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Hydroperoxides or peroxols are compounds containing the hydroperoxide functional group (ROOH). If the R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of
organic peroxide 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 b ...
s, which have the formula ROOR. Organic hydroperoxides can either intentionally or unintentionally initiate explosive polymerisation in materials with unsaturated chemical bonds.


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 The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical s ...
of , less than half the strengths of C−C, C−H, and C−O bonds. Hydroperoxides are typically more volatile than the corresponding alcohols: * ''tert''-BuOOH (b.p. 36°C) vs ''tert''-BuOH (b.p. 82-83°C) * CH3OOH (b.p. 46°C) vs CH3OH (b.p. 65°C *
cumene hydroperoxide Cumene hydroperoxide is the organic compound with the formula C6H5CMe2OOH (Me = CH3). An oily liquid, it is classified as an organic hydroperoxide. Products of decomposition of cumene hydroperoxide are methylstyrene, acetophenone, and cumyl ...
(b.p. 153°C) vs cumyl alcohol (b.p. 202°C)


Miscellaneous reactions

Hydroperoxides are mildly acidic. The range is indicated by 11.5 for CH3OOH to 13.1 for Ph3COOH. Hydroperoxides can be reduced to
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s 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. Another way to evaluate the content of peracids and peroxides is the volumetric titration with
alkoxide In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, wh ...
s such as sodium ethoxide. The
phosphite ester The general structure of a phosphite ester showing the lone pairs on the P In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of ...
s 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 ''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, for example the Halcon process. It is normally supplied as a 69– ...
(TBHP) is employed for the production of propylene oxide. Of specialized interest, chiral epoxides are prepared using hydroperoxides as reagents in the
Sharpless epoxidation The Sharpless epoxidation reaction is an enantioselective chemical reaction to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols. The oxidizing agent is ''tert''-butyl hydroperoxide. The method relies on a catalyst formed fro ...
.


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: :C6H12 + O2 → (CH2)5CO + H2O Drying oils, as found in many paints and varnishes, function via the formation of hydroperoxides.


Hock processes

Compounds with
allyl In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...
ic and
benzyl In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. Nomenclature In IUPAC nomenclature, the prefix benzyl refers to a substi ...
ic C−H bonds are especially susceptible to oxygenation. Such reactivity is exploited industrially on a large scale for the production of phenol by the
Cumene process The cumene process (cumene-phenol process, Hock process) is an industrial process for synthesizing phenol and acetone from benzene and propylene. The term stems from cumene (isopropyl benzene), the intermediate material during the process. It was i ...
or Hock process for its
cumene Cumene (isopropylbenzene) is an organic compound that contains a benzene ring with an isopropyl substituent. It is a constituent of crude oil and refined fuels. It is a flammable colorless liquid that has a boiling point of 152 °C. Nearl ...
and
cumene hydroperoxide Cumene hydroperoxide is the organic compound with the formula C6H5CMe2OOH (Me = CH3). An oily liquid, it is classified as an organic hydroperoxide. Products of decomposition of cumene hydroperoxide are methylstyrene, acetophenone, and cumyl ...
intermediates. 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.Heinz G. O. Becker ''Organikum'', Wiley-VCH, 2001, pp. 206–207


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 ''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, for example the Halcon process. It is normally supplied as a 69– ...
,
cumene hydroperoxide Cumene hydroperoxide is the organic compound with the formula C6H5CMe2OOH (Me = CH3). An oily liquid, it is classified as an organic hydroperoxide. Products of decomposition of cumene hydroperoxide are methylstyrene, acetophenone, and cumyl ...
and
ethylbenzene hydroperoxide 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 hydroperox ...
: :R-H + O2 → ROOH :
Auto-oxidation Autoxidation (sometimes auto-oxidation) refers to oxidations brought about by reactions with oxygen at normal temperatures, without the intervention of flame or electric spark. The term is usually used to describe the gradual degradation of organic ...
reaction is also observed with common
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...
s, such as diethyl ether,
diisopropyl ether Diisopropyl ether is secondary ether that is used as a solvent. It is a colorless liquid that is slightly soluble in water, but miscible with organic solvents. It is used as an extractant and an oxygenate gasoline additive. It is obtained indust ...
, tetrahydrofuran, and 1,4-dioxane. An illustrative product is diethyl ether peroxide. Such compounds can result in a serious explosion when distilled. To minimize this problem, commercial samples of THF are often inhibited with
butylated hydroxytoluene Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidation ...
(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: :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: : 2C(O2H)sub>2O22Csub>2(O2)2 + 2 H2O Addition of this initial adduct to a second equivalent of the carbonyl: :R2C=O + R2C(OH)OOH → 2C(OH)sub>2O2 Further replacement of alcohol groups: : 2C(OH)sub>2O2 + 2 H2O22C(O2H)sub>2O2 + 2 H2O Triphenylmethanol reacts with hydrogen peroxide gives the unusually stable hydroperoxide, Ph3COOH.Bryant E. Rossiter and Michael O. Frederick "Triphenylmethyl Hydroperoxide" E-EROS Encyclopedia of Reagents for Organic Synthesis, 2013.


Naturally occurring hydroperoxides

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


References

{{Functional group Organic compounds Food additives Functional groups