Hydroperoxide

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The general structure of an organic hydroperoxide with the blue marked functional group, where R stands for any group, typically organic FunktionelleGruppen Hydroperoxide.svg
The general structure of an organic hydroperoxide with the blue marked functional group, where R stands for any group, typically organic

Hydroperoxides or peroxols are compounds of the form ROOH, where R stands for any group, typically organic, which contain the hydroperoxy functional group (−OOH). Hydroperoxide also refers to the hydroperoxide anion (−OOH) and its salts, and the neutral hydroperoxyl radical (•OOH) consist of an unbond hydroperoxy group. When R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of organic peroxides, which have the formula ROOR. Organic hydroperoxides can either intentionally or unintentionally initiate explosive polymerisation in materials with unsaturated chemical bonds. [1]

Contents

Properties

The O−O bond length in peroxides is about 1.45  Å, and the R−O−O angles (R = H, C) are about 110° (water-like). Characteristically, the C−O−O−H dihedral angles are about 120°. The O−O bond is relatively weak, with a bond dissociation energy of 45–50 kcal/mol (190–210 kJ/mol), less than half the strengths of C−C, C−H, and C−O bonds. [2] [3]

Hydroperoxides are typically more volatile than the corresponding alcohols:

Miscellaneous reactions

Hydroperoxides are mildly acidic. The range is indicated by 11.5 for CH3OOH to 13.1 for Ph3COOH. [4]

Hydroperoxides can be reduced to alcohols with lithium aluminium hydride, as described in this idealized equation:

4 ROOH + LiAlH4 → LiAlO2 + 2 H2O + 4 ROH

This reaction is the basis of methods for analysis of organic peroxides. [5] Another way to evaluate the content of peracids and peroxides is the volumetric titration with alkoxides such as sodium ethoxide. [6] The phosphite esters and tertiary phosphines also effect reduction:

ROOH + PR3 → OPR3 + ROH

Uses

Precursors to epoxides

"The single most important synthetic application of alkyl hydroperoxides is without doubt the metal-catalysed epoxidation of alkenes." In the Halcon process tert-butyl hydroperoxide (TBHP) is employed for the production of propylene oxide. [7]

Of specialized interest, chiral epoxides are prepared using hydroperoxides as reagents in the Sharpless epoxidation. [8]

The Sharpless epoxidation Sharpless epoxidation DE.svg
The Sharpless epoxidation

Production of cyclohexanone and caprolactone

Hydroperoxides are intermediates in the production of many organic compounds in industry. For example, the cobalt catalyzed oxidation of cyclohexane to cyclohexanone: [9]

C6H12 + O2 → (CH2)5C=O + H2O

Drying oils, as found in many paints and varnishes, function via the formation of hydroperoxides.

Hock processes

Synthesis of cumene hydroperoxide Hock-Phenol.png
Synthesis of cumene hydroperoxide

Compounds with allylic and benzylic C−H bonds are especially susceptible to oxygenation. [10] Such reactivity is exploited industrially on a large scale for the production of phenol by the Cumene process or Hock process for its cumene and cumene hydroperoxide intermediates. [11] Such reactions rely on radical initiators that reacts with oxygen to form an intermediate that abstracts a hydrogen atom from a weak C-H bond. The resulting radical binds O2, to give hydroperoxyl (ROO•), which then continues the cycle of H-atom abstraction. [12]

Synthesis of hydroperoxides of alkene and singlet oxygen in an Schenck ene reaction Schenk-En-Reaktion.png
Synthesis of hydroperoxides of alkene and singlet oxygen in an Schenck ene reaction

Formation

By autoxidation

The most important (in a commercial sense) peroxides are produced by autoxidation, the direct reaction of O2 with a hydrocarbon. Autoxidation is a radical reaction that begins with the abstraction of an H atom from a relatively weak C-H bond. Important compounds made in this way include tert-butyl hydroperoxide, cumene hydroperoxide and ethylbenzene hydroperoxide: [7]

R−H + O2 → R−OOH


Tetrahydrofuran peroxide formation.svg

Auto-oxidation reaction is also observed with common ethers, such as diethyl ether, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane. An illustrative product is diethyl ether peroxide. Such compounds can result in a serious explosion when distilled. [12] To minimize this problem, commercial samples of THF are often inhibited with butylated hydroxytoluene (BHT). Distillation of THF to dryness is avoided because the explosive peroxides concentrate in the residue.

