Phototransformation of 4-chloro-2-methylphenoxy acetic acid (MCPA)

Article abstract of DOI:10.1524/zpch.1999.213.part_1.087

MCPA was irradiated in various conditions: in aqueous solution at different wavelengths, on silica in the absence of water, in the presence of TiO₂ in aqueous suspension. In solution a wavelength effect was observed: the formation of 4-hydroxy-2-methylphen-oxyacetic acid is the main pathway at wavelengths shorter than 300 nm, whereas 4-chloro-2-methylphenol is the main product resulting from sunlight irradiation. Direct photolysis on silica and photocatalytic transformation mainly lead to the formation of 4-chloro-2-methylphenol. by Oldenbourg Wissenschaftsverlag, Mu?nchen.

Full text of DOI:10.1524/zpch.1999.213.part_1.087

Bd.
S. 87-92
(1999)
Zeitschrift für
©
Chemie,
213,
Physikalische
München
Oldenbourg
Wissenschaftsverlag,
by
of
Phototransformation
4-chloro-2-methyl-
Acetic Acid
(MCPA)
phenoxy
*
A.
T.
P.
Sehili2 and Boule1
Zertal2,
By
'
Université
UMR CNRS 6505, F-63177
Université
Laboratoire
Photochimie Moléculaire et Macromoléculaire,
Blaise Pascal,
de
Aubière
France
cedex,
2
Laboratoire de Photochimie et
Unité de
Environnement,
de
Constantine,
Recherche en Chimie, 25000
Constantine,
Algeria
December
10,
1998;
10, 1998)
(Received August
accepted
Phototransformation IPhotohydrolysis
I
MCPA I
acid
I
4-chloro-2-methylphenoxyacetic
4-hydroxy-2-methylphenoxyacetic
acid
in
solution different
at
was irradiated in various conditions
:
MCPA
aqueous
wavelengths,
In
absence of
in the
of
in
on silica in the
Ti02
water,
suspension.
presence
aqueous
observed: the formation of
effect was
solution
a
wavelength
4-hydroxy-2-methylphen-
4-chloro-
whereas
acid is the main
at
shorter than 300
wavelengths
nm,
irradiation. Direct
oxyacetic
pathway
product
main
from
mainly
is the
resulting
sunlight
photolysis
2-methylphenol
on silica and
transformation
lead
the formation of 4-chloro-2-
to
photocatalytic
methylphenol.
1. Introduction
a
is
for the elimination of
dis-
in surface
wave-
Direct
way
photolysis
significant
pesticides
It
occur on
or
the surface of soil
be drained.
in the environment.
may
persed
more
can
soluble
short
at
where the
can
waters
Photolysis
also be involved in the treatment of water. So it is
to
important
lengths
behaviour of xenobiotics
the
and
specially pesticides
study
photochemical
and short
for
Moreover
photoca-
in both
(254 nm).
wavelengths
sunlight
range
of
and it is useful
4-chloro-2-
often
waters
waste
was
depollution
talysis
proposed
behaviour of these
know the
to
photocatalytic
compounds.
is used
herbicide and it is
studied
named
acid
as
a
commonly
methylphenoxyacetic
al.
et
is
the
and
major
MCPA. Its
was
[1]
photodegradation
previously
by Soley
et
that
al.
[2].
Clapés
*
They reported
4-chloro-2-methylphenol
author.
Corresponding
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88
Sehili and Boule
P.
A.
T.
Zertal,
nm
solution
formed in
be sensitized
irradiated
290
and that its for-
near
initially
product
mation
the
can
riboflavine in simulated
aim of
The
sunlight.
by
work is
the
transformation of MCPA
to
compare
photochemical
present
in
various conditions:
solutions different
direct
at
and
wavelengths,
aqueous
sand in the
of
water
in the
absence
on
photolysis
photocatalysis
pres-
TiO, in
of
ence
suspension.
aqueous
2.
MCPA
GC-MS.
