Synthesis and bioactivities of clopyralid hydrazide-hydrazones

Article abstract of DOI:10.1080/00397910903013762

A series of clopyralid hydrazide-hydrazone derivatives (4a-p) have been synthesized. Their structures were confirmed by elemental analysis, infrared, and 1H NMR spectra. The bioactivities of compounds 4a-p were tested with barnyard grass, rape, and S. aureus, but the results showed that they could not be considered the promising herbicidal or antibacterial agents.

Full text of DOI:10.1080/00397910903013762

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Synthesis and Bioactivities of Clopyralid
Hydrazide-Hydrazones
Jie Zhang a , Tianhua Shen a , Lijuan Xu a , Fenfang Shen a , Quan
Qin a , Chunan Ma a & Qingbao Song a
a State Key Laboratory Breeding Base of Green Chemistry–Synthesis
Technology, College of Chemical Engineering and Materials Science,
Zhejiang University of Technology, Hangzhou, China
Version of record first published: 22 Feb 2010.
To cite this article: Jie Zhang , Tianhua Shen , Lijuan Xu , Fenfang Shen , Quan Qin , Chunan Ma
& Qingbao Song (2010): Synthesis and Bioactivities of Clopyralid Hydrazide-Hydrazones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
40:6, 814-820
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Synthetic Communications1, 40: 814–820, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903013762
SYNTHESIS AND BIOACTIVITIES OF CLOPYRALID
HYDRAZIDE-HYDRAZONES
Jie Zhang, Tianhua Shen, Lijuan Xu, Fenfang Shen, Quan Qin,
Chunan Ma, and Qingbao Song
State Key Laboratory Breeding Base of Green Chemistry–Synthesis
Technology, College of Chemical Engineering and Materials Science,
Zhejiang University of Technology, Hangzhou, China
A series of clopyralid hydrazide-hydrazone derivatives (4a–p) have been synthesized. Their
structures were confirmed by elemental analysis, infrared, and 1H NMR spectra. The
bioactivities of compounds 4a–p were tested with barnyard grass, rape, and S. aureus,
but the results showed that they could not be considered the promising herbicidal or
antibacterial agents.
Keywords: Bioactivities; clopyralid; hydrazide-hydrazone; synthesis
INTRODUCTION
Clopyralid (3,6-dichloropicolinic acid) is herbicide that is effective on many
weeds.[1] However, it also damages sensitive plants, including popular agricultural
and garden crops such as tomatoes, peppers, potatoes, peas, beans, clovers, alfalfas,
and sunflowers, at very low concentration, sometimes even less than 10 parts per
billion (ppb) in the growing media of the plants (e.g., soil).[2,3] Thus, some improve-
ments are necessary.
Hydrazide-hydrazones are a kind of azomethine compound that can be
obtained by the condensation of aldehydes or ketones with hydrazines[4,5] in the pres-
ence of an acid catalyst. Hydrazide-hydrazones have been demonstrated to possess
antibacterial,[6–8] anticonvulsant,[9,10] and antitubercular[11,12] activities.
According to these observations, some novel clopyralid hydrazide-hydrazones
were synthesized, and their possible weeds and antimicrobial activities were detected.
RESULTS AND DISCUSSION
The synthetic route to compounds 2, 3, and 4a–p is shown in Scheme 1.
Clopyralid (3,6-dichloropicolinic acid, 1) was chosen as starting compound to
Received February 10, 2009.
Address correspondence to Qingbao Song, State Key Laboratory Breeding Base of Green
Chemistry–Synthesis Technology, College of Chemical Engineering and Materials Science, Zhejiang
University of Technology, Hangzhou 310032, China. E-mail: qbsong@zjut.edu.cn
814

CLOPYRALID HYDRAZIDE-HYDRAZONES
815
Scheme 1. Synthetic route of 4a–p. (a) EtOH, H2SO4, reflux; (b) EtOH, NH2NH2 ꢀ H2O; (c) EtOH, reflux.
synthesize several novel hydrazide-hydrazones. Ethyl 3,6-dichloropicolinate (2)
was prepared by the reaction of clopyralid (1) and ethanol in the presence of a
few drops of concentrated sulfuric acid under reflux. 3,6-Dichloropicolinohydra-
zide (3) was synthesized by compound 2 and 85% hydrazine hydrate in ethanol.
