Photochemistry of vinclozolin in water and methanol-water solution

Article abstract of DOI:10.1002/(SICI)1096-9063(199911)55:11<1116::AID-PS65>3.0.CO;2-Y

The photolysis of the fungicide vinclozolin in aqueous and methanol- water (50+50 by volume) solution has been examined. Irradiation at λ=254nm for 10 minutes resulted in <90% and ≤95% substrate transformation respectively. The dissipation of vinclozolin both in water and methanol+water was linear and the calculated half-lives were 1.01 and 2.0min respectively. Irradiation (8h) with UV light (λ≥290nm) resulted in 10% degradation of the chemical, which is of the same magnitude as that of the control (not irradiated). Irradiation (8h) under artificial sunlight (Suntest) in the presence of commercially available humic acid (K-salt) resulted in 55% degradation of the chemical. Photolysis leads to the opening of the 2,4- oxazolidine-dione ring, forming 3,5-dichlorophenyl isocyanate and 3,5- dichloroaniline. In addition, dechlorination and elimination of the -CH=CH₂ moiety takes place, and one or both the chlorine atoms are replaced by a methoxy group.

Full text of DOI:10.1002/(SICI)1096-9063(199911)55:11<1116::AID-PS65>3.0.CO;2-Y

Pesticide Science
Pestic Sci 55:1116±1122 (1999)
Photochemistry of vinclozolin in water and
methanol–water solution
Bernhard Schick, Pran N Moza,* Klaus Hustert and Antonius Kettrup
¨
GSF - National Research Center for Environment and Health, Institute for Ecological Chemistry, Ingolstadter Landstraße 1, D-85758
Neuherberg, Germany
Abstract: The photolysis of the fungicide vinclozolin in aqueous and methanol±water (50‡50 by
volume) solution has been examined. Irradiation at l=254nm for 10minutes resulted in <90% and
ꢀ95% substrate transformation respectively. The dissipation of vinclozolin both in water and
methanol‡water was linear and the calculated half-lives were 1.01 and 2.0min respectively.
Irradiation (8h) with UV light (lꢁ290nm) resulted in 10% degradation of the chemical, which is of
the same magnitude as that of the control (not irradiated). Irradiation (8h) under arti®cial sunlight
(Suntest) in the presence of commercially available humic acid (K-salt) resulted in 55% degradation of
the chemical. Photolysis leads to the opening of the 2,4-oxazolidine-dione ring, forming 3,5-
dichlorophenyl isocyanate and 3,5-dichloroaniline. In addition, dechlorination and elimination of
the ÐCH
group.
=CH2 moiety takes place, and one or both the chlorine atoms are replaced by a methoxy
# 1999 Society of Chemical Industry
Keywords: vinclozolin; photochemistry
1
Vinclozolin [3-(3,5-dichlorophenyl)-5-methyl-5-
INTRODUCTION
tion and chemical nature of the photoproducts of
vinclozolin irradiated with UV light (lꢁ290 and
254nm) in water and methanol-water solution. In
addition, the effect of commercially available humic
acid (K-salt) on the rate of degradation of vinclozolin
in arti®cial sunlight (suntest-apparatus, emitting light
with a spectrum close to that of sunlight) was also
examined.
vinyl-1,3-oxazolidine-2,4-dione] (I, Fig 1) is a protec-
tant fungicide. It is widely used for controlling fungal
diseases caused by Botrytis spp, Sclerotinia spp, and
Monilinica spp in grapes, fruits, vegetables, ornamen-
tals, hops, rapeseed, and turfgrass.1 The hydrolysis of
vinclozolin has been well studied,2±4 and two main
degradation products, 2-[(3,5-chlorophenyl)carba-
moyloxy]-2-methyl-3-butenoic acid and 3',5'-di-
chloro-2-hydroxy-2-methylbut-3-enanilide have been
reported. The decline of the residue of vinclozolin in
different grape vines has been studied by Gennari et al5
who reported that the minimum half-life was 1.2 days
for the normal dose and 2.0 days for the double dose.
