Oxidation reactions clayfen

Oxidation of Oximes A different type of N-oxidation reaction involves the direct oxidation of oximes to nitro compounds. Although a variety of oxidizing agents have been described for this reaction, the use of non-heme iron-based systems is rather limited. In this context, the oxidation of the oxime group in tetrahydro-4H-pyrido[ 1,2-a]pyrimidines was carried out at room temperature in the presence of 50 mol% of Clayfen [K10 montmorillonite-supported iron(III) nitrate] (Scheme 3.45) [147]. Under these conditions the corresponding nitro derivatives were obtained in 32-35% yield. 1SN mass studies revealed that the reaction involved the direct oxidation of the hydroxyimino group. 

A facile method for the oxidation of alcohols to carbonyl compounds has been reported by Varma et al. using montmorillonite K 10 clay-supported iron(III) nitrate (clayfen) under solvent-free conditions [100], This MW-expedited reaction presumably proceeds via the intermediacy of nitrosonium ions. Interestingly, no carboxylic acids are formed in the oxidation of primary alcohols. The simple solvent-free experimental procedure involves mixing of neat substrates with clayfen and a brief exposure of the reaction mixture to irradiation in a MW oven for 15-60 s. This rapid, ma-nipulatively simple, inexpensive and selective procedure avoids the use of excess solvents and toxic oxidants (Scheme 6.30) [100]. Solid state use of clayfen has afforded higher yields and the amounts used are half of that used by Laszlo et al. [17,19]. 

Oxidation of 1,4-dihydropyridines. Clay-supported Fe(NO,).i or Cu(NO,) (Clay-cop) oxidizes 1,4-dihydropyridines to pyridines at 25". Reactions are generally slower with Claycop than with Clayfen, but yields are usually higher. 

Oxidation of the cyclic sulfide 4-oxothiophene to the respective sulfoxide 4-ox-othiophenesulfoxide was achieved by heating with iron(III)nitrate impregnated on montmorillonite Kio clay in methylene chloride for 12h to give a 79% yield. Much faster reaction took place using clayfen under MWI to give 83% yield within... 

The oxidation of benzoin is representative of die general procedure used for the oxidation of alcohols. Clayfen (0.125 g) was thoroughly mixed with benzoin (0.106 g, 0.5 mmol) in the solid state using a vortex mixer and the material was placed in an alumina bath inside a household microwave oven equipped with a turntable and irradiated at full power (900 Watts). The reaction was monitored by TLC using, hexane AcOEt (10 1, v ). Upon completion, the product was extracted into methylene chlori. The bulk temperature of the alumina bath, whidi serves as a beat sink and convenient site to bold the reaction vessel inside the microwave oven, reached 65 °C after 30 seconds of irradiation as measured by inserting a thermomet into the alumina bath. 

The first part of this article specifically deals with representative laboratoiy applications to fine chemistry of clearly identified, unaltered KIO, excluding its modified forms (cation-exchanged, doped by salt deposition, pillared, etc.) and industrial uses in bulk. This illustrative medley shows the prowess of KIO as a strong Brpnsted acidic catalyst. The second part deals with cation-exchanged (mainly Fe ") montmorillonite. Clayfen and claycop, versatile stoichiometric reagents obtained by metal nitrate deposition on KIO, are used in oxidation and nitration reactions. They are treated under Iron(III) Nitrate-KlO Montrrufrillonite Clay and Copperfll) Nitrate-KlO Bentonite Clay. 

---