federal Environment Agency recommends: "In the interests of a preventive substance policy, EDTA and other complexing agents that are difficult to break down, such as diethylenetriaminepentaacetic acid (DTPA) or propylenediaminetetraacetic acid (PDTA), should be replaced by substances that are as easily degradable as possible and can therefore be removed in sewage treatment plants." are nitrilotriacetic acid (NTA) and its sodium salts, citrates , gluconates , β-alaninediacetic acid sodium salt (ADA), methylglycinediacetic acid (MGDA), and the like. am In Switzerland, the placing on the market of detergents, cleaning agents and deodorisers with a mass content of more than 0.5% or 1% EDTA or its salts is prohibited.