After condensation of 3 with carbonyl compounds in the presence of a few drops
of acetic acid, the clopyralid hydrazide-hydrazones derivatives (4) were obtained.
The physical characteristics and elemental analysis data of hydrazide-
hydrazones (4a–p) are shown in Table 1. All of the clopyralid hydrazide-hydrazones
derivatives (4a–p) are solid and stable in air; insoluble in water; slightly soluble
in ordinary organic solvents such as methanol, ethanol, acetone, ethyl acetate,
and tetrahydrofuran (THF); and soluble in dimethylformamide (DMF) and
dimethylsulfoxide (DMSO). Thin-layer chromatography (TLC) showed that these
compounds (4a–p) possess big polarity.
The structures of compounds 4a–p were conformed by elemental analysis
1
(Table 1), infrared (IR) (Table 2), and H NMR spectra (Table 3). In addition,
the structure of 4c was confirmed by single-crystal x-ray diffraction analysis.[13]

816
J. ZHANG ET AL.
Table 1. Physical character and elemental analysis of 4a–p
Elemental analysis (calculated value) (%)
No.
Color
Yield (%)
Mp (ꢂC)
Rf (P:E)a
C
H
N
4a
4b
4c
4d
4e
4f
White
White
Yellow
White
Yellow
White
White
White
Yellow
White
Yellow
Red
90
80
70
91
89
78
96
82
85
92
87
87
83
88
90
79
228–229
249–250
218–220
211–212
274–275
207–208
212–214
199–200
279–280
221–222
280–282
195–196b
159–160b
162–163
170–171
230–231
0.53 (4:1)
0.50 (3:1)
0.47 (3:1)
0.48 (3:1)
0.63 (3:1)
0.60 (4:1)
0.47 (4:1)
0.53 (3:1)
0.58 (3:1)
0.46 (3:1)
0.38 (3:1)
0.63 (3:1)
0.68 (4:1)
0.67 (3:1)
0.56 (4:1)
0.59 (4:1)
53.04 (53.08)
41.76 (41.85)
47.34 (47.52)
41.78 (41.85)
50.30 (50.35)
48.50 (48.55)
50.78 (50.87)
50.78 (50.87)
42.96 (43.01)
43.40 (43.43)
33.32 (33.35)
50.70 (50.78)
51.88 (51.96)
43.86 (43.93)
43.88 (43.93)
46.46 (46.53)
3.08 (3.08)
2.16 (2.16)
2.44 (2.45)
2.14(2.16)
2.92 (2.92)
4.06 (4.08)
3.68 (3.70)
3.66 (3.70)
1.94 (1.94)
2.60 (2.60)
1.50 (1.51)
3.24 (3.26)
3.62 (3.63)
3.68 (3.69)
3.68 (3.69)
3.50 (3.51)
14.24 (14.29)
11.24 (11.26)
12.71 (12.79)
11.22 (11.26)
13.48 (13.55)
15.40 (15.44)
11.80 (11.86)
11.78 (11.86)
11.50 (11.58)
10.84 (10.85)
8.96 (8.98)
4g
4h
4i
4j
4k
4l
10.42 (10.45)
10.08 (10.10)
17.06 (17.08)
17.04 (17.08)
16.26 (16.28)
4m
4n
4o
4p
Red
White
White
White
aP:E, petrolum ether=ethyl acetate.
bDecomposition temperature.
