Aldehydes Aniline dyes

The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethyl aniline in aqueous acid (Fig. 2). The reaction mass is made alkaline and the excess dimethylaniline is removed by steam distillation. The resulting leuco base is oxidized with freshly prepared lead dioxide to the carbinol base, and the lead is removed by precipitation as the sulfate. Subsequent treatment of the carbinol base with acid produces the dye, which can be isolated as the chloride, the oxalate [2437-29-8] or the zinc chloride double salt [79118-82-4]. 

The reduction of nitrobenzene to aniline is a major industrial process at the heart of the production of polyurethanes, and it is also often used as a marker reaction to compare activities of catalysts [1,2], It can be performed over a variety of catalysts and in a variety of solvents. As well as its main use in polymethanes, aniline is used in a wide range of industries such as dyes, agrochemicals, by further reaction and functionalisation. Reductive alkylation is one such way of functionalising aromatic amines [3, 4], The reaction usually takes place between an amine and a ketone, aldehyde or alcohol. However it is possible to reductively alkylate direct from the nitro precursor to the amine and in this way remove a processing step. In this study we examined the reductive alkylation of nitrobenzene and aniline by 1-hexanol. 

The nucleophilic displacement of suitable para substituents in analogues of malachite green is used as a means of synthesis of some important acid dyes. For example, Cl Acid Blue 83 (6.176 R = H) is made by the aldehyde method, using 4-chlorobenzaldehyde and N-ethyl-N-(3-sulphobenzyl)aniline. The resulting leuco base is oxidised to the colour salt,... 

The entire group of these compounds dates back to the very beginnings of organic dye chemistry. In 1858, E. Verguin in France oxidized a material which he named aniline but which was in actual fact a mixture of aniline, o-toluidine, and p-toluidine. He performed the reaction in nitrobenzene in the presence of tin(IV)chloride or iron(III)chloride and received bluish red fuchsin (120). The process has been industrially exploited since 1859. The central carbon atom is furnished by the CH3 group of p-toluidine, which is initially oxidized to its aldehyde. 

An important class of cationic dyes, particularly for yellow to bluish-red hues, is derived from Fischer s base by condensation with 4-formyl-substituted anilines, or from Fischer s aldehyde (which may be prepared from Fischer s base via Vilsmeier formylation (B-71MI11205)) and an aromatic amine (Scheme 3). There are many examples of resonating charge dyes of this type which include a variety of aromatic amines and aldehydes. Of heterocyclic interest are the dyes formed by condensation of Fischer s aldehyde with... 

The chief impurities in commercial ether are alcohol and water, with traces of aldehyde, methyl alcohol, acetone, due to it being made from methylated spirit. It may be purified as above. The presence of alcohol may be proved by shaking with a spirit soluble dye, e.g., aniline violet. If alcohol is present a blue solution is obtained. Water is detected by the cloudiness formed on mixing with carbon disulphide. 

In the Vilsmeier formylation of iV-( 3-hydroxyethyl)anilines the hydroxyl group is simultaneously replaced by chlorine [60], The resulting aldehydes condense with l,3,3-trimethyl-2-methyleneindoline to form very brilliant dyes [61], With 4-(W-methyl-iV- 3-chloroethylamino)benzaldehyde a commercial dye is obtained. A methyl group in the 2-position to the methine chain produces a bluish-red color (27). 

In the preparation of commercial fuchsine aniline is heated with a mixture of ortho and para toluidine. p-Toluidine is oxidized to the aminoaldehyde which condenses with one molecule of both aniline and o-toluidine to form homorosaniline hydrochloride- At the same time there is also formed pararosaniline hydrochloride owing to the reaction of two molecules of aniline with the aldehyde. The differences in the structure of leuco base, color base, and dye are shown by comparison of their respective formulas (1), (2), and (3). 

The presence of the aldehyde is shown by treating the product of the reaction with aniline, C6H5.NH2, and hydrochloric acid with these reagents the aldehyde produces an intense red dye. When warmed with hydrochloric acid and phloroglucinol (537) pentosans and pentoses produce a cherry-red coloration. 

Furfuraldehyde yields an intense red dye when treated with aniline and hydrochloric acid it serves, thus, as a convenient test for pentoses and pentosans. Furfuraldehyde is a liquid which possesses an agreeable odor and boils at 162°. It possesses the characteristic properties of an aromatic aldehyde. 

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