An earlier study6 of the long-time (14 days) photolysis
of vinclozolin has described the formation of 3,5-
2
EXPERIMENTAL
2.1 Materials
Vinclozolin, analytical standard grade (99%) was
supplied by Dr Ehrenstorfer, Germany, and was
puri®ed further by recrystallization from hexane
‡ethyl acetate. Methyl chloroformate (99%), 3,5-
dichloroaniline (98%), 3-chloroaniline (99%), 3-
chlorophenyl isocyanate, S-( )methyl lactate (98%)
and triethylamine (99%) were obtained from Aldrich
Chemical Co. 3-Methoxyphenyl isocyanate (98%)
and humic acid (K-salt) were obtained from Fluka,
Germany, and phenyl isocyanate (95%) was received
from Merck, Germany. These chemicals were used to
synthesize comparison products.
dichlorophenyl
methyl 3,5-dichlorophenylcarbamate and 3-(3-chloro-
phenyl)-5-methyl-5-vinyl-oxazolidine-2,4-dione in
isocyanate,
3,5-dichloroaniline,
methanol solution. Vinclozolin is a colourless crystal-
line solid and is only slightly soluble in water (1mg
litre 1 at 20°C). In order to increase its solubility and
to produce enough of the photoproducts for structural
elucidation, irradiation experiments were carried out
in methanol-water solution. To our knowledge very
little is known on the in¯uence of humic materials
(present in soil and surface waters) on the photo-
degradation of vinclozolin. In the present work, a
comparative study was made of the photodecomposi-
2.2 Apparatus
Concentrations of vinclozolin after various intervals of
irradiation were measured by HPLC using a Gilson-
Abimed Model 302 liquid chromatograph equipped
with
a Macherey±Nagel reversed-phase column
* Correspondence to: PN Moza, GSF - National Research Center for Environment and Health, Institute for Ecological Chemistry, Ingolsta¨dter
Landstrasse 1, D85758, Neuherberg, Germany
(Received 5 November 1998; revised version received 24 May 1999; accepted 8 July 1999)
# 1999 Society of Chemical Industry. Pestic Sci 0031±613X/99/$17.50
1116

Photochemistry of vinclozolin in water/methanol
Figure 1. Photodegradation pathway of
vinclozolin in methanol‡water.
(Nucleosil C18-CN; 5mm, 20Â0.4cm ID) and a UV
detector set at 210nm. The solvent system used for
monitoring the loss of the parent compound was
acetonitrile‡water (60‡40 by volume) at a ¯ow rate
of 1ml min 1. For HPLC comparison (retention
times) of the photoproducts with the standards, the
instrument, the column and the detection wavelength
were the same as for the quantitative analysis. The
solvent system used was a gradient acetonitrile/water,
¯ow chart given in Table 1.
Macherey±Nagel capillary column (Permabond; SE-
52-DF-0.5, 25mÂ0.32mm ID) coated with a 0.5mm
®lm of phenyl ethyl silicone; injector temperature
230°C; carrier gas helium; temperature program 80±
240°C; 5°C min 1. Retention times of the photo-
products were compared with the standards on a
Hewlett Packard model 5890 GC instrument. The
GC conditions were the same as for GC-MS analysis
except nitrogen (¯ow rate 1ml min 1) was used as
carrier gas instead of helium.
[1H] and [13C]NMR spectra (400 and 100MHz
respectively) of deuterochloroform solutions were
obtained on a Bruker AC-400 instrument with
tetramethylsilane as an internal standard.
Vinclozolin photoproducts were separated in var-
ious fractions by semi-preparative high performance
liquid chromatography using a Microsorb C18 re-
versed-phase column (Rainin Instruments Co, USA,
5mm, 25cmÂ1cm ID). The pumps were Gilson
Abimed Model 305 and 302 (in gradient mode of
operation), with a UV detector Gilson Abimed Model
115 set at 210nm. Optimal separation of the peaks was
achieved with a 35min gradient acetonitrile/water
starting at 50‡50 by volume and ending at 100%
acetonitrile at a ¯ow rate of 1ml min 1. The gradient
¯ow chart is given in Table 1.
