- The radiolysis of succinic acid in aqueous solutions induced by
gamma irradiation from ⁶⁰Co has been studied with respect to the
identification and estimation of degradation products. Detailed information
on the radiolysis of succinic acid is important in determining
what effect two carboxyl groups in the same molecule would have on
the reaction mechanisms and products relative to the degradation of
the hydrocarbon chain resulting from gamma irradiation. ¹⁴C-labeled
succinic acid was employed to facilitate product identification and estimation.
In addition, specifically labeled succinic acid-¹⁴C and
malic acid-¹⁴C were utilized for the elucidation of reaction mechanisms.
The irradiation experiments were performed in both oxygenated
and oxygen-free systems.
The principal means of identification of the radiolytic products
were by paper chromatography and autoradiography, utilizing the
technique of co-chromatography. The estimation of each radiolytic
product was determined by radiochemical assay using liquid scintillation
The oxidation reactions in both oxygenated and oxygen-free
systems may possibly follow the same reaction mechanisms, since
the degradation products resulting from these reactions are the same
in the oxygenated and oxygen-free systems, although the yields are
greater in the oxygenated system. The oxidation products identified
from the radiolysis of succinic acid were malic, malonic, oxaloacetic,
pyruvic, oxalic, mesoxalic, glyoxylic, propionic, acetic, and formic
acids, glyoxal, and carbon dioxide. The products of molecular
weight greater than succinic acid produced exclusively from radiolysis
in the oxygen-free system were 1, 2, 3, 4-butane-tetracarboxylic,
1, 2, 4-butane-tricarboxylic, tricarballylic, glutaric, and adipic
The radiochemical yields of the radiolytic oxidation products
from specifically labeled succinic acid-¹⁴C were determined to be
greater in the oxygenated system than in the oxygen-free system.
This fact indicates that oxygen plays an important role in the radio-lytic degradation of succinic acid. The graphical presentation of the
degradation of succinic acid and the formation of malonic and malic
acids with increasing cumulative dose follow the same course in both
oxygenated and oxygen-free systems. However, the radiolytic degradation of succinic acid and the formation of malonic and malic
acids were greater in the oxygenated system.
The formation of malonic acid from radiolysis of succinic acid
aroused considerable interest, since this acid was produced in unusually
high yield. Therefore, studies were carried out to elucidate the
mechanism for malonic acid formation. The results for radiolysis
of ¹⁴C specifically labeled succinic acid indicated that malic acid
probably was an intermediate in the formation of malonic acid. In
order to verify this result, specifically labeled malic acid-¹⁴C was
used in similar irradiation experiments. The results of this experiment
indicated that malonic acid formation resulted from C-1 decarboxylation
of malic acid followed by oxidation of the intermediate.
Several reaction mechanisms were suggested as possible mechanisms
for the formation of malonic acid. The most likely mechanism involved
OH addition across the double bond of the enol form of oxaloacetic
acid, in which decarboxylation of the adduct accompanied by
oxidation resulted in the formation of malonic acid.