Nov. 24,1923 
Studies on Rancidity 
325 
of ketoxystearic acid, while Nicolet and Jurist ( 26 ) have prepared diketo- 
stearic acid by oxidizing oleic acid with chromic anhydrid in acetic acid 
solution. 
Employing a more vigorous oxidation with nitric acid, Redtenbacher 
(31) noted the formation of volatile fatty acids and dicarboxylic acids; 
Carette (6) identified glutaric acid; Laurent (23, p. 166) detected hep- 
tylic, suberic, pimelenic, adipic, and azelaic acids; Bromeis (4) obtained 
suberic, pimelenic, and adipic acids; while Arppe (1) has noted the for¬ 
mation of azelaic acid. 
Harries and Thieme (38) have studied the action of ozone on oleic 
acid and have found that the initial reaction consists in the addition of 
ozone across the double bond with the formation of oleic acid ozonid. 
The isolated ozonid is described as being a comparatively unstable, 
sirupy liquid of penetrating odor, which, when subjected to hydrolysis, 
breaks down into azelaic half aldehyde and pelargonic aldehyde (or their 
peroxids), which may in turn be oxidized to the corresponding acids. 
Many of the above-mentioned oxidation products of oleic acid have 
been observed both in fats and in oleic acid after the spontaneous devel¬ 
opment of rancidity. Scala in particular has identified formic, acetic, 
butyric, heptylic, azelaic, and apparently dihydroxystearic acids as prod¬ 
ucts of the atmospheric oxidation of oleic acid ( 36 ), and has recovered 
pelargonic, heptylic, caproic, and butyric aldehydes as well as the corre¬ 
sponding acids and formic acid from a specimen of rancid fat (37); while 
Nicolet and Liddle (27) have isolated as much as 10 per cent of azelaic 
acid from a sample of rancid cottonseed oil. It is surprising that atmos¬ 
pheric oxygen is able so completely to reproduce the profound changes 
effected artificially in the oleic acid molecule by the more vigorous oxi¬ 
dizing agents mentioned above. 
Engler and Weissberg (11) have shown, however, that ordinary molec¬ 
ular oxygen may attack the double bond in much the same manner as 
may ozone. In this process, known as autoxidation, the oxygen is added 
molecularly across the double bond with the formation of a particular 
type of peroxid which they term moloxid: 
R R 
h— c: ° h— i—o 
h4 + ^h-<U 
I 0 I 
While the isolation of these peroxids presents many difficulties, a few of 
them have been prepared and the existence of many others seems to 
have been fairly well established. In properties they are said to resem¬ 
ble the ozonids described by Harries and Thieme ( 38 ), being character¬ 
ized by instability and generally, according to Durrans (9), by a 
penetrating odor due to intramolecular stress. Like the ozonids, they 
readily undergo cleavage with the formation of aldehydes. Engler and 
Weissberg (n) classify the unsaturated fatty acids as compounds that 
are subject to autoxidation. 
It appeared, therefore, that the development of rancidity in fats might 
be attributed provisionally, as had already been suggested by Winckel 
