PRODUCTS

PHOSPHOTUNGSTIC ACID

Phosphotungstic Acid

Phosphotungstic Acid = Tungstophosphoric acid

CAS Number = 12501-23-4
EC Number = 603-020-3
Formula = H3PW12O40 xH2O
Molecular Weight = 2880.05
IUPAC Name = phosphoric acid, trioxotungsten, hydrate

Computed Properties
Property Name   Property Value
Molecular Weight   2898.1
Hydrogen Bond Donor Count   4
Hydrogen Bond Acceptor Count   41
Rotatable Bond Count   0
Exact Mass   2897.21628
Monoisotopic Mass   2899.21558
Topological Polar Surface Area   693 Å²
Heavy Atom Count   54
Formal Charge   0
Complexity   112
Isotope Atom Count     0
Defined Atom Stereocenter Count   0
Undefined Atom Stereocenter Count   0
Defined Bond Stereocenter Count   0
Undefined Bond Stereocenter Count   0
Covalently-Bonded Unit Count   14
Compound Is Canonicalized   Yes

Appearance (Color): White to Off-White
Appearance (Form): Powder
Solubility (Color): Colorless to Faint Yellow
Solubility (Turbidity): Clear to Slightly Hazy
Loss on Drying < 15 %
Sulfate (SO4) Conforms < or = 0.02%
Chloride (Cl) Conforms < or = 0.03%

Physicochemical Information
Melting Point   95 °C
pH value   2 (H₂O, 20 °C)
Vapor pressure   25.62 hPa (25 °C)
Bulk density   960 kg/m3

Phosphotungstic acid (PTA) is an electron dense, water-soluble heteropoly acid.
Available in a variety of quantities, PTA can be used as a catalyst, a histological stain component, a negative stain for transmission electron microscopy, etc.

Phosphotungstic Acid Hydrate is generally immediately available in most volumes, including bulk orders.
American Elements can produce materials to custom specifications by request, in addition to custom compositions for commercial and research applications and new proprietary technologies.
American Elements also casts any of the rare earth metals and most other advanced materials into rod, bar or plate form, as well as numerous other machined shapes, nanomaterials, and in the form of solutions and organometallic compounds.
American Elements produces to many standard grades when applicable, including Mil Spec (military grade); ACS, Reagent and Technical Grade; Food, Agricultural and Pharmaceutical Grade; Optical Grade, USP and EP/BP (European Pharmacopoeia/British Pharmacopoeia) and follows applicable ASTM testing standards.
Typical and custom packaging is available.
Additional technical, research and safety (MSDS) information is available as is a Reference Calculator for converting relevant units of measurement.

PTA is a commonly used negative stain for viruses, polysaccharides, nerves, other biological issue material to be viewed by transmission electron microscopy. There have also been some so-far-as-we-know unpublished reports that PTA can be used for the staining of various nylons, a polymer apparently not readily stained by other electron dense stains. One major advantage of using PTA is that the pH can always be adjusted as desired. Some protocols also call for the use of PTA as a fixative.

Thanks to its high acid strength and environment friendliness, a heteropoly acids (HPA) are widely used as heterogeneous catalysts.
Of them, Keggin 12-H3PW12O40 is the one with strongest acid strength.
However, because of the lack of effective characterization technology, some fundamental issues about the acid, such as the location and acid strength of acid protons, are controversial.

A heteropoly acid formally derived from phosphoric acid and tungstic acid
it is used as an analytical reagent.

Phosphotungstic Acid, Crystal, Reagent, also referred to as tungstophosphoric acid. It is a crystal like yellow-green solid that melts at 89°C, has no odor and is water soluble. It has many uses among which are pigments and dyeing, as a catalyst and in histology for specimen staining. Its reagent grade means this is the highest quality commercially available for this chemical and that the American Chemical Society has not officially set any specifications for this material.

Phosphotungstic acid hydrate is a reagent suitable to detect alkaloids and nitrogenous bases.
It is suitable in manufacturing organic pigments, additive in plating industry.
It imparts water resistance to plastics, adhesives and cement.
It also is suitable as a catalyst for organic reactions.

Phosphotungstic Acid any of several acids obtainable from solutions of phosphoric acid and tungstic acid and used chiefly as precipitants (as for alkaloids and for basic dyes for pigments) and in analytical reagents
especially : a greenish yellow crystalline acid H3PW12O40·xH2O used as a reagent and as a biological stain

Phosphotungstic acid (PTA), tungstophosphoric acid (TPA), is a heteropoly acid with the chemical formula H3PW12O40.nH2O.
It is normally isolated as the n = 24 hydrate but can be desiccated to the hexahydrate.
EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology.
It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 H2O hydrate).
It is odorless and soluble in water (200 g/100 ml).
It is not especially toxic, but is a mild acidic irritant.
The compound is known by a variety of names and acronyms (see 'other names' section of infobox).

