Clayfen, iron nitrate

The direct conversion of styrene to P-nitrostyrene using clay doped with nitrate salts has been reported. Styrene and clayfen (iron nitrate on clay) or clayan (ammonium nitrate on clay) are mixed well and then heated at 100-110 °C in solid state to give P-nitrostyrene in 68% yield.551 A more simple one-pot synthesis of P-nitrostyrene from styrene has been reported P-nitrostyrene is prepared in 47% yield on treatment of styrene with CuO HBF4,12, andNaN02 in MeCN at room temperature.55b... 

Keywords sulfide, clayfen, iron(III) nitrate, microwave irradiation, sulfoxide... 

Bakke et al. (1982) have shown how montmorillonite catalyses chlorination and nitration of toluene nitration leads to 56 % para and 41 % ortho derivative compared to approximately 40 % para and 60 % ortho derivatives in the absence of the catalyst. Montmorillonite clays have an acidity comparable to nitric acid / sulphuric acid mixtures and the use of iron-exchanged material (Clayfen) gives a remarkable improvement in the para, ortho ratio in the nitration of phenols. The nitration of estrones, which is relevant in making various estrogenic drugs, can be improved in a remarkable way by using molecular engineered layer structures (MELS), while a reduction in the cost by a factor of six has been indicated. With a Clayfen type catalyst, it seems possible to manipulate the para, ortho ratio drastically for a variety of substrates and this should be useful in the manufacture of fine chemicals. In principle, such catalysts may approach biomimetic chemistry our ability to predict selectivity is very limited. 

Scheme 4.3 Oxidation of alcohols by iron(lll) nitrate supported on clay (clayfen).

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]. 

Reaction of 6-formyl-5,7,8,9-tetrahydro-ll//-pyrido[2,l-b]quinazolin-ll-one (135) with Clayfen [K-10 montmorillonite clay supported iron(III) nitrate] in boiling methylene chloride for 2.5 h gave a mixture of 6,6-dinitro-6,7,8,9-tetrahydro (136) and 6-formyl-8,9-dihydro-ll//-pyrido[2,l-6]-quinazolin-ll-ones (137) (90JOC6198). 

Clayfen (1.13 g, 1.2 mmol of iron(III) nitrate) is thoroughly mixed with neat thioacetal lb (0.227 g, 1 mmol) in the solid state. The material is transferred in a test tube and placed in an alumina bath inside the microwave oven and irradiated (40 s). Upon completion of the reaction, monitored on TLC (hexane-EtOAc, 8 2, v/v), the product was extracted into ethylene chloride. The resulting solution is passed through a small bed of neutral alumina. Evaporation of the solvent delivers pure p-nitrobenzaldehyde 2b in 97% yield. In the case of cyclic thio acetals and ketals, the liberated dithiols bind to the clay surface rather tightly and a simple washing of the clayfen affords clean products. 

In a small beaker oxime (10 mmol) and freshly prepared clayfen reagent (6.6 mmol of iron(III) nitrate) were mixed together to make an intimate mixture. The beaker was placed in a household microwave oven for the specified time. The residue was washed with CH2C12 (10 mL) and filtered. The filtrate was evaporated to dryness to afford the corresponding carbonyl compound. 

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. 

Although it is possible to obtain the acetone solvate of anhydrous iron(III) nitrate, this oil decomposes in a vigorous exothermic reaction. However, it is possible to stabilize the oil by impregnation on the KIO acidic montmorillonite. The name clayfen has been given to the resulting reagent. ... 

The scope of the Ritter reaction can also be extended by avoiding strong acid as the carbenium ion initiator. In at least one case it is possible to omit this reagent entirely because of the facility of 5 1 reaction. Thus, reflux of r-butyl bromide in acetonitrile or propionitrile for 24 h led to formation of A -f-butylamide products. Less commonly used initiators have included cation exchange resins and clayfen. In this latter case, the clay-supported iron(III) nitrate is believed to give rise to nitrosonium ions, which react with the alkyl halide substrate to produce a carbenium ion. Yields of amide from this technique are generally modest (21-35%). 

A rapid MW oxidation protocol for the oxidation of alcohols to carbonyl compounds has been reported by Vanna et al. using montmorillonite KIO clay-supported iron(III) nitrate (clayfen) (Scheme 7). The simple solvent-free experimental procedure involves mixing of neat substrates... 

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... 

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 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. 

Activation. KIO clay may be used crude, or after simple thermal activation. Its acidic properties are boosted by cation exchange (i.e. by iron(III) or zinc(II) ) or by deposition of Lewis acids, such as zinc(II) or iron(III) chloride (i.e. clayzic and clayfec ). In addition, KIO is a support of choice for reacting salts, for example nitrates of thallium(III), iron(III) ( clayfen ), or copper(II) ( claycop ). Multifarious modifications (with a commensurate number of brand names) result in a surprisingly wide range of applications coupled with the frequent imprecise identification of the clay (KIO or one of its possible substitutes mentioned above), they turn KIO into a Proteus impossible to grab and to trace exhaustively in the literature. 

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