Oxidation oxon-alumina

Other Metallic Oxidants - Copper Sulfate or Oxone-Alumina... 

A rapid microwave oxidation protocol for the oxidation of alcohol to carbonyl compound has been reported by Varma (2001). Different types of oxidizing reagents have been used with microwave irradiations. Alcohols were converted into corresponding carbonyl compounds in the presence of montmorillonite KIO clay-sup-ported iron (111) nitrate (Clayfen), Oxone-alumina, IBD-alumina, 35% MnO doped silica, CrO,-alumina or CuSO-alumina under microwave irradiation and solvent-free conditions in few minutes (0.25-3.5 min). 

The regeneration of carbonyl compounds from 1,3-dithianes can be achieved using potassium hydrogen persulfate, Oxone , supported on wet alumina <96SL767> and by periodic acid under non-aqueous conditions <96TL4331>. The deprotection of benzyl substituted 1,3-dithianes can be achieved using the one electron oxidant [Fe(phen)3](PF6)3 <96SL315>. 

Symmetrical and unsymmetrical benzoins have been rapidly oxidized to benzils in high yields using solid reagent systems, copper(II) sulfate-alumina [105] or Oxone-wet alumina [105, 106] under the influence of microwaves (Scheme 6.32). Conventionally, the oxidative transformation of a-hydroxy ketones to 1,2-diketones is accomplished by reagents such as nitric acid, Fehling s solution, thallium(III) nitrate (TTN), ytterbium(III) nitrate, ammonium chlorochromate-alumina and dayfen. In addition to the extended reaction time, most of these processes suffer from drawbacks such as the use of corrosive acids and toxic metals that generate undesirable waste products. 

Scheme 6.32 Oxidation of a-hydroxyketones with alumina-supported copper sulfate or Oxone.

Oxone has been successfully used in aprotic solvents for oxidation reactions by dispersing it on an alumina surface. Thus, the oxidation of secondary aliphatic, alicyclic and benzylic alcohols using Oxone/wet alumina oxide in CH2CI2 or CH3CN afforded ketones in good to excellent yields (70-96%). Similarly, the conversion of cycloalkanones to lactones is also reported. 

Oxidation of sulfides and sulfoxides using Oxone dispersed on silica gel or alumina was reported . A study of surface mediated reactivity of Oxone compared its reactivity with that of ferf-butyl hydroperoxide. Oxidation of sulfides to sulfones in aprotic solvents mediated by Oxone on wet montmorillonite or clay minerals proceeds in high yields. Interestingly, when Oxone on alumina is applied for selective oxidation of sulfides in aprotic solvents, the product distribution is temperature-dependent and sulfoxides or sulfones are obtained in good to excellent yields (equation 56) . ... 

A new method for conversion of oximes to the corresponding em-halonitro derivatives using NaCl or KBr with Oxone and wet basic alumina was reported (equation 64) °. When the reaction was carried out under the same conditions but by using wet neutral alumina, complex mixtures of compounds in which the parent ketone is the most abundant product (>50%), due to the oxidative deprotection of the oxime, was obtained. 

Oxidation ofaUeyelie ketones to lactones.3 Cycloalkanones in CH2CI2 are oxidized to lactones by Oxone (1) mixed with slightly wet alumina as a heterogeneous mixture. Efficient stirring is necessary to obtain reproducible results. Yields are about 80% for 5- and 6-membered ketones, but are low with higher-membered ketones. 

Shin et al. have used a two-step route to obtain 2-unsubstituted pyrimidines from 2-thioxo DHPM derivatives. Oxidation of 22 using Oxone on wet alumina (method A) or hydrogen peroxide in the presence of a catalytic amount of vanadyl sulfate (method B) provided 1,4-dihydropyr-imidines 41, which were oxidized to 2-unsubstituted pyrimidines 44 by KMn04. However, 22 (X = S, O) with KMn04 furnished 2-hydroxypyri-midine 45 (Scheme 20) (09SL599). 

Interestingly, the reaction of a solid slurry of Oxone and wet Alumina with solutions of cyclic ketones in CH2CI2 provokes Baeyer-Villiger oxidation to give the corresponding lactones (eq 2). The same wet alumina-Oxone reagent can be used to oxidize secondary alcohols to ketones (eq 3). Aldehydes are oxidized to acids by aqueous Oxone. ... 

The partial oxidation of sulfides to sulfoxides has been accomplished in a few cases by careful control of the reaction stoichiometry and conditions. A biphasic procedure for sulfoxide formation from diaryl sulfides is shown in eq 23. However, a more attractive and versatile procedure uses a solid Oxone-wet alumina reagent with a solution of the sulfide. This method permits control of the reaction to form either the sulfoxide or the sulfone simply by adjusting the amount of oxidant and the reaction temperature, as illustrated in eq 24. These oxidations are compatible with other functionality. 

Oxone has also been recently more thoroughly studied as reagent for the oxidation of aldehydes. Aryl- and aliphatic aldehydes can be efficiently converted directly to acids or esters depending on the choice of solvent (eq 34). They can also be converted to nitriles in one pot by reaction with hydroxylamine on alumina with microwave irradiation (eq 35). ... 

Oxone adsorbed on silica gel or alumina is a very effective oxidant for the selective oxidation of primary and secondary amines to hydroxylamines without overoxidation. These reactions can even be accomplished under solvent-free conditions and with very short reaction times with heating or microwave irradiation (eq 53). Pyridine and trialkylamines were also readily oxidized to their A-oxides. It is suggested that the hydroxylamines are protected from overoxidation because of their strong adsorption to the silica gel or alumina surface. 

Oximes can be converted to their corresponding nitro compounds with Oxone and refluxing acetonitrile (eq 58). They can also be cleaved to their parent carbonyl compounds by Oxone in conjunction with glacial acetic acid, or silica gel/alumina and microwave irradiation (eq 58). Ketoximes and aldoximes are both converted to carbonyl compounds in high yields using the microwave and alumina procedure. Several of the above transformations are highlighted in the oxidative decarboxylation of a-amino acids to form ketones and carboxylic acids. ... 

Oxone in refluxing acetonitrile cleaves TMS and THP ethers to alcohols and acetals to carbonyls.In contrast, BnPhsPHSOs has been used to oxidatively cleave TMS and THP ethers and ethylene acetals to carbonyl compounds under microwave irradiation with BiCls (eqs 86 and 87). No overoxidation products were observed with this method. Oxone on alumina has also been used to cleave ketals to diols and carbonyl compounds under solvent-free conditions with microwave irradiation. 

The oxidation of aldehydes to carboxylic acids is an important transformation in organic synthesis and several methods have been developed to accomplish this conversion (Srivastava and Venkataramani, 1998). Oxidation of benzaldehydes with oxone (2 KHSO, KHSO, K2S04)/wet-alumina under microwave irradiation in solventless system is a rapid, manipulatively simple, inexpensive and selective protocol. (Nikje and Bigdeli, 2004). 

Using sohd reagent systems, copper (II) sulfate-alumina, or oxone-wet alumina symmetrical and unsymmetrical benzoins can be rapidly oxidized to benzils in high yields under the influence of microwaves (Varma et al., 1999). 

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