Claycop

Clay-supported ferric nitrate (Clayfen) or clay-supported cupric nitrate (Claycop), pentane, rt, 60-97% yield. ... 

The oxidation has also been accomplished with Claycop (montmorillonite K-10 clay supported cupric nitrate). The reaction of 96 to 102 was complete in 1.5-7 h with 81-93% yields. The time can be reduced to 5-10 minutes using ultrasound with minimal effect on yields. The major limitation of this protocol was the observation that only R = aryl gave product. Oxidation of 4-alkyl substituents was inert to these conditions with recovery of starting 96. 

Copper(II) nitrate immobilized on K 10 clay (claycop)-hydrogen peroxide system is an effective oxidant for a variety of substrates and provides excellent yields (Scheme 6.31) [104] wherein the maintenance of pH of the reaction mixture is not required. 

Scheme 6.31 Oxidation reactions with claycop and hydrogen peroxide.

To elevate p-selectivity in nitration of toluene is another important task. Commercial production of p-nitrotoluene up to now leads with twofold amount to the unwanted o-isomer. This stems from the statistical percentage of o m p nitration (63 3 34). Delaude et al. (1993) enumerate such a relative distribution of the unpaired electron densities in the toluene cation-radical—ipso 1/3, ortho 1/12, meta 1/12, and para 1/3. As seen, the para position is the one favored for nitration by the attack of NO (or NO2 ) radical. A procednre was described (Delande et al. 1993) that used montmorillonite clay supported copper (cupric) nitrate (claycop) in the presence of acetic anhydride (to remove excess humidity) and with carbon tetrachloride as a medinm, at room temperature. Nitrotoluene was isolated almost quantitatively with 23 1 76 ratio of ortho/meta/para mononitrotoluene. 

Laszlo introduced an oxidative cleavage of dithioacetals by their clayfen (4) and claycop reagents under mild conditions with excellent yields [46, 47]. These reagents are convenient sources of the nitrosonium ion NO+, a soft reactive Lewis acid species, well adapted for attack of the soft sulfur atom. 

Claycop was prepared in a similar manner [47] and, unlike clayfen, showed no loss of reactivity on standing in an open box. 

The dithioacetal (0.01 mol) was stirred for a few hours at room temperature with clayfen (4) (10.4 g, 11 mmol of ferric nitrate) or with claycop (12.1 g, 20 mmol of copper nitrate) in toluene, n-pentane or, preferably, dichloromethane (120ml). Evolution of nitrogen oxides occurred rapidly. Stirring was maintained until gas evolution ceased. The clay was then filtered off and washed twice with portions (50 ml) of the solvent. The resulting pale-yellow or slightly green solution was filtered through a small quantity of neutral aluminium oxide and the solvent was evaporated under vacuum. In the case of dithiane and dithiolane derivatives, this afforded the pure carbonyl compound in excellent yield. 

Aromatic nitrations performed in the presence of KIO montmori11onite lead to increased para selectivity. With toluene as test molecule, the proportion of para-nitrotoluene reaches 79% when using clay-supported copper(II) nitrate ("claycop") in the presence of acetic anhydride under high dilution conditions in CC1 (ref. 

The reported improvement in yields and selectivities in both mono- and poly-nitration of aromatic compounds using Claycop with acetic anhydride (and if necessary nitric acid) in tetrachloromethane has been investigated.28 The reagent system is found to be modestly catalytic and regioselective in the mononitration of toluene but is neither catalytic nor regioselective in the nitration of 2-nitrotoluene. 

Laszlo and co-workers[11,25-271 developed a reagent known as claycop, which is Cu(NC>3)2 supported on acidic montmorillonite clay, that selectively nitrates toluene using nitric acid, and acetic anhydride as water trapping reagent (Menke conditions). The reaction conditions required to obtain high selectivity of the para-isomer... 

Normally, nitration of deactivated compounds (and therefore polynitration of toluene) is carried out using aggressive nitric acid - oleum mixtures. Dinitration of toluene with mixed acids produces a 4 1 ratio of 2,4- and 2,6-dinitrotoluenes, from which the former is isolated for manufacture of toluenediisocyanate (TDI) and toluenediamine, both of which are used in the manufacture of polyurethanes. Zirconium and hafnium derivatives catalyse nitration of o-nitrotoluene, but ratios of 2,4- 2,6-dinitrotoluene are modest (66 34).12 Dinitration of toluene using Claycop (copper nitrate on K10 clay), acetic anhydride and nitric acid in the presence of carbon tetrachloride produced dinitrotoluenes in a yield of 85% with a ratio of 2,4- 2,6-dinitrotoluene of 9 1.13 This method, however, requires a large excess of nitric acid, the use of an unacceptable solvent and long reaction times. The direct nitration of toluene to 2,4-dinitrotoluene using nitric acid over a zeolite P catalyst, with azeotropic removal of water, is reported to give a 2,4 2,6 ratio of 14, but full results are yet to be published.14... 

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. 

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