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tape EN Oe RL 
NATURE 
aS A 
Oy 
[Sepz. 18, 1873 
student at Giessen, undertook the further investigation of this 
subject, and established the formula C,,H,,0j. the one in fact 
now in use. In the course of this investigation, which he carried 
further than merely settling the percentage composition of this 
acid, he describes what to us now is of most interest, a new 
substance having peculiar and very marked properties. He 
says that when a salt of quinic acid is burnt at a gentle heat he 
gets aqueous vapour, the vapour of formic acid, and a deposit of 
golden needles which are easily sublimed. Afterwards he 
describes how this same golden substance may be obtained from 
any salt of quinic acid by heating it with manganic dioxide and 
dilute sulphuric acid; it then distils over, condensing in 
golden yellow needles on the sides of the receiver, and may be 
rendered pure by resublimation, The composition of this body 
he finds to be C,H,O, and names ic quinoyl, a name strongly 
objected to by Benzelius, as conveying a wrong impression of 
the nature of the body ; he proposes in place of it the name 
quinone, by which it is still known. Far as this body would 
seem to be removed from alzarine, yet is the study of its 
properties which led to the artificial production of alizarine. 
Some years afterwards Wohler also explained them by the 
decomposition of quinic acid; he prepares again this quinone 
and follows exactly the process described by Woskrensky. He 
states that with regard to the properties of this remarkable body 
he has nothing particular to add. However, he proposes a 
different formula for it, and discovers and describes other bodies 
allied to it. Among’ these is Hydroquinone C,H ,O.. 
afterwards shows that the formula proposed by Wohler is incon- 
sistent with his and Gerhard’s views, and by experiment confirms 
the former formula for this body. Although many other chemists 
devoted much attention to this substance, still its real constitution 
and relation to other compounds remained unknown. 
Thus Wohler, Laurent, Hofmann, Stadler, and Hesse, all 
had worked at it, and much experimental knowledge with regard ' 
to it had been acquired. One important point in its history was 
first the discovery of chloranil by Erdmann in 1841, and then 
Hofmann, showing that by heating quinone with potassic chlorate 
and hydrochloric acid chloranil could be obtained from it ; that, 
in fact, chloranil was quinone in which all the hydrogen had 
been replaced by chlorine. Perhaps the most general impression 
among chemists was that in constitution it was a kind of alde- 
hyde, certainly its definite place among chemical compounds 
was unknown. 
Kekulé suggests a rational formula for it, but it is to Carl 
. Graebe that we owe our knowledge of its true constitution, In 
1868 he published a remarkable and very able paper on the 
quinone group of compounds, and then first brought forward the 
view that quinone was a substitution derivative of the hydro- 
carbon benzol (C,H,). On comparing the compounds 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 the 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 satisfactiory appli- 
cation to all the then known reactions of this body. ‘This 
suggestion really proved to be the key, not only to the expla- 
nation of the natural constitution of quinone and its deriva- 
tives, but to much important discovery besides. At this time 
q tinone 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 other really analogous bodies, other quinones 
in fact, already exist. He studied with great care this quinone 
series of compounds and the relation they bore to one another, 
the relation the hydrocarbon, benzole, bore to its oxidised 
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 chemists, that in fact naphthalin (C;j>Hg) was the parent 
hydrocarbon and that the chloroxynaphthalin chloride (C,)H, 
Cl,0,) and the perchloroxynaphthalin chloride (Cy Cl,0.) were 
really chlorine substitution compounds of the quinone of this 
series, corresponding to the bichloroquinone and to chloranil. 
