4
Tetrahedron
Representative method for the conversion of benzaldehyde
into benzonitrile
In a round bottom flask (50 mL), benzaldehyde (1 mmol, 106
mg) was properly mixed with potassium hexacyanoferrate (II) (1
mmol, 422 mg) in the presence of minimum volume of water (1-
2 mL) and allowed to stir at room temperature for 5 minutes. To
this mixture, AgNPs-Av (3 mL, 5 mg, 0.03 mmol) was added and
continued the stirring at 50 °C till the completion of the reaction
(monitored by TLC). After completion of the reaction, ethyl
acetate was poured (3x10 mL) and extracted the desired product.
Having done this, the reaction mixture (in ethyl acetate) was
washed with water and brine, dried over anhydrous Na2SO4,
concentrated in a rotary evaporator, and finally the crude product
was purified by column chromatography (10% ethyl acetate:
hexane as the eluent). Colorless liquid; Sweet almond odour; Rf =
0.51 (15% AcOEt: hexane); 1H NMR (400 MHz, CDCl3 TMS):
7.57-7.44 (m, 5H, Ar-H); 13C NMR (100 MHz, CDCl3, TMS):
133.7, 132.4, 128.6, 116.4, 112.6; IR (KBr pellets) νmax: 2242 cm-
1 (CN); Anal. Calcd (%) for C7H5N: C, 81.53; H, 4.89; N, 13.58;
Found C, 81.49, H, 4.93, N, 13.54. All the products listed in
Table 2 have been synthesized akin to this and characterized by
comparison of melting points, MS, FTIR and NMR data with that
in the literature.
Figure 5. AFM image of AgNPs-Av
The EDX spectra along with SEM image of AgNPs-Av has
been shown in [Fig. 6 (a) and (b)]. The typical characteristic
absorption signal for silver nanoparticles was absorbed in EDX
profile at approximately 2.5-3.5 keV which was due to surface
Plasmon resonance confirming the formation of AgNPs. The
elemental composition of synthesized AgNPs was analysed
through EDX [Fig. 6 (a)]. In addition to peaks for Ag, the
presence of peaks for C and O was due to the capping of AgNPs
by bio molecules of Aloe vera extract.
4. Conclusions
This study employed a greener method for the transformation
of aldehydes into nitriles utilizing less toxic K4Fe(CN)6 catalyzed
by highly active AgNPs-Av. The procedure puts forward several
improvements including excellent yields of the products, safe
handling, experimental simplicity and “green-ness” which make
it constructive, attractive and benign substitutes over the existing
methodologies. Hence, as divulged here, we are hopeful that
metal nanoparticles including silver nanoparticles would find
mounting applications for new chemical transformations,
including those which allow the synthesis of complex natural
products and derivatives.
Figure 6. (a) EDX spectrum and (b-d) elemental mapping of synthesized
AgNPs-Av
Supplementary Material
A transmission electron microscope (TEM) demonstrated that
the AgNPs were largely uniform with narrow size distribution
(Fig. 7). TEM images of AgNPs illustrated that the particles were
spherical in shape with an average diameter of about 25-28 nm.
General experimental methods and the image of gradual color
change of AgNPs-Av from colorless to brown.
Acknowledgments
The authors thank DBT (BT/473/NE/TBP/2013, dated
13/02/2014), India for the financial assistance and Dr. Shree
Varaprasad N.S. for AFM analysis.
References and notes
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ed.; Georg Thieme: Stuttgart, 2001.
Figure 7. TEM image of AgNPs-Av
3. Experimental
3.
Method for the preparation of catalyst
4.
5.
Sundermeier, M.; Zapf, A.; Beller, M.; Sans, S. Tetrahedron Lett.
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About 2.0 g of Aloe vera gel was cleaned with de-ionized
water and made into a paste using a blender. The aqueous gel
extract was prepared by shaking (20 min) in 50 mL of water at 50
ºC, followed by filtration using a muslin cloth. 2 mL of the
extract was added to 0.01 M AgNO3 in 25 mL of 5% (w/v)
poly(ethylene glycol). Formation of AgNPs was indicated by
gradual color change from colorless to brown.
6.
7.
8.