Aromatic Nitro Compounds with Other Functional Groups

Aromatic Nitro Compounds with Other Functional Groups + + +... 

Aromatic Nitro Compounds with Other Functional Groups Aromatic Nitro Compounds with Other Functional Groups Pentachloronitrobenzene Aromatic Organophosphorous Compounds Aromatic Organophosphorous Compounds Parathion... 

AROMATIC NITRO COMPOUNDS WITH OTHER FUNCTIONAL GROUPS... 

AletalHydrides. Metal hydrides can sometimes be used to prepare amines by reduction of various functional groups, but they are seldom the preferred method. Most metal hydrides do not reduce nitro compounds at all (64), although aUphatic nitro compounds can be reduced to amines with lithium aluminum hydride. When aromatic amines are reduced with this reagent, a2o compounds are produced. Nitriles, on the other hand, can be reduced to amines with lithium aluminum hydride or sodium borohydride under certain conditions. Other functional groups which can be reduced to amines using metal hydrides include amides, oximes, isocyanates, isothiocyanates, and a2ides (64). 

In a bifunctional compound, if a reagent reacts with one functional group preferentially, even though the other is apparently susceptible to the reaction conditions, the reaction is said to be chemoselective. Two illustrative examples are the reduction of a carbonyl group in the presence of a cyano, nitro or alkoxycarbonyl group (Section 5.4.1, p. 519 see also Metal hydrides, Section 4.2.49, p. 445) and the acylation of an aromatic amino group in the presence of a phenolic group (Section 6.9.3, p. 984). 

Reduction. The selective reduction of aromatic nitro compounds to the amines by using PdCl and a water-soluble phosphine ligand with CO in aqueous NaOH and xylene does not affect other functional groups, such as double bond, ketone, nitrile, and halide groups. 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Again this year several accounts have appeared which describe the cyclization of o-substituents. As these do not involve the aromatic ring directly, only a few examples will be mentioned. Dopp has continued his studies on the photochemistry of aryl nitro-compounds and has further commented upon the cyclization of o-substituents, particularly t-butyl, with the nitro function 168 this and a variety of other light-induced processes of aryl nitro-compounds are the subject of an excellent review by the same author.74 The two nitro-groups in 2,2 -dinitrodiphenylmethane undergo light-induced cyclization and the process is reported to provide a new route to the dibenzo[c,/][l,2]diazepine system (134).16 ... 

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