4-Nitro-aniline

Vapours which can be readily condensed e.g., chloroform, aniline, nitro-benzene, etc.) are readily detected by the device shown in Fig. 5 i(b). It is essentially a cold finger with a deep indentation or weU at the lower end. In this way two or three drops of liquid can easily be collected and removed by a capillary tube for qualitative tests. 

Apart from tetryl, which is discussed in the chapter on nitramines (Vol. Ill), the only aniline nitro derivative that has gained any considerable importance as an explosive is hexanitrodiphenylamine, or hexyl. None of the other nitro derivatives has proved of greater interest though some achieved temporary importance (as for example tetranitroaniline) or aroused a theoretical interest. 

Compounds which are vanishingly weakly basic in H20, such as nitro-anilines, nitro-aromatic or halo-nitro-aromatic compounds are protonated to a greater or less extent in superacids, allowing them to be used as indicators in Hammett Acidity Function measurements. Cl- which has essentially zero base strength in H20 is protonated by the superacids to HC1, which being monomolecular is expelled as a gas from the highly associated solvents. This provides a commonly-used important route to synthesis of anhydrous fluorides, fluorosulfates and triflates. 

Preparation of Aniline.—In preparing aniline, nitro benzene is usually reduced by means of tin and hydrochloric acid or iron and hydrochloric acid, the latter being the commercial process. In the reaction with tin, molecular proportions of the tin and acid must be used and the hydrogen produced must be sufficient for the reduction of the nitro benzene. The reaction proceeds as follows ... 

Copper, chromium, iron, most metals or their salts, alcohols, acetone, organic materials, aniline, nitro-methane, combustible materials Fuming nitric acid, oxidizing gases Acids, activated carbon... 

White crystals, m.p. 114" C. Manufactured by reacting aniline with excess ethanoic acid or ethanoic anhydride. Chief use is in the manufacture of dye intermediates such as p-nitro-acetanilide, p-nitroaniline and p-phenylene-diamine, in the manufacture of rubber, and as a peroxide stabilizer. 

N-phenylhydroxylamine, PhNHOH and further reduction can give azoxybenzene, azobenzene, hydrazobenzene and aniline. The most important outlet commercially for the nitro-compounds is the complete reduction to the amines for conversion to dyestufTs. This is usually done in one stage with iron and a small amount of hydrochloric acid. 

Place 24 ml. (24 5 g.) of aniline, 13 ml. (15 5 g.) of nitro-benzene,t and 62 ml. (75 g.) of the anhydrous glycerol in the flask and mix thoroughly. (If the glycerol is still warm from the dehydration, cool the mixture in water.) Now add slowly 36 ml. (66 g.) of concentrated sulphuric acid, shaking the mixture thoroughly during the addition. The mixture at first... 

Only the mono-amines are described here. The diamines are more frequently encountered as reduction products of dinitrobenzenes and nitro-anilines, and the chief reactions of the phenylenediamines are therefore given in Section 23, pp. 384-388. 

Various basic substances, such as aromatic amines (naphthyl-amines dissolve with difficulty in dil. HCl, diphenylamine only in cone. HCl, triphenylamine insoluble) nitro-anilines some amino-carboxylic acids. 

The diazonium salts 145 are another source of arylpalladium com-plexes[114]. They are the most reactive source of arylpalladium species and the reaction can be carried out at room temperature. In addition, they can be used for alkene insertion in the absence of a phosphine ligand using Pd2(dba)3 as a catalyst. This reaction consists of the indirect substitution reaction of an aromatic nitro group with an alkene. The use of diazonium salts is more convenient and synthetically useful than the use of aryl halides, because many aryl halides are prepared from diazonium salts. Diazotization of the aniline derivative 146 in aqueous solution and subsequent insertion of acrylate catalyzed by Pd(OAc)2 by the addition of MeOH are carried out as a one-pot reaction, affording the cinnamate 147 in good yield[115]. The A-nitroso-jV-arylacetamide 148 is prepared from acetanilides and used as another precursor of arylpalladium intermediate. It is more reactive than aryl iodides and bromides and reacts with alkenes at 40 °C without addition of a phosphine ligandfl 16]. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Benzyloxy-6-bromo-4-nitro-JV-(2-propeny])aniline (5.82 g, 16 mmol), tetra-ii-butylammonium bromide (5.16 g, 16 mmol) and titjN (4.05 g, 40 mmol) were dissolved in DMF (15 ml). Palladium acetate (72 mg, 2 mol%) was added and the reaction mixture was stirred for 24 h. The reaction mixture was diluted with EtOAc, filtered through Cclite, washed with water, 5"/o HCl and brine, dried and evaporated in vacuo. The residue was dissolved in CHjClj and filtered through silica to remove colloidal palladium. Evaporation of the eluate gave the product (4.32 g) in 96% yield. 

Attack on the electrophilic C-2 may occur as in the 2-aminothiazoles series, which probably explains the rearrangements observed in acidic medium (121, 711, 712, 723, 724), in aqueous medium with NaOAc (725), or with aqueous NaHCOj (725) (Scheme 232). That the initial attack probably involves the C-2 atom is substantiated by the fact that this rearrangement occurs under extremely mild conditions for 2-iinino-3-substituted-5-nitro-4-thiazolines (725). As the whole mechanism proposed (see p. 92) is reversible, when imino derivatives are submitted to such rearrangement conditions the rearrangement is expected to occur faster if steric interaction between 3- and 4-substituents exists in the 2-imino isomer. Another reaction may occur in acidic medium phenylimino-2-bipheny]-3,4-4-thiazoline hydrolyzed with hydrochloric acid gives the corresponding 4-thiazoline-2-one and aniline (717). 

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