That the chloroxynaphthalic acid C,)H,Cl(HO)O, and the per- 
chloroxynaphthalic acid C,)Cl;(H O)O,, all compounds pre- 
viously discovered by Laurent, were really bodies belonging to that 
Laurent | 
have the means of forming alizarine artificially. 
series, and further the supposed isomeric of alizarin discovered by 
Martius and Griess was really related to this last compound, 
having the composition C;,H; (H O) O,. Further he was 
able to confirm this by obtaining the quinone ilself of this 
series, the body having the formula C,,H, (O,) containing also 
two atoms less of hydrogen, and two atoms more of oxygen 
than the hydrocarbon naphthalin, and to the body he gave the 
characteristic name of naphthodtinone. The chlorine com- 
pounds just named are thus chloro-naphthoquinone, or chloroxy- 
naphthoquinone, and correspond to the former chloroquinones, 
Martius and Griess compound will be an oxynaphthoquinone ; 
many other compositions of this series are also known. Another 
step confirmatory of this existence of a series of quinones was 
made by Graebe and Borgmann, as the chloranil could be formed 
by treating phenol by potassic chlorate and hydrochloric acid and 
quinone derived from it, they showed that in the next higher series 
to the phenol series, viz. with cressol, the same reaction held good, — 
and by treating it in the same way they obtain a di- and a tri- 
CH, CH, a 
chlorotolu-quinone C, (0%) cd (O,)" which in physical por- 
a Cl 
H 3 
perties very closely resemble the corresponding compounds in 
the lower series. Other compounds haye also been prepared. 
In the next step we have the application, which connects these 
series of discoveries with alizarine. Following the clue of a 
certain analogy which they believed to exist between the 
chloranilic acid Chia) and the chloroxynaphthalic acid 
2 
CyyH,Cl tz) which they had proved to be quinone compounds” 
2 
and alizarine, believing that a certain similarity of properties 
indicated a certain similarity of constitution, Graebe and 
Liebermann were lead to suppose that alizarine must also 
be a derivative from a quinone, and have the formula 
C,H, ae This theory they were able afterward to prove ; the | 
first thing was to find the hydrocarbon ‘from which the quinone 
might be derived ; this was done by taking alizarine itself, and 
heating it with a very large excess of zinc powder in a lon 
tube, sealed at one end. A product distilled over, and condens\ 
in the cool part of the tube, and collecting it and purifying it 
by recrystallisation, they found they had not a new substance, 
but a hydrocarbon discovered as long ago as 1832 by Dumas 
and Laurent, and obtained by them from tar. They had given it 
the formula C,; Hy, and as apparently it thus contained one 
and a half times as many atoms of carbon and hydrogen as 
naphthalin did, they named it Paranaphthalin ; afterwards Laurent 
changed its name to“Anthracene, by which it is still known. 
Fritzsche, in 1857, probably obtamed the same body, but gave 
it the formula C,, Hy). Anderson also met with it in his 
researches, established its composition and found some derivatives 
from it. Limprich in 1866 showed it could be formed syn- 
thetically by heating benzolchloride (C;H,Cl) with water and 
Berthelot has since proved that it is formed by the action of 
heat on many hydrocarbons. This first step was thus complete 
and most satisfactory; from alizarin they had obtained its 
hydrocarbon, and this hydrocarbon was a body already known, 
and with such marked properties that it was easy to identify it, 
But would the next requirement be fulfilled, would it like 
benzol and naphthalin yield a quinone? The experiment had ~ 
not to be tried, for when they found that anthracene was the 
hydrocarbon found, they recognised in a body already known 
to exist, the quinone derivable from it. It had been prepared 
by Laurent by the action of nitric acid on anthracene, and 
called by him anthraceneuse, and the same substance was also 
discovered by Anderson and called by him oxanthracene. The 
composition of this body was proved by Anderson and Laurent to’ 
be C,,H,Os, and it thus bears the same relation to its hydrocarbon 
anthracene, that quinone and naphthaquinone do to their hydro- 
carbons. Graebe gave to it the systematic name of anthraquinone. 
We have then, now, three hydrocarbons CgH,, Cy,Hg, and 
C,4Hjo, differing by C,H, and all forming starting points for these 
different quinone series. Anthroquinone acted upon by chlorine 
gave substitution products such as might have been foretold. It 
is an exceedingly stable compound, not attacked even by fusion 
with potassic hydrate. Bromine does not act upon it in the cold, 
but at 100° it forms a bibromanthraquinone. Other bromine 
compounds have also been found. Now, if the analogies which 
have guided them so far still hold good, they would seem to 
Their,theory is ~ 
