Quick Search
Description
In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing C−PO(OR)2 groups (where R = alkyl, aryl, or just hydrogen).
Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents, but soluble in water and common alcohols.
Many commercially important compounds are phosphonates, including glyphosate (the active molecule of the herbicide Roundup), and ethephon, a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis.
In biochemistry and medicinal chemistry, phosphonate groups are used as stable bioisoteres for phosphate, such as in the antiviral nucleotide analog, Tenofovir, one of the cornerstones of anti-HIV therapy.
And there is an indication that phosphonate derivatives are "promising ligands for nuclear medicine."
Phosphonates (or phosphonic acids) are a broad family of organic molecules based on phosphorus (chemical symbol P), carbon (C), oxygen (O) and hydrogen (H).
A variety of phosphonates (including many amino phosphonates) occur naturally and in many different types of organisms.
The metabolic functions of phosphonates in organisms include cell signalling, metabolism of cell membrane molecules, and the biological synthesis of natural antibiotics.
Some bacteria, yeast and fungi can break down phosphonates and use them as a source of food and/or phosphorus.
Phosphonates include the chemical group: ‑CH2-PO3H2:
The –CH2-PO3 group confers unique physical and chemical properties on the phosphonates molecules.
Because of these properties, phosphonates exhibit:
High solubility in water
Strong adsorption on various mineral surfaces
Ability to sequester (chelate) metal ions
Inhibition or modification of water hardness deposits
Resistance to corrosion or oxidation
Stability under harsh conditions such as acidity, alkalinity or low/high temperatures
Compatibility with other chemicals and components in formulations.
Phosphates have conventionally been used in detergents to control scale.
Both simple phosphates, like STPP (Sodium Tripolyphosphate), and complex phosphates, like TSPP (Tetrasodium Pyrophosphate) were used as builders in detergents to improve performance by chelating calcium and magnesium ions in hard water.
However, phosphates can cause serious ecological damage when disposed of into the watercourse.
Phosphonates are generally capable of offering the same level of scale control as phosphates but can be included in formulations at concentrations one order of magnitude lower than phosphates.
As such much less Phosphonates ends up being sent to drain after the rinsing process.
In sewage works using only primary treatment over 50% of phosphonates are removed from water to the sewage sludge, while those using secondary treatment remove 60 – 80%.
While phosphonates used in detergents are not readily biodegradable they do not bioaccumulate and cause no chronic or aquatic toxicity that negates the issue of ready biodegradability. Although not readily biodegradable, phosphonates are not immune to photodegradation, hydrolysis or biodegradation over time.
The phosphonate anion HPO32- is the active molecule and is derived from phosphonate (HPO(OR)2).
The phosphonate is placed on the market under more than one name: potassium phosphonate, dipotassium phosphonate, monopotassium monopotassium phosphonate, disodium phosphonate, ...
The phosphonate ion (and/or salt) is sometimes incorrectly called ‘phosphite’.
Problems with Phosphate
The main problem with phosphate use is the potential to cause ecological damage in rivers and lakes via eutrophication.
When phosphates are discharged into the watercourse, most commonly from detergents, fertilisers and sewage, they cause a spike in the nutrients required for plant growth.
Phosphate acts as a food source to plants and algae present in rivers and streams.
An increase in phosphate levels can lead to a surge in growth often resulting in algal blooms which blanket the surface of the water preventing sunlight penetrating to organisms below. After the initial surge of plant growth, the lack of light for plants below the surface causes them to die.
As bacteria work to break down the dead plant matter they consume vast amounts oxygen resulting in severe oxygen depletion of the water in the area.
Depletion of oxygen levels in the water can cause the widespread death of animal and plant life, effectively creating a dead zone.
In light of this problem many industries have attempted to limit phosphate use and water companies have imposed strict limits on the levels that can be discharged.
Phosphonates are a type of salt from the family of phosphonic acid.
Phosphonate occurs naturally, and they are commonly used in a lot of industries because of the special chemical structure that makes it rather easy to work with them.
These salts are used in industrial cleaners, to form other biological compounds, fungicides, rust removes, improve bleaching for the pulp and paper industry, are present in oil fields as gellants, and are used as intermediates in the production of synthetic DNA.