2.3 Irradiation
Vinclozolin (1; 0.2mg) in 200ml deionized water was
irradiated for 10min with a high-pressure mercury
lamp (HPK 125W, Philips) jacketed with a water-
cooled quartz ®lter to get maximum intensity of UV
light down to l=254nm. Similar experiments with 1
were performed in methanol‡water (50‡50 by
volume) (l=254nm). Samples of the solution of 1
were held in the dark as controls. To investigate the
effect of humic acid on the photodecomposition of
A Hewlett Packard Model 5995 GC-MS instrument
at an ionization potential of 70eV was used to obtain
the MS spectra. The GC conditions were as follows: a
Table 1. Gradient flow chart for the separation of peaks by HPLC
Time (min)
0
5
10
15
20
25
30
35
Solvent acetonitrile/water (by volume)
50/50
50/50
60/40
70/30
80/20
90/10
100/0
100/0
Pestic Sci 55:1116±1122 (1999)
1117

B Schick et al
vinclozolin, 5mg of humic acid (potassium salt) was
added to an aqueous solution (1mg litre 1) of the
pesticide, and the solution was irradiated in a Suntest
apparatus (Heraeus, Hanau, Germany). According to
the manufacturer's speci®cations, the lamp emits light
with a spectrum close to that of sunlight (300±
800nm). Similar experiments were carried out with a
high-pressure mercury lamp jacketed with a water-
cooled pyrex ®lter (lꢁ290nm). Samples of 1 in
aqueous solutions with and without humic acid were
held in the dark as controls.
re¯ux for 2h and cooled to ambient temperature. The
usual work-up followed by recrystallization (hexane
‡ethyl acetate, 1‡1 by volume) afforded a crystalline
substance (0.46g, 83%), mp 173±174°C. [1H]NMR d
3.77 (s, 3H), 6.91 (s, 1H), 7.02 (t, J=1.82Hz, 1H),
7.32 (d, J=1.74Hz). [13C]NMR d 52.7 (OCH3),
116.9, 123.4, 135.4, 139.8 (aromatic carbons), 153.6
(C
=O).
2.4.5 5-methyl-3-phenyloxazolidine-2,4-dione (5, Fig 1)
To a mixture of phenylisocyanate (1.14g, 10mmol)
and methyl lactate (0.884g; 10mmol) in dry toluene
(30ml) was added triethylamine (1.01g; 10mmol) in
toluene (10ml). The reaction mixture was heated at
re¯ux for 12h and cooled to room temperature. The
mixture was ®ltered and the crystals of (C2H5)3N
OCH3 were washed with toluene. The ®ltrate and the
washings were combined and washed with water
(3Â20ml). The organic phase was dried over sodium
sulfate, and the solvent was removed at reduced
pressure. The residue, a transparent liquid, was
triturated with methanol and a white solid separated
out. Crystallization from hexane‡ethyl acetate (1‡1
by volume) yielded 0.81g (42%), mp 113±116°C, of a
white powder. [1H]NMR d 1.71 (d, J=7Hz, 3H),
5.01 (q, J=7Hz, 1H), 7.45 (m, 5H). [13C]NMR d
16.7 (CH3), 75.9 (CH), 129.3, 128.9 (aromatic
carbons), 153.9 (N-COO), 172.4 (N-CO-R).
2.4 Preparation of comparison compounds
2.4.1 Methyl 3-methoxyphenylcarbamate (7, Fig 1)
Methyl chloroformate (0.747g, 5mmol) in dry toluene
(10ml) was added slowly to a solution of 3-methoxy-
aniline (1.23g, 10mmol) in dry toluene (20ml), and
the mixture was heated at re¯ux for 3h, cooled to room
temperature, poured into ice-water and acidi®ed with
hydrochloric acid (1M). The organic phase was
washed with water and dried over anhydrous sodium
sulfalt. After removal of the solvent at reduced
pressure, the resulting brown product was puri®ed
by column chromatography on silica gel 60 with
chloroform‡hexane (50‡50 by volume), yielding
colourless crystals (0.24g, 27%), mp 126±128°C.
[1H]NMR d 3.79 (s, 3H), 3.76 (s, 3H), 6.92 (s, 1H),
6.6 (ddd, J=8.28Hz, J=2.48Hz, J=0.86Hz, 1H),
6.87 (dd, J=8.03Hz, J=0.91Hz, 1H), 7.11 (s, 1H),
7.18 (t, J=8.15Hz, 1H). [13C]NMR d 52.2 (OCH3),
55.1 (CH3), 104.5 (CH), 109.1 (CH), 110.9 (CH),
2.4.6 3-(3-chlorophenyl)-5-methyloxazolidine-2,4-dione
(9, Fig 1)
129.6 (CH), 139.1, 154.0 (C
=
O).
