Periodate is an

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

composed of

iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

. It is one of a number of

oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...

s of iodine and is the highest in the series, with iodine existing in

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

+7. Unlike other perhalogenates, such as

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...

, it can exist in two forms: metaperiodate and orthoperiodate . In this regard it is comparable to the

tellurate In chemistry tellurate is a compound containing an oxyanion of tellurium where tellurium has an oxidation number of +6. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central tellurium atom.

ion from the adjacent

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

. It can combine with a number of

counter ion 160px, Polystyrene sulfonate, a cation-exchange resin, is typically supplied with as the counterion.">cation-exchange_resin.html" ;"title="Polystyrene sulfonate, a cation-exchange resin">Polystyrene sulfonate, a cation-exchange resin, is typical ...

s to form periodates, which may also be regarded as the salts of

periodic acid Periodic acid ( ) is the highest oxoacid of iodine, in which the iodine exists in oxidation state +7. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula , and metaperiodic acid, which has the formula . ...

. Periodates were discovered by

Heinrich Gustav Magnus Heinrich Gustav Magnus (; 2 May 1802 – 4 April 1870) was a notable German experimental scientist. His training was mostly in chemistry but his later research was mostly in physics. He spent the great bulk of his career at the University of Ber ...

and C. F. Ammermüller; who first synthesised periodic acid in 1833.

Synthesis

Classically, periodate was most commonly produced in the form of sodium hydrogen periodate (). This is commercially available, but can also be produced by the oxidation of

iodate An iodate is the polyatomic anion with the formula . It is the most common form of iodine in nature, as it comprises the major iodine-containing ores. Iodate salts are often colorless. They are the salts of iodic acid. Structure Iodate is pyram ...

s with

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

and sodium hydroxide. Or, similarly, from

iodide An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine defic ...

s by oxidation with

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...

and sodium hydroxide: :\overset + Cl2 + 4 NaOH -> Na3H2IO6 + 2NaCl + H2O :NaI + 4 Br2 + 10 NaOH -> Na3H2IO6 + 8 NaBr + 4 H2O Modern industrial scale production involves the

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...

oxidation of iodates, on a

lead dioxide Lead(IV) oxide is the inorganic compound with the formula PbO2. It is an oxide where lead is in an oxidation state of +4. It is a dark-brown solid which is insoluble in water. It exists in two crystalline forms. It has several important applicatio ...

() anode, with the following

standard electrode potential In electrochemistry, standard electrode potential E^\ominus, or E^\ominus_, is a measure of the reducing power of any element or compound. The IUPAC "Gold Book" defines it as: ''"the value of the standard emf (electromotive force) of a cell in wh ...

: :H5IO6 + H+ + 2e- -> IO3- + 3 H2O Metaperiodates are typically prepared by the dehydration of sodium hydrogen periodate with

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

, or by dehydrating orthoperiodic acid by heating it to 100 °C under vacuum. :Na3H2IO6 + 2 HNO3 -> NaIO4 + 2 NaNO3 + 2 H2O :H5IO6 -> HIO4 + 2 H2O They can also be generated directly from iodates by treatment with other strong oxidizing agents such as

hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ble ...

s: :NaIO3 + \overset -> NaIO4 + NaCl

Forms and interconversion

Periodate can exist in a variety of forms in aqueous media, with pH being a controlling factor. Orthoperiodate has a number of

acid dissociation constant In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :HA ...

s. :H5IO6 <=> H4IO6- + H+ :H4IO6- <=> H3IO6^2- + H+ :H3IO6^2- <=> H2IO6^3- + H+ The ortho- and metaperiodate forms also exist in equilibrium. :H4IO6- <=> IO4- + 2 H2O For this reason orthoperiodate is sometimes referred to as the di

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

of metaperiodate, written ; however, this description is not strictly accurate as

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

of shows 5 equivalent groups. At extremes of pH additional species can form. Under basic conditions a dehydration reaction can take place to form the diperiodate (sometimes referred to as mesoperiodate). :2H3IO6^2- <=> H2I2O10^4- + 2 H2O Under strongly acid conditions periodic acid can be protonated to give the '' orthoperiodonium'' cation. :H6IO6+ <=> H5IO6 + H+

Structure and bonding

In both the ortho- and metaperiodate the iodine is

hypervalent In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pe ...

, as it forms more bonds than would classically be allowed. This has been explained in terms of

dative bond In coordination chemistry, a coordinate covalent bond, also known as a dative bond, dipolar bond, or coordinate bond is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ...

s, confirming the absence of double bonding in these molecules. Exact structures vary depending on counter ions, however on average orthoperiodates adopt a slightly deformed octahedral geometry with X-ray diffraction showing I–O bond lengths of 1.89 Å. Metaperiodates adopt a distorted tetrahedral geometry with an average I–O distance of 1.78 Å.

Reactions

Cleavage reactions

Periodates can cleave carbon–carbon bonds on a variety of 1,2-difunctionalised alkanes. The most common example of this is

diol cleavage Glycol cleavage is a specific type of organic chemistry oxidation. The carbon–carbon bond in a vicinal (chemistry), vicinal diol (glycol) is Cleavage (chemistry), cleaved and instead the two oxygen atoms become double-bonded to their respective ca ...

, which was also the first to be discovered ( Malaprade reaction). In addition to diols, periodates can cleave 1,2-hydroxy ketones, 1,2-diketones, α-keto acids, α-hydroxy acids,

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s, 1,2-amino alcohols, and 1,2-diamines, to give aldehydes, ketones, and carboxylic acids. In the presence of strong acid catalyst, like H₂SO₄ or HNO₃

epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...

s are also converted into aldehyde or ketones or dicarbonyl compounds. Periodate cleavage reactions (simple)

Alkenes can also be oxidised and cleaved in the

Lemieux–Johnson oxidation The Lemieux–Johnson or Malaprade–Lemieux–Johnson oxidation is a chemical reaction in which an olefin undergoes oxidative cleavage to form two aldehyde or ketone units. The reaction is named after its inventors, Raymond Urgel Lemieux and Will ...

