2.4- Dinitroaniline diazotization

In 1969 a serious explosion took place in Basle when 287 kg (1.3 kmol) of 2-chloro-4,6-dinitroaniline was diazotized in 384 kg 40% nitrosylsulfuric acid. The temperature was increased from 30 °C to 50 °C and kept at that level. Shortly afterwards the explosion occurred three workers were killed and 31 injured, some seriously. The reaction had been carried out twice before in the same way without difficulty. Detailed investigations (Bersier et al., 1971) with the help of differential scanning calorimetry showed that, at the high concentration of that batch, a strongly exothermic reaction (1500 kJ/kg) starts at about 77 °C. In contrast, when the reactants were diluted with 96% sulfuric acid to twice the volume, the reaction was found to begin at 146 °C, generating only 200 kJ/kg. 

If the water content of the diazotization system is too high, the halogen atom in halogen-substituted mono- and dinitroanilines may be replaced by a hydroxy group in a bimolecular aromatic substitution. Analogous behaviour was observed in the diazotization of pentafluoroaniline, where the 4-fluoro substituent became hydrolysed (Brooke et al., 1965). As already mentioned in Section 2.1, this side reaction does not take place if the diazotization is conducted in a dichloromethane-aqueous sulfuric acid two-phase system in the presence of tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (Iwamoto et al., 1983a, 1984). 

The so-called self-diazotization was developed by Sihlbohm (1951, 1953 a, 1953 b). It is based on the observation that several nitroaniline derivatives, on treatment with hydrochloric acid in acetic acid solution, form the corresponding chlorobenzenedi-azonium ions. 2,5-Dinitroaniline will serve as an example (Scheme 2-37). This reaction had already been discovered in principle by Meldola and Eyre in 1901. The method did not become important. 

A colorimetric procedure is described for the determination of small amounts of Compound 118 (1,2,3,4,10,10-hexa-chloro - 1,4,4a,5,8,8a - hexahydro - 1,4,.5,8 - dimethano-naphthalene). Reaction with phenyl azide to form a di-hydrotriazole derivative and subsequent treatment with diazotized dinitroaniline in strongly acid medium produce an intense red color. Amounts of the insect toxicant of 10 to 40 micrograms in the final 10-ml. aliquot are readily determined with a spectrophotometer. Commonly used insect toxicants do not interfere. 

The excess phenyl azide is then removed in vacuo at 1 to 2 mm. by almost completely immersing each cell in a beaker of water at 45° to 50° and attaching each cell directly to the vacuum pump for 3 minutes. The nearly colorless film residue at the bottom of the cell is now ready for coupling with diazotized dinitroaniline. 

Procedure. A hexane solution of Compound 118 is diluted or concentrated so as to bring the 118 content within a range of 15 to 150 micrograms per ml. In cases where the hexane solution requires concentration, the evaporation is carried out in a beaker on a steam bath with a gentle stream of air passing over the surface. The concentrated or diluted solution of 118 is washed with hexane into a volumetric flask and made up to volume with the hexane washings. One milliliter of the adjusted Compound 118 solution is precisely measured into a spectrophotometer cell, 2 drops of phenyl azide are added, and the dihydrotriazole is quantitatively formed and then treated with diazotized dinitroaniline to produce the red color as in the preparation of the standard curve. A blank, starting with 1.0 ml. of hexane and 2 drops of azide, is run at the same time. 

Nitrosylsulfuric acid, prepared by dissolving sodium nitrite in concentrated sulfuric acid, is employed for amines of low basicity, whose diazonium salts will hydrolyze in dilute acid. In order to synthesize Pigment Orange 5, for instance, 2,4-dinitroaniline is dissolved in concentrated sulfuric acid and diazotized preferably with nitrosylsulfuric acid. Coupling is carried out with a (3-naphthol suspension, produced by acidifying a sodium naphtholate solution. 

Pigment Orange 5 [3468-63-1] 12075 monoaZo (Dinitraniline Orange) coupling of diazotized 2,4-dinitroaniline with 2-naphthol... 

Whereas p -naphthylaminesulfonic acids always couple at the adjacent a position, in a-naphthylaminesulfonic acids, the coupling location is influenced by the position of the sulfonic acid group 1,6-, 1,7-, and 1,8-naphthylaminesulfonic acids couple at the 4-position 1,5-naphthylaminesulfonic acid (Laurent acid) only couples with very strong couplers (e g., 2,4-dinitroaniline), mainly at the 4-position. With diazotized aniline, chloroaniline, or diazotized aniline sulfonic acids the 2-aminoazo dyes are obtained, but with diazotized nitroaniline, mixtures of the 2-and 4-coupling products form (Scheme 2.1). 

The procedure given can be used for diazotizing all primary amines whose basicity is so low that they do dissolve in aqueous acids, such as the tri- and tetrahalogenanilines, dihalogennitroanilines, dinitroaniline, aminoanthraquinone, etc. If necessary, the amount of sulfuric acid can be increased in order to obtain complete solution. The sulfates of diazo-anthraquinones are very difficultly soluble in dilute sulfuric acid. Hence, they can be filtered off after pouring the concentrated sulfuric acid solution onto ice, and thus freed from most of the excess acid. 

While the nitrite must be used in exactly the amount theoretically required, an excess of acid is always used. For laboratory preparations, as a rule, the excess acid used is about 0.5 equivalent over the theoretically required 2 equivalents. The excess of acid must be increased to 1 to 3 equivalents in diazotizations of weakly basic amines whose salts are readily hydrolyzed (e.g., chloro- and nitroanilines). In some cases where even this larger excess of acid is insufficient to dissolve the base (e.g., nitrochloroaniline), the diazotization may be carried out in suspension provided that the base is present in a finely divided state. Thus, a solution of the base in concentrated sulfuric acid may be poured into ice water, the base filtered off and washed and then made up into a paste. Even this method fails to work with some bases such as dinitroaniline and m trodichloroaniline these compounds can be diazotized smoothly only in concentrated sulfiuric acid solution. 

Certain diazonium salts, however, are unstable in the presence of water. Thus, 2-methoxy-4,6-dinitroaniline when diazotized in sulfuric acid containing an equal volume of water gives, in addition to the expected diazonium salt, a diazo oxide (XVII). Apparently the nitro group imdergoes hydrolytic cleavage, a hydroxybenzenediazonium salt (XVI) being intermediate in the diazo oxide formation. 

For colorimetric analysis, plasma and urine samples are prepared by alkalinization and chloroform extraction. Methocarbamol couples with diazotized dinitroaniline to give an orange-red compound33. Alternatively, colorimetric determination with chromotropic acid is possible after alkaline hydrolysis (10 mins, in boiling water) of the carbamate and periodate oxidation to formaldehyde34. 

Sandmeyer reaction. Application of the reaction to 2,6-dinitroaniline is of particular interest because of the special method employed for diazotization of this... 

Disperse reds are second only to blues as the most important disperse color manufactured. AH commercial disperse reds are monoazo dyes. In 1988, Disperse Red 73 (98, R = CN) had production of 270 tons valued at neady 1.6 million. Disperse Violet 24 (99) is produced from diazotized 2-bromo-4,6-dinitroaniline by coupling with 2-(ZV-butyl-/tf-toluidine)ethanol. 

For example, 2,4-dinitrobenzenesulfinic acid is obtained in 74.1% yield from diazotized 2,4-dinitroaniline and sulfur dioxide on addition of iron(n) sulfate 466... 

Diazotization of 2,4-dinitroaniline in aqueous solution is accompanied by some conversion to phenols in which a nitro group is replaced by a hydroxy group. 

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