Aromatic amines separation

Acid-treated clays Alcylation reactions (e.g. of benzene with benzyl chloride) Dimerization reactions (e.g. of a-methylstyrene) Etherification reactions (e.g. of ferf-butanol with methanol) Condensation reactions (e.g. of cyclohexanone) Separation of close boiling aromatic amines Separation of isomers of xylene... 

It is convenient to include under Aromatic Amines the preparation of m-nitroaniline as an example of the selective reduction of one group in a polynitro compound. When wt-dinitrobenzene is allowed to react with sodium polysulphide (or ammonium sulphide) solution, only one of the nitro groups is reduced and m-nitroanUine results. Some sulphur separates, but the main reaction is represented by ... 

In general, benzoylation of aromatic amines finds less application than acetylation in preparative work, but the process is often employed for the identification and characterisation of aromatic amines (and also of hydroxy compounds). Benzoyl chloride (Section IV, 185) is the reagent commonly used. This reagent is so slowly hydrolysed by water that benzoylation can be carried out in an aqueous medium. In the Schotten-Baumann method of benzoylation the amino compound or its salt is dissolved or suspended in a slight excess of 8-15 per cent, sodium hydroxide solution, a small excess (about 10-15 per cent, more than the theoretical quantity) of benzoyl chloride is then added and the mixture vigorously shaken in a stoppered vessel (or else the mixture is stirred mechanically). Benzoylation proceeds smoothly and the sparingly soluble benzoyl derivative usually separates as a solid. The sodium hydroxide hydrolyses the excess of benzoyl chloride, yielding sodium benzoate and sodium chloride, which remain in solution ... 

SULPHONATION OF AROMATIC AMINES If aniline is treated with excess of concentrated sulphuric acid and the resulting mixture, which contains aniline sulphate, is heated at 180° until a test portion when mixed with sodium hydroxide solution no longer liberates aniline, p-aminobenzenesulphonic acid or sulphanilic acid is formed this separates as the dihydrate upon pouring the cooled mixture into water. The reaction prohahly proceeds as follows ... 

Diphenylamine is a weak base, = 9 x lO ". Dilute acids are used to separate DPA from primary aromatic amines, such as aniline,... 

Protective group chemistry for these amines has been separated from the simple amines because chemically they behave quite differently with respect to protective group cleavage. The increased acidity of these aromatic amines makes it easier to cleave the various amide, carbamate, and sulfonamide groups that are used to protect this class. A similar situation arises in the deprotection of nucleoside bases (e.g., the isobutanamide is cleaved with methanolic ammonia ), again, because of the increased acidity of the NH group. 

The most versatile derivative from which the free base can be readily recovered is the picrate. This is very satisfactory for primary and secondary aliphatic amines and aromatic amines and is particularly so for heterocyclic bases. The amine, dissolv in water or alcohol, is treated with excess of a saturated solution of picric acid in water or alcohol, respectively, until separation of the picrate is complete. If separation does not occur, the solution is stirred vigorously and warmed for a few minutes, or diluted with a solvent in which the picrate is insoluble. Thus, a solution of the amine and picric acid in ethanol can be treated with petroleum ether to precipitate the picrate. Alternatively, the amine can be dissolved in alcohol and aqueous picric acid added. The picrate is filtered off, washed with water or ethanol and recrystallised from boiling water, ethanol, methanol, aqueous ethanol, methanol or chloroform. The solubility of picric acid in water and ethanol is 1.4 and 6.23 % respectively at 20°. 

Voltammetry has been adapted to HPLC (when the mobile phase is conducting), and CE as a detection technique for electroactive compounds. In this usage, the voltammetric cell has been miniaturised (to about 1 p.L) in order not to dilute the analytes after separation. This method of amperometric detection in the pulsed mode is very sensitive. However, this device makes it possible to detect few analytically important molecules besides phenols, aromatic amines and thiols. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

The results in this paper support an N-C bond cleavage mechanism (Schemes I and II) for the photolysis of both TDI and MDI based polyurethanes. The substituted anilinyl radicals observed no doubt are formed by diffusion from a solvent cage after the primary N-C bond cleavage. Although not specifically shown in this paper, the reported photo-Fries products (6) are probably formed by attack of the carboxyl radical on the phenyl ring before radical diffusion occurs. The solvent separated anilinyl radicals rapidly abstract hydrogens from the solvent to give the reported aromatic amine product (6). 

