i =o NOTES ON SCIENTIFIC RESEARCH. 105 
Vavon’s*) indications, through catalytical reduction of carvone with hydrogen and 
platinum black. By adding bromine in drops to the chloroform solution of tetrahydro- 
carvone, dibromotetrahydrocarvone (m.p. 81°) is obtained. On being shaken with 
potash lye, it passes into buchu camphor, and this more quickly and more completely 
than dibromomenthone’). 
As regards the absorption spectrum of buchu camphor in the ultraviolet region 
see page 74. 
Acids. 
Camphenic acid. The constitution of camphenic acid (camphenecamphoric acid), 
an oxidation product of camphene, had not, so far, been established with certainty*). A 
little while ago, P. Lipp*) prepared synthetically d,l-cis-camphenic acid and recognized 
it to be a 1,3-carboxycyclopentaneisobutyric acid, as Aschan had presumed already at 
eae ae oO Fie ah ee 
CH, SS | von COR 
| 
HC CH:CO.R H,C——_CH-CO,R 
(1) ethyl 1,3-cyclopentanone (II) 1,3-carbethoxycyclopentanol- 
carboxylate. isobutyrate. 
HaC - C——C(CHs) Be comets EC CH CCH): 
| CH CO.H | CH, CO:H CH: COnH 
H,C—CH-CO.H H,C—CH-CO,H eo CH a 
(II) (IV) (V) 1,3-carboxycyclopentaneisobutyric acid 
1, 3-carboxycyclopenteneisobutyric acid. (camphenic acid) (Aschan’s formula). 
the time. He started from ethyl 1,3-cyclopentanone carboxylate (I), which may be 
prepared even though with some difficulty according to the method described by Kay 
and Perkin as well as by Haworth and Perkin®). With zinc and «-bromoisobutyrate, 
this ester affords ethyl 1,3-carbethoxycyclopentanolbutyrate (II). On being treated with 
potassium pyrosulphate at 170 to 180°, it yields, in addition to the expected ethyl 
1,3-carbethoxycyclopenteneisobutyrate, an unsaturated ester acid, which presumably 
contains tertiary carboxyl still in the form of an ester. Both furnish on saponification 
with alcoholic potash 1,3-carboxycyclopenteneisobutyric acid, for which two formulas 
are possible (Ill and IV). The hydrogenation of this acid according to Fokin-Will- 
statter’s method leads to 1,3-carboxycyclopentaneisobutyric acid, which proved to be 
identical with d,l-cis-camphenic acid (V). It melts at 135 to 137°, and there is no 
lowering of the melting point when it is mixed with pure d,l-cis-camphenic acid. 
The paper published by Lipp agrees in many respects with an investigation of the 
structure of camphene, undertaken by W.N. Haworth and A. T. King®), following up 
previous examinations’), but the results of which they had not yet published. They 
now refrain from reporting fully on their work, describing only some syntheses 
which Lipp had not mentioned. This refers to the condensation of ethyl as-dimethyl 
1) Comp. Report October 1911, 150. —+,2, Comp. Report April 1914, 139. — *) Comp. Report April 
1911, 188; October 1911, 132; October 1913, 131. — *) Berl. Berichte 47 (1914), 871. — 5) Comp. Report 
October 1908, 164. — *) Journ. chem. Soc. 105 (1914), 1342. — 7%) Comp. Report April 1913, 135. 
