Photodegradation of tribenuron-methyl in aqueous solution
(sym.). [1H]NMR: d 7.6–8.3 (m, 4H, aromatic), 5.8
(s, 2H, NH ), 3.9 (s, 3H, OCH ). GC-MS : m/z 215
(M`), 199 (M` [ 16), 184 (M` [ 31), 120
(M` [ 95), 105 (M` [ 110).
tentatively identiüed by GC-MS (Table 2, Fig 1)
and by comparison with authentic standards.
Photoproduct 2, N-methyl-4-methoxy-6-methyl-
1,3,5-triazin-2-amine (M` 154) was identiüed by
matching the mass spectrum with that of a known
standard.
The mass spectrum of photoproduct 3 showed a
molecular ion peak at m/z 215 (M`) with a base peak
at m/z 199, and fragment ion peaks at m/z 184, 120
and 104. It was identiüed as methyl 2-sulfamoyl
benzoate (3) by comparison with a reference stan-
dard.
The photoproduct 4 was tentatively identiüed as
4-methoxy-6-methyl-1,3,5-triazin-2-amine and its
mass spectrum showed a molecular ion peak at m/z
140 (M`) (Table 2).
The mass spectrum of the photoproduct 5 showed
a molecular ion peak at m/z 197 (M`) and a base
peak at m/z 181. It was tentatively identiüed as
N-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N-methyl
urea (Fig 1).
2
3
2.6.3 N-Methyl-4 -methoxy-6 -methyl-1,3,5 -triazin-
2-amine (2)
Tribenuron-methyl (500mg) was stirred with
aqueous hydrochloric acid (pH 3.0) at 40¡C for 48h.
The reaction product was extracted with chloroform.
The chloroform layer was separated, dried over
anhydrous sodium sulfate and distilled oþ. The solid
thus obtained was recrystallised from methanol;
mp 155¡C. The IR spectrum showed the presence
of NH at 3256 cm~1 and CxN at 1558 cm~1.
[1H]NMR: d 6.0 (bs, 1H, NH), 3.9 (s, 3H, OCH ),
3
3.1 (d, 3H, NCH ), 2.45 (s, 3H, CH ). GC-MS : m/z
3
3
154 (M`), 139 (M` [ 15), 124 (M` [ 30), 110
(M` [ 44).
2.6.4. 2-[4-Methoxy-6-methyl-1,3,5-triazin-2-
yl(methyl)carbamoylsulfamoyl]benzoic acid
Photoproduct 6 was tentatively identiüed as N-(4-
methoxy-6-methyl-1,3,5-triazin-2-yl) urea and its
mass spectrum showed a molecular ion peak at m/z
183 (M`).
In a conical ýask (250ml capacity) tribenuron-
methyl (200mg), distilled water (20ml) and sodium
hydroxide solution (0.2M; 50ml) were mixed and
stirred for 1 h at room temperature. After stirring,
the mixture was neutralised by adding hydrochloric
acid (0.2 M; 52ml) using litmus paper as indicator.
The aqueous layer was extracted with methylene
chloride, which was separated, dried over anhydrous
sodium sulfate and completely evaporated at low
temperature (25¡C). Oþ-white solid so obtained was
recrystallised from a mixture of hexane and acetone.
The IR spectrum showed the presence of CxO at
1729 cm~1, CxN at 1578 cm~1, NH at 3250 and
3368 cm~1, OxSxO at 1354 cm~1 (asym.) and
1170 cm~1 (sym.). [1H]NMR: d 7.5–8.2 (m, 4H,
A molecular ion peak at m/z 331 (M`) in the
mass spectrum of photoproduct 7 helped to identify
the compound as N-(2-carbomethoxyphenyl)-N-
(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N@-methyl
urea. The mass spectrum of photoproduct 8 showed
a molecular ion peak at m/z 317 (M`) with fragment
ion peaks at m/z 302, 274, 194, 150, 126 and 81
(Table 2). It was tentatively identiüed as N-(2-car-
bomethoxyphenyl)- N - (4-methoxy-6-methyl-1, 3, 5-
triazin-2-yl) urea. Photoproduct 9 was identiüed as
N-(2-carbomethoxy phenylsulfonyl)-N@-methyl urea
(Fig 1) and its mass spectrum showed a molecular
ion peak at m/z 271 (M`).
aromatic), 6.1 (bs, 1H, NH), 4.1 (s, 3H, OCH ), 3.2
3
(s, 3H, NCH ), 2.4 (s, 3H, CH ).
Photoproduct
10
was
identiüed
as
2-
3
3
sulfamoylbenzoic acid (M` 201). The identiücation
was conürmed by matching the mass spectrum of
photoproduct 10 with that of a known standard.13
Photoproduct 11 was identiüed as o-benzoic sul-
ümide (M` 183). The mass spectrum of 11 was
similar to the mass spectrum of the authentic sample
prepared.14 Photoproduct 12 was tentatively identi-
üed as N-methyl-o-benzoic sulümide by its mass
spectrum which showed a molecular ion peak at m/z
197 (M`) with a base peak at m/z 104 (Table 2).
2.7 Photolysis kinetics
Aqueous solutions of tribenuron-methyl in HPLC
grade water, irrigation water, tap water and tubewell
water (50mg litre~1) were irradiated in quartz tubes
under both UV light (24h) with a medium-pressure
Hg lamp and sunlight (35 days, 8h day~1 from May
to June, 1996). The sunlight intensity at 300–400 nm
wavelength was 570, 1420 and 200 mW cm~2 at the
beginning, middle and end of the day, respectively.
Non-irradiated samples of the aqueous solution of
tribenuron-methyl kept in the dark served as con-
trols. At various time intervals, samples were with-
drawn in triplicate and analysed by HPLC.
Photoproduct 13 was identiüed by its IR and
[1H]NMR spectra as 2-[4-methoxy-6-methyl-1,3,5-
triazin-2-yl(methyl) carbamoyl sulfamoyl]benzoic
acid (Fig 1). The IR spectrum of 13 showed the
presence of N-H, CxO and OxSxO groups at
3249, 1729, 1354 and 1170 cm~1, respectively.
[1H]NMR spectra further conürmed its structure by
showing a multiplet at d 8.2–7.5 due to aromatic
protons, three proton singlets at d 4.1, 3.2 and 2.4 for
OCH , NCH and CH groups, respectively, and a
3
RESULTS AND DISCUSSION
3.1 Identification of photoproducts
HPLC analysis of the brown residue obtained after
irradiation showed the formation of a number of deg-
radation products. The degradation products were
3
3
3
broad singlet at d 6.1 corresponding to NH proton.
Pestic Sci 55:183–188 (1999)
185