Radioactive tracer techniques have been
used to study the effect of ionizing radiation (60Co
γ-radiation and 45 kV X-rays) on [14C]benzoic acid (both
carboxyl- and uniformly-labelled) and on [carboxy-14C]salicylic acid
in aerated aqueous solutions.
�� The
production of o-, m-, and p-hydroxybenzoic acids from benzoic acid (Loebl,
Stein, and Weiss 1951) has been cord3rmed. The approximate initial G values for
these products were : ortho, 0.74 ; meta, 0.42 ; para, 0.33. The ratio o : m :
p was thus approximately 9 : 5 : 4 whereas Loebl, Stein, and Weiss found the
corresponding ratio to be 5 : 2 : 10. Benzoic acid and sodium benzoate were
also decarboxylated [G(CO2) : 0.73 � 0.03]. The extent of
decarboxylation was independent of the initial concentration of benzoic acid in
the range studied (0.5-7.0 X 10-3 M). The total reaction of the
benzoic acid corresponded to a G value of approximately 2.6. Very little, if
any, diphenyl was produced.
The main non-volatile products from
salicylic acid were 2,3- and 2,5-dihydroxy- benzoic acids which were obtained
in the ratio 2,5 : 2,3 :: 1 : 1.6. The 2,4- and 2,6- isomers were not detected.
Salicylic acid was also decarboxylated, G(CO2) being 1 53 � 0.07 in
alkaline solutions.
The above results are compared with other
results relating to free-radical reactions. The possible use of the
decarboxylation of sodium [carboxy-14C]benzoate as a sensitive
dosimeter for ionizing radiation is suggested.