MCPA
Experimental part
>
was
98%
Chem Service. Its
with
controlled
was
provided by
purity
by
irradiated in
sand Fon-
P25 in
was
water
on
device,
of
TiO,
Milli-Q
purified
tainebleau
in
were
Prolabo
the
or
provided
by
Degussa
sand
before
presence
removed
substances
from
use
suspension. Organic
by
at
several hours
500 °C.
warming during
Unbuffered solutions
irradiated
various
at
were
wave-
3.5—3.7)
(pH
with different
254
devices :
lengths
in
surrounded
6
nm: reactor
by "germicide" lamps,
quartz
Reactor
nm:
290—350
in
surrounded
6
Duke Sun-
"Pyrex"
by lamps
near
GL20
light"
emission
310
(maximum
nm),
lamp
"black
85% of radiant
365
a few
at
(about
nm,
energy
percents
Phi-
334 and 313
HPW
MCPA
in
reactor
surrounded
3
at
nm):
"Pyrex"
by lamps
125,
lips
was
transformed with
TLD
in
sus-
the
Ti02
W
photocatalytically
aqueous
a
with
nm,
in
15
pension (2
1)
lamp Philips
emitting
g
300—450
was
range
MCPA
sand from Fontainebleau
100
in
on
on
(10
dispersed
mg
g)
ether.
290—350
and
sand
After
irradiated
was
the
using
range
round bottom
with internal
evaporation
drying,
4
nm
with
GL20. After irradiation
a
lamps
through
flask
around horizontal
a
axis and
rotating
equipped
to
favour the
extracted with methanol and
of the
sand,
spikes
mixing
photoproducts
with HPLC.
on
were
analysed
with
45%
HPLC
+
column
were
a
C18
Photoproducts
analysed
X
250
4
Eluent
of
55%
with
mm
mm.
was
CH3CN
H20
(acidified
acetic
acid).
The
and
deduced from
structure
and
I
II
NMR
was
photoproducts
recorded
Bruker AC 400
MS
and Hewlett-Packard
on
spectra
spectra
5985
respectively.
3.
Results
MCPA
to
3.1
of
spectrum
Adsorption
pKa
The
of MCPA
be 3.07
nm
The maximum
was
[3].
reported
absorption
of the anionic form is located
279
coefficient
at
(molar
eA
absorption
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of
Phototransformation
MCPA
Acetic Acid
89
4-chloro-2-methylphenoxy
(MCPA)
Solar
photon.cm"2.s''.nm"'
spectrum
IO13
9
IO3
M"1.cm'1
279nm
5
june
/
240
400
280
360
( ,)
1. UV
of MCPA.
Solar
Fig.
to Frank and
spectrum
spectrum according
[4].
Klöpffer
1550 ±15
The
±15 M"1
maximum
of the
neutral form is located
at
' ').
1395
277
nm
In the unbuffered
solutions
4
(
cm-1).
4
8X 10
M
used
to
the
in
behaviour
the anionic
form
little
is
at
study
photochemical
It
nm.
can
dominant.
be
1
that
MCPA
seen
absorbs
Fig.
only
very
>
300
3.2 Irradiation
of
solutions
aqueous
4
An
unbuffered
M
on the
air-saturated
was
solution 6.4
X
10
irradiated
chromatogram
determined
3.5)
(pH
at
Two
254
main
were
nm.
HPLC
photoproducts
appeared
isolated
and their
structure
2a).
was
(Fig.
They
by
NMR and GC-MS.
I
unstable
mass
in
its
was
mass
GC,
Actually product
spec-
corrob-
obtained
GC-MS after
direct
methylation.
trum was
orated
by
in
the
and
107
by
injection
spectrometer
108
(100);
m/z
I:
182
164
136
\20);
(20-60);
(M'
(=50);
(«50)
m/z 196
137
123
(100)
(M-+,45);
(15);
-^-methylated
6.71
6.65
6.57
4.62
2.18
(d);
(d);
d'ppm:
(2 H,s);
(3H,s)
(dd);
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90
A.
.
and P.
Senili
Zertal,
Boule
MCPA
MCPA
I
McQH;
/
<?>
III
Ill
ÜJ
5
10
5
10
R.T.
(min)
R.T.
(min)
MCPA
4 M)
2.
HPLC
of an
Eluent
Fig.
air-saturated
solution
of MCPA
ir-
chromatogram
(6.4X10
radiated in
55%. Detection
various
conditions.
+
45%
CH,CN
with
acetic
H20
(acidified
acid)
1
·
280 nm.
the
range
(conversion
Flow 1.8
at
ml min
290-350 nm
irradiated
(a)
254
(c)
nm
(conversion
=56%),
irradiated
in
in
(b)
(conversion
irradiated
a
few
=40%),
during
days
sunlight
=26%).