Triethylamine (2.02g; 20mmol) in toluene (10ml)
was added to a mixture of 3-chlorophenylisocyanate
(3.07g, 20mmol) and methyl lactate (1.79g,
20mmol) in toluene (20ml). The reaction mixture
was heated at re¯ux for 12h. Work-up of the reaction
mixture as in the case of compound 8 yielded an oil,
which upon cooling gave a solid, recrystallized from
hexane‡ethylacetate (1‡1 by volume) yielded a white
powder (0.81g; 36%), mp 166±169°C. [1H]NMR d
1.69 (d, J=7.01Hz, 3H), 5.01 (q, J=7.02Hz, 1H),
7.39 (m, 3H), 7,5 (dt, J=1.84Hz, J=0.76Hz, 1H),
[13C]NMR d 16.7 (CH3), 75,9 (CH), 123.5, 125.6,
129.1, 130.2, 131.9 (aromatic carbons), 134.9 (CN),
153.3 (N-COO), 171.9 (N-CO-R).
2.4.2 Methyl 3,5-dimethoxyphenylcarbamate (11, Fig 1)
To a stirred mixture of 3,5-dimethoxyaniline (0.766g;
5mmol) in dry toluene (20ml) was added methyl
chloroformate (0.237g; 2.5mmol) dissolved in
toluene (10ml). The reaction mixture was heated at
re¯ux for 2h. The usual work-up followed by
recrystallization (hexane‡ethyl acetate, 10‡1 by
volumn) afforded 11 as a colourless crystalline
substance, 0.43g (81%), mp 31±34°C, bp 245±
247°C.
2.4.3 Methyl 3-chlorophenylcarbamate (4, Fig 1)
To a stirred mixture of 3-chloroaniline (0.64g,
5mmol) in dry toluene (20ml) was slowly added
methyl chloroformate (0.237g; 2.5mmol) in toluene
(10ml) and the mixture was re¯uxed for 2h. Work-up
of the reaction mixture as in the case of compound 11
yielded yellowish plates (0.44g, 95%), mp 136±
138°C. [1H]NMR d 3.77 (s, 3H), 6.69 (s, 1H),
7.01 (m, 1H), 7.20 (m, 2H), 7.48 (s, 1H). [13C]NMR
d 52,5 (OCH3), 116.6, 118.8, 123.5, 130.0 (aromatic
2.5 Isolation and identification of photoproducts
To produce enough of the photoproducts for structur-
al elucidation, 1 (10mg) in methanol‡water (50‡50
by volume; 1litre) was irradiated in ®ve batches (2mg
in 200ml for 10min through a quartz ®lter. The
irradiated solutions were combined and the solvent
removed at reduced pressure and ®nally freeze-dried.
The residue, dissolved in methanol (2ml) showed
upon GC analysis a number of substances in addition
to a very small amount of vinclozolin. Separation of the
unchanged vinclozolin and its photoproducts was
attempted by semipreparative HPLC (100ml per
injection). Gradient elution (Table 1) was performed
with water (eluant A) and methanol (eluant B). Nine
carbons), 153.8 (C
=O).
2.4.4 Methyl 3,5-dichlorophenylcarbamate (8, Fig 1)
Methyl chloroformate (0.74g, 5mmol) in dry toluene
(10ml) was added to a solution of 3,5-dichloroaniline
in dry toluene (20ml), and the mixture was heated at
1118
Pestic Sci 55:1116±1122 (1999)

Photochemistry of vinclozolin in water/methanol
‡
main fractions (1±9 in order of increasing retention
times) were collected. Corresponding eluates from
several injections were combined, and the solvent was
removed on a rotary evaporator.
atom. On the basis of fragments m/z 207 (M -CO2),
‡
and 153 (M -CO2-C(CH3)-CH
=CH2), which is
similar to that of vinclozolin except that the major
ions contained one chlorine atom, the structure 3-(3-
chlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-
dione (10, Fig 1) was assigned to this molecule.
