Hydroperoxide

Source: Wikipedia, the free encyclopedia.
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

unsaturated chemical bonds.[1]

Properties

The O−O

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

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
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

Compounds with

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 ene reaction

Formation

By autoxidation

The most important (in a commercial sense) peroxides are produced by

tert-butyl hydroperoxide, cumene hydroperoxide and ethylbenzene hydroperoxide:[7]

R−H + O2 → R−OOH


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.

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.[15]

References

  1. ISBN 978-3527306732
    .
  2. doi:10.1021/ja961838i
    .
  3. ISBN 978-0-470-77173-0
    .
  4. ISBN 978-3527306732
    .
  5. doi:10.1021/ja01150a073
    .
  6. doi:10.1021/ac60121a022
    .
  7. ^
    doi:10.1002/9780470771730.ch6
    .
  8. doi:10.15227/orgsyn.063.0066
    .
  9. ISBN 978-3527306732
    .
  10. doi:10.15227/orgsyn.034.0090
    ..
  11. ISBN 3-8274-1579-9
    (in German)
  12. ^
    ISBN 3-527-29985-8
    pp. 206–207
  13. doi:10.1021/ja01638a012
    .
  14. doi:10.1002/047084289X.rt363m.pub2
  15. PMID 16595187
    .
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