Oxidation alkyl hydroperoxides

The most common precursor to phenolic resins is phenol. More than 95% of phenol is produced via the cumene process developed by Hock and Lang (Fig. 7.1). Cumene is obtained from the reaction of propylene and benzene through acid-catalyzed alkylation. Oxidation of cumene in air gives rise to cumene hydroperoxide, which decomposes rapidly at elevated temperatures under acidic conditions to form phenol and acetone. A small amount of phenol is also derived from coal. 

SCHEME 11. Preparation of alkyl hydroperoxides by oxidation of zinc-organometalUcs... 

As already mentioned above, sulfides are oxidized to the corresponding sulfoxides with alkyl hydroperoxides in the presence of various metal catalysts like Mo, W, Ti and V. In the presence of excess hydroperoxide further oxidation to the sulfone occurs. Sulfides are generally oxidized much faster than alkenes, which is reflected in the selective oxidation of unsaturated sulfides exclusively at the sulfur atom. During the last years many asymmetric versions of this reaction have been developed and can be mainly divided... 

In Studying asymmetric oxidation of methyl p-tolyl sulfide, employing Ti(OPr-/)4 as catalyst and optically active alkyl hydroperoxides as oxidants, Adam and coworkers collected experimental evidence on the occurrence of the coordination of the sulfoxide to the metal center. Therefore, also in this case the incursion of the nucleophilic oxygen transfer as a mechanism can be invoked. The authors also used thianthrene 5-oxide as a mechanistic probe to prove the nucleophilic character of the oxidant. 

Alkyl hydroperoxides can oxidize a variety of other nucleophilic substrates in the presence of d° metal catalysts. Thus molybdenum and vanadium catalysts have been used for the selective oxidation of tertiary amines to the corresponding JV-oxides (equations 79 and 80).225,254... 

Tetrafluoroammonium hexafluoromanganate, 4378 Tetrafluoroammonium hexafluoronickelate, 4379 Tetrafluoroammonium hexafluoroxenate, 4380 Tetranitromethane, 0543 Titanium tetraperchlorate, 4164 1,1,1 -Triacetoxy-1,2-benziodoxol-3-one, 3604 Trifluoromethyl hypofluorite, 0352 Trimethylsilyl chlorochromate, 1297 Trioxygen difluoride , 4317 Uranium hexafluoride, 4369 Vanadium trinitrate oxide, 4758 Vanadium(V) oxide, 4860 Vanadyl perchlorate, 4146 Xenon hexafluoride, 4371 Xenon tetrafluoride, 4347 Xenon tetrafluoride oxide, 4340 Xenon tetraoxide, 4857 Xenon trioxide, 4851 Xenon(II) pentafluoroorthoselenate, 4376 Xenon(II) pentafluoroorthotellurate, 4377 Zinc permanganate, 4705 ACETYLENIC PEROXIDES ACYL HYPOHALITES ALKYL HYDROPEROXIDES ALKYL TRIALKYLLEAD PEROXIDES AMINIUM IODATES AND PERIODATES AMMINECHROMIUM PEROXOCOMPLEXES BIS (FLUOROOXY)PERHALOALKANES BLEACHING POWDER CHLORITE SALTS... 

The C8 aldehyde ester may be produced by cleavage of the 9-hydroperoxide of ethyl llnoleate followed by terminal hydroperoxidation. Further oxidation would produce the corresponding dicarboxylic acid which upon decarboxylation would give rise to ethyl heptanoate. The 8-alkoxy radical may also decompose to give the C7 alkyl radical, which would yield ethyl heptanoate or form a terminal hydroperoxide, and so on. Polymerization, both intra- and intermolecular, is also a major reaction in high temperature oxidation. Combination of alkyl, alkoxy, and peroxy radicals yields a variety of dimeric and polymeric compounds with C-O-C or C-O-O-C crosslinks. 

A. Supported Mo Catalysts with Alkyl Hydroperoxides as Oxidants... 

Such reactions of hydroperoxide alkyl radicals are of importance during the oxidation of hydrocarbons in the gaseous phase where they give a relatively high yield of cyclic ethers. 

Sn2 displacement on the peroxidic bond 0-0 accounts for the reduction of alkyl-hydroperoxides and oxidation of the hydroperoxide-decomposing antioxidant (HD, Eq. 3-17) in products, generally HD(O) or HD(0)2. 

Wong s group32 investigated the chloroperoxidase-catalyzed oxidation of p-sub-stituted alkyl phenyl sulfides by hydrogen peroxide or racemic alkyl hydroperoxides as oxidant in aqueous buffer. Slow addition of H202 to the reaction mixture afforded nearly enantiopure sulfoxides (97-99% ee). Interestingly, when racemic alkyl hydroperoxides were used as oxidant, optically active alcohols and alkyl hydroperoxides were obtained (Scheme 4). 

The well-known Sharpless system for the enantioselective epoxidation of allyl alcohols has been investigated [23]. This system employs a tetra-alkoxy titanium precursor, a dialkyltartrate as an auxiliary, and an alkyl hydroperoxide as oxidant, to effect the enantioselective epoxidation. The key intermediate is thought to be a dimeric complex in which titanium is simultaneously coordinated to the chelating tartarate ligand, the substrate in the form of an oxygen bound / -allyl-oxide and an -tert-butylperoxide. 

Optimization of asymmetric oxidation of sulfides catalyzed by a Fe(salan) complex has been carried out. ° Using alkyl hydroperoxide as oxidant for sulfides, a Ti(IV) chelate of... 

Thus, 1 seems to be a true catalyst rather then a new kind of free radical initiator. This behavior is in contrast to the behavior of related manganese complexes. For example, Mn(II) carboxylates are known to decompose CHP during autoxidation of cumene l dinuclear Mn(III) complexes decompose tetralin hydroperoxide during oxidation of tetralin (an inner-sphere Mn-alkyl hydroperoxide intermediate has been proposed) trinuclear, carboxylate and oxo-bridged complexes containing Mn(II) were found to decompose CHP during the catalyzed oxidation of cumene. 

Several framework titanium-substituted mesoporous silicates, including Ti-MCM-41 (42,43), Ti-HMS (198), Ti-MCM-36 (180), Ti-MCM-48 (199), and Ti-SBA-15 (200), have shown promising activity for the epoxidation of bulky olefins with alkyl hydroperoxides as oxidants. Unfortunately, compared with the microporous MFI-type titanium silicates, the mesoporous materials exhibit low activity for epoxidation reactions. The hydrophilic nature of mesoporous silica catalysts with isomorphous titanium substitution is considered to be one of the major reasons for the low activity (179). Various attempts have been made to improve the activity. Using a different synthetic procedure, titanium species have been grafted onto... 

Diacetoxyiodo)benzene in the presence of tert-butyl hydroperoxide readily oxidizes alkenes at the allylic position (Scheme 3.88) [269]. This reaction proceeds via initial formation of the tert-butylperoxy radical and it can be extended to the oxidation of unactivated C—H bonds in alkyl esters and amides to give the corresponding keto compounds under mild conditions [270]. 

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