Synthesis and Herbicidal Activity of 2-Cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates

Article abstract of DOI:10.1021/jf035312a

A series of 2-cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates were synthesized as herbicidal inhibitors of PSII electron transport. All of these compounds exhibited good herbicidal activities. In particular, (Z)-ethoxyethyl 2-cyano-3-isopropyl-3-(2-chlorothiazol-5-yl)methylaminoacrylate showed excellent herbicidal activities even at a dose of 75 g/ha. A suitable group at the 3-position of acrylate was essential for high herbicidal activity. 2-Cyanoacrylates containing a 2-chloro-5-thiazolyl group are a novel class of herbicides and display herbicidal activities comparable to existing analogues bearing chloropyridyl or chlorophenyl.

Full text of DOI:10.1021/jf035312a

1918 J. Agric. Food Chem. 2004, 52, 1918−1922
Synthesis and Herbicidal Activity of
2-Cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates
QINGMIN WANG, HENG LI, YONGHONG LI, AND RUNQIU HUANG*
State Key Laboratory of Elemento-Organic Chemistry, Research Institute of
Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
A series of 2-cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates were synthesized as herbicidal
inhibitors of PSII electron transport. All of these compounds exhibited good herbicidal activities. In
particular, (Z)-ethoxyethyl 2-cyano-3-isopropyl-3-(2-chlorothiazol-5-yl)methylaminoacrylate showed
excellent herbicidal activities even at a dose of 75 g/ha. A suitable group at the 3-position of acrylate
was essential for high herbicidal activity. 2-Cyanoacrylates containing a 2-chloro-5-thiazolyl group
are a novel class of herbicides and display herbicidal activities comparable to existing analogues
bearing chloropyridyl or chlorophenyl.
KEYWORDS: 2-Cyanoacrylates; 2-cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates; herbicidal activity;
inhibitors of PSII electron transport
INTRODUCTION
The herbicidal activity of cyanoacrylates has been the subject
of intense interest for decades (1-3). A detailed study of
compounds with general structure 1 revealed that cyanoacrylates
are inhibitors of photosystem II (PSII) electron transport and
inhibit the growth of weeds by disrupting photosynthetic electron
transport at a common binding domain on the 32 kD polypeptide
of the PSII reaction center. Among these cyanoacrylates,
compund 2 exhibits the highest inhibitory activity of the Hill
reaction yet reported (4-6). Bayer AG reported compound 3,
but little information was given on its herbicidal activity (7). It
has been reported that the D1 protein of PSII is the herbicide
binding site, where the benzyl group of cyanoacrylate fits into
the hydrophobic domain of the site maximizing van der Waals
ring stacking interactions with aromatic amino acids (Phe 211,
Phe 255, Tyr 262) flanking this part of the binding domain (8-
10). However, the complete nature and topography of this
hydrophobic domain of the D1 protein are unknown, and
cyanoacrylates have not commercialized as herbicides because
of their high dose rates.
Bioisosterism is an important concept of bioactive compound
design. Substitution of a 2-chloro-5-pyridyl group by a 2-chloro-
5-thiazolyl group represents a successful example of bioiso-
sterism, as follows: Neonicotinoids are a new class of insec-
ticides (13). The first successful member of this family is
imidacloprid, developed by Nihon Bayer Agrochem KK in 1991
(14). As second and third neonicotinoids of the subclass
chloronicotinyl compounds, nitenpyram from Takada Chemical
Industries (15) and acetamiprid from Nippon Soda (16) have
been brought to the market in 1995 and 1996, respectively.
These three compounds possess 2-chloro-5-pyridyl groupa.
However, thiamethoxam, possessing a 2-chloro-5-thiazolyl
group, has exceptional insecticidal activity comparable to
chloronicotinyl compounds and was introduced into the market
by Novartis Crop Protection in 1997 (17-18). Takada have also
developed acyclic nitroguanidine analogues with a thiazol-5-
ylmethyl group (19). As a result, 2-chloro-5-thiazole is a
bioisosteric analogue of 2-chloro-5-pyridine. Encouraged by
these reports, we developed an idea that the replacement of
2-chloro-5-pyridyl with 2-chloro-5-thiazolyl in 2-cyanoacrylates
could improve the herbicidal activities. Herein we are reporting
the synthesis of a series of 2-cyano-3-(2-chlorothiazol-5-yl)-
methylaminoacrylates and evaluation for herbicidal activity.
