Oxidation of glyoxal initiated by OH in oxygenated aqueous solution
Abstract
The kinetics and mechanism of the oxidation of glyoxal,
which is a constituent of cloud water, initiated by
OH in oxygenated solution have been investigated
using pulse radiolysis with optical and conductivity
detection of the transient species, and steady-state
radiolysis with spectrophotometric and ion chromatographic
analysis of the permanent products. The data obtained are
consistent with glyoxal being present in the form of the
dihydrate [CH(OH)
2
]
2
which is oxidised
to glyoxylic acid (pK
a
=3.4) and hydrogen
peroxide via a peroxyl radical
O
2
C(OH)
2
CH(OH)
2
that splits off HO
2
in a non-rate
determining step. The following rate constants have been
determined:
k{
OH+[CH(OH)
2
]
2
}=(1.10±0.04)×10
9
dm3 mol
-1
s
-1
and
k[
C(OH)
2
CH(OH)
2
+O
2
]=(1.38±0.11)×10
9
dm3 mol
-1
s
-1
. It is
concluded that oxidation of glyoxal by
OH in
cloud water can proceed by a chain reaction involving
H
2
O
2
.
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