Imidazole derivatives as the organic precursor of ZnO nano particle

Article abstract of DOI:10.1016/j.tetlet.2010.03.058

N₁-Hydroxy-2,4,5-trisubstituted imidazoles were synthesized starting from 1,2-diketones. The crystal structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazol-1-ol has been determined. An unusual intermolecular hydrogen bonding through the associ

Full text of DOI:10.1016/j.tetlet.2010.03.058

Tetrahedron Letters 51 (2010) 2751–2753
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Imidazole derivatives as the organic precursor of ZnO nano particle
b
c
a
b
Arun Kumar Padhy a, , Bolin Chetia , Sasmita Mishra , Anita Pati , Parameswar Krishnan Iyer
*
a Department of Chemistry, National Institute of Science & Technology, Palur Hills, Berhampur 761 008, Orissa, India
b Department of Chemistry, Indian Institute of Technology, Guwahati, Assam, India
c Apex Institute of Technology & Management, Bhubaneswar, Orissa, India
a r t i c l e i n f o
a b s t r a c t
Article history:
N1-Hydroxy-2,4,5-trisubstituted imidazoles were synthesized starting from 1,2-diketones. The crystal
structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazol-1-ol has been determined. An unusual inter-
molecular hydrogen bonding through the association of water molecule has been reported. These imid-
azole derivatives can be thought of as the organic precursor for the synthesis of zinc oxide nano particles.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 7 February 2010
Revised 11 March 2010
Accepted 16 March 2010
Available online 20 March 2010
Key words:
Imidazole
ZnO nano particle
TEM
ZIF
The imidazole ring is found in highly significant biomolecules,
aminoacidsandalkaloids,whichhavebeenshowntoexhibitinterest-
ing biological activities such as antimicrobial, anticryptococcal, and
inhibition of nitric oxide synthase and cytotoxic activities.1 Molecular
recognition through fluorescence sensing has attracted much atten-
tion in recent times.2 A significant number of imidazole derivatives
were being reported to be implemented in electronic devices,
optoelectronic devices, etc.3 In continuation of our search for suitable
sensing element to sense urea or thiourea4 we have synthesized
N1-hydroxy-2,4,5-trisubstituted imidazoles5 (Scheme 1).
merized and are in the zwitterion formwith theuncoordinated imid-
azole imine N-atom being protonated and the oxime O-atom
deprotonated. Further, the solvate water molecule makes three
hydrogen bonds to the protonated amine, the oxime O-atom and to
a perchlorate O-atom. Furthermore, theintramolecular protontrans-
ferinanaqueousmediumisquitehigh, thathasbeenproposedbythe
theoretical calculation using SCRF models8 for prototropic tautomer-
ism of imidazolone in an aqueous solution. Thus, our finding is well
established with reference to the works7,8 and we herein report that
it is not during the complexation the imidazole imine nitrogen get
protonated8 rather the ligand structure itself is associated with the
zwitterion form. Furthermore the stabilization of the protonated
amine is so high that during the process of synthesis liquid NH3 is
used which is unable to remove this proton. It emphasizes that the
nucleophilicity of the nitrogen is quite high. The delocalization of
the charge within the imidazole is quite evident with respect to the
behavior of the imidazole nucleus. The solvate water molecule form
three hydrogen bonds to the protonated amine, the oxime O-atom
and the nitro group O-atom resulting in the self-assembly (Fig. 2).
1H NMR data6 is in accordance with that of the desired struc-
ture. A lot of work has been reported with respect to the imidazole
derivatives but exact structural feature of the said compound was
not provided. Thus we report here in the crystal structure of N1-hy-
droxy-2-(m-nitrophenyl)-4,5-dimethyl imidazole.
We have started our work with an intention of synthesizing the
imidazole derivative and to study the reactivity of these imidazole
derivatives. The study of X-ray crystallographic analysis revealed
the co-crystallization of these imidazoles with water (Fig. 1) even
though the crystal is being grown from DMSO and the nitrogen
of the imidazole get protonated forming quaternary nitrogen with-
out any counter ion. Further analysis of the data has revealed that
the water molecule is responsible for the intermolecular hydrogen
bond and thus results in an array of imidazole molecules with the
help of the hydrogen bonding (Fig. 2).
R
R
NOH
N
ArCHO
NH4OAc/AcOH
& liq. NH3
R
Ar
R
O
N
McCann and co-workers7 have reported that in the process of
complexation, the neutral N-hydroxyimidazole ligands have tauto-
OH
R=CH3, C6H5
Ar= m-NO2C6H4, p-OHC6H4, p-ClC6H4, 3,5-(OCH3)C6H3
* Corresponding author. Tel.: +91 94370 67761; fax: +91 680 2492627.
E-mail addresses: arun_nist@hotmail.com, arunkpadhy@nist.edu (A.K. Padhy).
Scheme 1. Synthesis of Imidazole derivatives.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.03.058