In our previous work, the cyanoacrylate structure 4 modified
by the replacement of phenyl with pyridine heterocycles showed
higher herbicidal activities than parent compounds 2 and 3 (11).
Through the comparisons of structure and herbicidal activity,
we concluded that a suitable substituent (chlorine or alkoxy) at
the 2-position of pyridine ring and a well-fit group (methylthio
or alkyl) at the 3-position of acrylate were essential for high
herbicidal activity (12).
* To whom correspondence should be addressed. Tel.: +86-(0)22-
23502673. Fax: +86-(0)22-23503438. E-mail: wang98h@263.net.
10.1021/jf035312a CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/04/2004

2-Cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates
J. Agric. Food Chem., Vol. 52, No. 7, 2004 1919
MATERIALS AND METHODS
amount in the water separator. The mixture was filtered, and the
filtration was washed with 10% sodium dicarbonate and brine, dried
over anhydrous sodium sulfate, and distilled under reduced pressure
to afford the corresponding esters.
General Synthetic Procedures for 12a-d. To a mixture of
2-cyanoacetate 7 (0.025 mol), triethylamine (5.05 g, 0.05 mol),
magnesium chloride (2.37 g, 0.025 mol), and anhydrous acetonitrile
(25 mL) was added acid chloride (0.025 mol) under an ice-salt bath.
The reaction was continued for 5 h, and the solvent was evaporated.
To the residue was added 5 N aqueous hydrochloric acid solution (20
mL) and ether (50 mL). The organic layer was separated, dried over
anhydrous magnesium sulfate, filtered, and distilled under reduced
pressure to give a colorless liquid (used without further purification).
The gas of diazomethane (0.013 mol) synthesized from 1.32 g of
R-nitroso-R-methylurea according to the reported method (20) was
dissolved in a solution of the above liquid (1.07 g, 0.005 mol) in
anhydrous ether (10 mL). The reaction mixture was stirred for 12 h.
Evaporation of the solvent afforded a yellow oil (used without further
purification).
General Synthetic Procedure for 2-Cyano-3,3-dimethylthioacry-
late (13). Compound 11b (20 mmol) was added dropwise to a mixture
of potassium hydroxide powder (2.24 g, 40 mmol) and anhydrous
acetonitrile (30 mL) at 5 °C. The mixture was stirred for 0.5 h, then a
solution of carbon disulfide (1.50 g, 20 mmol) in anhydrous acetonitrile
(5 mL) was added over about 10 min. The reaction mixture was stirred
for 3 h at room temperature. After the solution was cooled to 4 °C,
dimethyl sulfate (5.04 g, 40 mmol) was added. The reaction mixture
was stirred at room temperature for 4 h. The solvent was evaporated
under reduced pressure, then water (25 mL) and ethyl acetate (50 mL)
were added to the residue. The organic layer was separated and dried
with anhydrous magnesium sulfate. Ethyl acetate was evaporated to
afford corresponding 13.
Synthetic Procedures. Proton NMR spectra were obtained at 200
MHz using a Bruker AC-P 200 spectrometer. Chemical shift values
(δ) are given in ppm and were downfield from internal TMS. Infrared
spectra were recorded on a Shimadzu-435 spectrometer. Elemental
analyses were determined on an MT-3 elemental analyzer. Mass spectra
were recorded with HP 5988A spectrometer using the EI method.
Synthesis of 1,2,3-Trichloropropane (6). A mixture of 3-chloro-
1-propene (7.65 g, 0.1 mol) and a cat. mount of benzoyl peroxide in
carbon tetrachloride (10 g) was heated to 85 °C. To the mixture, sulfuryl
chloride (13.5 g, 0.1 mol) was added dropwise. Then, the mixture was
stirred at 90 °C for 4 h. Carbon tetrachloride was distilled off, and the
residue was distilled to give a colorless liquid (14.8 g) in 50.2% yield
(bp 154-156 °C/760 mm Hg).
