Preparation of Dis-Azo Dyes Derived from p …
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.