Azo Dyes - School of Chemistry | School of Chemistry

In 1959 and 1961, respectively, ICI and Hoechst filed patents for reactive dyes containing two different functional groups (heterobifunctional dyes), but the first dye of this type was not manufactured until 1975 when Hoechst made available Remazol Brilliant Red SBB, which contained three reactive groups. The first series of multifunctional dyes, the Sumifix Supra range, was introduced by Sumitomo of Japan in 1979, and thirteen of these colorants are now available. They all contain a monochlorotriazine and a vinylsulfone group. Hoechst, Nippon Kayaku, Bayer and CIBA-GEIGY brought out similar colorants in the 1980s, and the number of patent applications for this group has now reached well over one hundred.[71] Reactive dyes are a principal product of the German-Japanese partnership of Hoechst with Mitsubishi Kasei Co. Ltd.

Preparation of Dis-Azo Dyes Derived from p …

Diazonium Salts, Azo Dyes | Amine | Molecules

toluene diisocyanate and azo dye

Nearly all the synthetic dyes are derived from one or other of the five hydrocarbons, benzene, toluene, xylene, naphthalene and anthracene. The most convenient source of these hydrocarbons is coal-tar, obtained in the high temperature carbonization of coal for the manufacture of illuminating gas or of metallurgical coke. The more volatile hydrocarbons, benzene and toluene, are contained also in considerable quantities in the gas produced in these operations and can be extracted therefrom by washing or "scrubbing" the gas with high-boiling solvents. In addition to the hydrocarbons mentioned above, coal-tar contains a large number of other substances, bases, phenols, and more complex hydrocarbons, most of which find no application in dye stuff manufacture.

Reaction pathway for the synthesis of the azo-dye ..

The general formula for making an azo dye requires two organiccompounds- a coupling component and a diazo component. Since these can bealtered considerably, an enormous range of possible dyes are available,especially as the starting molecules are readily available and cheap. Furthermore, the simplicity of the reactions mean that the process can be scaledup or down very easily, which is always a key factor in the cost ofchemicals. Energy requirements for the reaction are low, since most of thechemistry occurs at or below room temperature. The environmental impact isreduced by the fact that all reactions are carried out in water, which is easyand cheap to obtain, clean and dispose of. As other dye classes becomeless viable from either an environmental or economic reasons, azo dyes becomeever more attractive options.

Design, synthesis, and characterization of new iron-complexed azo ..

With these hydr. carbons as starting mate rials the various dyestuffs are built up in successive stages. In the first place the hydrocarbons are converted into so-called "inter mediate products," which are obtained by replacing one or more atoms of hydrogen attached to the carbon nucleus by simple atomic groups such as the amido group the dimethylamido group the hydroxy group OH, the sulphonic group etc. Only a few illustrations can be given. Thus from benzene there is prepared by treatment with nitric acid, nitro benzene, and from this by reduction (hydrogenation) aniline:— From naphthalene there is prepared by the action of sulphuric acid the a and (3-sulphonic acids, which upon fusion with caustic soda give a and (3-naphthols :— By the action of nitric acid upon naphthalene, nitronaphthalene is obtained, which upon reduction gives a-naphthylamine. On the other hand f3-naphthylamine is obtained by heating 13-naphthol with ammonia and sodium bisulphite under pressure. Again, from the hydrocarbon anthracene there is obtained by oxidation. anthra quinone, a very important intermediate for fast dyestuffs; whilst by oxidation of toluene there is produced benzaldehyde, and of naphthalene, phthalic anhydride:— Methyl- and ethyl-anilines are obtained by heating aniline with methyl or ethyl alcohol and an acid under pressure. Diphenyla mine derivatives are prepared by causing chloro compounds to react with amido compounds. The base benzidine (q.v.), which is an important intermediate for direct dyeing cotton colouring matters, is obtained by a molecular transposition from hydrazo benzene under the influence of acids, this substance itself being prepared by alkaline hydrogenation of nitrobenzene :— By applying these and similar chemical treatments, and thus introducing two or more of such atomic groups, either of the same or of different kinds, into the hydrocarbon nucleus, there are obtained a great variety of intermediate compounds,—diamines, dihydroxy compounds, amidophenols, naphthol sulphonic acids, naphthylamine sulphonic acids, amidonaphthols, amidonaphthol sulphonic acids, etc. In these compounds isomerism plays an important role, since the position occupied by the respective groups in reference to the carbon skeleton is a factor of great importance in determining the properties of the colouring-matter finally resulting.