Synthesis of 2,3-Dichloro-1-propene (7). Aqueous sodium hydrox-
ide (4.4 g, 0.11 mol, dissolved in 30 mL ethanol and 10 mL water)
was added dropwise to 1,2,3-trichloropropane (14.8 g, 0.1 mol) at 100
°C. Then, the resulting mixture was refluxed for 4 h and distilled to
collect the distillation cut of 72-76 °C. Water (30 mL) was added to
the distillate, and the organic phase was washed with water (15 mL)
and dried over anhydrous magnesium sulfate. After the solvent was
distilled off, the residue was distilled, yielding 2,3-dichloro-1-propene
(7.2 g) in 64.7% yield (bp 92-98 °C/760 mm Hg).
Synthesis of 2-Chloro-2-propenyl Isothiocyanate (8). Under a
nitrogen atmosphere, a mixture of 2,3-dichloro-1-propene (11.1 g, 0.1
mol), potassium thiocyanate (9.7 g, 0.1 mol), and water (70 mL) was
heated gradually to 104 °C and stirred for 10 h. Then, the resulting
mixture was cooled to room temperature. The water phase was extracted
three times with chloroform (10 mL). The extraction solvent was
combined with the organic phase, washed two times with water (20
mL), and dried over anhydrous magnesium sulfate. Chloroform was
distilled off, and the residue was heated to 120 °C and stirred for 2 h.
Then, the residue was distilled under reduced pressure, yielding
2-chloro-2-propenyl isothiocyanate (7.5 g) in 56.2% yield (bp 64-67
General Synthetic Procedures for Target Compounds 14a-e. The
mixture of intermediate 12 or 13 (5 mmol), 2-chloro-5-aminomethyl-
thiazoles 10 (6 mmol) and ethanol (12 mL) was refluxed for 3 h then
evaporated under reduced pressure to give crude product. The product
was purified by vacuum column chromatography on a silica gel.
1
°C/10 mm Hg). H NMR (CDCl3) δ: 4.21 (s, 2H, CH2NCS), 5.40,
5.51 (d, 2H, dCH2).
Synthesis of 2-Chloro-5-chloromethylthiazole (9). To a solution
of 2-chloro-2-propenyl isothiocyanate (13.4 g, 0.1 mol) in chloroform
(50 mL) was added dropwise sulfuryl chloride (16.2 g, 0.12 mol), while
maintaining the temperature at 30 °C. Following the addition, the
reaction mixture was stirred for 3 h at 36 °C. The solvent and the excess
of sulfuryl chloride were removed by distillation. The residue was
cooled to room temperature to give a yellow solid (15.9 g) in 94.6%
1
Data for 14a. Yield, 80.3%; mp, 67-69 °C. H NMR (CDCl3) δ:
1.18 (t, 3JHH ) 7 Hz, 3H, CH3), 2.71 (s, 3H, SCH3), 3.54 (q, 3JHH ) 7
3
3
Hz, 2H, OCH2), 3.66 (t, JHH ) 5 Hz, 2H, CH2O), 4.27 (t, JHH ) 5
3
Hz, 2H, CO2CH2), 4.87 (d, JHH ) 6 Hz, 2H, CH2N), 7.44 (s, 1H,
thiazole), 10.35 (s, 1H, NH). Anal. Calcd. for C13H16ClN3O3S2: C,
43.15; H, 4.46; N, 11.61. IR (KBr, cm-1) 3158, 2204, 1654, 1566,
1417, 1396, 1261, 1231. Found: C, 42.90; H, 4.39; N, 11.66. EIMS
m/z (%): 361(M+), 131.9(100).
1
yield. H NMR (CDCl3) δ: 4.69 (s, 2H, CH2), 7.47 (s, 1H, thiazole).
Synthesis of 2-Chloro-5-aminomethylthiazoles (10). To a mixture
of hexamethylenetetramine (16.7 g, 0.11 mol) and chloroform (100
mL) was added dropwise 2-chloro-5-chloromethylthiazole (16.8 g, 0.1
mol) at refluxed temperature, then the resulting mixture was refluxed
for 3 h. The solid was collected by filtration, and the filtrate was
concentrated to obtain the solid again. The solid was combined and
washed with chloroform. Finally, the yellow solid (30.1 g) was obtained
in 96.7% yield. To the above solid, 100 g of 36% hydrochloric acid
and 100 mL of ethanol were added. The mixture was stirred under
reflux for 1 h then allowed to stand for 12 h. The solid was filtered
off, and the filtrate was concentrated to about half of the original
volume. The solid formed was filtered off again, and the filtrate was
concentrated to dryness. To the residue was added 50 mL of acetone,
and insoluble material was filtered off. To the filtrate was added 50
mL of water and 6 N aqueous sodium hydroxide to pH ) 13. The
mixture was extracted three times with dichloromethane, and the
dichloromethane layer was washed with saturated aqueous sodium
chloride and dried over anhydrous potassium carbonate. The solvent
was removed by distillation to give a yellow solid (14.0 g) in 94.3%
yield.