Infrared Spectra
The absorption bands of IR spectra of (4a–p) in the 3163–3226 cmꢁ1 regions were
attributed to the stretching of N-H.[14] The absorption bands representing carbonyl
groups and azomethine were observed at 1626–1698 cmꢁ1 and 1562–1609 cmꢁ1 regions,
respectively.[14] The characteristic bands of ferrocenyl groups in the compounds 4m and
Table 2. Important IR absorption bands of 4a–p (in cmꢁ1 a
)
Compound t (N-H) t (Py-H) t (C O) t (C N) d (N-H) t (N-N) t (Py-2,3,6)b t (CꢁH)
=
=
4a
4b
4c
4d
4e
4f
3179m
3197m
3164m
3185m
3190m
3163m
3173m
3196m
3196m
3188m
3169m
3200m
3189m
3213m
3178m
3226m
3031m
3047m
3064m
3049m
3050m
3066m
3036m
3041m
3041m
3048m
3046m
3059m
3061m
3062m
3071m
3049m
1670vs
1670vs
1698vs
1667vs
1673vs
1665vs
1664vs
1667vs
1673vs
1675vs
1626vs
1672vs
1668vs
1676vs
1665vs
1668vs
1603vs
1596s
1547vs
1537vs
1559vs
1540vs
1544vs
1550s
940vs
940vs
940vs
934vs
940vs
962m
974vs
962vs
960vs
955vs
946vs
951vs
999vs
947vs
962m
957vs
823s
849s
823s
822vs
826s
829s
831s
803vs
825s
838s
844s
824vs
837s
833s
828s
844s
—
—
1595vs
1605vs
1606vs
1562s
—
—
—
2974m
2960s
2999s
—
4g
4h
4i
1597vs
1603vs
1596s
1547vs
1554vs
1560vs
1554vs
1547vs
1545vs
1548vs
1544vs
1554s
4j
1600vs
1609vs
1605vs
1563s
2987s
—
—
4k
4l
4m
4n
4o
4p
2993s
2976s
2999s
2952s
1626vs
1562s
1586s
1539vs
avs, very strong; s, strong; m, medium.
bt (Py-2,3,6) ¼ 2,3,6-trisubstituted pyridine.

CLOPYRALID HYDRAZIDE-HYDRAZONES
817
Table 3. 1H NMR chemical shift of 4a–p
d (ppm)a
Compound
=
10.52 (s, 1H, NH), 8.39 (s, 1H, N CH), 7.83–7.85 (m, 3H, py-H, bz-H), 7.43–7.46 (m,
4H, py-H, bz-H)
4a
=
4b
10.65 (s, 1H, NH), 8.68 (s, 1H, N CH), 8.25 (d, 1H, J ¼ 7.2 Hz, bz-H), 7.86 (d, 1H,
J ¼ 8.8 Hz, py-H), 7.59 (d, 1H, J ¼ 8.4 Hz, bz-H), 7.47 (d, 1H, J ¼ 8.4 Hz, py-H), 7.38
(t, 1H, J ¼ 6.8 Hz, bz-H), 7.26–7.30 (m, 1H, bz-H)
=
4c
4d
4e
10.56 (s, 1H, NH), 8.37 (s, 1H, N CH), 7.84 (d, 1H, J ¼ 8.4 Hz, py-H), 7.75 (d, 2H,
J ¼ 8.8 Hz, bz-H), 7.45 (d, 1H, J ¼ 8.4 Hz, py-H), 7.40 (d, 2H, J ¼ 8.8 Hz, bz-H)
=
10.57 (s, 1H, NH), 8.36 (s, 1H, N CH), 7.84 (d, 1H, J ¼ 8.8, py-H), 7.68 (d, 2H,
J ¼ 8.4 Hz, bz-H), 7.56 (d, 2H, J ¼ 8.8 Hz, bz-H), 7.45 (d, 1H, J ¼ 8.4 Hz, py-H)
=
10.58 (s, 1H, NH), 8.55 (s, 1H, N CH), 7.86 (d, 1H, J ¼ 8.4 Hz, py-H), 7.48 (d, 1H,
