Permanganate phase transfer-assisted

Anilines are converted into nitrosoarenes ArNO by the action of hydrogen peroxide in the presence of [Mo(0)(02)2(H20) (HMPA)]224, whereas catalysis of the reaction by titanium silicate and zeolites results in the formation of azoxybenzenes ArN (0)=NAr225. Azo compounds ArN=NAr are formed in 42-99% yields by the phase-transfer assisted potassium permanganate oxidation of primary aromatic amines in aqueous benzene containing a little tetrabutylammonium bromide226. The reaction of arylamines with chromyl chloride gives solid adducts which, on hydrolysis, yield mixtures of azo compounds, p-benzoquinone and p-benzoquinone anils 234227. 

The Phase-Transfer-Assisted Permanganate Oxidation of Alkenes and Alkynes... 

Although CY-diketones are only rarely isolated from aqueous permanganate oxidations there is conclusive proof that they are intermediates in the reaction (16). Of-Diketones are resistant to further oxidation under anhydrous conditions and can thus be isolated in good yields from the phase transfer assisted reactions. Howeverf under aqueous conditions oxidative cleavage takes place rapidly, thus preventing the accumulation of these products. 

The mechanisms of permanganate oxidations have been the subject of a fairly intensive study which has now lasted for almost a century. While many of these studies were carried out in aqueous solutions, much of what was learned is also germane to an understanding of the reactions which occur in phase transfer assisted reactions. Although most of these studies are interrelated they can conveniently be discussed under the following headings products, substituent effects, isotope effects, and solvent effects, with the latter being of particular importance to the phase transfer assisted reactions. 

Solvent Effects. Information on the effect of solvent polarity of the phase transfer assisted permanganate oxidation of alkenes has been obtained by studying the oxidation of methyl cinnamate by tetrabutylammonium permanganate in tv/o different solvents, acetone and methylene chloride (37). 

Less rigorous reaction conditions are required to cleave the double bond to form ketones and carboxylic acids. Phase-transfer-assisted permanganate oxidations in the presence of quaternary ammonium salts,439 652-654 crown ethers,439,655 or polyethers566 usually ensure high yields. Terminal alkenes are transformed to carboxylic acids with one carbon atom less than the starting compound.653,654... 

Phase-Transfer-Assisted Permanganate Oxidations of Terminal... 

For a review of phase-transfer assisted permanganate oxidations, see Lee, D.G., in Trahanovsky, W.S. Oxidation in Organic Chemistry, pt. D Academic Press, NY, 1982, pp. 147-206. 

The phase-transfer-assisted permanganate oxidation of alkynes and alkenes has been reviewed. Terminal and internal alkynes are oxidized to 1,2-dicarbonyl compounds by the combined action of diphenyl disulphide, ammonium peroxidisulphate and water or by sodium periodate in the presence of ruthenium dioxide (equation 34). Other reagents for the conversion of acetylenes into 1,2-dicarbonyl compounds are hydrogen peroxide in the presence of (2,6-dicarboxylatopyridine)iron(II), the complex oxo(A, A -ethylenebissalicylideneiminato)chromium(V) trifluoromethanesulphonate (216)and ruthenium tetroxide as a mediator in electrooxidation. l-Acetoxyalkan-2-ones 217 are obtained by the oxidation of terminal acetylenes with sodium perborate and mercury(II) acetate in acetic acid ". Terminal alkynes give a-ketoaldehydes 218 on treatment with dilute hydrogen peroxide, combined with mercury(II) acetate and sodium molybdate or sodium tungstate under phase-transfer conditions. ... 

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