In these names the "12" or "dodeca" reflects the fact that the anion contains 12 tungsten atoms.
Some early workers who did not know the structure.
called it phospho-24-tungstic acid, formulating it as 3H2O·P2O5 24WO3·59H2O, (P2W24O80H6)·29H2O, which correctly identifies the atomic ratios of P, W and O.
This formula was still quoted in papers as late as 1970.

Phosphotungstic acid is used in histology as a component for staining of cell specimens, often together with haematoxylin as PTAH.
It binds to fibrin, collagen, and fibres of connective tissues, and replaces the anions of dyes from these materials, selectively decoloring them.

Phosphotungstic acid is electron dense, opaque for electrons.
It is a common negative stain for viruses, nerves, polysaccharides, and other biological tissue materials for imaging by a transmission electron microscope.

Structure
Structure of the phosphotungstate anion
Gouzerh summarises the historical views on the structure of phosphotungstic acid leading up to Keggin's determination of the structure as:

H7[P(W2O7)6] proposed by Miolati and further developed by Rosenheim
H3[PO4W12O18(OH)36] (Pauling)
The structure was determined by J.F Keggin first published in 1933 and then in 1934 and is generally known as the Keggin structure.
The anion has full tetrahedral symmetry and comprises a cage of twelve tungsten atoms linked by oxygen atoms with the phosphorus atom at its centre.
The picture on the right shows the octahedral coordination of oxygen atoms around the tungsten atoms, and that the surface of the anion has both bridging and terminal oxygen atoms.
Further investigation showed that the compound was a hexahydrate not a pentahydrate as Keggin had proposed.

Appearance
Phosphotungstic acid appears as colorless-grayish or slightly yellow-green crystals.

Solubility
Phosphotungstic acid is soluble in water and polar solvents organics as ethanol.

Uses
Phosphotungstic acid ( PTA ) is normally present as dehydrate and EPTA is the name of ethanolic phototungstic acid which is an alcoholic solution used in biology
Phosphotungstic acid is used as raw material for catalysts.

Catalyst
In common with the other heteropolyacids phosphotungstic acid is a catalyst and its high acidity and thermal stability make it a catalyst of choice according to some researchers.
It is in solution as a homogeneous catalyst, and as a heterogeneous catalyst "supported" on a substrate e.g.
alumina, silica.
Some acid catalysed reactions include:

the homogeneous catalysis of the hydrolysis of propene to give 2-propanol
the homogeneous catalysis of the Prins reaction
the heterogeneous catalysis of the dehydration of 2-propanol to propene and methanol to hydrocarbons.
Dyeing and pigments
Phosphotungstic acid has been used to precipitate different types of dyes as "lakes".
Examples are basic dyes and triphenylmethane dyes, e.g.
pararosaniline derivatives.

Histology
Phosphotungstic acid is used in histology for staining specimens, as a component of phosphotungstic acid haematoxylin, PTAH, and “trichrome” reagents, and as a negative stain for imaging by a transmission electron microscope.

Phosphotungstic acid haematoxylin (PTAH)
Mallory described the reagent now generally known as PTAH in 1897.
PTAH stains tissues either reddish brown or blue depending on their type.
This property of simultaneously staining two different colours is different from other haematoxylin reagents e.g.
alum-haematoxylin.
The role of phosphotungstic acid and the mechanism of staining is not fully understood.
The active component of haematoxylin is the oxidised form, haematin, although this rarely acknowledged in the literature which refer to haematoxylin staining.
Phosphotungstic acid forms a lake with haematin.
The make –up of the reagent is uncertain, examination of a year old sample showed there to be three coloured components, blue, red and yellow.
These were not identified.
Some investigations of “model” systems, reacting various compounds such as amino acids, purines, pyrimidines and amines with PTAH show that they give rise to different colours.
Trichrome reagents
In these reagents two or three basic dyes are used with phosphotungstic acid, in either a one step or multi-stage procedure.
These reagents colour different tissue types different colours.
Again the mechanism of staining is not fully understood.
Some explanations include the proposal that phosphotungstic acid acts as a mordant to bind the dye to the tissue or that alternatively it binds to tissue blocking it to dye molecules.
Negative staining
Adsorption onto tissue or the surface of viruses and its electron density are the bases of phosphotungstic acids action as a negative stain.
This electron density arises from the presence of the 12 tungsten atoms which each have an atomic number of 74.
The mechanism of the adsorption onto tissue has been proposed as being electrostatic rather than involving hydrogen bonding, as adsorption is not affected by pH.
Analysis
The potassium salt is only slightly soluble, unlike most other phosphotungstate salts, and has been proposed as a method for the gravimetric analysis of potassium.

