Phosphoric acid ester
Phosphoric acid esters (also alkyl phosphates ) are esters of orthophosphoric acid , which formally or actually arise from the reaction of the acid and alcohols with elimination of water. They can be referred to as organic phosphates / organophosphates , but do not belong to the group of organophosphorus compounds , as there is no carbon- phosphorus bond.
A distinction is made between monoester, diester and triester:
In organism organophosphate are vital because they are involved as intermediates of many metabolic processes virtually all biological processes (see, eg. As adenosine triphosphate ) . A distinction must be made between the phosphoric acid esters and the partly highly toxic thiophosphoric acid and dithiophosphoric acid esters , which are also organophosphorus compounds .
Importance in biochemistry
Phosphates or phosphate residues play an important role in the biochemistry of living organisms. They are involved in the construction of biologically important molecules, such as deoxyribonucleic acid (DNA). In the phosphorus diester / phosphorus triester system of adenosine diphosphate (ADP) and adenosine triphosphate (ATP), ADP is “energetically charged” through the transfer of a phosphate group (ADP + P i + energy ⇒ ATP) and ATP can by splitting off a phosphate group - elsewhere in the cell - release energy again (ATP ⇒ ADP + P i + energy). Phosphorylation is also important in biochemistry . i.e., the selective transfer of phosphate to proteins . Phosphate covalently bound to proteins acts as a molecular switch and enables regulation of metabolic processes. They are transmitted here by the large class of protein kinases , which are split off again by protein phosphatases.
Phosphoric acid esters are used in plastics and paints as plasticizers , flame retardants , hardeners, as pickling agents and adhesives when applying paints and varnishes, in metal surface treatment as cleaning, corrosion-inhibiting and adhesion-promoting substances, as auxiliaries for textiles and paper , as cleaning and cleaning agents, and hydraulics -Fluid, oil and fuel additives.
Use as pesticides and chemical warfare agents
Organophosphorus compounds and phosphoric acid esters are the most extensive and diverse group of active substances against insects ( insecticides ) and mites ( acaricides ). Examples of insecticides in this class of substances are Phoxim , Dichlorvos (DDVP), Fenthion , Chlorpyrifos , Parathion (E 605) and its methyl and ethyl derivatives , as well as tetraethyl pyrophosphate (Bladan).
The development of this class of compounds began in early 1900 by August Michaelis and Alexander Arbusow , who are the founders of classical phosphorus chemistry. The biological effect of the organic phosphoric acid ester was not recognized until the mid- 1930s by Gerhard Schrader , who synthesized the warfare agents tabun (1936) and sarin (1939) while searching for acaricides and insecticides . Later the nerve agents Soman and VX were developed.
- easily hydrolyzable (splittable by water) and also easily enzymatically and abiotic degradable
- partly very soluble in fat ( lipophilic )
- high toxicity and the associated low application rate
- great variability of connections, d. That is, many different compounds are possible so that the development of resistance is reduced.
The poisonous effect in humans is based on an inhibition of the esteratic center (irreversible) of acetylcholinesterase and thus initially leads to an acetylcholine overflow with muscarinic and nicotinic symptoms (see also acetylcholine receptors and cholinergic crisis ). Subsequently, the constant nerve impulses lead to cramps and then death from respiratory failure . The toxicity of the individual compounds is very different, however. Other symptoms include slow heartbeat, constricted pupils , increased salivation and shortness of breath, as well as nausea, diarrhea and urinary incontinence. In emergency medicine, atropine and obidoxime chloride are administered for antagonization .
Presentation and extraction
Mono- and diesters are formed with alcohols .
- Irmo Stark: Insecticides and Nerve Gases : Poisoning and Therapy, Chemistry in Our Time , 18th year 1984, No. 3, pp. 96-106, doi: 10.1002 / ciuz.19840180304 .
- Ronald A. Hites, Jonathan D. Raff: Environmental Chemistry An introduction with tasks and solutions . John Wiley & Sons, 2017, ISBN 978-3-527-67297-4 , pp. 224 ( limited preview in Google Book search).
- Ralf Steudel : Chemistry of Non-Metals, Syntheses - Structures - Bonding - Use , 4th edition, 2014 Walter de Gruyter GmbH & Co. KG, Berlin / Boston, ISBN 978-3-11-030439-8 , p. 408 -409, doi: 10.1515 / 9783110307979.377 .