1940
M. Kidwai et al. / Journal of Organometallic Chemistry 696 (2011) 1939e1944
solvents usage, employment of large amount of catalyst, which lead
to create difficulty inproduct separation and non-recyclability of the
catalyst. None of the methods employed easily accessible catalyst.
In continuation of our research for developing economically
viable and environmentally benign methodologies for organic
reactions and to reveal the efficient utility of transition metals and
2.5. Spectral data of synthesized compounds
2.5.1. 3,5-Dimethyl-1-phenyl-1H-pyrazole (3a) [27]
Orange colour liquid 1H NMR (CDCl3):
(s, 3H, CH3), 5.99 (s, 1H, CH), 7.31e7.44 (m, 5H, C6H5) IR (nujol film):
v (cmꢀ1) 1682 (w, C]C), 1596 (m, C]N) B.pt 255 ꢁC, MS (ESI): m/z
172.13[M]þ.
d
¼ 2.29 (s, 3H, CH3), 2.30
their derivatives [29e32]. We report herein for the first time Zn[(L)
proline]2 catalyzed an efficient synthesis of pyrazoles in pure water.
Many advantages such as higher solubility in water, insolubility in
organic solvents, inexpensiveness, eco-friendly nature, uncompli-
2.5.2. 3,5-Dimethylpyrazole (3b) [27]
M.pt ¼ 108 ꢁC (reported ¼ 107 ꢁC, white solid) 1H NMR (CDCl3):
cated handling, convenient work up, recyclability make Zn[(
L)
d
¼ 2.29 (d, 6H, 2CH3, 4JH, H ¼ 0.6 Hz), 5.81 (q, 1H, ]CH,
proline]2 as an efficient catalyst in organic synthesis.
4JH,H ¼ 0.6 Hz),10.68 (br s,1H, NeH) IR (KBr): v (cmꢀ1) 3108 (s, NeH),
1662 (w, C]C), 1594 (m, C]N). MS (ESI): m/z ¼ 96.14 (M)þ.
2. Experimental part
2.5.3. (3,5-Dimethyl-pyrazol-1-yl)-phenyl-methanone (3c) [33]
Off white colour solid M.pt ¼ 230e233 ꢁC (reported ¼
2.1. General
231e234 ꢁC) 1H NMR (CDCl3):
d
¼ 2.24 (s, 3H, CH3), 2.63 (s, 3H, CH3),
6.06 (s, 1H, CH), 7.43e7.56 (m, 3H, Ph), 7.98 (d, J ¼ 7.4 Hz, 2H, Ph) IR
(KBr): v (cmꢀ1) 3143 (m, C]CeH), 1709 (s, C]O), 1642 (s, C]C),
1606 (m, C]N) MS (ESI): m/z ¼ 200.35 (M)þ.
All chemicals were purchased from SigmaeAldrich and Lan-
caster and were used as such. All reactions and purity of dicarbonyl
compounds and hydrazines and hydrazides were monitored by thin
layer chromatography(TLC) using aluminium plates coated with
silica gel (Merck) using 30% ethylacetate and 70% hexane . The
isolated products were further purified by column chromatography
using silica gel (SigmaeAldrich 24, 217e9, 70, 35e70, mesh 40 Ao
surface area 675 m2/g). IR spectra were recorded on PerkineElmer
FTIR-1710 spectrophotometer using Nujol film and KBr pellet. 1H
NMR spectra were recorded on a Bruker Avance Spectrospin 300
(300 MHz) using TMS as internal standard and chemical shift are in
d. GCeMS mass spectra were recorded on a Waters LCT micromass.
The melting point of the compounds was measured through
a ThomaseHoover melting point apparatus and is uncorrected.
Powder XRD wad done on Bruker D8 Discover at 1600W. TEM
images were taken on Technai G2 30 U-TWIN at 300 KV.
2.5.4. 1-(3,5-Dimethyl-1H-pyrazol-yl)ethanone (3d) [27]
Colourless oil 1H NMR (CDCl3):
d
¼ 2.24 (s, 3H, CH3), 2.54 (s, 3H,
CH3), 2.66 (s, 3H, CH3), 5.96 (s,1H, CH), IR (nujol film): v (cmꢀ1) 1730
(vs, C]O),1628 (s, C]C),1583 (s, C]N). MS (ESI): m/z ¼ 138.04 (M)þ.
2.5.5. 1-(2,4-Dinitro-phenyl)-3,5-dimethyl-1H-pyrazole (3e)
Orange solid M.pt ¼ 140 ꢁC (reported ¼ 144 ꢁC) 1H NMR (CDCl3):
d
¼ 2.40 (s, 3H, CH3), 2.7 (s, 3H, CH3), 6.43 (s, 1H), 8.38 (dd, J ¼ 9.2,
3.0 Hz,1H, PhH), 8.77 (d, J ¼ 3.0 Hz,1H, PhH) IR (KBr): v (cmꢀ1) 1615
(s, C]N),1562 (s, C]C),1342 (vs, NO2) MS (ESI): m/z ¼ 262.21 (M)þ.
Calcd for C11H10N4O4: C, 50.38; H, 3.84; N, 21.37. Found C, 50.39;
H, 3.80; N, 21.33.
