25 августа, 2015 
Pokraskin Many methods have been evolved for oxidizing organic compounds. Oxidation may be brought about by:
(1) Air, often in the presence of a catalyst. Examples of this method are the preparation of phthalic anhydride from naphthalene by air and vanadium oxide (Wohl’s method, page 171), and the analogous oxidation of anthracene to anthraquinone. In the latter case, anthracene which is not entirely pure can be used.
(2) Chromic acid. This method is very important in the preparation of many heterocyclic dyes, such as methylene blue. The reaction is frequently carried out in the presence of oxalic acid.
(3) Manganese dioxide (Mn02), or the so-called “Weldon mud” which is a manganous-manganic oxide (xylene blue V, page 303).
(4) Sodium hypochlorite (see dinitrostilbenedisulfonic acid, page,167).
(5) Nitric acid (seldom used).
(6) Lead peroxide, for triphenylmethane dyes.
(7) Nitrosylsulfuric acid (aurin dyes by Sandmeyer’s method).
(8) Ferric chloride (with certain triphenylmethane dyes, e. g., Helvetia blue).
(9) Chlorination of a side chain (in toluene and xylene) followed by hydrolysis of the chlorinated product. Examples of the procedure are:
(a) toluene -* benzyl chloride -* benzyl alcohol, or
(b) toluene -* benzal chloride -* benzaldehyde.
(10) An excess of one of the dye-forming reactants (examples are very numerous, e. g., gallamine blue, Meldola’s blue, etc.).
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