1
Data for 14b. Yield, 78.9%; mp, 88-89 °C. H NMR (CDCl3) δ:
1.19 (t, 3JHH ) 7 Hz, 3H, CH3), 2.33 (s, 3H, dCCH3), 3.53 (q, 3JHH
)
7 Hz, 2H, OCH2), 3.68 (t, 3JHH ) 5 Hz, 2H, CH2O), 4.27 (t, 3JHH ) 5
3
Hz, 2H, CO2CH2), 4.64 (d, JHH ) 6 Hz, 2H, CH2N), 7.43 (s, 1H,
thiazole), 10.15 (s, 1H, NH). Anal. Calcd. for C13H16ClN3O3S: C, 47.34;
H, 4.89; N, 12.74. Found: C, 47.06; H,5.01; N, 12.84.
1
Data for 14c. Yield, 82.4%; mp, 79-81 °C. H NMR (CDCl3) δ:
3
1.08-1.24 (m, 6H, CH3, CH3), 2.59 (q, JHH ) 6 Hz, 2H, CH2), 3.47
3
(q, J ) 7 Hz, 2H, OCH2), 3.59 (t, JHH ) 5 Hz, 2H, CH2O), 4.20 (t,
3JHH ) 5 Hz, 2H, CO2CH2), 4.63 (d, 3JHH ) 6 Hz, 2H, CH2N), 7.39 (s,
1H, thiazole), 10.05 (s, 1H, NH). Anal. Calcd. for C14H18ClN3O3S: C,
48.95; H, 5.28; N, 12.22. Found: C, 48.70; H, 5.29; N, 12.40.
1
Data for 14d. Yield, 79.6%; mp, 66-67 °C. H NMR (CDCl3) δ:
3
3
1.11 (t, JHH ) 7 Hz, 3H, CH3), 1.35 (d, JHH ) 6 Hz, 6H, C(CH3)2),
3
3
3.20 (m, 1H, CH), 3.47 (q, JHH ) 7 Hz, 2H, OCH2), 3.61 (t, JHH
)
)
5 Hz, 2H, CH2O), 4.19 (t, 3JHH ) 5 Hz, 2H, CO2CH2), 4.62 (d, 3JHH
6 Hz, 2H, CH2N), 7.17 (s, 1H, thiazole), 10.35 (s, 1H, NH). Anal.
Calcd. for C15H20ClN3O3S: C, 50.35; H, 5.63; N, 11.74. Found: C,
50.34; H, 5.40; N, 11.75.
1
General Synthetic Procedures for Esters 11a and b. A mixture
of cyanoacetic acid (25.5 g, 23.8 mmol), alkanol (31.5 mmol), sodium
bisulfate monohydrate (0.7 g, 5.1 mmol) and toluene (15 mL) was
placed in a flask equipped with a Dean Stark trap carrying a reflux
condenser at its upper end and then heated under reflux. The reaction
was not stopped until no more water was collected in appreciable
Data for 14e. Yield, 82.3%; mp, 58-60 °C. H NMR (CDCl3) δ:
3
2.33 (s, 3H, dCCH3), 3.38 (s, 3H, OCH3), 3.61 (t, JHH ) 5 Hz, 2H,
CH2O), 4.28 (t, 3JHH ) 5 Hz, 2H, CO2CH2), 4.63 (d, 3JHH ) 6 Hz, 2H,
CH2N), 7.43 (s, 1H, thiazole),10.15 (s, 1H, NH). Anal. Calcd. for
C12H14ClN3O3S: C, 41.43; H, 4.06; N, 12.08. Found: C, 41.51; H,
4.07; N, 11.99.

1920 J. Agric. Food Chem., Vol. 52, No. 7, 2004
Wang et al.
Scheme 1
Scheme 3
Scheme 4
Scheme 2
Scheme 5
Biological Assay. The herbicidal activities of the compounds 14a-e
and the reported compound 2 were evaluated using a previously reported
procedure (7, 12, 21).