Properties and uses
Phosphonates have three main properties: they are effective chelating agents for di- and trivalent metal ions, they inhibit crystal growth and scale formation and they are quite stable under harsh chemical conditions.
An important industrial use of phosphonates is in cooling waters, desalination systems, and in oil fields to inhibit scale formation.
In pulp and paper manufacturing and in textile industry they are used as peroxide bleach stabilizers, acting as chelating agents for metals that could inactivate the peroxide.
In detergents they are used as a combination of chelating agent, scale inhibitor and bleach stabilizer.
Phosphonates are also used more and more in medicine to treat various bone and calcium metabolism diseases and as carriers for radionuclides in bone cancer treatments (see Samarium-153-ethylene diamine tetramethylene phosphonate).
In 1998 the consumption of phosphonates was 56,000 tons worldwide - 40,000 tons in the US, 15,000 tons in Europe and less than 800 tons in Japan.
The demand of phosphonates grows steadily at 3% annually. In detergents they are used as a combination of chelating agent, scale inhibitor, and bleach stabilizer.
Phosphonates are also increasingly used in medicine to treat disorders associated with bone formation and calcium metabolism.
Phosphonates are also used as concrete retarder.
They delay the cement setting time, allowing a longer time to place the concrete or to spread the cement hydration heat on a longer period of time to avoid too high temperature and resulting cracks.
They also have favourable dispersing properties and so are investigated as a possible new class of superplasticizers.
However, presently, phosphonates are not commercially available as superplasticizers.
Superplasticizers are concrete admixtures designed to increase the concrete fluidity and workability of concrete or to decrease its water-to-cement (w/c) ratio.
By reducing the water content in concrete, Phosphonates decreases its porosity, improving so the mechanical properties (compressive and tensile strength) and the durability of concrete (lower water, gas and solutes transport properties).
Occurrence in nature
The first natural phosphonate, 2-aminoethylphosphonic acid, was identified in 1959 and occurs in plants and many animals, mostly in membranes.
Phosphonates are quite common among different organisms, from prokaryotes to eubacteria and fungi, mollusks, insects and others.
The biological role of the natural phosphonates is still poorly understood.
Until now no bis- or polyphosphonates have been found to occur naturally.
Environmental behavior
Phosphonates have properties that differentiate them from other chelating agents and that greatly affect their environmental behavior.
Phosphonates have a very strong interaction with surfaces, which results in a significant removal in technical and natural systems.
Due to this strong adsorption, little or no remobilization of metals is expected.
No biodegradation of phosphonates during water treatment is observed but photodegradation of the Fe(III)-complexes is rapid.
Aminopolyphosphonates are also rapidly oxidized in the presence of Mn(II) and oxygen and stable breakdown products are formed that have been detected in wastewater.
The lack of information about phosphonates in the environment is linked to analytical problems of their determination at trace concentrations in natural waters.
Phosphonates are present mainly as Ca and Mg-complexes in natural waters and therefore do not affect metal speciation or transport.
Biodegradation
In nature bacteria play a major role in phosphonate biodegradation.
Due to the presence of natural phosphonates in the environment, bacteria have evolved the ability to metabolize phosphonates as nutrient sources.
Those bacteria able of cleaving the C-P bond are able to use phosphonates as a phosphorus source for growth.
Aminophosphonates can also be used as sole nitrogen source by some bacteria.
The polyphosphonates used in industry differ greatly from natural phosphonates such as 2-aminoethylphosphonic acid, because they are much larger, carry a high negative charge and are complexed with metals.
Biodegradation tests with sludge from municipal sewage treatment plants with HEDP and NTMP showed no indication for any degradation.
An investigation of HEDP, NTMP, EDTMP and DTPMP in standard biodegradation tests also failed to identify any biodegradation.
Phosphonates was noted, however, that in some tests due to the high sludge to phosphonate ratio, removal of the test substance from solution observed as loss of DOC was observed.
Phosphonates was attributed to adsorption rather than biodegradation.
However, bacterial strains capable of degrading aminopolyphosphonates and HEDP under P-limited conditions have been isolated from soils, lakes, wastewater, activated sludge and compost.