J ¼ 8.4 Hz, py-H), 7.34 (t, 1H, J ¼ 6.8 Hz, bz-H), 7.25–7.27 (m, 1H, bz-H), 7.05 (d, 1H,
J ¼ 8.0 Hz, bz-H), 6.93 (t, 1H, J ¼ 6.8 Hz, bz-H)
4f
4g
4h
4i
9.91 (s, 1H, NH), 7.81 (d, 1H, J ¼ 8.4 Hz, py-H), 7.41 (d, 1H, J ¼ 8.4 Hz, py-H), 2.61 (t,
2H, J ¼ 6.8 Hz, cy-H), 2.42 (t, 2H, J ¼ 6.8 Hz, cy-H), 1.90–1.97 (m, 2H, cy-H),
1.79–1.86 (m, 2H, cy-H)
=
10.55 (s, 1H, NH), 8.66 (s, 1H, N CH), 7.83 (d, 1H, J ¼ 8.4 Hz, py-H), 7.66 (d, 1H,
J ¼ 3.2 Hz, bz-H), 7.44 (d, 1H, J ¼ 8.4 Hz, py-H), 6.97 (dd, 1H, J ¼ 9.0 Hz, 3.0 Hz,
bz-H), 6.87 (d, 1H, J ¼ 8.8 Hz, bz-H), 3.86 (s, 3H, OCH3), 3.84 (s, 3H, OCH3)
=
10.47 (s, 1H, NH), 8.29 (s, 1H, N CH), 7.83 (d, 1H, J ¼ 8.4 Hz, py-H), 7.55 (d, 1H,
J ¼ 2 Hz, bz-H), 7.44 (d, 1H, J ¼ 8.8 Hz, py-H), 7.16 (dd, 1H, J ¼ 8.2 Hz, 2 Hz, bz-H),
6.88 (d, 1H, J ¼ 8.0 Hz, bz-H), 3.97 (s, 3H, OCH3), 3.93 (s, 3H, OCH3)
=
10.71 (s, 1H, NH), 8.76 (s, 1H, N CH), 8.18 (dd, 1H, J ¼ 8.4 Hz, 1.6 Hz, bz-H), 7.86 (d,
1H, J ¼ 8.8 Hz, py-H), 7.53 (dd, 1H, J ¼ 8.0 Hz, 1.6 Hz, bz-H), 7.48 (d, 1H, J ¼ 8.8 Hz,
py-H), 7.29 (d, 1H, J ¼ 8.0 Hz, bz-H)
4j
10.54 (s, 1H, NH), 7.84 (d, 1H, J ¼ 8.4 Hz, py-H), 7.79 (d, 2H, J ¼ 8.0 Hz, bz-H), 7.53 (d,
2H, J ¼ 8.0 Hz, bz-H), 7.46 (d, 1H, J ¼ 8.4 Hz, py-H), 2.37 (s, 3H, CH3)
=
12.15 (s, 1H, OH), 10.69 (s, 1H, NH), 8.38 (s, 1H, N CH), 8.09 (s, 2H, bz-H), 8.00 (d,
4k
4l
1H, J ¼ 8.4 Hz, py-H), 7.61 (d, 1H, J ¼ 8.0 Hz, py-H)
=
10.29 (s, 1H, NH), 8.33 (s, 1H, N CH), 7.82 (d, 1H, J ¼ 7.6 Hz, py-H), 7.42 (d, 1H,
J ¼ 8.0 Hz, py-H), 4.73 (s, 2H, C5H4-H), 4.44 (s, 2H, C5H4-H), 4.23 (s, 5H, C5H5-H)
10.34 (s, 1H, NH), 7.82 (d, 1H, J ¼ 7.6 Hz, py-H), 7.43 (d, 1H, J ¼ 7.2 Hz, py-H), 4.77 (s,
2H, C5H4-H), 4.40 (s, 2H, C5H4-H), 4.19 (s, 5H, C5H5-H), 2.28 (s, 3H, CH3)
4m
4n
4o
4p
=
10.16 (s, 1H, NH), 7.80 (d, 1H, J ¼ 8.4 Hz, py-H), 7.67 (s, 1H, N CH), 7.42 (d, 1H,
J ¼ 8.8 Hz, py-H), 2.46 (m, 2H, CH2), 1.18 (t, 3H, J ¼ 7.4 Hz, CH3)
10.11 (s, 1H, NH), 7.81 (d, 1H, J ¼ 8.4 Hz, py-H), 7.42 (d, 1H, J ¼ 8.4 Hz, py-H), 2.17 (s,
6H, CH3)
=
10.24 (s, 1H, NH), 7.91 (d, 1H, J ¼ 9.2 Hz, N CH), 7.81 (d, 1H, J ¼ 8.4 Hz, py-H), 7.41
=
=
(d, 1H, J ¼ 8.4 Hz, py-H), 6.40–6.46 (m, 1H, CH CH), 6.19–6.24 (m, 1H, CH CH),
1.92 (dd, 3H, J ¼ 6.6 Hz, 1.8 Hz, CH3)
apy ¼ py, bz ¼ benzene, cy ¼ cyclopentylidene.
