Oxidizing agents convert anthracene into anthraquinone; the production of this substance by oxidizing anthracene in glacial acetic acid solution, with chromic acid, is the usual method employed for the estimation of anthracene.
A more delicate method consists in adding a very little anthraquinone and sodium amalgam; absolute alcohol gives a green coloration, but in the presence of minute traces of water a red coloration appears.
Vapour baths of iron are used in connexion with boiling anthracene (335°), anthraquinone (368°),sulphur(444°),phosphoruspentasulphide(518°); molten lead may also be used.
ANTHRAQUINONE, C 14 H 8 O 3, an important derivative of anthracene, first prepared in 1834 by A.
When the oxidation is complete, the anthraquinone is separated in a filter press, washed and heated to 120° C. with commercial oil of vitriol, using about 22 parts of vitriol to i of anthraquinone.
This compound on heating with phosphoric anhydride loses water and yields anthraquinone, CsH4 O 15 CsH
Anthraquinone crystallizes in yellow needles or prisms, which melt at 277° C. It is soluble in hot benzene, sublimes easily, and is very stable towards oxidizing agents.
Various sulphonic acids of anthraquinone are known, as well as oxy-derivatives, for the preparation and properties of which see Alizarin.
For naphthalene quinones see Naphthalene; for anthracene quinone see Anthraquinone; and for phenanthrene quinone see Phena Nt H Rene.
Perkin; the method being to sulphonate anthraquinone, and then to convert the sulphonic acid into its sodium salt and fuse this with caustic soda.
It is then oxidized to anthraquinone by means of sodium dichromate and sulphuric acid in leaden vats, steam heated so that the mixture can be brought to the boil.
When oxidation is complete the crude anthraquinone is separated in filter presses and heated with an excess of commercial oil of vitriol to 120° C., the various impurities present in the crude material being sulphonated and rendered soluble in water, whilst the anthraquinone is unaffected; it is then washed, to remove impurities, and dried.
The anthraquinone so obtained is then heated for some hours at about 150-160° C. with fuming sulphuric acid (containing about 40-50% SO 3), and by this treatment is converted into anthraquinone-O-monosulphonic acid.
After the separation of the silver salt (see above) obtained on sulphonating anthraquinone, the remaining acid liquid gives on treatment with calcium carbonate the calcium salt of anthraquinone 2.6 disulphonic acid (anthraquinone-a-disulphonic acid).
In a similar manner anthrapurpurin is prepared by alkali fusion of anthraquinone 2.8 disulphonic acid.
KOnigs, and the observation that anthraquinone yielded oxyanthraquinones when treated in the cold with strong sulphuric acid, and the recent introduction of fuming sulphuric acid for the oxidation of naphthalene to phthalic acid, a process of great value in the manufacture of artificial indigo, may be noted.