Aromatics amines, nitration

Nitrations are highly exothermic, ie, ca 126 kj/mol (30 kcal/mol). However, the heat of reaction varies with the hydrocarbon that is nitrated. The mechanism of a nitration depends on the reactants and the operating conditions. The reactions usually are either ionic or free-radical. Ionic nitrations are commonly used for aromatics many heterocycHcs hydroxyl compounds, eg, simple alcohols, glycols, glycerol, and cellulose and amines. Nitration of paraffins, cycloparaffins, and olefins frequentiy involves a free-radical reaction. Aromatic compounds and other hydrocarbons sometimes can be nitrated by free-radical reactions, but generally such reactions are less successful. 

Nitration. Direct nitration of aromatic amines with nitric acid is not a satisfactory method, because the amino group is susceptible to oxidation. The amino group can be protected by acetylation, and the acetylamino derivative is then used in the nitration step. Nitration of acetanilide in sulfuric acid yields the 4-nitro compound that is hydroly2ed to -rutroaruline [100-01-6]. 

Nitration of aromatic amines with urea nitrate in sulfuric acid is reported to yield the -nitro derivative exclusively (44). When the para position is blocked, the meta product is obtained in excellent yield. 

MDA reacts similarly to other aromatic amines under the proper conditions. For example, nitration, bromination, acetylation, and dia2oti2ation (1 3) all give the expected products. Much of the chemistry carried out on MDA takes advantage of the diftmctionality of the molecule in reacting with multiftmctional substrates to produce low and high molecular weight polymers. 

Aminoisothiazoles have all been prepared by nitration and subsequent reduction, usually in good yield, although the reduction of 4-nitroisothiazole to 4-aminoisothiazole has only been achieved in 35% yield. 4-Aminoisothiazoles behave as normal aromatic amines and the diazonium salts undergo the Sandmeyer reaction and reductive deamination. ... 

After a few minutes drying in air sterol hydroperoxides, nitrate esters, triazines and aromatic amines yield blue-violet chromatogram zones on a pale blue to violet background [1, 3]. Polynitroaromatics yield yellow to dark beige zones [3]. 

The detection limits per chromatogram zone are 50 ng substance for sterol peroxides [1], 20-100 ng for nitrate esters [3] and 5-25 ng for aromatic amines [5]. 

Since many dyes contain aromatic amines one of the most important reactions carried out in the synthesis of dye intermediates is aromatic nitration, involving use of stoichiometric amounts of nitric and sulfuric acid as discussed previously. Many cleaner nitration processes have been proposed, but here discussion will be limited to the use of lanthanide... 

Attempts have been made to incorporate functional groups into the phosphonates in zinc phosphonate structures. Zn(03P(CH2)2C02H) H20 was reacted with aromatic amines but no amide formation was observed. However, Zn(03P(CH2)2C0NHC6H5) could be synthesized directly from zinc nitrate, (2-carboxyethyl)phosphonic acid, and aniline in a one-step procedure.406... 

See Anilinium nitrate, etc., also Aromatic amines (reference 3), both above Aromatic compound... 

Azo dye-containing wastewaters seems to be one of the most polluted wastewaters, which require efficient decolorization and subsequent aromatic amine metabolism. On the basis of the available literature, it can be concluded that anaerobic-aerobic SBR operations are quite convenient for the complete biodegradation of both azo dyes and their breakdown products. Nevertheless, like the other methods used for biological treatment, SBRs treating colored wastewaters have some limitations. Presence of forceful alternative electron acceptors such as nitrate and oxygen, availability of an electron donor, microorganisms, and cycle times of anaerobic and aerobic reaction phases can be evaluated as quite significant. 

The synthesis of an aromatic amine generally starts from the corresponding nitro compound. Nitration and subsequent reduction are key reactions in the synthesis of intermediates for azo pigments. 

From the recent advances the heteroatom-carbon bond formation should be mentioned. As for the other reactions in Chapter 13 the amount of literature produced in less than a decade is overwhelming. Widespread attention has been paid to the formation of carbon-to-nitrogen bonds, carbon-to-oxygen bonds, and carbon-to-sulfur bonds [29], The thermodynamic driving force is smaller in this instance, but excellent conversions have been achieved. Classically, the introduction of amines in aromatics involves nitration, reduction, and alkylation. Nitration can be dangerous and is not environmentally friendly. Phenols are produced via sulfonation and reaction of the sulfonates with alkali hydroxide, or via oxidation of cumene, with acetone as the byproduct. 

Nitrations of aromatic amines often involve the intermediate formation of N-nitramines, although these are rarely seen under the strongly acidic conditions of mixed acid nitration (Section 4.5). N,2,4,6-Tetranitro-N-methylaniline (tetryl) is an important secondary high explosive usually synthesized from the nitration of N,N-dimethylaniline or 2,4-dinitro-N-methylaniline. ° The synthesis of tetryl is discussed in Section 5.14. 

The course of a reaction involving At-nitration of an aromatic amine is very dependent on both the substrate and the reaction conditions, i.e. nitrating agent, temperature, work-up etc. The nitration of 3-amino-2,5-dinitrotoluene with mixed acid in glacial acetic acid at 0 °C yields the corresponding diazophenol with no trace of the intermediate nitramine. In contrast, nitration of the same substrate at ambient temperature with mixed acid composed of 90 % nitric acid and 96 % sulfuric acid yields the corresponding nitramine. ... 

The first use of dinitrogen pentoxide as an A-nitrating agent appears to have been for the conversion of aromatic amines to arylnitramines. Difficulties in preparing pure dinitrogen pentoxide meant that reactions with aliphatic amines were not properly examined for another 60 years. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

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