. This uses a catalytic loading of

osmium tetroxide Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of unusual properties, one being that the ...

which is regenerated in situ by the periodate. The overall process is equivalent to that of

ozonolysis In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds of alkenes (), alkynes (), or azo compounds () are cleaved with ozone (). Alkenes and alkynes form organic compounds in which the multiple carbon–carbon b ...

Cleavage reactions proceed via a cyclic intermediate called a periodate ester. The formation of this may be affected by pH and temperature but is most strongly affected by the geometry of the substrate, with ''

cis Cis or cis- may refer to: Places * Cis, Trentino, in Italy * In Poland: ** Cis, Świętokrzyskie Voivodeship, south-central ** Cis, Warmian-Masurian Voivodeship, north Math, science and biology * cis (mathematics) (cis(''θ'')), a trigonome ...

''-diols reacting significantly faster than ''

trans Trans- is a Latin prefix meaning "across", "beyond", or "on the other side of". Used alone, trans may refer to: Arts, entertainment, and media * Trans (festival), a former festival in Belfast, Northern Ireland, United Kingdom * ''Trans'' (fil ...

''-diols. The reactions are exothermic and are typically performed at 0 °C. As periodate salts are only readily soluble in water reactions are generally performed in aqueous media. Where solubility is an issue periodic acid may be used, as this is soluble in alcohols;

phase transfer catalyst In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of heterogeneous catalysis. Ionic rea ...

s are also effective in

biphasic Biphasic, meaning having two phases, may refer to: * Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform. Examples ...

reaction mixtures. In extreme cases the periodate may be exchanged for

lead tetraacetate Lead(IV) acetate or lead tetraacetate is an organometallic compound with chemical formula . It is a colorless solid that is soluble in nonpolar, organic solvents, indicating that it is not a salt. It is degraded by moisture and is typically store ...

which reacts in a similar manner and is soluble in organic solvents (

Criegee oxidation The Criegee oxidation is a glycol cleavage reaction in which vicinal diols are oxidized to form ketones and aldehydes using lead tetraacetate. It is analogous to the Malaprade reaction, but uses a milder oxidant. This oxidation was discovere ...

Periodate cleavage is often utilized in molecular biochemistry for the purposes of modifying

saccharide In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ma ...

rings, as many five- and six-membered sugars have vicinal diols. Historically it was also used to determine the structure of monosaccharides. Periodate cleavage may be performed on an industrial scale to form

dialdehyde starch Dialdehyde starch is a polysaccharide derived by chemical modification from starch. It is prepared by periodate oxidation of starch. It has found use in the paper industry, where in it has been shown to improve the wet strength The wet strength ...

which has uses in

paper production The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products. Manufacturing process The pulp is fed to a paper machine where it is formed as a paper web a ...

Oxidation reactions

Periodates are powerful

oxidising agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

s. They can oxidise

catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amoun ...

to 1,2-benzoquinone and

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para' ...

to 1,4-benzoquinone.

Sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...

s can be effectively oxidised to

sulfoxide In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...

s. Periodates are sufficiently powerful to generate other strong inorganic oxidisers such as

permanganate A permanganate () is a chemical compound containing the manganate(VII) ion, , the conjugate base of permanganic acid. Because the manganese atom is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion is a tra ...

and

ruthenium tetroxide Ruthenium tetroxide is the inorganic compound with the formula RuO4. It is a yellow volatile solid that melts near room temperature. It has the odor of ozone. Samples are typically black due to impurities. The analogous OsO4 is more widely used ...

Niche uses

Periodates are highly selective etchants for certain

ruthenium Ruthenium is a chemical element with the Symbol (chemistry), symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to ...

-based oxides. Several

staining Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology (microscopic study of biological tissues), in cytology (microscopic study of cells), and in the ...

agents use in microscopy are based around periodate (e.g.

periodic acid–Schiff stain Periodicity or periodic may refer to: Mathematics * Bott periodicity theorem, addresses Bott periodicity: a modulo-8 recurrence relation in the homotopy groups of classical groups * Periodic function, a function whose output contains values tha ...

and

Jones' stain Jones' stain, also Jones stain, is a methenamine silver-Periodic acid-Schiff stain used in pathology. It is also referred to as methenamine PAS which is commonly abbreviated MPAS. It stains for basement membrane and is widely used in the investi ...

). Periodates have also been used as oxidising agents for use in

pyrotechnics Pyrotechnics is the science and craft of creating such things as fireworks, safety matches, oxygen candles, explosive bolts and other fasteners, parts of automotive airbags, as well as gas-pressure blasting in mining, quarrying, and demolition. ...

. In 2013 the

US Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

announced that it would replace the environmentally harmful chemicals

barium nitrate Barium nitrate is the inorganic compound with the chemical formula Ba( NO3)2. It, like most barium salts, is colorless, toxic, and water-soluble. It burns with a green flame and is an oxidizer; the compound is commonly used in pyrotechnics. Man ...

and potassium perchlorate with sodium metaperiodate for use in their tracer ammunition.

Other oxyanions

Periodate is part of a series of oxyanions in which

can assume

s of −1, +1, +3, +5, or +7. A number of neutral

iodine oxide Iodine oxides are chemical compounds of oxygen and iodine. Iodine has only two stable oxides which are isolatable in bulk, iodine tetroxide and iodine pentoxide, but a number of other oxides are formed in trace quantities or have been hypothesize ...

s are also known.

References

{{reflist, 30em Periodates