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A. K. Padhy et al. / Tetrahedron Letters 51 (2010) 2751–2753
Figure 1. Single crystal structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-imidazol-
1-ol.
Figure 2. Self-assembled crystal structure of 4,5-dimethyl-2-(3-nitrophenyl)-1H-
imidazol-1-ol.
This delocalization of the charge is quite significant and thus
can be thought worthy to be used as Organic Laser, as it is quite
evident that the water bridge that is existing, is corresponding to
the metastable state. The charge balance could nicely be explained
through the extensive delocalization of the charge over the quater-
nary nitrogen.
The water bridge also opens up much opportunity to syntheti-
cally tune the molecule and get appropriate result. In this context,
the recent finding of Zeolite Imidazolate Framework (ZIF)9 is
noteworthy.
Figure 3. TEM picture of ZnO nano particle.
The structural feature of the hydroxy imidazole derivative pro-
vides an excellent groove with the hydroxyl, nitro group and the
nitrogen atom for the metal ions to bind in. The complex can be
thought as a probable precursor for the preparation of metal oxide
nano particles. Thus, we have prepared the zinc oxide nano parti-
cles from the zinc complex of the imidazole derivatives5 (Scheme
2). The zinc complexes were subjected to calcination.10
The calcined zinc complex of N1-hydroxy-2-(m-nitrophenyl)-
4,5-dimethyl imidazole, is shown to be having pure ZnO, whereas
the zinc oxide nano particles obtained from the N1-hydroxy-2-(m-
hydroxyphenyl)-4,5-dimethyl imidazole and N1-hydroxy-2-(p-
hydroxyphenyl)-4,5-dimethyl imidazole contain trace amount of
carbon in the nano size as evident from the XRD analysis. TEM pic-
ture of zinc oxide nano particles (Fig. 3) obtained from N1-hydroxy-
2-(m-nitrophenyl)-4,5-dimethyl imidazole seems to be all spheri-
cal and free from any carbon as expected from the XRD-data.
Thus, we report herein the unusual hydrogen bonding in case of
N1-hydroxy-2-(m-nitrophenyl)-4,5-dimethyl imidazole with the
solvent assistance. This also helps in the self-assembly of the imid-
azole molecules in a regular order forming an interesting water
R
N
Zn(OAc)2
Calcination
ZnO
Zinc Complex
R
Ar
liq. NH3
N
OH
R=CH3, C6H5
Ar= m-NO2C6H4, p-OHC6H4,
p-ClC6H4, 3,5-(OCH3)C6H3
Scheme 2. Preparation of ZnO nano particles.

