SYNTHESIS AND EVALUATION OF PYRAZOLE DERIVATIVES
117
chloroform. Yield 80%, off-white solid, mp 98–100°C,
Rf 0.7 (CH2Cl2–hexane, 8:2). IR spectrum, ν, cm–1:
3158 (N–H), 3072 (C–H), 2966 (C–H), 1686 (C=C),
Nematicidal activity. Pyrazole derivatives 3, 6, and
9a–9c were screened for their nematicidal activity, i.e.,
egg hatch inhibition and mortality of second stage
juveniles of Meloidogyne incognita, at six different
concentrations, 1500, 750, 500, 250, 125, and
50.00 ppm. The observations were recorded after 24,
48, 72, and 96 h.
1
1433 (C=N), 1237 (C–N), 559 (C–Br). H NMR spec-
trum, δ, ppm: 7.70 s (2H, CH), 13.13 br.s (1H, NH).
13C NMR spectrum, δC, ppm: 91.71, 133.86. Found, %:
C 24.23; H 1.91; N 18.57. C3H3BrN2. Calculated, %:
C 24.48; H 2.04; N 19.04.
a. Egg hatch inhibition assay. A pure culture of root
knot nematodes was raised in brinjal crop. Five egg
masses were taken and placed in a solution (5 mL) of 3,
6, or 9a–9c at a concentration of 1500, 750, 500, 250,
125, or 50.00 ppm. A very small amount of acetone was
used to dissolve the compounds in distilled water for
making stock solution which was further diluted to
a required concentration. Distilled water containing the
same amount of acetone was used as control. Three
replications of each treatment were made. Egg hatching
after 24, 48, 72, and 96 h at 27±2°C was recorded
[28, 29]. The percent hatch inhibition was calculated as
(C – T)/C×100, where C is the number of nematodes in
the control sample, and T is the number of nematodes
after treatment.
1-Alkyl-4-bromo-1H-pyrazoles 9a–9c (general
procedure). A mixture of 4-bromo-1H-pyrazole (6,
5.26 mmol), tetrabutylammonium hydrogen sulfate,
and alkyl halide 8a–8c (160 mmol) in a round-bottom
flask was cooled to 0°C, and 50% aqueous sodium
hydroxide (2.0 mL) was slowly added while stirring at
0°C. The mixture was stirred for 30 min at 0°C and
allowed to warm up to room temperature. After com-
pletion of the reaction (TLC), the mixture was neutral-
ized using 1.0 N aqueous HCl, and the product was
isolated by extraction.
4-Bromo-1-propyl-1H-pyrazole (9a). Yield 65%,
colorless liquid, Rf 0.6 (EtOAc–hexane, 8.5:1.5). IR
spectrum, ν, cm–1: 2955 (C–H), 2924 (C–Haliph), 1464
(C=N), 1377 (C–N), 609 (C–Br). 1H NMR spectrum, δ,
ppm: 0.93 t (3H, CH3, J = 7.32 Hz), 1.33 q (2H, CH2,
J = 7.32 Hz,), 1.52–1.60 m (2H, CH2), 7.55 s (2H,
b. Second stage juvenile mortality. Freshly hatched
stage two juveniles (j2) were taken instead of egg
masses for mortality test. The number of juveniles per
milliliter of distilled water was counted which was
found to be average of 20 juveniles. Solutions of the
test compounds (5 mL) were prepared as described
above for the egg hatch assay test with 3 replications
each along with control. A juvenile suspension (1 mL)
was placed in each solution with a concentration of
1500, 750, 500, 250, 125, and 50 ppm, and the results
were recorded after 24, 48, 72, and 96 h [28, 29]. The
percent juvenile mortality was calculated as the ratio
of the number of dead nematodes to the total number
of nematodes multiplied by 100%.
13
3-H, 5-H). C NMR spectrum, δC, ppm: 13.48, 19.51,
23.74, 58.51, 92.43, 134.02. Found, %: C 37.92;
H 4.55; N 14.56. C6H9BrN2. Calculated, %: C 38.09;
H 4.76; N 14.81.
4-Bromo-1-butyl-1H-pyrazole (9b). Yield 60%,
colorless liquid, Rf 0.6 (EtOAc–hexane, 8.5:1.5). IR
spectrum, ν, cm–1: 3108 (C–H), 2961 (C–Haliph), 1463
1
(C=N), 1372 (C–N), 608 (C–Br). H NMR spectrum,
δ, ppm: 0.93 t (3H, CH3, J = 7.44 Hz), 1.32 q (2H, CH2,
J = 7.48 Hz), 1.77–1.84 m (2H, CH2), 4.08 t (2H, CH2,
J = 7.20 Hz), 7.38 d (2H, 3-H, 5-H, J = 20.08 Hz).
13C NMR spectrum, δC, ppm: 13.53, 19.68, 32.22,
52.55, 92.52, 129.04, 139.46. Found, %: C 40.98;
H 5.03; N 13.53. C7H11BrN2. Calculated, %: C 41.30;
H 5.41; N 13.79.
ACKNOWLEDGMENTS
The authors gratefully acknowledge Sophisticated
Analytical Instrumentation Facility, Panjab University,
Chandigarh, for the analysis of compounds reported in this
article.
4-Bromo-1-hexyl-1H-pyrazole (9c). Yield 62%,
light yellow liquid, Rf 0.7 (EtOAc–hexane, 8.5:1.5). IR
spectrum, ν, cm–1: 3122 (C–H), 2927 (C–Haliph), 1458
1
CONFLICT OF INTEREST
The authors declare no conflict of interest.
REFERENCES
(C=N), 1311 (C–N), 608 (C–Br). H NMR, δ, ppm:
0.86 t (3H, Me, J = 6.88 Hz), 1.27 s (6H, CH2), 1.81 q
(2H, CH2, J = 7.24 Hz), 4.05 t (2H, CH2, J = 7.12 Hz),
7.37 s and 7.42 s (1H each, 3-H, 5-H). 13C NMR spec-
trum, δC, ppm: 13.88, 22.37, 26.08, 30.11, 31.17, 52.75,
92.43, 128.92, 139.32. Found, %: C 46.54; H 6.31;
N 11.93. C9H15BrN2. Calculated, %: C 46.75; H 6.49;
N 12.12.
1. Sharma, A., Singh, S., and Utreja, D., Curr. Org. Synth.,
2016, vol. 13, p. 484.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020
Dhillon, N. K.
