Reduction of aryl nitro compound

Reduction of aryl nitro compounds (Sec tion 22 9) The standard method for the preparation of an arylamine is by nitra tion of an aromatic ring followed by reduction of the nitro group Typical re ducing agents include iron or tin in hydro chloric acid or catalytic hydro genation... 

Reduction of aryl nitro compounds with less-powerful reducing agents, especially in alkaline media, gives what may appear to be a mysterious conglomerate of bimolecular reduction products. For example, with nitrobenzene,... 

This is most practically carried out via the use of aryl diazonium salts (Ar-N2 Cl ) which are derived from aryl amines(Ar-NH2) which are themselves produced by the catalytic reduction of aryl nitro compounds (Ar-N02). Thus, we would seem to need to put a nitro group para to the original hydroxyl group. We must be aware of phenol s immense reactivity and the subsequent danger of polynitration. To avoid this danger, we treat phenol with dilute nitric acid instead of with concentrated nitric acid and with concentrated sulfuric acid as the catalyst. 

Reduction of aryl carbonyl compounds.2 This reduction has been conducted traditionally by the Clemmenson or Wolff-Kishner method or by reduction of dithioketals. Actually it can be conducted in high yield with W-7 Raney nickel in 50% aqueous ethanol (2-5 hours). Nitro, halo, and cyano groups are also reduced. Examples ... 

The reduction of aromatic nitro compounds to N-aryl-hydroxylamines by o-xylene-a,a -dithiol occurs when an iron... 

Primary Amines—Several new and improved methods for the preparation of aromatic primary amines have been described. " The catalytic reduction of aromatic nitro-compounds to amines with hydrazine hydrate in the presence of iron(iii) oxide hydroxide proceeds smoothly and in high yields. Nitroarenes (1) react with Grignard reagents in the presence of copper(i) iodide, and are alkylated selectively on the aromatic moiety, accompanied by reduction of the nitro-group to the amine (Scheme 1). Both aryl and alkyl azides are rapidly... 

The reduction of aromatic nitro compounds in the presence of molybdenum hexacarbonyl and a carboxylic acid leads to the formation of A -aryl-carboxamides. 

The reduction of several indolo[2,3-a]quinolizidines by BY gave novel products resulting from reduction of the indole double bond, cleavage of the C-D ring junction, or reduction of a lactame to a carbinol amine [371]. The known reduction of aromatic nitro compounds has been used as a key step in the synthesis of 2-aryl-2/f-benzotriazoles. Thus, treatment of the o-nitrophenylazo dye 342 gave the 2-aryl-2/7-benzotriazole-l-oxides 343 in good yields [513]. 

Scheme 4. The compounds and intermediates on the rear plane of the bicubic system (farthest from the reader) are protonated on the pyridine nitrogen atom those on the front plane (nearest the reader) are not. Laviron s work has shown that the reduction of 14 and its corresponding N-oxide34, and indeed probably most aryl nitro compounds, proceeds by an ECEC sequence leading to the neutral N,N-dihydroxy [ArN(OH)2] intermediate at all proton concentrations from Ho = —6 to pH 9.6. This substance then loses water to form the nitroso compound, which then undergoes a second sequence leading to the arylhydroxylamine.

The facile homogeneous catalysed reduction of acid chlorides to alcohols has many advantages over reduction with sodium borohydride in hydroxylic solvents where rapid reaction of the acid chloride with the solvent can occur [10]. The procedure has been incorporated into a simple one-pot conversion of aroyl chlorides into the corresponding benzyl chlorides (Scheme 11.1) under liquidrliquid or solid-liquid two-phase conditions [11], The reduction of a limited number of aryl compounds was reported with ca. 70% overall yields, although poorer yields result from the reduction of 4-nitro-, 2-cyano- and 2,4-dichlorobenzoyl chlorides, and the reduction failed completely with terphthaloyl chloride and with its 2,3,5,6-tetrafluoro derivative [11]. 

The nitro group of aromatic nitro compounds has been removed with sodium bor-ohydride. This reaction involves an addition-elimination mechanism. Reduction of the C—N bond on aromatic amines with Li metal in THF generates the aryl compounds.Sodium nitrite, sodium bisulfite in EtOH/water/acetic acid does a similar reduction.Conversion of the aniline derivative to the methanesulfona-mide and subsequent treatment with NaH and NH2CI gives the same result. The BuaSnH reagent also reduces isocyanides, RNC (prepared from RNH2 by for-mylation followed by 17-31), to a reaction that can also be accomplished... 

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