Английская Википедия:Hydroperoxide
Hydroperoxides or peroxols are compounds of the form ROOH, where R stands for any group, typically organic, which contain the hydroperoxy functional group (Шаблон:Chem2). Hydroperoxide also refers to the hydroperoxide anion (Шаблон:Chem2) 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]
Properties
The Шаблон:Chem2 bond length in peroxides is about 1.45 Å, and the Шаблон:Chem2 angles (R = H, C) are about 110° (water-like). Characteristically, the Шаблон:Chem2 dihedral angles are about 120°. The Шаблон:Chem2 bond is relatively weak, with a bond dissociation energy of Шаблон:Convert, less than half the strengths of Шаблон:Chem2, Шаблон:Chem2, and Шаблон:Chem2 bonds.[2][3]
Hydroperoxides are typically more volatile than the corresponding alcohols:
- tert-BuOOH (b.p. 36Шаблон:Nbsp°C) vs tert-BuOH (b.p. 82-83Шаблон:Nbsp°C)
- [[Methyl hydroperoxide|Шаблон:Chem2]] (b.p. 46Шаблон:Nbsp°C) vs [[Methanol|Шаблон:Chem2]] (b.p. 65Шаблон:Nbsp°C)
- cumene hydroperoxide (b.p. 153Шаблон:Nbsp°C) vs cumyl alcohol (b.p. 202Шаблон:Nbsp°C)
Miscellaneous reactions
Hydroperoxides are mildly acidic. The range is indicated by 11.5 for [[Methyl hydroperoxide|Шаблон:Chem2]] to 13.1 for Шаблон:Chem2.[4]
Hydroperoxides can be reduced to alcohols with lithium aluminium hydride, as described in this idealized equation:
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:
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]
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]
Drying oils, as found in many paints and varnishes, function via the formation of hydroperoxides.
Hock processes
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 Шаблон:Chem2, to give hydroperoxyl (ROO•), which then continues the cycle of H-atom abstraction.[12]
Formation
By autoxidation
The most important (in a commercial sense) peroxides are produced by autoxidation, the direct reaction of Шаблон:Chem2 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]
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]
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:
In some cases, these hydroperoxides convert to give cyclic diperoxides:
Addition of this initial adduct to a second equivalent of the carbonyl:
Further replacement of alcohol groups:
Triphenylmethanol reacts with hydrogen peroxide gives the unusually stable hydroperoxide, Шаблон:Chem2.[14]
Naturally occurring hydroperoxides
Many hydroperoxides are derived from fatty acids, steroids, and terpenes. The biosynthesis of these species is affected extensively by enzymes.
References
- ↑ Шаблон:Ullmann
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ Шаблон:Ullmann
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ 7,0 7,1 Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Ullmann
- ↑ Шаблон:Cite journal.
- ↑ Brückner, R. Reaktionsmechanismen: organische Reaktionen, Stereochemie, moderne Synthesemethoden, pp. 41–42, Spektrum Akademischer Verlag, Munich, 2004, Шаблон:ISBN (in German)
- ↑ 12,0 12,1 Heinz G. O. Becker Organikum, Wiley-VCH, 2001, Шаблон:ISBN pp. 206–207
- ↑ Шаблон:Cite journal
- ↑ Bryant E. Rossiter and Michael O. Frederick "Triphenylmethyl Hydroperoxide" E-EROS Encyclopedia of Reagents for Organic Synthesis, 2013. Шаблон:Doi
- ↑ Шаблон:Cite journal