2.5.6. 5-Ethoxy-3-methyl-1-phenyl-1H-pyrazole (3f)
2.2. Synthesis and characterization of Zn[(
L
)proline]2
1H NMR (CDCl3):
d
¼ 1.42e1.45 (t, J ¼ 7.0 Hz, 3H, CH3), 2.28
(s, 3H, CH3), 4.11e4.16 (q, J ¼ 7.1 Hz, 2H, CH2), 6.19 (s, 1H, CH),
7.21e7.72 (m, 5H, C6H5) IR (nujol film): v (cmꢀ1) 1700 (s, d, C]C),
1632 (s, C]N), 1180 (m, CeO) MS (ESI): m/z ¼ 202.04 (M)þ.
As reported by Darbre et al., the Zinc amino complex was
prepared by adding Et3N (0.6 ml) to the amino acid (4.34 mmol) in
MeOH (10 ml), after 10 min, followed by zinc acetate (2.17 mmol).
After stirring for 45 min a white precipitate was collected by
filtration (23e95% yield). Complexes were characterized by
1H NMR, IR, and ESI-MS [1,35]
2.5.7. 5-Ethoxy-3-methyl-1H-pyrazole (3g)
White solid M.pt ¼ 120 ꢁC 1H NMR (CDCl3):
¼ 2.28 (s, 3H, CH3),
d
3.98 (q, J ¼ 7.1 Hz, 2H, CH2), 5.91 (s, 1H, CH), 10.68 (br s, IH, NeH) IR
(KBr): v (cmꢀ1) 3004 (s, NeH), 1690 (s, C]C), 1592 (s, C]N), 1161
(m, CeO) MS (ESI): m/z ¼ 126.09 (M)þ. C6H10N2O: C, 57.12; H, 7.99;
N, 22.21. Found C, 57.00; H, 8.074; N, 22.29.
2.3. General procedure for the synthesis of pyrazoles
In a 100 ml round bottom flask, 1,3-dicarbonyl compound
(1 mmol), hydrazine/hydrazide/diamine(1 mmol) were added in
pure water and stirred at r.t. To the reaction mixture, Zn[(L)proli-
2.5.8. (5-Ethoxy-3-methyl-pyrazol-1-yl)-phenyl-methanone (3h)
Colourless liquid 1H NMR (CDCl3):
d
¼ 1.5e1.6 (t, J ¼ 7.0 Hz, 3H,
CH3), 2.28 (s, 3H, CH3), 4.11e4.16 (q, J ¼ 7.1, 2H, CH2), 5.92 (s,1H, CH),
7.21e7.72 (m, 5H, C6H5) IR (KBr): v (cmꢀ1) 3153 (C]CeH), 1664
(m, C]N), 1627 (s, C]O) MS (ESI): m/z ¼ 230.12 (M)þ.
ne]2was added. The progress of reaction mixture was monitored by
TLC. After completion of reaction the product was extracted using
ethylacetate (in case of liquid product) and dried over anhydrous
sodium sulphate. Solvent was evaporated under reduced pressure.
Otherwise filtered as it is. Water extract was further used for
consecutive runs. Obtained products were further purified by
column chromatography using hexane:ethylacetate (70:30) as an
eluent. Compounds were characterized by spectral data.
2.5.9. 1-(5-Ethoxy-3-methyl-pyrazol-1-yl) ethanone (3i)
Colourless liquid 1H NMR (CDCl3):
d
¼ 1.5e1.6 (t, J ¼ 7.0 Hz, 3H,
CH3), 2.3 (s, 3H, CH3), 2.6 (s, 3H, CH3), 4.2 (q, J ¼ 7.1 Hz, 2H, CH2), 6.2
(s, 1H, CH) IR (nujol film): v (cmꢀ1) 1640 (s, C]N), 1660 (vs, C]O),
1135 (s, CeO) MS (ESI): m/z ¼ 168.01 (M)þ.
2.4. Spectral data of Zn[(
L
)proline]2
2.5.10. 1-(2,4-Dinitro-phenyl)-5-ethoxy-3-methyl-1H-pyrazole (3j)
Light orange solid M.pt ¼ 222e225 ꢁC 1H NMR (CDCl3):
White solid 1H NMR (300 MHz, D2O)
d
: 1.81 (m, br, 3H); 2.22 (m,
d
¼ 1.6e1.7 (t, J ¼ 7.0 Hz, 3H, CH3), 2.38 (s, 3H, CH3), 4.3e4.4
br, 1H); 2.98 (s, br, 1H); 3.14 (m, br, 1H); 3.85 (m, br, 1H) (spectrum
included) IR (KBr): v (cmꢀ1) 3217 (vs), 2960 (m), 1603 (vs), 1449 (s),
1412 (s), 1329 (m), 848 (m) MS (ESI): m/z ¼ 291.21 (M)þ.
(q, J ¼ 7.1 Hz, 2H, CH2), 6.23 (s, 1H, CH), 8.38 (dd, J ¼ 9.2 Hz, 3.0 Hz,
Ph), 8.77 (d, J ¼ 3.0 Hz, 1H, PhH) IR (KBr): v (cmꢀ1) 1620 (s, C]N),
1562 (s, C]C), 1342 (vs, eNO2), 1335 (s, CeO) MS (ESI): m/