Plant Material. The three broadleaf species used to test the herbicidal
activity of compounds were alfalfa (Medicago satiVa L.), rape (Brassica
napus), and amaranth pigweed (Amaranthus retroflexus). Seeds of
Amaranthus retroflexus were reproduced outdoors and stored at room
temperature. Seeds of alfalfa and rape were bought from the Institute
of Crop, Tianjin Agriculture Science Academy.
Culture Method. Seeds were planted in 6-cm-diameter plastic boxes
containing artificial mixed soil. Before plant emergence, the boxes were
covered with plastic film to keep moist. Plants were grown in the green
house. Fresh weight of the above ground tissues was measured 10 days
after treatment. The inhibition percent is used to describe the control
efficiency of the compounds.
Treatment. Dosage (activity ingredient) for each compound is 1.5
kg/ha. Purified compounds were dissolved in 100 ul N,N-dimethyl-
formamide with the addition of a little Tween 20 and then were sprayed
using a laboratory belt sprayer delivering at 750 L/ha-spray-volume.
The mixture of same amount of water, N,N-dimethylformamide, and
Tween 20 were sprayed as control. Triplicate each treatment. Activity
numbers represent percent diplaying herbicidal damage as compared
to control. Error of the experiments are 2%.
two moles of dimethyl sulfate in a one-pot reaction using
potassium hydroxide as alkali (Scheme 3).
Intermediates 12 or 13 were reacted with 2-chloro-5-amino-
methylthiazole (10) in refluxing absolute ethanol to give the
target compounds 14 in good yields (Scheme 4). This reaction
is assumed to go through a nucleophilic addition and elimination
reaction (Scheme 5). The amine attached the R,â-unsaturated
double bond to form a transition state in which the orientation
of thiazolemethylamino and ester carbonyl is cis because of the
presence of an intramolecular hydrogen bonding. We confirmed
configuration of existing analogue bearing chloropyridyl by
X-ray and demonstrated the presence of a planar core stablized
by an intramolecular hydrogen bond between the ester carbonyl
oxygen and the pyridinemethylamino hydrogen atom (11, 29).
All compounds were confirmed by 1H NMR, elemental, IR, and
mass spectrum analyses.
Preemergence Treatment. Compounds were sprayed immediately
after seeds planting.
Postemergence Treatment. Compounds were sprayed after the
expansion of the first true leaf.
Structure-Activity Relationship. In our previous work, the
cyanoacrylate structure modified by the replacement of phenyl
with substituted pyridyl showed higher herbicidal activities than
the parent compound (11).
To further amplify the interaction of these cyanoacrylates with
the lipophilic binding domain of the PSII reaction center, pyridyl
was replaced by thiazole heterocycles in 2-cyanoacrylates, and
all of the products 14 showed good herbicidal activities (Table
1). Most of the compounds 14 showed greater herbicidal
activities in post-emergence treatment than in preemergence
treatment as seen for substituted-pyridinemethylaminoacrylates.
Compound 14b showed excellent activities to alfalfa and
amaranth pigweed. By comparing herbicidal activities of 14 and
(Z)-ethoxyethyl 2-cyano-3-isopropyl-3- (4-chlorophenyl)methane-
aminoacrylate (2), we found that 2-cyanoacrylates containing
the 2-chloro-5-thiazolyl group provides higher herbicidal activi-
ties than compounds containing phenyl.
At the rate of 750 g/ha, compounds 14a, 14b, and 14d
exhibited good herbicidal activities (Table 2). Their activities
to amaranth pigweed decreased remarkably when the dose was
reduced. At the rate of 187.5 g/ha, compound 14d still exhibited
excellent herbicidal activity to rape.
(Z)-ethoxyethyl 2-cyano-3-methylthio-3-(2-chloro-5-pyridyl)-
methaneaminoacrylate (4a) was prepared for comparison of
herbicidal activity with 14d. This comparison (Table 3) clearly
showed consistently better activity, with compound 14d having
a higher level of herbicidal activity against rape than compound
RESULTS AND DISCUSSION
Synthesis. To date, five synthetic routes for 2-chloro-5-
chloromethylthiazole (9) have been published (22-26). We
prepared this important synthetic intermediate 9 from 3-chloro-
1-propene (5) as shown in Scheme 1. 3-Chloro-1-propene (5)
was treated with sulfuryl chloride in the presence of benzoyl
peroxide to obtain 1,2,3-trichloropropane (6). It was reacted with
sodium hydroxide to give 2,3-dichloro-1-propene (7) Subsequent
reaction with potassium thiocyanate yielded 2-chloro-2-propenyl
isothiocyanate (8). Further reaction with sulfuryl chloride
provided 2-chloro-5-chloromethylthiazole (9) in good yield.
