10. Summary Of The Most Important Methods Used In The Preparation Of Synthetic Dyes
Description
This section is from the book "The Fundamental Processes Of Dye Chemistry", by Dr. Hans Eduard Fierz-David. Also available from Amazon: The Fundamental Processes of Dye Chemistry.
10. Summary Of The Most Important Methods Used In The Preparation Of Synthetic Dyes
1. An aromatic substance is treated with concentrated sulphuric acid.
2. An aromatic substance is treated with sulphuric acid containing sulphur trioxide (Oleum).
3. By heating the acid sulphate of an amino compound to a moderately elevated temperature (Bake process).
4. Sulphonation with chlorsulphonic acid.
5. By converting a nitroso compound into the hydroxylamine sulphonic acid, and this in its turn into the amino-hydroxy sulphonic acid.
6. Replacing an easily removable chlorine atom in an aromatic substance by a sulphonic group, by heating with a sulphite.
Nitrations
1. Direct nitration by means of concentrated nitric acid.
2. The substance to be nitrated is first sulphonated and the sulphonic group is then replaced by No2 by the vigorous action of nitric acid, frequently with the assistance of sulphuric acid.
3. By nitrosating an amine, oxidizing with dilute sulphuric acid, to the nitramine, which is then transformed to the nitro compound.
4. By heating a diazonium nitrate with dilute nitric acid.
Reductions
1. Reduction with iron and water, in presence of much, little, or no acid, or in presence of caustic soda lye.
2. Reduction with hydrogen sulphide or with its neutral and acid salts.
3. Reduction by means of sulphurous acid.
4. Reduction by means of zinc, zinc dust, or tin.
5. Reduction by means of nascent electrolytic hydrogen.
6. Reduction with ferrous hydroxide (very occasionally).
7. Reduction by means of hydrosulphite (anthraquinone series).
Oxidations
1. Oxidation with atmospheric oxygen.
2. Oxidation with chromic acid.
3. Oxidation with MnO2 or manganese mud (Mn3O4).
4. Oxidation with sodium hypochlorite in alkaline solution.
5. Oxidation with nitric and nitrous acids.
6. Indirect oxidation, by chlorinating and subsequent treatment of the chloride with water.
7. Oxidation with lead peroxide (PbO2).
8. Oxidation by means of nitrosyl sulphuric acid (Aurine, Sandmeyer).
9. Oxidation with ferric chloride (Helvetia Blue, formation of sulphones from sulphinic acids and p-diamines).
10. Oxidation with bichromate plus a ferrous salt (Safranine, Methylene Blue, etc.).
11. Oxidation in presence of an excess of one of the components used for a condensation (nitroso dimethylaniline in the preparation of Oxazines, for example).
Alkali Fusions
1. Open melt with caustic soda, caustic potash, or mixture of the two.
2. Fusion with sodamide alone, or mixed with caustic soda and caustic potash (Indigo).
3. By heating with aqueous alkali under pressure.
4. Melting with alkali with the addition of an oxidizing agent (Alizarin, Indanthrene).
5. Fusion with lime (which in the anthraquinone series prevents the entrance of further hydroxyl groups).
Methods Of Coupling
1. Coupling is effected in the presence of sodium carbonate.
2. Coupling is effected in the presence of caustic soda.
3. Coupling is effected in the presence of sodium carboriate, caustic soda, or ammonia being added subsequently.
4. Coupling is effected in the presence of lime or magnesia, especially in the case of nitroamino compounds (Sandmeyer).
5. Coupling is effected in the presence of sodium acetate, to combine with the acid (the acetate may usually be replaced by the formate, but this requires subsequent neutralization).
6. Coupling is effected in the presence of mineral acid, either without neutralization, or the mineral acid is neutralized cautiously by means of sodium carbonate or acetate.
7. Very easily oxidizable substances may be coupled under a layer of petroleum (e.g. 1:5-dihydroxynaphthalene).
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