Brom anthraquinone

When this 2-benzoyl 3-brom benzoic acid is heated with sulphuric acid water is lost and brom anthraquinone is obtained. 

In the preceding reactions the benzene nucleii have been numbered I and II in order to follow their course through the various transformations. It may be readily seen, therefore, that the benzene nucleus in brom anthraquinone which remains as a benzene ring in t r//f )-phthalic acid is the nucleus which does not contain bromine. This was derived from the benzene constituent of the s)mthesis and, in anthraquinone, it is linked to the carbonyl groups by ortho positions. Therefore, both benzene nucleii in anthraquinone are linked by ortho positions and both are derived from true benzene ring compounds or may remain as benzene rings on the decomposition of the quinone. 

I-2-Di-hydroxy Anthraquinone, Baeyer and Caro.— To test this point they prepared a di-brom anthraquinone and fused it with potassium hydroxide. The product proved to be alizarin, thus establishing it as di-hydroxy anthraquinone. 

Character of Center Nucleus.—As was stated in connection with anthracene itself we can not say positively as to the character of the center nucleus in either the hydrocarbon or the quinone. In anthracene the aliphatic character of this center nucleus is indicated by its formation from an ethane residue, by the tetra-brom ethane synthesis. This does not, however, preclude the possibility of its becoming a true benzene nucleus when condensed with two benzene rings, for benzene itself may be made from aliphatic hydrocarbons, from acetylene by polymerization (p. 478), and from hexane through hexa-methylene with the loss of hydrogen after the formation of the cyclo-paraffin (p. 469). Also naphthalene, in which there is no doubt of the benzene character of the two nuclei, may have one nucleus formed from an aliphatic chain as in the syntheses given (p. 767) from phenyl butylene bromide, from phenyl vinyl acetic acid and from tetra-carboxy ethane. In the same way the facts in regard to anthraquinone do not prove... 

The remarkable thing is, that while there are ten possible di-brom or di-hydroxy anthraquinones, the particular one necessary was obtained by Graebe and Liebermann. The positions of the two hydroxyl groups were determined by Baeyer and Caro. When alizarin is heated pyro-catechinol, i-2-di-hydroxy benzene, is obtained. Also when pyro-catechinol is heated with ortho- hXhaXic acid and sulphuric acid alizarin results. This last synthesis is analogous to that of anthraquinone from benzene and o //io-phthalic acid (p. 796). 

---