Precipitation of proteins
In a number of analytical procedures one of the roles of phosphotungstic acid is to precipitate out proteins.
It has been termed a "universal" precipitant for polar proteins.
Further studies showed that no precipitation occurred with α-amino groups but did occur with guanidino, ε-amino and imidazole groups.

Medicinal
Very little work appears to have been carried out in this area.
One example relates to liver necrosis in rats.

Composite proton exchange membranes
The heteropoly acids, including phosphotungstic acid, are being investigated as materials in composite proton exchange membranes, such as Nafion.
The interest lies in the potential of these composite materials in the manufacture of fuel cells as they have improved operating characteristics.

Application
Phosphotungstic acid hydrate may be used as a staining agent for the transmission electron microscope (TEM) imaging of cetyltrimethylammonium bromide (CTAB) coated gold nanorods.
It may be used in the preparation of:
Phosphotungstic acid doped ormosil hybrid networks.
Niobia supported phosphotungstic acid (PTA) catalysts.
Titanium dioxide (TiO2) nanoparticles /phosphotungstic acid (HPW) films.

Preparation and chemical properties
Phosphotungstic acid can be prepared by the reaction of sodium tungstate, Na2WO4·2H2O, with phosphoric acid, H3PO4, acidified with hydrochloric acid, HCl.

Phosphotungstic acid solutions decompose as the pH is increased.

The species [PW11O39]7− is a lacunary, or defective Keggin ion.
The [P2W18O62]6− has a Dawson structure.
At pH less than 8, the presence of ethanol or acetone stabilises the anion, [PW12O40]3−, reducing decomposition.

Tungstophosphoric acid is thermally stable up to 400 °C, and is more stable than the analogous silicotungstic acid, H4SiW12O40.

Large quantities of polar molecules such as pyridine are absorbed into the bulk phase and not simply on the surface.
Solid state NMR studies of ethanol absorbed in the bulk phase show that both protonated dimers, ((C2H5OH)2H+) and monomers, (C2H5OH2+) are present.

Phosphotungstic acid is less sensitive to reduction than phosphomolybdic acid.
Reduction with uric acid or iron(II) sulfate produces a brown coloured compound.
the related silicotungstic acid when reduced forms a similar brown compound where one of the four W3 units in the Keggin structure becomes a metal-metal bonded cluster of three edge shared W(IV) octahedra.

Phosphotungstic acid is the strongest of heteropolyacids.
Its conjugate base is the PW12O403− anion.
Its acidity in acetic acid has been investigated and shows that the three protons dissociate independently rather than sequentially, and the acid sites are of the same strength.
One estimate of the acidity is that the solid has an acidity stronger than H0 =−13.16, which would qualify the compound as a superacid.
This acidic strength means that even at low pH the acid is fully dissociated.

Storage instructions
Store at Room Temperature.
Store under desiccating conditions.
The product can be stored for up to 12 months.

Handling
Wherever possible, you should prepare and use solutions on the same day.
However, if you need to make up stock solutions in advance, we recommend that you store the solution as aliquots in tightly sealed vials at -20°C.
Generally, these will be useable for up to one month.
Before use, and prior to opening the vial we recommend that you allow your product to equilibrate to room temperature for at least 1 hour.

Personal protective equipment
Eye/face protection
Use equipment for eye protection tested and approved under appropriate
government standards such as NIOSH (US) or EN 166(EU).
Tightly fitting safety
goggles

Skin protection
This recommendation applies only to the product stated in the safety data sheet,
supplied by us and for the designated use.
When dissolving in or mixing with other
substances and under conditions deviating from those stated in EN374 please
contact the supplier of CE-approved gloves

Full contact
Material: Nitrile rubber
Minimum layer thickness: 0,11 mm
Break through time: 480 min
Material tested:KCL 741 Dermatril® L

Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0,11 mm
Break through time: 480 min
Material tested:KCL 741 Dermatril® L

Body Protection
Acid-resistant protective clothing

Synonyms of Phosphotungstic Acid

12-wolframophosphoric acid
tungstophosphoric acid
dodecatungstophosphoric acid
Phosphotungstic acid hydrate
12501-23-4
Tungstophosphoric acid
phosphoric acid;trioxotungsten;hydrate
12-Tungstophosphoric acid hydrate
Hydrogen phosphotungstate hydrate (H3PW12O40.xH2O)
MFCD00011342
Phosphotungstic acid, AR
DTXSID30583755
MFCD00149915
AKOS005111017
SB66354
Phosphotungstic acid hydrate, reagent grade
Phosphotungstic acid hydrate, for microscopy
Phosphotungstic acid hydrate, p.a., 99.5%
Phosphotungstic acid hydrate, SAJ special grade
A890325
Phosphoric acid--trioxotungsten--water (1/12/1)
Phosphotungstic acid hydrate, Vetec(TM) reagent grade
Phosphotungstic acid hydrate, 99.995% trace metals basis (Purity excludes up to 300 ppm Si)