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Peroxymonophosphoric acid () is an
P2O5 + 2H2O2 + H2O -> 2H3PO5
: H4P4O12 + 4H2O2 -> 4H3PO5
: H4P2O7 + H2O2 -> H3PO5 + H3PO4
A less vigorous method of preparing peroxyphosphoric acid by introducing the inert solvent
Peroxymonophosphoric acid is a colorless, viscous liquid. It is stabilized by an intramolecular hydrogen bond. The compound is a triprotic acid with acid dissociation constants pKa1 = 1.1, pKa2 = 5.5 and pKa3 = 12.8. In aqueous solutions it slowly undergoes hydrolysis to hydrogen peroxide and phosphoric acid.
:
With excess water, the hydrolysis can be considered pseudo-first order. The half-life for this decomposition is dependent on the pH and temperature, being about 31 hours at 35 °C and 2.5 hours at 61 °C. A solution in acetonitrile also slowly degrades, losing 30% of active oxygen after 26 days of storage at 5 °C. Relatively stable salts can be obtained by neutralization with bases, for example with
The oxidation of 
Peroxymonophosphoric acid is an effective reagent for the hydroxylation of aromatic rings. The conversion of 
The compound can be used as an effective oxidizing agent for the Baeyer-Villiger oxidation. Substituted 
Tertiary aromatic amines like 
Oxidation of
oxyacid
An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce ...
of phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. It is a colorless viscous oil. Its salts are called peroxymonophosphates. Another peroxyphosphoric acid is peroxydiphosphoric acid, .
Preparation
Peroxyphosphoric acids were first synthesized and characterized in 1910 by Julius Schmidlin and Paul Massini via the reaction betweenphosphorus pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4 O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant and dehydra ...
and highly-concentrated aqueous solution of hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
. However, this reaction proceeds very vigorously and is difficult to control. Aside from phosphorus pentoxide, syntheses from metaphosphoric acid
A phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. ...
and diphosphoric acid were also reported.
: acetonitrile
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...
was described by Gerrit Toennies in 1937. This method was shown to be unsuitable in diethyl ether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...
or isoamyl alcohol
Isoamyl alcohol is a colorless liquid with the formula , specifically (H3C–)2CH–CH2–CH2–OH. It is one of several isomers of amyl alcohol (pentanol). It is also known as isopentyl alcohol, isopentanol, or (in the IUPAC recommended nomencla ...
.
Contemporary methods
Peroxyphosphoric acid is usually produced by treating phosphorus pentoxide and concentrated hydrogen peroxide within an inert solvent like acetonitrile orcarbon tetrachloride
Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...
..
:
One method of preparation is the hydrolysis of potassium of lithium peroxydiphosphate in a strong acid such as perchloric acid. The peroxydiphosphate salts can be obtained by electrolysis of their respective phosphate salts.
:
Peroxydiphosphoric acid is obtained when phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
is treated with fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
or oxidized electrolytically.
Properties
Peroxymonophosphoric acid is a colorless, viscous liquid. It is stabilized by an intramolecular hydrogen bond. The compound is a triprotic acid with acid dissociation constants pKa1 = 1.1, pKa2 = 5.5 and pKa3 = 12.8. In aqueous solutions it slowly undergoes hydrolysis to hydrogen peroxide and phosphoric acid.
:
With excess water, the hydrolysis can be considered pseudo-first order. The half-life for this decomposition is dependent on the pH and temperature, being about 31 hours at 35 °C and 2.5 hours at 61 °C. A solution in acetonitrile also slowly degrades, losing 30% of active oxygen after 26 days of storage at 5 °C. Relatively stable salts can be obtained by neutralization with bases, for example with potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
to give the hygroscopic potassium dihydrogenperoxymonophosphate KH2PO5.
Uses and reactions
Peroxyphosphoric acids and peroxyphosphates have few commercial uses.Reactions with organic compounds
They have been examined in the context of organic synthesis, as an electrophilic reagent for the oxidation ofalkenes
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
, alkynes
\ce
\ce
Acetylene
\ce
\ce
\ce
Propyne
\ce
\ce
\ce
\ce
1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no ...