2.5.1 Identi®cation of fractions
2.5.1.1 Fraction 1. (Colourless liquid, Rt 13.49min)
upon GC and GC-MS analysis was found to be a
mixture of two compounds. One (GC Rt 19.24min),
molecular ion m/z 191 and fragment ions at m/z 119
2.5.1.6 Fraction 6. (Rt 23.39min); molecular ion 281,
‡
‡
fragments at m/z 237 (M -CO2), 208 (M -CO2-CH3-
‡
CH
=
CH2) and 174 (M -CO2-Cl-C2H3‡1). The
‡
‡
(M -CO2-C2H4), 91 (M -CO2-C2H4-CO2), and 64
(M -CO2-C2H4-CO2-HNC) was identi®ed as 5-
mass spectrum was similar to that of vinclozolin except
that the major ions contained one chlorine atom. The
structure of this compound was assigned as 3-(3-
chloro-5-methoxyphenyl)-5-methyl-5-vinyl-1,3-oxa-
zolidine-2,4-dione (13, Fig 1).
‡
methyl-3-phenyl-1,3-oxazolidine-2,4-dione (5, Fig 1)
by chromatography (GC and HPLC) and MS com-
parison with an authentic sample of this compound
synthesized as described above. The other compound
(GC Rt 29.24min), molecular ion m/z 247 and
2.5.1.7 Fraction 7. (Rt 24.04min); molecular ion m/z
‡
‡
fragments at m/z 160 (M -CO2-CO-CH3) and 149
‡
225, fragments at m/z 153 (M -CO2-CHCH3) and
‡
(M -CO2-C(CH3)-CH=CH2) has been assigned the
tentative structure 3-(3-methoxyphenyl)-5-methyl-5-
vinyl-1,3-oxazolidine-2,4-dione (14, Fig 1).
125 (M -CO2-CHCH3-CO). This was identi®ed as
3-(3-chlorophenyl)-5-methyl-1,3-oxazolidine-2,4-
dione (9, Fig 1) by direct chromatographic (GC and
HPLC) and mass spectrum comparison with an
authentic sample of this compound synthesized as
described above.
2.5.1.2 Fraction 2. (liquid, Rt 14.55min) was also a
mixture of two compounds (GC Rt 20.08 and
25.58min). The compound GC Rt 20.08, molecular
‡
ion m/z 181, fragment ions at m/z 149 (M -COCH3),
2.5.1.8 Fraction 8. (Rt 25.46min); molecular ion m/z
‡
‡
‡
‡
122 (M -HOCH3-CO‡1) and 93 (M -HOCH3-
HNC-1) was identi®ed as methyl 3-methoxyphenyl-
carbamate (7, Fig 1) by GC and MS comparison with
an authentic sample of this compound. GC retention
time (25.58min) molecular ion m/z 211 and fragment
161, fragments at m/z 126 (M -Cl), 99 (M -Cl-
‡
CNH) and 63 (M -Cl-HNC-1). This compound was
identi®ed as 3,5-dichloroaniline (3, Fig 1) by direct
chromatographic (GC Rt 15.4min) and MS compari-
son with the authentic standard.
‡
‡
ions at m/z 179 (M -HOCH3), 150 (M -HOCH3-
‡
CO-1) and 136 (M -HOCH3-CO-CH3) of the
second component were in good agreement with those
of methyl 3,5-dimethoxyphenylcarbamate (11, Fig 1).
2.5.1.9 Fraction 9. (Rt 26.36min). This fraction upon
GC and GC-MS analysis was found to be a mixture of
three components.
The ®rst component (GC Rt 11.8min), showed a
molecular ion m/z 187 and the presence of two
chlorine atoms. On the basis of the fragments m/z
2.5.1.3 Fraction 3. (Rt 16.92min). The amount of this
fraction was so small that, except for mass analysis, no
spectral data could be obtained. The mass spectrum,
‡
‡
‡
159 (M -CO), 124 (M -CO-Cl), 97 (M -CO-Cl-
‡
‡
molecular ion m/z 217, fragments at m/z 173 (M -
‡
CNH) and 61 (M -CO-Cl-CNH-Cl) the compound
was identi®ed as 3,5-dichlorophenyl isocyanate (2, Fig
1).
‡
CO2), 144 (M -CO2-CH3-CH2), 119 (M -CO2-
‡
C(CH3)-CH
CH
in the molecule. The fragments suggest the compound
is 5-methyl-5-vinyl-3-phenyl-1,3-oxazolidine-2,4-
=
CH2) and 91 (M -CO2-C(CH3)-
=
CH2-CO) showed absence of chlorine atoms
The second GC component (Rt 23.58min); mol-
‡
ecular ion m/z 219, fragments at m/z 187 (M -
‡
‡
HOCH3), 159 (M -HOCH3-CO), 124 (M -
‡
dione (6, Fig 1). Furthermore, the fragmentation
pattern of this compound was similar to vinclozolin
except for that the main fragments were without
chlorine atoms.
