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ANTHRACEN AND ITS DERIVATIVES.

IN the year 1832 Dumas and Laurent discovered a hydrocarbon, which they obtained from those portions of coal-tar which boil at the highest temperature. From their analyses they deduced the formula C1,H12, and as this formula was 11⁄2 times the molecular weight of naphthalin, they named the newly discovered body paranaphthalin. Laurent, who examined this compound further, and described some of its derivatives, proposed the name of Anthracen in place of paranaphthalin. He was led to this change by the consideration that a number of hydrocarbons, polymeres of naphthalin, were present in coal-tar, all of which were entitled to the generic appellation of paranaphthalin. The name anthracen appeared to him also better fitted for forming the names of the derivatives according to his system, e.g. anthracenuse. The next addition to our knowledge of this body was due to Fritzsche in 1857. He described a solid hydrocarbon, obtained from coal-tar, to which he attributed the formula C11H10, and pointed out that this compound had many properties in common with Laurent's anthracen, but differed from it essentially in many others. Thus Dumas and Laurent had observed the melting-point at 180°, whilst Fritzsche found it 210°. The latter chemist, on its analysis, obtained numbers exactly corresponding with the formula C1H10, which was confirmed by the composition of the picrate C1H1CH2 (NO2),OH. Fritzsche, therefore, left the identity of the

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compound which he had examined, with Laurent's anthracen, an open question, and gave no name to the compound. Shortly afterwards Anderson made an extended investigation of the solid constituents of tars boiling at high temperatures, and published his results in 1862. He described under the name of anthracen a hydrocarbon of the same formula as that discovered by Fritzsche, and prepared from it a series of interesting derivatives. Although many of his observations differed essentially from Laurent's statements, he retained the name given by the latter chemist. He also declared his

anthracen identical with the hydrocarbon of Fritzsche. In 1866 Limpricht discovered the synthetic formation of this body by heating the chloride of benzyl to 180° with water. In the same year Berthelot announced that anthracen is formed from various more simple hydrocarbons by the action of heat. He found that toluol alone, or a mixture either of styrol and benzol or of benzol and ethylen, yielded anthracen if passed through an ignited tube. At the same time he made a communication on the extraction of anthracen from tar, confirmatory of the views of Anderson. A year later (1867) Fritzsche returned to the hydrocarbon which he had previously described, giving an account of its purification and of its physical properties, and of one of its derivatives, of importance as a reagent. In opposition to Anderson and Berthelot, he contested its identity with anthracen. In 1868 Graebe and Liebermann discovered that a hydrocarbon could be obtained from alizarin by reduction, possessing the same properties as Anderson's anthracen.

Whilst Berthelot, Limpricht, Graebe, and Liebermann regarded the hydrocarbon described by Anderson as a chemical individual, Fritzsche considered it as a mixture of two bodies, which he named photen and phosen. Anderson's anthracen and Fritzsche's photen, however, scarcely differ from each other in their properties. The melting-point is the same, and the accounts as to solubility and behaviour

with reagents show no discrepancy. The diversity existing as to the magnitude of the crystals and as to fluorescence only proves that Fritzsche succeeded in preparing anthracen absolutely free from the foreign admixtures which still adhere to Anderson's specimens. But that anthracen is a distinct chemical entity may be inferred with certainty from the derivatives obtained both by Anderson and by Graebe and Liebermann, all of which appear as well-characterised chemical compounds. It is, however, by no means denied that other hydrocarbons with high boiling-points may be found in coal-tar. Berthelot, indeed, has shown the existence of compounds, which he has named acenaphten and fluoren, and his statement is confirmed by Graebe and Liebermann.

Dumas and Laurent have doubtless examined an anthracen mixed with these compounds. That the substance described by these chemists is to be regarded thus, and not with Berthelot as methylanthracen, appears from the following reasons. Dumas and Laurent obtained their paranaphthalin from that portion of coal-tar which boils at high temperatures, just as Anderson procured the hydrocarbon which he describes. Their description agrees perfectly with an impure anthracen. Their published analyses show too little hydrogen for methylanthracen. The carbon is too low both for methylanthracen and for anthracen, and is therefore untrustworthy, the sum of the percentage of carbon and hydrogen being notably below 100.

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The vapour density as determined by Dumas, 6.74 (Troost, 6-3, C4H10 requiring 6.17, and C1,H12 6·65), can

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afford no proof, since the specimen employed, according to its description, did not possess the character of purity. Laurent's anthracenuse, however, proves more decidedly the correctness of the view of Graebe and Liebermann. This compound is identical with Anderson's oxanthracen, the anthrachinon (anthraquinon) of Graebe and Liebermann, as was already assumed by Kraut in Gmelin's 'Handbuch.' The earlier analyses of Laurent agree distinctly with the formula CHO2, but very badly with his own C1HO2. The properties of this oxidation-product, so highly characteristic of anthracen, leave no doubt that Laurent obtained anthraquinon in a state of purity, and that the substance from which it was prepared must have consisted mainly of anthracen.

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Constitution of Anthracen and its Derivatives.

Graebe and Liebermann were the first to express the view that anthracen was formed of three benzol rings, in the same manner manner as naphthalin of two. The following formula shows how the chemical structure of anthracen is to be regarded upon this hypothesis :

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The reasons which Graebe and Liebermann adduce for this view depend, firstly, upon Kekule's theory of the aromatic compounds, and secondly, upon the assumption that naphthalin is formed of two benzol-nuclei.

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