Compound 9 was converted into 2-chloro-5-aminomethyl-
thiazoles (10) in excellent yield by its amination using hexa-
methylenetetramine.
Esters 11 were prepared conveniently from cyanoacetic acid
and primary alcohols in the presence of a catalytic amount of
sodium bisulfate monohydrate (27). Intermediate 2-cyano-3-
methoxyacrylates 12 (Z and E mixture) were synthesized by
treating ester 11 with acid chloride followed by methylation
with diazomethane in good yields (Scheme 2) (28).
Intermediate 2-cyano-3,3-dimethylthioacrylate 13 was achieved
by treating corresponding ester 11b with carbon disulfide and

2-Cyano-3-(2-chlorothiazol-5-yl)methylaminoacrylates
J. Agric. Food Chem., Vol. 52, No. 7, 2004 1921
Table 1. Herbicidal Activities of Products 14a−e and 2 (1.5 kg/ha)a
that a suitable group at the 3-position of acrylate was essential
for high herbicidal activity. 2-Cyanoacrylates containing 2-chloro-
5-thiazolyl groups are a novel class of herbicides and display
herbicidal activities comparable to existing analogues bearing
chloropyridyl or chlorophenyl group.
LITERATURE CITED
postemergence
treatment
preemergence
treatment
(1) Banham, W. K.; Huppatz, J. L.; Phillips, J. N. N-Methylanilino-
cyanoacrylate photosystem II inhibitors. Structure-activity
relationships. Z. Naturforsch. 1993, 48C, 136-139.
amaranth
amaranth
1
2
R
R
alfalfa pigweed rape alfalfa pigweed rape
(2) McFadden, H. G.; Phillips, J. N. Synthesis and use of radiolabeled
cyanoacrylate probes of photosystem II herbicide binding site.
Z. Naturforsch. 1990, 45C, 196-202.
14a CH CH CH S
49
94
70
19
26
28
78
100
83
96
81
100
95
100
100
100
96
28
47
46
16
0
76
87
70
54
45
52
40
93
91
96
78
0
3
2
3
14b CH CH CH
3
2
3
14c CH CH C H
2 5
3
2
14d CH CH CH(CH )
3
2
3 2
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Naturforsch. 1987, 42C, 684-689.
14e CH
CH
3
3
2
94
0
a Triplicate each treatment. Activity numbers represent percent diplaying
herbicidal damage as compared to control. 0 mean no activity. Error of these
numbers is 2%.
Table 2. Herbicidal Activities of Products 14a−da
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acrylates with the D1 peptide. Z. Naturforsch. 1993, 48C, 132-
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postemergence treatment
compd.
rate g/ha
rape
amaranth pigweed
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2-cyanoacrylic acid ester herbicides. U.S. Patent 4,832,733, 1989;
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14a
187.5
375
750
187.5
375
750
187.5
375
750
187.5
375
750
48
57
100
39
59
96
29
60
69
41
48
91
73
78
98
42
50
57
67
81
100
14b
14c
14d
100
100
100
a Triplicate each treatment. Activity numbers represent percent diplaying
herbicidal damage as compared to control. Error of these numbers is 2%.
Table 3. Herbicidal Activities of Products 14d and 4a against Rape
(Post-emergence treatment)a
rate (g/ha)
4a
14d
18.75
37.5
75.0
150.0
300.0
11
45
77
95
100
15
52
98
100
100
a Triplicate each treatment. Activity numbers represent percent diplaying
herbicidal damage as compared to control. Error of these numbers is 2%.
4a. At the rate of 75 g/ha, compound 14d still showed excellent
herbicidal activity, whereas herbicidal activity of compound 4a
began to reduce significantly.
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Received for review November 8, 2003. Revised manuscript received
February 5, 2004. Accepted February 9, 2004. This work was supported
by the National Natural Science Foundation of China (20272030).
JF035312A