Displacement of other groups

The displacement of both halides and nitro groups from polynitroarylenes has been covered in Sections 4.8.1 and 4.8.2. The centres of low electron density induced by electron-withdrawing nitro groups also allow the displacement of many other groups, including hydrogen, alkoxy, aryloxy, sulfonate ester etc. 

Hydrogen displacement from unsymmetrical substrates like 1,3-dinitrobenzene can produce a mixture of products. Reaction of 1,3-dinitrobenzene with hydroxylamine produces a mixture of 2,4-dinitroaniline and 2,6-dinitroaniline l,3-diamino-2,4-dinitrobenzene is formed if two equivalents of hydroxylamine are employed. ° 

The effect which amino functionality has on the thermal and impact sensitivity of polyni-troarylenes (Section 4.8.1.4) makes amination by VNS a method with much future potential for energetic materials synthesis. Other carbon, nitrogen, oxygen and sulfur nucleophiles can displace aromatic hydrogen examples with 1,3-dinitrobenzene and 1,3,5-trinitrobenzene are extensive. 

6-Trinitrophenetole (8) can be prepared by heating 2,4,6-trinitroanisole (7) in ethanol containing a catalytic amount of sodium ethoxide. This reaction is so facile that methanol 

Aryloxy groups are much easier to displace compared to primary and secondary alkox-ide anions and so, aryl ethers are generally more useful in displacement reactions. Amine nucleophiles react with unsymmetrical aryl ethers to form the amine of the heavier nitrated moiety.Accordingly, 2,4,6-trinitrodiphenyl ether reacts with ammonia to expel phenoxide 

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The most useful method of preparing azides involves the displacement of other groups by N3, for example, Eq. (1). Other useful methods involve the... 

In comparison with conventional nucleophilic displacement of other groups, such as chlorine, bromine and iodine, fluorodenitration is much faster. Therefore, substitution can be carried out under milder reaction conditions. In particular, lower temperatures allow the synthesis of complex, thermolabile derivatives, e.g. [ F]spiroperidol from its inactive nitro analog using rubidium [ F]fluoride. ... 

A few studies on solvolyses by alcohols and by water are available. The hydrolyses studied include displacement of alkylamino groups from acridine antimalarials and of halogen from other systems. In all cases, these reactions appeared to be first-order in the heterocyclic substrate. By a detailed examination of the acid hydrolysis of 2-halogeno-5-nitropyridine, Reinheimer et al. have shown that the reaction rate varies as the fourth power of the activity of water, providing direct evidence that the only reactive nucleophile is neutral water, as expected. 

With certain exceptions, primary fluorination of carbohydrate derivatives is very facile. Fluoride displacement of sulfonyloxy groups by potassium, or cesium, fluoride in 1,2-ethanediol and a variety of other solvents has frequently been used. Tetrabutylammonium (sometimes tetraethylammonium) fluoride in dipolar, aprotic solvents (mainly ace-... 

CONDENSATION REACTIONS A. Displacement of Other Functional Groups by Azide Ion... 

The electron-withdrawing character of Cr(CO)3 can be used to promote the displacement of leaving groups on nonactivated aromatic rings in SNAr reactions.117 Perhaps other SNAr reactions can be run, taking advantage of Cr(CO)3 and of PTC activation.117a... 

The XH NMR specrum of 201 showed all four dimethylamino groups to be equivalent, an indication of rapid exchange between them. This presumably occurs by rapid displacement of one group by the other. 

An ideal process would, in principle, be one where elemental fluorine could be used as indicated in Figure 9.1. Recent work with elemental fluorine has demonstrated that this is a reasonable approach in some circumstances, e.g. when the opportunity for forming isomers is limited. However, nucleophilic displacement of other halogens, or mobile groups such as nitro, by fluoride ion, when the aromatic compound is susceptible to nucleophilic attack, is a more versatile approach at the present time (Figure 9.2). 

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