CD-R discs use blue azo dye as the ..

The Diazo-reaction.—The most largely used of all methods of dye-stuff synthesis is the diazo-reaction (P. Griess, 1864), by which the very large class of compounds known as azo-dyes are ob tained. The procedure depends upon the fact that almost all primary amino-derivatives of aromatic hydrocarbons, when treated in acid aqueous solution with nitrous acid are converted into diazonium salts. These latter are for the most part colour less compounds of great instability and extremely reactive. When brought in contact with hydroxy or amino-derivatives of aromatic hydro-carbons they "couple" with the latter giving rise to com pounds in which the two hydro-carbon residues are united by a double nitrogen group (azo group). For example, when benzene diazonium chloride or diazo-benzene chloride, derived from aniline hydrochloride, is mixed with an alkaline solution containing, e.g., the sodium salt of Schaeffer's acid (2-naphthol-6-sulphonic acid), a bright orange dye-stuff (crocein orange) is at once produced :— use of the fact that certain phenols and aminophenols are capable of coupling with more than one molecule of a diazo-compound, azo-dyes can be built up containing three, four or more azo groups, and a correspondingly increased number of hydro-carbon residues. With growing molecular complexity, the colour of the dye-stuff obtained increases in depth, especially when naphthalene residues are introduced into the reaction. The diazo-reaction can be applied not only for producing dye-stuffs in substance but also for their synthesis within or upon textile fibres, whereby colours can be obtained. Thus when cotton which has been impregnated with an alkaline solution of /3-naphthol is passed through a cold solution of diazotized p-nitroaniline, the bright scarlet "para red" is immediately produced and remains fixed on the cotton.

3,5-dibromotoluene from toluene]

Among the many other methods of dye-stuff synthesis, de pendent upon the linking together of hydro-carbon nuclei into more complex molecules, may be mentioned the production of synthetic indigo. The raw materials in this case are aniline and chloro-acetic acid, which upon condensation give phenylglycine. This, upon fusion with caustic alkali, produces indoxyl and by air oxidation indigo :— The most complex molecular structures are those possessed by the vat dyes of the anthraquinone class. These are obtained by the linking together of two or more anthraquinone residues or by the fusion of these residues with other groups in such a way as to produce new carbon rings. The very fast indanthrene blue RS or duranthrene blue is obtained by heating (3-aminoanthra quinone with caustic alkalis and subsequent oxidation by air. The change is thus represented :— This method of dye-stuff synthesis has proved capable of wide application and is very suitable for technical employment, since it can be effected in cold aqueous solution, gives almost theo retical yields and allows of any required substituent being intro duced in prearranged position into the final dye-stuff. When applied to diamino-compounds such as benzidine, it gives rise to dyes containing three hydro-carbon residues (disazo-dyes), such as Congo red :— Disazo-dye-stuffs of another type are obtained by coupling diazo compounds with primary monoamino-derivatives, again diazo tizing the free amino-groups in these products and recoupling the diazo-compounds with suitable hydroxy or amino-derivatives. For example :— i3y applying a similar process to diamines, and also by making A still more complex example is the dye-stuff caledon jade green which has the structure :— It is obtained from anthraquinone, by first condensing with gly cerine, then fusing with caustic soda, oxidizing the product (dibenzanthrone), and finally introducing methyl groups in place of two hydrogen atoms. While initially all the alizarine or anthra quinone dyes were synthesized from anthracene, recently with the cheapening of phthalic anhydride, these dyes are also made by condensation of phthalic anhydride with benzene or its derivatives.