Although ether hydroperoxide often form adventitiously (i.e. autoxidation), they can be prepared in high yield by the acid-catalyzed addition of hydrogen peroxide to vinyl ethers: [13]

C2H5OCH=CH2 + H2O2 → C2H5OCH(OOH)CH3

From hydrogen peroxide

Many industrial peroxides are produced using hydrogen peroxide. Reactions with aldehydes and ketones yield a series of compounds depending on conditions. Specific reactions include addition of hydrogen peroxide across the C=O double bond:

R2C=O + H2O2 → R2C(OH)OOH

In some cases, these hydroperoxides convert to give cyclic diperoxides:

[R2C(O2H)]2O2 → [R2C]2(O2)2 + 2 H2O

Addition of this initial adduct to a second equivalent of the carbonyl:

R2C=O + R2C(OH)OOH → [R2C(OH)]2O2

Further replacement of alcohol groups:

[R2C(OH)]2O2 + 2 H2O2 → [R2C(O2H)]2O2 + 2 H2O

Triphenylmethanol reacts with hydrogen peroxide gives the unusually stable hydroperoxide, Ph3COOH. [14]

Naturally occurring hydroperoxides

Many hydroperoxides are derived from fatty acids, steroids, and terpenes. The biosynthesis of these species is affected extensively by enzymes.

Illustrative biosynthetic transformation involving a hydroperoxide. Here cis-3-hexenal is generated by conversion of linolenic acid to the hydroperoxide by the action of a lipoxygenase followed by the lyase-induced formation of the hemiacetal. LyaseNonenalHemiAc.png
Illustrative biosynthetic transformation involving a hydroperoxide. Here cis-3-hexenal is generated by conversion of linolenic acid to the hydroperoxide by the action of a lipoxygenase followed by the lyase-induced formation of the hemiacetal.

Inorganic hydroperoxides

Structure of a square planar palladium hydroperoxide complex Karen'sOOH.svg
Structure of a square planar palladium hydroperoxide complex

Although hydroperoxide often refers to a class of organic compounds, many inorganic or metallo-organic compounds are hydroperoxides. One example involves sodium perborate, a commercially important bleaching agent with the formula Na2[(HO)2B]2(OO)2)]. It acts by hydrolysis to give a boron-hydroperoxide: [16]

[(HO)2B]2(OO)2)2− + 2 H2O ⇌ 2 [(HO)3B(OOH)]−

This hydrogen peroxide then releases hydrogen peroxide:

[(HO)3B(OOH)]− + H2O ⇌ B(OH)−4 + H2O2

Several metal hydroperoxide complexes have been characterized by X-ray crystallography. Some form by the reaction of metal hydrides with oxygen gas: [17]

LnM−H + O2 → LnM−O−O−H (Ln refers to other ligands bound to the metal)

Some transition metal dioxygen complexes abstract H atoms (and sometimes protons) to give hydroperoxides:

LnM(O2) + H → LnMOOH

Related Research Articles

<span class="mw-page-title-main">Ether</span> Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R)

In organic chemistry, ethers are a class of compounds that contain an ether group—a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group. They have the general formula R−O−R′, where R and R′ represent the organyl groups. Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether". Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.

<span class="mw-page-title-main">Hydrogen peroxide</span> Chemical compound

Hydrogen peroxide is a chemical compound with the formula H2O2. 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 in water for consumer use and in higher concentrations for industrial use. Concentrated hydrogen peroxide, or "high-test peroxide", decomposes explosively when heated and has been used as both a monopropellant and an oxidizer in rocketry.

In chemistry, peroxides are a group of compounds with the structure R−O−O−R, where the R's represent a radical and O's are single oxygen atoms. Oxygen atoms are joined to each other and to adjacent elements through single covalent bonds, denoted by dashes or lines. The O−O group in a peroxide is often called the peroxide group, though some nomenclature discrepancies exist. This linkage is recognized as a common polyatomic ion, and exists in many molecules.

<span class="mw-page-title-main">Cumene process</span> Industrial process

The cumene process is an industrial process for synthesizing phenol and acetone from benzene and propylene. The term stems from cumene, the intermediate material during the process. It was invented by R. Ūdris and P. Sergeyev in 1942 (USSR), and independently by Heinrich Hock in 1944.

<span class="mw-page-title-main">Epoxide</span> Organic compounds with a carbon-carbon-oxygen ring

In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile.

<span class="mw-page-title-main">Diethyl ether peroxide</span> Chemical compound

Diethyl ether hydroperoxide is the organic compound with the formula C2H5OCH(OOH)CH3. It is a colorless liquid. Diethyl ether hydroperoxide and its condensation products are responsible for the explosive organic peroxides that slowly form upon exposure of diethyl ether to ambient air and temperature conditions.

<span class="mw-page-title-main">Peroxy acid</span> Organic acid with an −OOH group

A peroxy acid is an acid which contains an acidic −OOH group. The two main classes are those derived from conventional mineral acids, especially sulfuric acid, and the peroxy derivatives of organic carboxylic acids. They are generally strong oxidizers.

