Supports potassium permanganate

Scheme 6.36 Oxidation of enamines with alumina-supported potassium permanganate.

Systems currently marketed may be grouped by mechanisms or form. Two clearly defined systems are based on chemical reaction those utilising supported potassium permanganate in a sachet as a non-specific oxidant for many compounds, including ethylene (Abe, 1990 Robertson, 1991) and one novel method based on the specific reaction of 3,6-dicarboxy-1,2,4,5-tetrazine with some alkenes like ethylene at concentrations around one part in 10 , as required to prevent the ripening of some produce. A key difference between the opportunities for use of these two systems is that the tetrazine-based system functions in homogeneous solution in plastics films that are purple-coloured and which bleach as reaction occurs. 

The use of sofid supports in conjunction with permanganate reactions leads to modification of the reactivity and selectivity of the oxidant. The use of an inert support, such as bentonite (see Clays), copper sulfate pentahydrate, molecular sieves (qv) (151), or sifica, results in an oxidant that does not react with alkenes, but can be used, for example, to convert alcohols to ketones (152). A sofid supported permanganate reagent, composed of copper sulfate pentahydrate and potassium permanganate (153), has been shown to readily convert secondary alcohols into ketones under mild conditions, and in contrast to traditional permanganate reactivity, the reagent does not react with double bonds (154). 

Primary and secondary alcohols are oxidized slowly at low temperatures by benzyltriethylammonium permanganate in dichloromethane primary alcohols produce methylene esters (60-70%), resulting from reaction of the initially formed carboxylate anion with the solvent, with minor amounts of the chloromethyl esters and the carboxylic acids. Secondary alcohols are oxidized (75-95%) to ketones [34] the yields compare favourably with those obtained using potassium permanganate on a solid support. 1,5-Diols are oxidized by potassium permanganate under phase-transfer catalytic conditions to yield 8,8-disubstituted-8-valerolactones [35] (Scheme 10.1). 

Trans -substituted diarylalkenes undergo oxidative cleavage upon treatment by potassium permanganate in the presence of moist alumina as a solid support (equation 32)158. Under the same conditions, cyclic alkenes, with medium-sized rings, give acyclic dialdehydes (equation 33). 

The well known ease with which a terlary bromide loses hydrobromic.,acid to give an unsaturated compound has led Ostling to question the structure of 1,1,2 trimethylcyclopropane. Zelinsky who prepaBed it states that it slowly decolorizes potassium permanganate. Certain products of the action of nitric acid, however,support tha cyclopropane structure very strongly and the compound can best be considered to have a cyclic structure. 

Syn hydroxyladon is most commonly performed using osmium tetroxide or potassium permanganate, and addition usually occurs hx)mrhe less hindered side of the double bond in the absence of other directing effects. With Aese reagents, the steieospecificity of syn addition results from formation of cyclic ester intermediates. Support for these arises from isolation of solid addition complexes (1) on reaction of... 

Potassium permanganate adsorbed on either silica or alumina can also be used to cleave double bonds under mild conditions and in good yields. In one procedure the alkene, dissolved in benzene, is passed through a column packed with KMn04 on a silica gel support.The reaction occurs rapidly at room temperature and is equally effective for the cleavage of all types of double bonds, even some that are inert to other traditionid methods. ... 

The theory that the oxygenated recoil species are formed in reactions between recoil atoms and surrounding oxyanions or dislodged oxygens is supported by the results of mixed crystal experiments. Mixed crystals (solid solutions) of potassium chromate in potassium sulfate [35) and fluoberyllate (50), and potassium permanganate in potassium perchlorate (67) have been investigated. The results are given in Table II. These... 

The role of the supports in the reactions just described is not clear. Even less clear is the function of copper sulfate pentahydrate, in the presence of which oxidations with solid potassium permanganate result in excellent yields of ketones. Traces of water are essential. Primary alcohols, on the other hand, give poor yields of aldehydes and acids [844 (equation 255). 

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