Acyl nitrates catalytic

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. 

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. 

The importance of the steric effect accounts for the spread of the data for lf-N in the substitution reactions. Nitration and non-catalytic chlorination, reactions of modest steric requirements, define points which fall above the arbitrary reference line. Bromination, a reaction of somewhat greater steric requirements, is not accelerated to the extent anticipated on the basis of the results for nitration or chlorination. The benzoylation reaction with large steric requirements is two orders of magnitude slower than the equally selective chlorination reaction. The unusually small ratio for lf-N/2f-N for the acylation reaction is a further indication of the steric effects. Apparently, the direct substitution reactions of naphthalene respond to the retarding steric influence of the peri hydrogen in much the same way as for other ortho substituents. 

One of the effective reagents for highly chemoselective dithioacetalization of carbonyl compounds is ceric ammonium nitrate (CAN) in chloroform. When a mixture of benzaldehyde and acetophenone was allowed to react with 1,2-ethanedithiol and a catalytic amount of CAN, the 1,3-dithiolane derived from the aldehyde was obtained in 84% yield while the ketone was recovered unchanged. It is noteworthy that aromatic ketones, 7-lactones, and acylic ketones did not react at all under these conditions and even at elevated temperatures for longer reaction times <1995T7823>. 

Various 2-oxo compounds have been subjected to a variety of reactions. Alkylation and acylation result in the formation of 1,3-disubstituted products.Similarly the Mannich reaction with morpholine gives products such as the bis compound 107. Halogenation of the 0x0 compound 108 with bromine in acetic acid," or chlorine in acetic acid, ° or with sulfuryl chloride results in formation of the monohalo derivatives 109. The chlorine atom in 109 (R = Cl) can be removed by hydrogenation over palladium on charcoal. Nitration of the chloro compound 110 with a mixture of nitric and sulfuric acids provides the nitro derivative 111, which may be catalytically reduced to the amino compound 112. If the reduction is carried out in the presence of an aldehyde, the product is a substituted amino derivative (113). Alternatively the amine 112 can be condensed with an aldehyde and the resultant Schiff base reduced to give the product 113. 

Around 4,000 t of 4-toluidine were produced in Western Europe in 1985 by the catalytic reduction of 4-nitrotoluene. It is used as an intermediate in the manufacture of organic pigments, for example those based on 3-nitro-4-aminotoluene, which is obtained by the acylation of 4-toluidine followed by nitration and removal of the protecting acyl group. Examples of important pigments based on this raw material are Pigment Yellow 1 (see Chapter 4.5.3.4) and Pigment Red 3. 

Sc(OTf)3 was widely used as a Lewis acid catalyst in Friedel-Crafts acylation [38-40], amination [41], chloromethylation [42], and nitration of aromatic compounds [43]. It also exhibited a superior catalytic activity for one-pot three-component phenol-imine Friedel-Crafts reactions to give the corresponding amino acid derivatives. Among various Lewis acids including La(OTf)3, Yb(OTf)3, YbCl3, InCl3, SnCU, and TiCU, Sc(OTf)3gave the best results (Scheme 12.21) [44]. 

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