<span class="mw-page-title-main">Organic peroxides</span> Organic compounds of the form R–O–O–R’

In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group. If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily breaks, producing free radicals of the form RO•. Thus, organic peroxides are useful as initiators for some types of polymerization, such as the acrylic, unsaturated polyester, and vinyl ester resins used in glass-reinforced plastics. MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can explosively combust. Organic peroxides, like their inorganic counterparts, are often powerful bleaching agents.

<span class="mw-page-title-main">Selenium dioxide</span> Chemical compound

Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium. It is used in making specialized glasses as well as a reagent in organic chemistry.

<span class="mw-page-title-main">Enol ether</span> Class of chemical compounds

In organic chemistry an enol ether is an alkene with an alkoxy substituent. The general structure is R2C=CR-OR where R = H, alkyl or aryl. A common subfamily of enol ethers are vinyl ethers, with the formula ROCH=CH2. Important enol ethers include the reagent 3,4-dihydropyran and the monomers methyl vinyl ether and ethyl vinyl ether.

<span class="mw-page-title-main">Dakin oxidation</span> Organic redox reaction that converts hydroxyphenyl aldehydes or ketones into benzenediols

The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide (H2O2) in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidised, whereas the H2O2 is reduced.

<span class="mw-page-title-main">Lithium peroxide</span> Chemical compound

Lithium peroxide is the inorganic compound with the formula Li2O2. Lithium peroxide is a white solid, and unlike most other alkali metal peroxides, it is nonhygroscopic. Because of its high oxygen:mass and oxygen:volume ratios, the solid has been used to remove CO2 from and release O2 to the atmosphere in spacecraft.

<i>tert</i>-Butyl hydroperoxide Chemical compound

tert-Butyl hydroperoxide (tBuOOH) is the organic compound with the formula (CH3)3COOH. It is one of the most widely used hydroperoxides in a variety of oxidation processes, like the Halcon process. It is normally supplied as a 69–70% aqueous solution. Compared to hydrogen peroxide and organic peracids, tert-butyl hydroperoxide is less reactive and more soluble in organic solvents. Overall, it is renowned for the convenient handling properties of its solutions. Its solutions in organic solvents are highly stable.

<span class="mw-page-title-main">Cumene hydroperoxide</span> Aromatic organic chemical compound

Cumene hydroperoxide is the organic compound with the formula C6H5C(CH3)2OOH. An oily liquid, it is classified as an organic hydroperoxide. Products of decomposition of cumene hydroperoxide are methylstyrene, acetophenone, and 2-phenyl-2-propanol.

<span class="mw-page-title-main">Chromium(VI) oxide peroxide</span> Chemical compound

Chromium(VI) oxide peroxide is the name given to a collection of chromium coordination complexes. They have the formula CrO(O2)2L where L is a ligand. These species are dark blue and often labile. They all feature oxo ligand and two peroxo ligands, with the remaining coordination sites occupied by water, hydroxide, ether, or other Lewis bases.

<span class="mw-page-title-main">Selenenic acid</span> Class of chemical compounds

A selenenic acid is an organoselenium compound and an oxoacid with the general formula RSeOH, where R ≠ H. It is the first member of the family of organoselenium oxoacids, which also include seleninic acids and selenonic acids, which are RSeO2H and RSeO3H, respectively. Selenenic acids derived from selenoenzymes are thought to be responsible for the antioxidant activity of these enzymes. This functional group is sometimes called SeO-selenoperoxol.

<span class="mw-page-title-main">Azoxybenzene</span> Chemical compound

Azoxybenzene is organic compound with the formula C6H5N(O)NC6H5. It is a yellow, low-melting solid. The molecule has a planar C2N2O core. The N-N and N-O bond lengths are nearly the same at 1.23 Å.

<span class="mw-page-title-main">Metal peroxide</span> Metal-containing compounds with peroxide (O2) ions/groups

In chemistry, metal peroxides are metal-containing compounds with ionically- or covalently-bonded peroxide groups. This large family of compounds can be divided into ionic and covalent peroxide. The first class mostly contains the peroxides of the alkali and alkaline earth metals whereas the covalent peroxides are represented by such compounds as hydrogen peroxide and peroxymonosulfuric acid. In contrast to the purely ionic character of alkali metal peroxides, peroxides of transition metals have a more covalent character.

<span class="mw-page-title-main">Ethylbenzene hydroperoxide</span> Chemical compound

Ethylbenzene hydroperoxide is the organic compound with the formula C6H5CH(O2H)CH3. A colorless liquid, EBHP is a common hydroperoxide. It has been used as an O-atom donor in organic synthesis. It is chiral. Together with tert-butyl hydroperoxide and cumene hydroperoxide, ethylbenzene hydroperoxide is important commercially.

