AUTOCATALYTIC OXIDATION OF β-ALANINE BY PEROXOMONOSULFATE
45
Although the kinetics of α-amino acids with PMS
has been studied extensively, but little information
is available in the literature about the oxidation of
β-amino acids, such as β-alanine, with PMS. More-
over, an α-amino acid undergoes oxidative decar-
boxylation and deamination, whereas a β-amino acid
undergoes oxidation by deamination only, because
the removal of direct conjugation between NH+3 and
COO− groups by the intervening CH2 groups is re-
sponsible for the difficulty in decarboxylative deami-
nation. Hence, it is proposed to study the kinetics of
the oxidation of β-alanine in buffered medium and the
results obtained are discussed in this paper.
Figure 1 Plot of log [PMS]t versus time [β-alanine] = 0.05
mol dm−3, [NaOAc] = 0.08 mol dm−3 [Cu(II)] = 2.5 × 10−3
mol dm−3, pH 4.2 0.1.
EXPERIMENTAL
is, [peroxomonosulfate]/[β-alanine] = 2.5 with [Cu2+
]
Potassium peroxomonosulfate was obtained from
Dupont (Lancaster, PA, USA) under the trade name
“Oxone.” The purity of the triple salt 2KHSO4·KHSO4·
K2SO4 was estimated by iodometry and was found to
be 98%. However, the presence of H2O2 in an oxone
sample was tested and it showed negative results, thus
eliminating the chances of the hydrolysis of oxone. A
fresh solution of peroxomonosulfate was prepared be-
fore starting the experiments. β-alanine was purchased
from Loba-Chemie Indo Austranal Co. (Mumbai,
India) and was used as such. All other chemicals used
in this study were of the Analar grade and were used
as such without any further treatment.
2.5 × 10−3 mol and pH 4.2 allowed to stand for 48 h.
The experiment was performed with different initial
concentrations of the oxidant and β-alanine by main-
taining the ratio at 2.5. Then, the unreacted oxidant
in each case was estimated by iodometry. After mak-
ing corrections for self-decomposition of the oxidant,
which was carried out under the same kinetic con-
ditions, stoichiometry was calculated as β-alanine:
PMS = 1:1. Thus, the stoichiometric ratio evident from
the data corresponds to the reaction and can be written
as
Doubly distilled water was employed throughout
the study; the second distillation was from alkaline
permanganate solution in an all glass still.
H2N CH2 CH2 COOH + PMS
Cu2+
−→ OHC CH2 COOH + Cu2+
pH4.0
The reaction mixtures containing all reactants
except peroxomonosulfate in glass-stoppered Erlen-
meyer flasks were immersed in the water bath ther-
mostated at 35 0.1◦C. Peroxomonosulfate was taken
in another flask to attain the same temperature of 35
0.1◦C. The required volume of the oxidant solution
was pipetted out into the reaction mixture. Experi-
ments were carried out in acetic acid/sodium acetate
buffered medium at various pHs ranging from 3.6 to
5.2. The rate of oxidation of β-alanine was followed
by monitoring the concentration of unreacted oxone by
iodometry. Autocatalysis was observed from the plot
of log10 (volume of thio) at various time intervals (Vt)
versus time (Fig. 1). The values of catalyzed and un-
catalyzed rate constants were calculated. The relative
standard errors of the above-mentioned rate constants
for a single run and the relative standard errors of the
mean were about 2%.
+ HSO−4 + NH+4
(1)
The product analysis was done under kinetic con-
ditions as described below. The reaction mixture con-
taining β-alanine at pH 4.2 and PMS in the presence
of Cu(II) was allowed to stand for 48 h for the comple-
tion of the reaction. After completion of the reaction,
the excess oxidant was destroyed by adding NaHSO3
and then extracted with dichloromethane. The organic
layer obtained was analyzed to identify the product.
FT-IR and H1 NMR data confirm the product as mal-
onic semialdehyde, and the retention time at 9.423 min
and 99.1% purity was confirmed by gas chromatog-
raphy/mass spectrometry. The chromatographic con-
ditions used for the oxidation kinetics to identify the
product were EC5, 30 m × 0.2 mm, 0.25-µm column
with nitrogen as a carrier gas with a flow of 1.0 mL/min.
Injection and detection temperatures for the study were
280◦C and 290◦C, respectively. The oven temperature
was initially started from 50◦C and held for 2 min, and
The stoichiometry of the reaction was determined
under the kinetic conditions by taking a known ex-
cess concentration of the oxidant over β-alanine, that
International Journal of Chemical Kinetics DOI 10.1002/kin