Route B of this process may be substantially improved in terms of yield and product quality (purity) of the resulting triarylaminoarylcarbonium pigment. To this end, the solution of the free dye base is treated with an excess of aqueous sulfuric acid (20 to 40% ) in a solvent such as chlorobenzene or an aromatic amine. This method produces the sulfate of the basic dye, which is insoluble in this medium, together with the soluble sulfates of the primary aromatic amines, which can therefore easily be separated. The isolated sulfate of the basic dye is then washed and in dry or wet condition monosulfonated with 85 to 100% sulfuric acid. Based on the dye base sulfate, this step affords 96 to 98% yield, compared to only 83 to 89% achieved by the previously described method. The entire synthesis, including the intermediate isolation of the triarylaminoarylmethane sulfate, may also be performed by continuous process [3]. 

An appendix systematically lists references to reactions of dialkylalkoxy-malonates with amines, including not only the common aliphatic and aromatic amines, but also a very wide variety of heterocyclic amines classified according to ring system. The appendix also provides systematic references to the different ring systems obtained by ring closure of the dialkylaminomethylenemalonates. The appendix should be used in conjunction with the subject index a separate subject index is provided for this monograph volume. 

Aromatic amines that have been used include o-toluidine, p-aminosali-cylic acid, p-aminobenzoic acid, diphenylamine and p-aminophenol. Their ability to react preferentially with a particular carbohydrate or class of carbohydrate is often useful, e.g. p-aminophenol, which shows some specificity for ketoses compared with aldoses and is useful for measuring fructose. These reagents have proved particularly useful for the visualization and identification of carbohydrates after separation of mixtures by paper or thin-layer chromatography, when colour variations and the presence or absence of a reaction aid the interpretation of the chromatogram. 

M.S. Narvekar and A.K. Srivastava, Separation of isomers of aromatic amines on HPTLC plates impregnated with 18-crown-6. J. Planar Chromatogr.-Mod. TLC 15 (2002) 120-123. 

Liquid chromatographic techniques have been frequently employed for the separation and identification of the toxic decomposition products of synthetic dyes. Thus, the amount of aromatic amines formed from azo dyes in toys has been determined. The chemical structures of the dyes included in the investigation are listed in Fig. 3.60. The dyes were... 

A similar study was carried out using a different set of synthetic dyes. The chemical structures of the dyes are listed in Fig. 3.62. The decomposition products were separated in an ODS column (250 X 4 mm i.d. particle size 7 /tm) using an isocratic mobile phase composed of methanol-water (45 55, v/v). The flow rate was 1.2 ml/min. The contents of aromatic amines determined by spectrophotometric and HPLC methods are compiled in Table 3.24. It was established that spectrophotometry can be used for the exact determination of the amines but it is inadequate for their separation. RP-HPLC proved to be a valuable method for the analysis of this class of decomposition products [131],... 

Separation of amines was realized in an ODS column (250 x 3 mm i.d. particle size 5 /tm) at 30°C. The flow rate was 0.3 ml/min and amines were detected at 280 nm. Solvents A and B for gradient elution were ACN and 3 mM phosphate buffer (pH = 7). The gradient started with 15 per cent A for 2 min then to 60 per cent A in 50 min. Chromatograms illustrating the separation of amines are shown in Fig. 3.72. It was established that the recoveries of both SFE and MAE were higher than those of traditional solvent extraction, therefore, their application for the analysis of carcinogenic aromatic amines in leather is highly advocated [140],... 

Metabolites formed during the decolourization of the azo dye Reactive red 22 by Pseudomonas luteola were separated and identified by HPLC-DAD and HPLC-MS. The chemical structures of Reactive red 22 (3-amino-4-methoxyphcnyl-/fhydroxyl-sulphonc sulphonic acid ester) and its decomposition products are shown in Fig. 3.92. RP-HPLC measurements were carried out in an ODS column using an isocratic elution of 50 per cent methanol, 0.4 per cent Na2HP04 and 49.6 per cent water. The flow rate was 0.5 ml/min, and intermediates were detected at 254 nm. The analytes of interest were collected and submitted to MS. RP-HPLC profiles of metabolites after various incubation periods are shown in Fig. 3.93. It was concluded from the chromatographic data that the decomposition process involves the breakdown of the azo bond resulting in two aromatic amines [154],... 

The clean and efficient production of azo dyes is a classical chemistry problem. The manufacture of this industrially important family of compounds is traditionally associated with the additional formation of large quantities of hazardous and colored waste. A method for the construction of both phenolic and amino azodyes has been reported using a polymer-supported nitrite reagent to effect diazoti-zation of aromatic amines (Scheme 2.53) [80]. Waste minimization and operational simplicity, along with improved separation technologies, are key advantages of polymer-supported reagents in this area. 

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