II: m/z 182
184
154
156
126
(M"+,75);
(M'+,21);
2.24
(100);
(35);
(25);
128
91
<(S1p0pm);:
(70)
7.05
3.66
(2H,q);
(2H,s);
(3H,s)
From
these
results the
formulae
:
deduced
were
following
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Phototransformation of
Acid
(MCPA)
91
Acetic
4-chloro-2-methylphenoxy
used
Product
I
isolated
Its
HPLC
calibrate HPLC.
to
formation
II
of obtained
was
by
accounted for about 85% of MCPA transformed. The
was
amount
I
and II
sufficient for calibration. The formation of
not
was
products
in
studies.
(III)
not
reported
Another
previous
photoproduct
was
as
identified
4-chloro-2-methylphenol
with standard
for
accounts
It
about
a
(commercial
same
by comparison
product).
The
reactions
2% of converted MCPA.
observed in
were
deoxygen-
ated solution.
Similar behaviour
observed when the solution
irradiated
in the
is
not so
was
was
290-350
it
transformation
However
does
noted that the
nm.
was
range
Product
I
accumulate and
with similar
not
the
a new
specific.
product
This
retention time
on
was
2b).
chromatogram (Fig.
product
appears
identified
of retention
as
tentatively
methylhydroquinone by comparison
times
little
is also
that
formation of
is
III
and UV
It
at
was
the
a
noteworthy
nm
spectra.
efficient than
solution
254
more
(6—8%).
The
irradiated in
46 °N altitude
same
(latitude
sunlight
was
400
ated
main
MCPA
transformed within a few
in
is III. It
The half-live
evalu-
the
was
m).
at
days.
c
in
in
that
8
—10
It
2
Fig.
sunlight
days
May. clearly
appears
for 40—50% of MCPA converted. The
accounts
photoproduct
III
formation of in
lar
is
was
lower in
solution. Simi-
UV
sunlight significantly
degassed
obtained
in
near
("black
phototransformation
by irradiating
light").
3.3 Irradiation
silica
transformation of MCPA
and
on
the
photocatalytic
In
both
Small
cases
was
major photoproduct
4-chloro-2-methylphenol.
were
of
detected
GC-MS
amounts
(4-chloro-2-methyl) phenylformate
by
(m/z
170-172).
Discussion
mechanisms
4.
and
<
>
Different
300
are
at
nm
at
and
nm.
mechanisms
I
involved
300
a
formation of is
The
mechanism of
explained by heterolytic
photohydro-
It
as
was
it
often
for chloroaromatic derivatives.
better
ac-
lysis
reported
nm
nm
290—300
was
cumulates
much
254
than
since it absorbs
observed with
at
at
near nm as
wavelengths
more
than MCPA
300
was not
it
photodiode
I
in
detector of HPLC.
detected
studies
for
previous
probably
array
several
irradiations
carried
290
and
were
out near
nm
reasons
:
i,
longer
retention times
similar for
HPLC
I
and
are
ii,
iii,
wavelengths;
hydroquinone,
methyl-
very
unstable in GC-MS.
is
I
thermally
formation of involves molecule of
it does
not
The
I
a
occur on
water,
silica.
dry
pés
identified
and
result from
Cla-
phenylbenzoquinone
Phenylhydroquinone
by Soley,
al.
the of I.
et
photolysis
may
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92
and
Boule
P.
A.
T.
Sehili
Zertal,
II
followed
results from
a
II on
by
Photoproduct
photo-Fries rearrangement
the HPLC
into lactone
probably
(peak
chromatogram
reported
cyclisation
was
reaction
[5].
for other
the
Such
com-
to
as
a
form).
open
corresponds
acid
such
2-naphtoxyacetic
pounds
nm
>
irradiated
300
The mechanism of formation of III in solutions
However
at
et
al.
time.
is
elucidated
the
at
not
Clapés
reported
Soley,
present
of riboflavine.
that it is favoured
the
by
presence
transformation of
In
MCPA the formation of III is
the
photocatalytic
radicals.
attributed
the oxidation of
to
by hydroxyl
méthylène
group
References
Chem.
Prod. Res. Dev.
25
15
1.
and S.
Ind.
J.
M.
645.
P.
Vicente,
Eng.
Rivera, Caixach and F. Ventura,
J.
Soley,
Clapés
Esplugas,
(1986)
2. P.
J.
395.
M.
J.
Vicente,
Chemosphere
639.
Clapés,
Soley,
(1986)
3. C. Tomiim, The Pesticide Manual 10th Ed. The Bath Press
4. R.
5. M. J.
Bath, 1994,
p.
Frank and
17
Agrie.
985.
W.
Klöpffer, Chemosphere
(1988)
45
1916.
Climent and
Miranda, J.
Food Chem.
M. A.
(1997)
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