106 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[August 10, 1872, 
methyl-propyl-b enzene, or «-cymene, because oil of tur¬ 
pentine yields terephthalic acid on oxidation. It 
appears most probable that it is a-cymene, as it has the 
same boiling point as the latter, and moreover oil of 
turpentine, as well as a-cymene, occur ready-formed in 
plants. The constitution of oil of turpentine is therefore 
probably the following :— 
H H 
\ / 
C=C CH 3 
/ \ I 
FoC—0 CH—CH 
^ / I 
. C—C—H CH 3 
/ \ 
H H. 
Oil of turpentine, therefore contains the aromatic 
nucleus, in which the connection between two carbon 
atoms has been loosened, and thus two combining units, 
which in the aromatic nucleus were linked together, 
are now saturated with hydrogen. As Baeyer has 
shown, such a loosening of the connection between two 
carbon-atoms takes place most readily between those 
which are combined with alcohol radicals. 
It has been already stated, that by abstracting four 
atoms of hydrogen from diamylene, a terpene is formed 
which seems to be identical with terebene. It has, how¬ 
ever, not been yet shown whether this artificial terebene 
yields terephthalic acid on oxidation. If this is found 
to be the case, the constitution of this hydrocarbon would 
be as follows, amylene being 
CH 3 
\CH—CH=CH 2 . 
CH g 
H„C CH 3 
' \c/ 
/ \ 
HC CH 
II II 
HC CH 
\c^ 
H 3 C—ch 3 .* 
I only have to mention a most singular reaction by 
which some of them are formed, discovered by Zincke 
(Ann. Chem. Pharm., clix. 367). This chemist intended 
to obtain dibenzyl by acting with finely-divided copper 
or zinc-dust upon benzyl chloride. In order to moderate 
the violent reaction, he diluted the benzyl chloride with 
ether and with paraffins, but under these circumstances 
no reaction took place. However, by employing 
aromatic hydrocarbons as diluents, action set in; but 
instead of dibenzyl being formed, he obtained a mixture 
of several other hydrocarbons, in the formation of which 
the aromatic hydrocarbons, in other respects so stable, 
take part with great energy. It is not possible to give 
an explanation of this fact, as all the products of this 
reaction have not yet been studied. But the fact exists 
that aromatic hydrocarbons, when heated with zinc-dust 
and benzyl chloride lose hydrogen and take part in the 
formation of new hydrocarbons. Thus, on employing 
benzene, one of the products is diphenyl-methane or 
benzyl-benzene, CH 2 q 6 ^ 5 ’ which is formed according 
the equation— 
C 6 H 5 .CH 2 C1 + C 6 H 6 = C 6 H 5 .CH 2 .C 6 H 5 + HC1. 
Further researches will no doubt throw more light 
upon this singular subject. 
Amongst the products of the destructive distillation of 
coal and other substances, there always occurs naphtha¬ 
lene, C 10 H g , a hydrocarbon which in its chemical cha¬ 
racter bears so great a resemblance to benzene that it 
must have a constitution very similar to the latter. 
Some years ago, Erlenmeyer pointed out that it had 
probably the following constitution :— 
H 
H 
C C 
^ \ / ^ 
H—C C C—II 
H—C 
*s‘ 
C 
/\ ^ 
•Y Y 
A A 
C—H 
The other isomeric hydrocarbons of the terpene group 
have, doubtless, constitutions similar to those above 
given, differing from each other either by containing 
different radicals, or by the different positions of the 
latter. 
Besides the hydrocarbons containing one aromatic 
nucleus, there exist also several in which this group 
occurs twice or more times. As most of these bodies, 
however, are obtained by well-understood reactions, I 
need not discuss them here. 
* Since the above has been written, von Richter (Deut. 
Chem. Ges. Ber. v. 334) has published a note on the con¬ 
densation of diamylene to rutylene and terebene. He thinks 
that von Schneider’s formula of diamylene does not explain 
either the property of this hydrocarbon of forming additive 
compounds, or its conversion into rutylene and terebene. He 
gives the following formulae as much more probable :— 
Diamylene. 
Terebene. 
h 3 c ch 3 
H 3 C CH3 
\/ 
\/ 
CH 
1 
CH 2 CHa 
CH 
CH—CH 
1 II 
CHs CH 
1 1 
CH 2 —CH 
1 II 
CHs CH 
1 I 
1 1 
CH=C 
I I 
CH 3 . ch 3 . 
The formula of terebene is, as will be seen, the same as 
that which Oppenheim has given for oil of turpentine. 
Naphthalene, therefore, would consist of two aromatic 
nuclei, which have two atoms of carbon in common. 
Graebe, who adopted this view, has proved the cor¬ 
rectness of this hypothesis in a very ingenious way 
(Ann. Chem. Pharm., cxlix. 21). His reasoning is as 
follows:—When naphthalene is oxidized, phthalic acid, 
C 6 H 4 (C0 2 H) 2 , is formed; this acid can be obtained in 
two different ways from naphthalene; viz., either by 
destroying the one or the other aromatic nucleus. Such 
an experiment cannot, of course, be made with naphtha¬ 
lene itself, because we have no means of distinguishing 
between the two groups. It appears, therefore, 
necessary, first, to replace hydrogen in one of the nuclei, 
and then find out which is attacked and which not. 
On oxidizing dichloronaphthaquinone, C 10 H 4 Cl 2 O./, 
phthalic acid is formed, a fact proving that in*this 
quinone all the oxygen and chlorine are combined with 
those four atoms of carbon which are oxidized, the 
formula of dichlornaphthaquinone being, therefore, 
C 6 H 4 .C 4 C1 2 0 2 ". By acting with phosphorous penta- 
chloride on this compound, the dyad group, 0 2 ", is 
replaced by chlorine, and, at the same time, one atom of 
hydrogen is substituted, pentachlomaphthalene being 
formed— 
C 10 H 4 Cl 2 O 2 " + 2PC1 5 =C 10 H 3 C1 5 + HC1 + 2P0C1 3 . 
Now, if by the oxidation of pentachlomaphthalene the 
same carbon-atoms are attacked as in the quinone, 
monochloro-phthalic acid would be formed ; but Graebe 
has shown that the product is tetrachlorophthalic acid, 
which proves that the second aromatic nucleus has now 
