the application of sulphuric acid, but no anthraquinons can be obtained from them. Phenol, hydroquinon, and pyrocatechin do not act upon phthalic acid without the addition of sulphuric acid, but then there are formed both phthaleins and anthraquinons. By this synthetic method there have been obtained oxyanthraquinon, erythroxyanthraquinon, alizarin, and quinizarin. But even before this synthesis of Baeyer's and Caro's was known, Piccard obtained anthraquinon from phthalic acid, and he was led to this synthesis by the observation of Weith and Bindschädler, that on sulphating anthraquinon phthalic acid was formed. He selected Finke's method, the separation of hydrochloric acid from a chloride and a hydrocarbon-in this case phthalic chloride and benzol-according to the following equation:

phthalic acid was converted by means of phosphoric chloride into phthalic chloride, and the latter, after rectification at 270°, was heated for twelve hours in a sealed tube to 220°, along with benzol and zinc powder. After extraction ať a boiling heat with alcohol and soda-lye, when a not inconsiderable amount of a brown matter passed into solution, the residue, on sublimation, yielded the well-known yellow needles of anthraquinon. The yield was small, so that it is doubtful whether the above formula expresses the main reaction. Piccard, however, proved beyond doubt that the body obtained was really anthraquinon, by an analysis according to Luck, and by conversion into alizarin.

After Behr and Van Dorp had shown that B-benzyltoluol, as also that B-tolylphenylketon, can be respectively transformed into anthracen and anthraquinon, whilst this transformation is not successful with the corresponding member

F

of the para-series, they investigated the two benzoylbenzoic acids in the same respect, and found that their behaviour corresponded with that observed in benzyltoluol.

Anthraquinon is formed from B-benzoylbenzoic acid, by the removal of water:

Behr and Van Dorp employed anhydrous phosphoric acid as a dehydrating agent. Two parts P,O,, and one part of B-benzylbenzoic acid were mixed, sand was added and the mass distilled; the distillate was pure anthraquinon.

Better results were obtained when the above-mentioned mixture was heated for some hours to 200° in the oil-bath, and the anthraquinon formed extracted by means of benzol.

Parabenzoylbenzoic acid, if treated in the same manner, yields no anthraquinon. Small quantities of anthraquinon were also obtained on distilling benzoic acid with P2O; B-benzoylbenzoic acid having been evidently formed from two molecules of benzoic acid with loss of water:

CH,. CO. OH

5

CH.CO. OH=CHCO. CH. CO. OH+H2O,

which then again loses a molecule of water, and is condensed to anthraquinon.

The formation of anthraquinon on the distillation of the benzoate of lime, which was also observed by Kékulé and Franchimont, depends in any case upon an analogous process, save that in one case H2O is split off, and in the other CaH2O, Anthraquinon is also probably formed during the distillation of B-benzoylbenzoate of lime.

2

The formation of anthraquinon from benzoate of lime may

FORMATION OF ANTHRAQUINON FROM BENZOPHENON. 67

appear also as a second anhydride of benzoic acid. We have, namely:

2C-H6O2=C11H1003+H2O, Benzoylanhydride.

14

C14H10O3=C14H,O2+H2O, Anthraquinon.

This condensation could be readily explained by the following formula :

As already stated, Kékulé and Franchimont obtained anthraquinon as a secondary product from the preparation of benzophenon. Benzophenon was obtained by the distillation of benzoate of lime, without the addition of quick-lime. When the benzophenon, already partially purified by distillation, was recrystallised from ether, there appeared upon the voluminous crystals of benzophenon fine yellow needles, relatively sparingly soluble in ether. The portion of the benzophenon boiling at a higher temperature yielded a larger quantity of this substance. The same needles were also deposited on the addition of ether to the portion which

distilled over at about 340° C., and no longer solidified. After repeated recrystallisation from hot benzol, these crystals displayed the exact composition and the properties of anthraquinon. They melted at 275°, sublimed below their meltingpoint, showed the characteristic red colour when heated with zinc-powder and potassa-lye, and when heated with zincpowder alone produced anthracen.

For the industrial preparation of anthraquinon, anthracen is employed, which, after a more or less perfect purification, is treated with oxidising agents, such as chromic acid, nitric acid, &c.

In order to prepare anthraquinon with nitric acid, it is boiled with acid of 1.2 sp. gr., the yellow mass which separates out is well washed and sublimed. In this procedure, employed by Laurent and Anderson, nitro-products are always formed along with anthraquinon, which impede the purification, and if the method is used on the large scale, are lost on the ultimate conversion into alizarin. It is better, therefore, to employ chromic acid or a chromate.

For the preparation of small quantities the best agents are glacial acetic acid and chromic acid. Anthracen, is dissolved in hot glacial acetic acid, and chromic acid, dissolved in the same manner, is added as long as reduction takes place. Needles of anthraquinon are deposited, and that which remains in solution is thrown down on the addition of water. The resulting mass is best purified by distillation or sublimation, when the anthraquinon is obtained pure. Instead of chromic acid, chromate of potash may be used, either alone or with sulphuric acid. The anthracen is dissolved as before in hot glacial acetic acid, and two parts of powdered chromate of potash are added. The reduction of chromic acid begins forthwith, heat being evolved. As the reaction slackens, it is aided by the heat of the water-bath, till the solution takes a deep green. It is then diluted with water, and the mass which separates out is well washed,

dried, and distilled. Anthraquinon distils over, whilst a considerable quantity of chromiferous charcoal remains behind. The bye-products which form this charcoal are more abundant when chromate of potash is used than in case of chromic acid. Perhaps they agree with the chromated products formed from phenol and cresol on oxidation with chromate of potash and glacial acetic acid. Like these, they leave, after being heated, a pyrophoric mixture of carbon and chromic oxide. Since also carbazol on oxidation with chromic acid yields a chromiferous oxidation-product, the chromiferous charcoal may have this origin when the anthracen employed contains carbazol.

In the preparation of anthraquinon on the large scale chromic acid is used, or at least a mixture of chromate of potash and sulphuric acid. The anthracen, preferably sublimed, is diffused in water, the corresponding amount of bichromate of potash is added, the mixture boiled, and the calculated quantity of sulphuric acid is run in. After the completion of the reaction, the liquid is allowed to cool, filtered, the product is well washed with water and dried.

The chrome solutions are either allowed to crystallise, when the crystals of chrome-alum may be applied to dyeing purposes, or they may be reconverted into chromate of potash.

The dried crude anthraquinon is heated with sulphuric acid to about 120° C.; the black liquid mass is diluted with water, filtered, washed well and dried. The anthraquinon is thus obtained as a greyish-green impalpable powder, containing 93 to 96 per cent. of pure anthraquinon.

Another process, which, if it could be carried out on the large scale, would be certainly the least expensive and most practical, has been patented in England by F. Baeyer, F. Weskott, and A. Siller. According to this process, one part of anthracen is heated with one to five parts of manganese to about 200°, when the anthraquinon is obtained direct as a sublimate. Unfortunately, the yield from this process is