HOCH3-CO-Cl) and 97 (M -HOCH3-CO-Cl-
HNC) was identi®ed as methyl 3,5-dichlorophenyl-
carbamate by direct chromatographic GC and MS
comparison with the synthesized compound (8, Fig 1).
The third GC component (Rt 28.7min); molecular
‡
2.5.1.4 Fraction 4. (yellowish solid, Rt 19,5min);
molecular ion m/z 185, fragment ions at m/z 153
ion m/z 259, fragments at m/z 187 (M -CO2-CH-
‡
CH3), and 159 (M -CO2-CH-CH3-CO), was as-
signed the tentative structure 3-(3,5-dichlorophenyl)-
5-methyl-1,3-oxazolidine-2,4-dione (12, Fig 1).
‡
‡
‡
(M -HOCH3), 125 (M -HOCH3-CO) and 98 (M -
HOCH3-CO-HNC). The mass spectra, NMR and
GC (Rt 19.24min) data were in good agreement with
those of the standard methyl 3-chlorophenylcarba-
mate (4, Fig 1).
3
RESULTS AND DISCUSSION
1
UV irradiation at l=254nm of a 1.0mg litre
2.5.1.5 Fraction 5. (Rt 21.36min); the molecular ion
m/z 251 had an isotope ratio indicative of one chlorine
methanol-water (50‡50 by volume) solution of
vinclozolin (1, Fig 2) resulted in rapid decomposition
Pestic Sci 55:1116±1122 (1999)
1119

B Schick et al
Figure 3. Photodegradation of vinclozolin (*) in the presence of humic
acid (l=290nm) and (Â) in Suntest equipment. (~) Control.
strate transformation of 60% in 8h (Fig 3). In control
experiments (not irradiated) with and without humic
acid, it was of the same magnitude (10%) as was
observed in methanol-water solution.
Figure 2. Photodegration of vinclozolin in (*) methanol‡water (1‡1 by
volume) and (Â) water at 254nm. (~) Control.
Humic acid is an important ingredient of soil and
many surface waters contain organic matter, such as
humic materials. These materials may sensitize the
photodegradation of pesticides by several indirect
processes7 and soil has been reported to produce
active oxygen species.8±10 Compounds 2 and 12 (Fig
1) were the main photoproducts identi®ed after 1 was
irradiated (l=290nm and in Suntest) in the presence
of humic acid.
(90 (Æ3)%, average of three runs) in 10min. Similar
experiments in deionized water also resulted in more
than 90% substrate decomposition, whereas the
compound degraded slowly (10% in 8h) when
irradiated at lꢁ290nm as shown in Fig 3. The high
decomposition rate at l=254nm is due to direct
photolysis near the absorption maximum (240nm). In
control experiments there was no degradation in
10min, whereas the compound under similar condi-
tions decomposed approximately 10% in 8h. The
results of the irradiated (lꢁ290nm) and non-irra-
diated aqueous solutions of 1 being of the same
magnitude (c 10%), it is presumed that the compound
is more susceptible to hydrolysis than to irradiation
with light close to the solar spectrum. The photolysis
rates in water and methanol‡water (50‡50 by
The oxazolidine ring of vinclozolin opens in ethanol,
methanol and water suspension and leads to the
formation of N-(2-hydroxy-2-methyl-1-oxo-buten-3-
yl)-3,5-dichlorophenylcarbamic
acid
and
its
decarboxylation product.2 In our experiments in the
presence of humic acid none of the above-mentioned
products was identi®ed, instead 2 and 3 (Fig 1) were
isolated and characterized. This study demonstrates
the photosensitized formation of 2, 3 and 12 from
vinclozolin in aqueous solution of humic acid.
volume) when
1
is irradiated with UV light
A photolysed (l=254nm) methanol-water solution
of 1 revealed on HPLC analysis a number of products
and, upon semi-preparative HPLC separation on a
RP-18 reversed-phase column, nine main fractions
were collected. Fraction 1 upon GC-MS analysis was
found to be a mixture of 4 and 13 (Fig 1), fraction 2
was a mixture of 6 and 10 and fraction 9 was found to
contain compounds 2, 7 and 11 (Fig 1). It is observed
that the clean separation of these compounds on semi-
preparative RP-18 column was not achieved. Probably
the compounds have very close polarities. Compounds
4 and 10 are the major photoproducts, followed by 2,
7, 8, 11 and 12.
l=254nm ®t a ®rst-order reaction model
lnꢂct=co† ˆ kt
with a half-life t1=2 ˆ lnꢂ2†=k
where co and ct are the concentrations of 1 at times 0
and t respectively, and k is the photolysis rate constant.