A. K. Padhy et al. / Tetrahedron Letters 51 (2010) 2751–2753
2753
was stirred for 24 h. The resulting mixture was diluted with water (20 mL) and
neutralized with liquor ammonia. The precipitate was filtered out and
recrystallized from ethanol to give the pure product (92% yield). Synthesis of
the Zinc Complex: General Procedure: To the imidazole derivative (0.001 mol)
in methanolic ammonia medium saturated solution of zinc acetate(0.0025 mol)
in methanol (20 mL) was added dropwise with stirring. After the complete
addition the mixture was allowed to stir for additional 1 h. After removal of the
solution the requisite solid was obtained (78% yield).
bridge in between. Further, the delocalization of the charge is quite
interesting and can open up an opportunity to be utilized as organ-
ic laser. Also, these imidazole derivatives can also be utilized as the
organic precursors to prepare the metal oxide nano particles as de-
picted by the formation of zinc oxide nano particles.
Further, the zinc oxide nano particles formed show very good
fluorescence behavior as expected and can be explored upon for
some electronic activity after suitable doping.
6. 1H NMR(400 MHz, Perkin Elmer, DMSO-d6, TMS standard) data: (a) 4,5-
dimethyl-2-(3-nitrophenyl)-1H-imidazol-1-ol: d 1.9 (dd, 3H); 2.3 (dd, 3H), 3.2
(s, 1H), 7.8–8.7 (m, 4H, ArH), mp 196–200 °C; (b) 4,5-dimethyl-2-(4-
hydroxyphenyl)-1H-imidazol-1-ol: d 1.9 (dd, 3H); 2.3 (dd, 3H), 3.2 (s, 1H),
6.8 (m, 2H, ArH), 7.3 (m, 2H, ArH) decomposed at 120 °C.
Acknowledgments
7. Abuskhuna, S.; McCann, M.; Briody, J.; Devereux, M.; Kavanagh, K.; Kayal, N.;
McKee, V. Polyhedron 2007, 26, 4573.
8. Sanchez-Migallon, A.; de la Hoz, A.; Lopez, C.; Claramunt, R. M.; Infantes, L.;
Motherwell, S.; Shankland, K.; Nowell, H.; Alkorta, I.; Elguero, J. Helv. Chim. Acta
2003, 86, 1026.
The authors are thankful to the Director, NIST for his support.
Also, the authors are thankful to Professor Bhisma Patel, IIT,
Guwahati and Professor A. K. Mishra, IIT, Madras for their valuable
suggestions.
9. Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.; O’Keeffe, M.; Yaghi, O.
M. Acc. Chem. Res. 2010, 43, 58.
10. For determining isothermal weight loss, studies were done in the temperature
range of 473–673 K. Known amount of the sample was taken inside a silica
crucible and was introduced into a muffle furnace having provision for step
wise increase in temperature. The samples were heated to the desired
temperature for 2 h, then cooled to 473 K in the furnace and kept inside
desiccators. All the weights were measured by a digital electronic balance
AFCOSET-180A with an accuracy of 0.1 mg. The total weight loss of a sample
at a particular temperature was calculated as given below:
References and notes
1. Luca, L. De. Curr. Med. Chem. 2006, 13, 1.
2. Louis, C.; Bazzi, R.; Bridot, J. L. Chem. Mater. 2005, 17, 1673; Blazquez, M. T.;
Muniz, F. M.; Saez, S.; Simon, L. M.; Alonso, A.; Raposo, C.; Lithgous, A.; Alazar,
V.; Moran, J. R. Heterocycles 2006, 69, 73; Costa, P. G. S.; Oliveira, E.; Lodeiro, C.;
Raposo, M. M. M. Sensors 2007, 7, 2096.
3. Fang, Z.; Wang, S.; Zhao, L.; Xu, Z.; Ren, J.; Wang, X.; Yang, Q. Mater. Lett. 2007,
61, 4803.
4. Chetia, B.; Iyer, P. K. Tetrahedron Lett., 2006, 47, 8115; ibid, 2007, 48, 47.
5. Synthesis of N1-hydroxy-2,4,5-trisubstituted imidazoles: General procedure:
To a mixture of diacetyl monoxime (0.01 mol) in acetic acid (20 mL) were
added aromatic aldehyde (0.01 mol) and ammonium acetate (4 g). The mixture
100ðw1 ꢀ w2Þ
% Weightloss ¼
w1
w1 = Weight of the sample before heating.
w2 = Weight of the sample after heating.