<span class="mw-page-title-main">Dicumyl peroxide</span> Chemical compound

Dicumyl peroxide is an organic compound with the formula (C6H5CMe2O)2 (Me = CH3). Classified as a dialky peroxide, it is produced on a large scale industrially for use in polymer chemistry. It serves as an initiator and crosslinking agent in the production of low density polyethylene.

References

  1. ↑ Klenk, Herbert; Götz, Peter H.; Siegmeier, Rainer; Mayr, Wilfried. "Peroxy Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_199. ISBN   978-3527306732.
  2. ↑ Bach, Robert D.; Ayala, Philippe Y.; Schlegel, H. B. (1996). "A Reassessment of the Bond Dissociation Energies of Peroxides. An ab Initio Study". J. Am. Chem. Soc. 118 (50): 12758–12765. doi:10.1021/ja961838i.
  3. ↑ Otto Exner (1983). "Stereochemical and conformational aspects of peroxy compounds". In Saul Patai (ed.). PATAI'S Chemistry of Functional Groups. Wiley. pp. 85–96. doi:10.1002/9780470771730.ch2. ISBN   978-0-470-77173-0.
  4. ↑ Klenk, Herbert; Götz, Peter H.; Siegmeier, Rainer; Mayr, Wilfried. "Peroxy Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_199. ISBN   978-3527306732.
  5. ↑ Higuchi, T.; Zuck, Donald Anton (1951). "Behaviors of Several Compounds as Indicators in Lithium Aluminum Hydride Titration of Functional Groups". Journal of the American Chemical Society. 73 (6): 2676. doi:10.1021/ja01150a073.
  6. ↑ Martin, A. J. (1957). "Potentiometric titration of hydroperoxide and peracid in Anhydrous Ethylenediamine". Analytical Chemistry. 29: 79–81. doi:10.1021/ac60121a022.
  7. 1 2 Roger A. Sheldon (1983). Patai, Saul (ed.). Syntheses and Uses of Hydroperoxides and Dialkylperoxides. PATAI'S Chemistry of Functional Groups. John Wiley & Sons. doi:10.1002/9780470771730.ch6.
  8. ↑ Hill, J. G.; Sharpless, K. B.; Exon, C. M.; Regenye, R. (1985). "Enantioselective Epoxidation Of Allylic Alcohols: (2s,3s)-3-propyloxiranemethanol". Org. Synth. 63: 66. doi:10.15227/orgsyn.063.0066.
  9. ↑ Michael T. Musser (2005). "Cyclohexanol and Cyclohexanone". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_217. ISBN   978-3527306732.
  10. ↑ Knight, H. B.; Swern, Daniel (1954). "Tetralin Hydroperoxide". Org. Synth. 34: 90. doi:10.15227/orgsyn.034.0090..
  11. ↑ Brückner, R. Reaktionsmechanismen: organische Reaktionen, Stereochemie, moderne Synthesemethoden, pp. 41–42, Spektrum Akademischer Verlag, Munich, 2004, ISBN   3-8274-1579-9 (in German)
  12. 1 2 Heinz G. O. Becker Organikum, Wiley-VCH, 2001, ISBN   3-527-29985-8 pp. 206–207
  13. ↑ Milas, Nicholas A.; Peeler, Robert L.; Mageli, Orville L. (1954). "Organic Peroxides. XIX. α-Hydroperoxyethers and Related Peroxides". Journal of the American Chemical Society. 76 (9): 2322–2325. doi:10.1021/ja01638a012.
  14. ↑ Bryant E. Rossiter and Michael O. Frederick "Triphenylmethyl Hydroperoxide" E-EROS Encyclopedia of Reagents for Organic Synthesis, 2013. doi : 10.1002/047084289X.rt363m.pub2
  15. ↑ Matsui K (2006). "Green leaf volatiles: hydroperoxide lyase pathway of oxylipin metabolism". Current Opinion in Plant Biology. 9 (3): 274–80. doi:10.1016/j.pbi.2006.03.002. PMID   16595187.
  16. ↑ Alexander McKillop and William R Sanderson (1995): "Sodium perborate and Sodium Percarbonate: Cheap, safe and versatile oxidising agents for organic synthesis". Tetrahedron, volume 51, issue 22, pages 6145-6166. doi : 10.1016/0040-4020(95)00304-Q
  17. ↑ Denney, Melanie C.; Smythe, Nicole A.; Cetto, Kara L.; Kemp, Richard A.; Goldberg, Karen I. (2006). "Insertion of Molecular Oxygen into a Palladium(II) Hydride Bond". Journal of the American Chemical Society. 128 (8): 2508–2509. Bibcode:2006JAChS.128.2508D. doi:10.1021/ja0562292.
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