Metal nitrates aromatic nitration with

Unsubstituted positions inpolyfluonnated aromatics are nitrated under vigorous conditions 1,3 5-Tnfluorobenzene reacts with oleum and a metal nitrate at elevated temperature to provide l,3,5-trifluoro-2,4,6 tnnitrobenzene [11] (equation 12)... 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

Davies and C. B. Thomas [58] reported an interesting instance of nitration of arylthallium (III) aromatic complexes with nitrogen dioxide at room tempera ture. Tallium (III) fluoroacetate was used as the agent metallating an aromatic ring which can react with NO2 ... 

Nitric acid salts in the presence of other acids have been previously described (Vol. I, p, 46). It was recently reported by Crivello [125] that metal nitrates in trifluoroacetic anhydride (TFAA) can nitrate aromatic compounds at room temperature in very good yields. Thus ammonium nitrate with TFAA nitrated benzene to nitrobenzene with a yield of 95%. 

Novel reagents consisting of metallic nitrates impregnated on montmorillonite have been introduced in aromatic nitration. With clay-supported copper(II) nitrate in the presence of acetic anhydride it is possible to nitrate toluene quantitatively with a high para preference (79% para, 20% ortho, 1% meta). Also, good para selectivities have been found on nitration of some other aromatic hydrocarbons with copper(II) nitrate on clay. Halobenzenes are mononitrated with clay-supported copper(II) nitrate in the presence of acetic anhydride. Compared to other methods high para ortho ratios are obtained under these conditions. ... 

The metal acetylacetonates have been successfully nitrated with several nitrating agents that have been used to nitrate reactive aromatic systems. Nitrating agents commonly used to nitrate aromatic and aliphatic compounds will destroy the metal chelate. 

Aliphatic nitro compounds cannot as a rule be prepared in the same way as the aromatic nitro compounds. The more rapid oxidation of aliphatic hydrocarbons by nitric acid is the main interfering factor, so that conditions must be chosen which minimize oxidation and promote nitration. The oxidation reactions are of such complexity in these cases that no attempt will be made to formulate them. Only a summary of the conditions favoring nitration will be given. The use of a solvent such as ether for carrying out the reaction is often successful. Also dilute nitric acid has been used, and alkyl (generally ethyl) nitrate. In the Friedel-Crafts reaction with ethyl nitrate, aluminium chloride is used as catalyst. In aliphatic nitrations with ethyl nitrate, alkalis such as metal alkoxides (NaOC Hs) are found to be best. The use of alkalis brings out the similarity of this reaction to aldol condensations which are also favored by alkalis. An example of aliphatic nitration, in comparison with an aromatic one may be given ... 

The nitration of aromatic compounds with nitric acid in an ionic liquid was shown by Earle et al. [96,97]. It was found that triflate and triflimide ionic liquids catalyze nitration reactions with nitric acid. This methodology has the advantage that water is the only by-product (Scheme 5.2-44). This process could also be carried out in phosphonium ionic liquids [46]. Acidic ionic liquids such as [EMIM][HS04] or the Davis-type ionic liquids [41] could also be used but gave lower reaction rates and selectivities [98]. The effect of metal triflates such as Yb(OTf)3 or Cu(OTf)2 dissolved in [N-butyl-N-methylpyrrolidium][triflimide] was investigated by Handy and Egrie [99]. These gave similar yields and selectivities to ionic liquids systems... 

One of the most successful approaches for altering the regioselectirity of aromatic nitration involves nitration via metallation fl35]. This was discovered as a catalytic nitration which at the same time also provides unusual isomer distribution. The most important metallative nitration reactions involve metallation with mercury, palladium, and thallium salts. 

MCM-41-supported metal (Yb, Zn) bis[(perfluoroalkyl)sulfonyl]imides were reported as effective catalysts for nitration of aromatic compounds with 1 eq. of 65 wt% nitric acid in the liquid phase Equation (8.68). The enhanced electron-drawing and steric effects from longer perfluori-nated alkyl chains were found to promote this action. Water exhibits also a positive effect. The catalysts were recycled without substantial loss of catalytic activity [103]. 

Primary aromatic amides are crystaUine sohds with definite melting points. Upon boiling with 10-20 per cent, sodium or potassium hydroxide solution, they are hydrolysed with the evolution of ammonia (vapour turns red htmus paper blue and mercurous nitrate paper black) and the formation of the alkah metal salt of the acid ... 

The most notable chemistry of the biscylopen-tadienyls results from the aromaticity of the cyclopentadienyl rings. This is now far too extensively documented to be described in full but an outline of some of its manifestations is in Fig. 25.14. Ferrocene resists catalytic hydrogenation and does not undergo the typical reactions of conjugated dienes, such as the Diels-Alder reaction. Nor are direct nitration and halogenation possible because of oxidation to the ferricinium ion. However, Friedel-Crafts acylation as well as alkylation and metallation reactions, are readily effected. Indeed, electrophilic substitution of ferrocene occurs with such facility compared to, say, benzene (3 x 10 faster) that some explanation is called for. It has been suggested that. 

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