4l were observed at 3092 cmꢁ1, 1102cmꢁ1, 819 cmꢁ1, 499 cmꢁ1 and 3095cmꢁ1
,
1108cmꢁ1, 821cmꢁ1, 503 cmꢁ1, respectively.[15,16] The other absorption bands are listed
in Table 2. These data indicated the existence of hydrazone configuration.
1H NMR Spectra
1
The H NMR spectrum of 3 displayed the ꢁNHꢁ and ꢁNH2 resonance in d
(ppm) ¼ 8.62 and 4.06, respectively. Both of these broad peaks disappeared after
treatment with D2O.

818
J. ZHANG ET AL.
The 1H NMR spectra of 4a–p were shown a broad singlet peak corresponding
to the resonance of imine protons at d (ppm) ¼ 9.91–10.71.[17] These signals
disappeared after treatment by D2O. The proton signals at the regions of d
=
(ppm) ¼ 7.91–8.68 were attributed to ꢁCH Nꢁ group in some aldehyde-hydra-
zones.[17] The compound 4m showed that the chemical shift of five protons on the
unsubstituted cyclopentadienyl ring were observed at d (ppm) ¼ 4.19 as a singlet.
The signals at d (ppm) ¼ 4.40 and d (ppm) ¼ 4.77 (two singlet, 2H in each) were
due to the protons on substituted cyclopentadienyl ring.[18]
Bioactivities
The herbicidal activities of the 16 compounds (4a–p) were determined with
barnyard grass and rape. All the compounds showed poor herbicidal efficacy (less
than 10% reduction in the height of the aboveground parts relative to the control)
at concentrations of 100 mg=ml.
In addition, the series of 16 compounds (4a–p) had large values of the minimal
inhibitory concentration (MIC > 50 mg=ml) and the minimal bactericidal concen-
tration (MBC > 50 mg=ml) in vitro antimicrobial activity with Staphylococcus aureus.
The results showed that the tested compounds cannot be considered as
promising new herbicidal or antibacterial agents.
EXPERIMENTAL
Melting points were determined on an X-4 digital display binocular microscope
and are uncorrected. Elemental analyses were performed on a Carlo Erba 1106
instrument, IR spectra were detected on a Bruker Vector-22 spectrometer with
1
KBr pellets, and H NMR were obtained on a Mercury Plus 400-MHz NMR spec-
trometer in CDCl3 with tetramethylsilane (TMS) as an internal reference. All of the
solvents and the others reagents were of analytical grade.
Ethyl 3,6-Dichloropicolinate (2)
Clopyralid (1) (55.0 g, 286.5 mmol) and ethanol (40 mL) were refluxed for 2 h
after a few drops of concentrated sulfuric acid was added. The mixture was adjusted
to neutral with Na2CO3 solution (5%), the aqueous layer was extracted with toluene
(3 ꢃ 50 mL), and the organic layers were combined, dried with Na2SO4, and distilled
in vacuum. The product 2 (52.7 g, 83.6%, mp 34 ꢂC) was obtained after recrystalliza-
tion from ethanol.
