3
1
1
0. Gogoi, K.; Dewan, A.; Gogoi, A.; Borah, G.; Bora, U.
Heteroatom Chem. 2014, 25, 127
1. Gogoi, P.; Bezboruah, P.; Gogoi, J.; Boruah, R. C. Eur. J. Org.
Chem. 2013, 32, 7291.
From a green chemistry viewpoint, the reusability of
22
12. Begum, T.; Gogoi, A.; Gogoi, P. K.; Bora, U. Tetrahedron Lett.
015, 56, 95.
catalysts makes them more attractive and one of advantages of
using heterogeneous catalyst. Therefore the reusability of the Ru
catalyst was performed. Based on our reusability test we found
that the Ru@imine–nanoSiO catalyst could be consistently used
2
up to six consecutive reactions of phenylboronic acid to give
phenol (Fig. 1). After completion of the first cycle, it could be
2
1
3. Mahanta, M.; Adhikari, P.; Bora, U.; Thakur, A. J., Tetrahedron
Lett., 2015, 56, 1780
1
4. (a) Webb, K. S.; Levy, D. Tetrahedron Lett. 1995, 36, 5117; (b)
Simon, J.; Salzbrunn, S.; Surya Prakash, G. K.; Petasis, N. A.;
Olah, G. A. J. Org. Chem. 2001, 66, 633.
easily recovered by centrifugation, and thoroughly washing with
15. (a) Prakash, G. K.S.; Chacko, S.; Panja, C.; Thomas, T. E.;
Gurung, L.; Rasul, G.; Mathew, T. ; Olah, G. A. Adv. Synth. Catal.
2009, 351, 1567;(b) Xu, J.; Wang, X.Y. ; Shao, C.W.; Su, D. Y.;
Cheng, G. L.; Hu, Y.F. Org. Lett. 2010, 12, 1964; (c) Yang, H. ;
Li, Y. ; Jiang, M.; Wang, J. ; Fu, H. Chem.Eur. J. 2011, 17, 5652.
i
PrOH:H O followed by EtOAc and drying inoven, it can be used
2
th
again for fresh reaction. The Ru content after 6 run was
determined by ICP-AES analysis, and found to be below
detection level. Amazingly, the catalyst remained efficient and
gives successful conversion to phenol with excellent yields up to
1
6. Jiang, H.; Lykke, L.; Pedersen, S. U.; Xiao, W.J.; Jorgensen, K. A.
Chem. Commun. 2012, 48, 7203.
12
1
7. (a) Mohamed, R.M.; Mkhalid, I.A.; Barakat, M.A. Arabian
Journal of chemistry. 2015, 8, 48. (b) Mora, M.; Sanchidrian, C.
J.; Ruiz, J.R. Curr. Org. Chem. 2012, 16, 1128.
the sixth run
1
8. (a) Qi, H. L.; Chen, D.S.; Ye, J.S.; Huang, J.M. J. Org. Chem.
2
013, 78, 7482; (b) Zou, Y.Q.; Chen, J.R.; Liu, X.P.; Lu, L.Q.;
Rebecca L. D.; Jørgensen, K. A.; Xiao, W.J. Angew. Chem. Int.
Ed. 2012, 51, 784.
1
2
9. Gogoi, N.; Begum, T.; Bora, U.; Gogoi, P. K. RSC Adv., 2015, 5,
9
5344.
0. General procedure for the hydroxylation of arylboronic acid: A 50
mL round bottom flask was charged with arylboronic acid (1
i
mmol), 5 mg Ru catalyst and 4 ml PrOH: H
2
O (1:1). The reaction
mixture was stirred at room temperature under aerobic condition.
The progress of the reaction was monitored by TLC. After the
completion of the reaction, the mixture was diluted with 20 mL of
water and extracted with diethyl ether. The combined organic
layers were washed with brine and dried over by anhydrous
2 4
Na SO and evaporated in a rotary evaporator under reduced
pressure. The crude was purified by column chromatography on
silica gel (hexane:ethyl acetate, 9:1) to afford the desired product.
1
13
The purity of the compound was confirmed by H NMR,
C
In summary, we have developed a clean and effeicient
protocol for the organic transformation of arylboronic acids to
phenols using bio-sourced nanosilica derived Ru@imine-
NMR.
2
2
1. (a) Stahl, S. S. Angew. Chem. Int. Ed. 2004, 43, 3400; (b)
Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105,
2329.
2. General procedure for reusability test: After completeion of the
reaction, the catalyst was isolated from the reaction mixture by
simple centrifugation process and washed with ethyl acetate and
water to remove the organic contaminants. After getting the solid
2
nanoSiO as heterogeneous catalyst. The advantageous features
of this protocol include (a) use of air as green oxidant in place
other oxidants; (b) it is a base and ligand free system; (c) take
place within short reaction time and at room temperature (d) use
of water as co-solvent (e) the current protocol is also effective
with a various substituted aryl and heteroaryl boronic acids
giving phenols as products in good to excellent yields.
ο
part of catalyst, it was drying at 110 C in an oven for whole night.
Then catalyst was used for further fresh reaction taking
phenylboronic acid as substrate. Reaction conditions were kept
similar to the other reactions.
Acknowledgements
We gratefully acknowledge SAIC-Tezpur University
for various analytical services and CDRI-Lucknow for NMR
analysis. N. Gogoi also thanks to UGC, New Delhi for financial
assistance in the form of UGC-BSR (RFSMS) Fellowship.
References and notes:
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