Nitroaromatic halides

The unreactivity of l-bromoadamantane with 02 demonstrated a lack of any appreciable electron transfer type substitution process (eq. 12). Although an electron transfer type mechanism has been demonstrated for nitroaromatic halides (see Section II. C), the difference in reduction potentials between O2 and aliphatic bromides is apparently too great to allow such a transfer to occur. 

Early investigations of reactions of organomagnesium compounds with nitro compounds led to mixtures of products, and gave little indication that they might be useful [5]. However, it has now been established that with two equivalents of an alkylmagnesium halide in THF, nucleophilic addition to the ring of a variety of nitroaromatic compounds occurs, as summarized in Table 4.1. The product of the addition is a nitronate anion, which may be converted into various products, as illustrated by the example of 2-nitronaphthalene. 

Although the superoxide ion was also successful in destroying some aliphatic and aromatic halogenated hydrocarbons, resulting in the formation of barium carbonate, soluble halides, and water, it was unsuccessful in destroying nitroaromatic compounds, or aliphatic compounds having an amine or a nitrile group attached to them... 

Carbonyl group Nitroaromatic group A-oxide function Carbon-carbon double bond Aryl halide... 

Although it is difficult to predict which drugs are likely to be prone to photodegradation, there are certain chemical functions that are expected to introduce photoreactivity, including carbonyl, nitroaromatic and N-oxide functions, aryl halides, alkenes, polyenes and sulfides. The mechanisms of photodegradation are of such complexity as to have been fully elucidated in only a few cases. We will consider two examples - chlorpromazine and ketoprofen. 

Poly(V-vinyl-2-pyrrolidone) has been studied as a carrier for palladium in the hydrogenation of oleflns f and nitroaromatics, hydrodehalogenation of organic halides,f t and carbonylation of aUyl halides. - In these cases PVP mostly likely played the role of supporting in situ formed colloidal Pd, rather than that of a well-defined ligand. 

Not only the nitroaromatic species, such as IV, but also some simpler compounds, which used to be considered as typical substrates of the 8 2 reactions, can be involved in multistep radical-forming nucleophilic substitutions. Evidence has been accumulating over the last years that the nucleophilic substitution with alkyl halides occurs, at least in some instances, by the single-electron transfer mechanism. It has been suggested [29,30] that the SET and Sn2 mechanisms represent the extremes of a wide spectrum of mechanistic possibilities for substitution reactions. It has been deduced on qualitative theoretical grounds that the propensity of alkyl halide R—X to react with nucleophiles via an electron-transfer step depends crucially on the stability of the three-electron bond R—X in the initially formed radical-anion species. A more electronegative R will stabilize this bond and bring about a shift in the mechanism from the Sn2 to the SET type, which has then experimentally been shown to be a correct conclusion, see Ref. [30]. 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

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