TRANSACTIONS OF THE SECTIONS. 



59 



derivative of the hydrocarbon benzol (CjUg). On comparing the composition of 

 these two bodies, it is seen that the quinone contains two atoms of oxygen more 

 and two atoms of hydrogen less than benzol ; and Graebe, from the study of the 

 decomposition of quinone and from the compounds it forms, suggested that the two 

 atoms of oxygen form in themselves a group which is divalent, and thus replace 

 the two atoms of hydrogen ; this supposition he very forcibly advocates, and shows 

 its simple and satisfactory application to all the then known reactions of this body. 

 This suggestion really proved to be the key, not only to the explanation of the 

 natural constitution of quinone and its derivatives, but to much important discovery 

 besides. 



At this time quinone seemed to stand alone ; no other similarly constituted body 

 was known to exist : but what strikingly confirms the correctness of Graebe's views, 

 and indicates their great value, is that immediately he is able to apply his lately 

 gained knowledge, and to show how really other analogous bodies, other quinones 

 in fact, already exist. He studied with great care this quinone series of com- 

 pounds and the relation they bore to one another — the relation the hydrocarbon 

 benzol bore to its oxidized "derivative quinone, and its relation to the chlorine 

 substitution-products derivable from it. At once this seems to have led Graebe 

 to the conclusion that another such series already existed ready formed, and that 

 its members were well known to chenusts — that, in fact, Daphthalin(C,(, H^) was the 

 parent hydrocarbon, and that the chloroxyuaphthalin chloride (C,oH^ Cl^O^) and 

 the perchloroxyuaphthalin chloride (CioCljO^) were really chlorine substitution- 

 compounds of the quinone of this series, corresponding to the bichloroquinone and 

 to chloranil— that the chloroxynaphthalic acid, CioH^ 01 (HO) O^, and the per- 

 chloroxynaphthalic acid, Ok, CI, (HO) O^, all comjDoimds previously discovered by 

 Laurent, were really bodies belonging to this series — and, further, that the sup- 

 posed isomer of alizarin discovered by Martins and Griess was really related to this 

 last compound, having the composition CioH5(HO)02. Further, he was able to 

 confirm this by obtaining the quinone itself of this series, the body having the 

 formula Ci„Hg(02)", containing also two atoms less of hydrogen and two atoms 

 more of oxygen than the hydrocarbon naphthalin ; and to this body he gave the 

 characteristic name of naphthoquinone. The chlorine compounds just named are, 

 then, chloruaphthoquinones or chloroxynaphthoquinones, and correspond to the 

 former chloroquinoues ; and Martius and Griess's compound will be an oxynaphtho- 

 quiuone : many other compounds of this series are also known. Another step confir- 

 matory of this existence of a series of quinones was made by Graebe and Bergmann : 

 as the chloranil could be found by treating phenol with potassic chlorate and hydro- 

 chloric acid, and quinone derived from it, they showed that in the next higher series 

 to the phenol series, viz. with cresol, the same reaction held good ; and by treat- 

 ing it in the same way, they obtained a di- and a trichlorotoluquinone, 0, 



1 CH3 

 C„ I (O.j", which in physical properties very closely resembled the corresponding 



(CI3 

 compounds in the lower series : other compounds have also been prepared. 



In the next step we have the application which connects these series of disco- 

 veries with alizarin. FoDowing the clue of a certain analogy which they believed 



to exist between the chloranilic acid i^a^hkiO) ) ^^^ ^^^ chloroxynaphthalic 



acid (c,o H^ 01 '[iK ) , which they had proved to be quinone compounds and alizarin, 



believing that a certain similarity of properties indicated a certain similarity of consti- 

 tution, Graebe and Liebermann were led to suppose that alizarin must also be a deri- 

 vative from a quinone, and have the formida (o^ H^ J^^'^. j . This theoiy they were 



able afterwards to prove. The first thing was to find the hydrocarbon from which 

 the quinone might be derived. This was done by taking alizarin itself and heating 

 it with a very large excess of zinc powder in a long tube, closed at one end. A pro- 



