Nitrobenzene halogenated, nucleophilic aromatic

The nucleophilic displacement of halogens in aromatic compounds by fluorine is aided by utilizing an appropriate catalyst. Polymer-supported aminopyridinium salts have been found to be versatile catalysts for the synthesis of aryl fluorides. The advantage of the catalyst is that it can be recycled and used again. l-Chloro-4-nitrobenzene (3) is converted to l-fluoro-4-nitrobenzene (4) in 71 % isolated yield using this method. The catalyst used has the structure 5.91... 

The formation of substituted anilides from the reaction of amides with nitrobenzene is the first example of the direct formation of aromatic amide bonds via nucleophilic aromatic substitution for hydrogen. This reaction proceeds in high yield and regioselectivity, and does not require the use of halogenated materials or auxiliary leaving groups. Furthermore, these studies have demonstrated that the use of O2 as the terminal oxidant in NASH reactions can result in a highly selective and environmentally favorable route for the production of PNA and PPD. 

The relative orders in which the halogens are displaced in nucleophilic aromatic substitution reactions has been advanced as an u-ment both for and against the intermediate complex mechanism. In particular Fierens and Halleux (91), who found the order, F < Cl < Br < I, for the reactions of the l-halo-2,4-dinitrobenzenes and the l-halo-2,4-dinitro-6-methylbenzenes with potassium iodide in dry acetone, and Hammond and Parks (92), who obtained the same order for the reactions of the l-halo-2,4-dinitrobenzenes with N-methylaniline in both nitrobenzene and 99.8% ethanol, have offered these results as support for a one-step mechanism, since this is the sequence observed in non-activated nucleophilic aromatic substitution reactions and in typical aliphatic displacements. Hammond has, however, pointed out that these experiments do not permit a distinction between a one-step mechanism and a two-step mechanism in which the second step is rate-determining (90). 

A variety of methods for the direct amination of nitrobenzene, that do not require halogenated aromatic compounds, have been reported, including both vicarious (eliminative) [16, 17,19,42] and oxidative versions of nucleophilic substitution of hydrogen. Recently, we have described the aminatimi of 1,3-dinitrobenzene promoted by fluoride ions through photochemical activation [43], Also, the use of KMn04 as oxidant is of great practical value [3,44]. 

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