3,6-Dichloropicolinohydrazide (3)
The ethanolic solution of 2 (11.3 g, 51.4 mmol, in 30 mL of EtOH) was added
to 85% hydrazine-hydrate (5.9 mL, 102.8 mmol) and was stirred for 3 h at room
temperature. The reaction mixture was allowed to cool overnight. The solid
precipitated was collected by a filter, washed three times with 95% ethanol, and
recrystallized from 20 mL ethanol. A colorless crystal of compound 3 was
obtained (10.1 g, 95.3%, mp 166–167 ꢂC). The intermediate C6H5Cl2N3O was

CLOPYRALID HYDRAZIDE-HYDRAZONES
819
analyzed as follows: found C, 34.92; H, 2.44; N, 20.36 (calcd. C, 34.98; H, 2.45; N,
20.40); IR (KBr, cmꢁ1): 3322, 3266, 3055, 1680, 1610, 1496, 1421, 1159, 832, 657;
1H NMR d (CDCl3): 8.62 (s, 1H, NH), 7.79 (d, 1H, J ¼ 8.4 Hz, pyridine-H), 7.41
(d, 1H, J ¼ 8.4 Hz, pyridine-H), 4.06 (s, 2H, NH2).
Procedure for the Synthesis of (E)-3,6-Dichloro-N0-
(ferrocenylmethylene)picolinohydrazide (4m)
A solution of 3 (1.00 g, 4.85 mmol), an equimolar amount of acetyl ferrocene
(1.11 g, 4.85 mmol), and a few drops of ice acetic acid in 20 mL of EtOH was heated
under reflux for 8 h with stirring. Then the solution was concentrated to half of its
original volume, cooled to room temperature, and allowed to sit overnight. The pre-
cipitated solid was collected by a filter, washed three times with 95% EtOH, dried,
and recrystallized from a 30-mL mixture of DMF=ethanol (1=2 in volume). After
drying in vacuo, a red crystal of 4m (1.76 g, 87.2%) was obtained. The decomposition
temperature was 195–196 ꢂC.
The preparation methods of other compounds of 4 were similar to those of 4m.
Herbicidal Activity Tests
The in vivo herbicidal activities were examined for growth inhibition on
barnyard grass (Echinochloa crusgalli L.) and rape (Brassica campestris L.). The
compounds to be tested (4a–p) were dissolved in DMF and emulsified with Tween
20 to disperse in water until they reached the concentration required (100 mg=ml).
A mixture of the same amount of water, DMF, and Tween 20 was used as control.
Ten seeds of barnyard grass (or rape) were placed in a 50-ml cup covered with a
layer of glass beads and a piece of filter paper at the bottom, to which 5 ml of
inhibitor solution had been added in advance. After growth at 25 ꢂC in a 10 Klux
light and photoperiod of 12 h=day for 5 days, the percentage reduction in the
height of the aboveground parts relative to the control was visually observed
(0–100 rating scale).
Antimicrobial Activity Tests
All of the compounds (4a–p) were screened in vitro for antimicrobial activity
by the microdilution susceptibility method. Staphylococcus aureus ATCC 25923
was used as the reference strain, and Mueller–Hinton broth (pH 7.3) was used as
the medium for the determination of antibacterial activity.
All the compounds of 4a–p were dissolved in DMSO at suitable concentra-
tions. Magainin was treated as contrast antibacterial agent. Each test was performed
twice, and the average of the results was calculated.[19]
ACKNOWLEDGMENTS
This work was supported by the Top Key Discipline of Applied Chemistry
of Zhejiang Province and the State Key Laboratory Breeding Base of Green
Chemistry–Synthesis Technology.

820
J. ZHANG ET AL.
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