The slope of a linear plot ln ct/co versus time gives the
photolysis
rate
constant
of
1
in
water
(k =1.14Â10 3s 1) which is greater than in metha-
nol-water (k =5.77Â10 3s 1) and the calculated half-
lifes were 1.01 and 2.0min respectively. Irradiation of
1 (l=290nm) in the presence of humic acid (K-salt)
led to faster degradation (50%, observed-control, 8h,
Fig 3) than in its absence (10%, Fig 3). A similar
experiment in the Suntest equipment showed sub-
Vinclozolin contains a 3,5-dichlorophenyl and a
2,4-oxazolidine-dione moiety. It was expected that the
oxazolidine-dione ring would open and produce 3,5-
dichloroaniline (3) and 3,5-dichloropheny isocyanate
1120
Pestic Sci 55:1116±1122 (1999)

Photochemistry of vinclozolin in water/methanol
Figure 4. Proposed reaction mechanism
for the formation of 12.
(2). In fact, both 2 and 3 were identi®ed and con®rmed
on photolysis (l=254nm) of 1. Long-time (14 days)
photolysis of 1 by previous workers6 also showed the
formation of these two compounds.
lysis.14,15 The photolysis of simple alkenes, upon
direct excitation or by sensitized processes, is quite
complex.16 The participation of the (p, p*) state
results in cis-trans isomerization, [1,3] hydrogen shift
The photodecomposition of vinclozolin involves
opening of the oxazolidine-dione ring, dechlorination
and the elimination of ÐCH=CH2 moieties. The
or hydration. It is presumed that ÐCH=CH2 is
hydrated and subsequently photo-oxidized to 18
before intramolecular cyclization to 12 takes place.
Photoproducts 9 and 5 are derivatives of 12. Previous
investigation6 has shown formation of only one
compound (10, Fig 1) when a methanolic solution of
1 was photolysed with UV light (l=254nm). Further-
more, analysis of an aqueous solution of 1 after
irradiation at 254nm revealed the formation of 2, 5,
7 and 9; 2 was identi®ed as one of the products by
previous workers.6
formation of compound 13 is probably the result of C-
Cl bond cleavage and abstraction of a hydrogen radical
from the medium. The replacement of chlorine by a
methoxy group in a number of photoproducts (Fig 1)
could be explained either by a radical process or by
photonucleophilic displacement, analogous to the
displacement of an NO2 group by OH.11 Further-
more, analysis of methanol-water solution of 1 after
irradiation (l=254nm) yielded 4, 5, 6, 7, 9, 11, 12
and 14. Urethane (8) could be formed from isocyanate
(2) and methanol present in the medium. We are of the
opinion that this compound is derived from the
intermediate 12 by decarboxylation and elimination
of the hydrogen radical from the medium and not from
the intermediate 2. Urethane synthesis12 involves
reagents free of water and reaction temperature over
80°C. The other carbamates (4, 7) are probably
derived from 8 by a free radical mechanism13 and 11
by nucleophilic substitution.
Considering the photodecomposition of vinclozolin
in arti®cial sunlight and in the presence of humic acid
when irradiated with UV light (lꢁ290nm) to yield
polar compounds in the presence of dissolved humic
material, it appears reasonable to expect these
compounds to be found in soil, plants or water
exposed to the fungicide.
ACKNOWLEDGEMENTS
Our thanks are due to Mrs Eva Schindlbeck for
recording [1H] and [13C]NMR and mass spectra.
A plausible pathway for the formation of compound
12 is drawn in Fig 4. Szeto et al4 have identi®ed
intermediate 16 as one of the hydrolysis products of
vinclozolin. Decarboxylation of 16 leading to 17 can be
explained by the free radical and intermolecular
processes that occur in organic acids upon photo-
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