, aromatic compounds
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
and amines
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
. Due to the strongly acidic nature, only relatively acid-stable epoxides can be prepared from alkenes, for example ''trans''-stilbene oxide from ''trans''-stilbene. Less stable epoxides are cleaved or react further; cyclohexene
Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes. Cyclohexene is not very stable upon long term storage with exposure to light a ...
, styrene
Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
, and α-methylstyrene yield no isolable epoxides. In the cases of styrene and α-methylstyrene, acid-catalyzed alkyl migrations lead instead to the main products phenylacetic acid
Phenylacetic acid (PAA; conjugate base phenylacetate), also known by various synonyms, is an organic compound containing a phenyl functional group and a carboxylic acid functional group. It is a white solid with a strong honey-like odor. Endogen ...
and 2-phenylpropionic acid, respectively.
The oxidation of diphenylacetylene
Diphenylacetylene is the chemical compound C6H5C≡CC6H5. The molecule consists of two phenyl groups attached to a C2 unit. A colorless solid, it is used as a building block in organic synthesis and as a ligand in organometallic chemistry.
Prep ...
at room temperature yields benzil
Benzil (i.e. Bz2, systematically known as 1,2-diphenylethane-1,2-dione) is the organic compound with the formula ( C6H5 CO)2, generally abbreviated ( PhCO)2. This yellow solid is one of the most common diketones. Its main use is as a photoinitia ...
, presumably through an oxirene
Oxirene is a hypothesized heterocyclic chemical compound which contains an unsaturated three-membered ring containing two carbon atoms and one oxygen atom. Because it has never been observed, the substance is mainly studied by quantum chemical c ...
intermediate.
Peroxymonophosphoric acid is an effective reagent for the hydroxylation of aromatic rings. The conversion of mesitylene
Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenze ...
to mesitol
Mesitol (2,4,6-trimethylphenol) is an organic compound with the formula (CH3)3C6H2OH. It is one of several isomers of trimethylphenol. The name and structure of mesitol derives from the combination of mesitylene and phenol
Phenol (also calle ...
can be achieved at room temperature in less than four hours.
The compound can be used as an effective oxidizing agent for the Baeyer-Villiger oxidation. Substituted acetophenones
Acetophenone is the organic compound with the formula C6H5C(O)CH3. It is the simplest aromatic ketone. This colorless, viscous liquid is a precursor to useful resins and fragrances.
Production
Acetophenone is formed as a byproduct of the cumene p ...
can be converted to the corresponding phenyl acetates at 30 °C in high yields. The rate is about 100 times higher in comparison to using peroxybenzoic acid
Peroxybenzoic acid is an organic compound with the formula C6H5CO3H. It is the simplest aryl peroxy acid. It may be synthesized from benzoic acid and hydrogen peroxide, or by the treatment of benzoyl peroxide with sodium methoxide, followed by ...
.
Tertiary aromatic amines like dimethylaniline
''N'',''N''-Dimethylaniline (DMA) is an organic chemical compound, a substituted derivative of aniline. It consists of a tertiary amine, featuring dimethylamino group attached to a phenyl group. This oily liquid is colourless when pure, but comm ...
are oxidized to the corresponding amine oxide
In chemistry, an amine oxide, also known as an amine ''N''-oxide or simply ''N''-oxide, is a chemical compound that contains the functional group , a nitrogen-oxygen coordinate covalent bond with three additional hydrogen and/or substituent-grou ...
.{{Cite journal, last1=Ogata, first1=Yoshiro, last2=Tomizawa, first2=Kohtaro, last3=Morikawa, first3=Takashi, date=1979, title=Kinetics of the Peroxymonophosphoric Acid Oxidation of Aromatic Amines, journal=J. Org. Chem.
''The Journal of Organic Chemistry'', colloquially known as ''JOC'', is a peer-reviewed scientific journal for original contributions of fundamental research in all branches of theory and practice in organic and bioorganic chemistry. It is publ ...
, volume=44, issue=3, pages=352–355, doi=10.1021/jo01317a009
Oxidation of THF
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
with peroxymonophosphoric acid gives γ-butyrolactone.
References