Table 4 The reaction of para-xylene with different alcoholsa
Entry
Alcohol
T/1C
t/min
Conversion (%)
Regioselectivity (%)
Isolated yield (%)
1
2
3
4
5
6
7
8
Benzyl alcohol
135
110
110
110
110
130
130
130
10
15
20
45
499
499
499
499
98c
499b
499b
499b
499b
499c
499c
499c
—
93
95
95
96
88
90
93
—
para-Methyl benzyl alcohol
ortho-Methyl benzyl alcohol
1-Phenylethanol
Diphenylmethanol
4-Biphenylmethanol
60
180
180
180
499c
499c
0c
ortho-Chlorobenzyl alcohol
para-(Trifluoromethyl) benzyl alcohol
a
b
c
For reaction conditions, see Table 1 footnote a. Determined by GC. Determined by H NMR.
1
by increasing the reaction time and temperature (Table 4,
Notes and references
entries 6 and 7). Most interestingly, the reaction of chloro-
benzyl alcohol with para-xylene resulted in a spectacular yield
(93%). It is worth noting that the latter reaction is one of the
few successful Friedel–Crafts benzylation reactions that work
well with deactivated arenes. However, the p-CF3 substituted
benzyl alcohol (Table 4, entry 8) was unreactive under the
conditions used.
1. J. Haber and E. Lalik, Catal. Today, 1997, 33, 119–137.
2. F. Di Gregorio and V. Keller, J. Catal., 2004, 225, 45–55.
3. O. Y. Gutierrez, F. Perez, G. A. Fuentes, X. Bokhimi and
T. Klimova, Catal. Today, 2008, 130, 292–301.
4. K. Aoki, M. Ohmae, T. Nanba, K. Takeishi, N. Azuma, A. Ueno,
H. Ohfune, H. Hayashi and Y. Udagawa, Catal. Today, 1998, 45,
29–33.
5. X. W. Lou and H. C. Zeng, Chem. Mater., 2002, 14,
4781–4789.
6. W. Y. Li, F. Y. Cheng, Z. L. Tao and J. Chen, J. Phys. Chem. B,
2006, 110, 119–124.
7. S. T. Wang, Y. G. Zhang, W. Z. Wang, G. L. Li, X. C. Ma,
X. B. Li, Z. D. Zhang and Y. T. Qian, J. Cryst. Growth, 2006, 290,
96–102.
8. W. Chen, L. Q. Mai, Y. Y. Qi and Y. Dai, J. Phys. Chem. Solids,
2006, 67, 896–902.
X-Ray diffraction patterns showed that MP, as well as
MC-MoO3, exhibiting typical (020), (110), (021) and (111) planes
(JCPDS #05-0508), were a-phases (ESI Fig. S1w). Field emission
scanning electron microscopy (FE-SEM) showed that both MP
and MC-MoO3 had a pellet morphology (ESI Fig. S3w). The MP
catalyst had
a narrow distribution of 400–500 nm and
MC-MoO3 had a broad distribution of 1–2 mm. Notably, the
thickness of MP was ca. 30 nm, which is much smaller than that
of MC-MoO3 (ca. 800 nm) and the other catalysts. The excellent
performance of the MP catalyst is attributed to the increased
number of surface defect sites, generated by the remarkable
reduction of particle dimensions to nanoscale. The light blue
colour of the MP catalyst indicates the existence of specific point
defects, such as F centres.23,24 It has been reported that such sites
could efficiently catalyze the activation of benzylic C–OH
bonds.17,25 We evaluated p-Me, p-H and p-CF3 substituted
benzyl alcohols in a one-pot competitive test (ESI Fig. S4w).
The rate ratio of the p-Me reaction over the p-H reaction after
2.5 min was 38, indicating that the formation of a carbocation
intermediate may be involved at some stage.26 The heterolytic
cleavage of the PhCH2–OH bond on defect sites leads to the
formation of the carbocation species, which further reacts with
an arene molecule to form the product.
9. P. Badica, Cryst. Growth Des., 2007, 7, 794–801.
10. G. A. Olah, Friedel–Crafts Chemistry, Wiley, New York,
1973.
11. M. Noji, Y. Konno and K. Ishii, J. Org. Chem., 2007, 72,
5161–5167.
12. M. Rueping, B. J. Nachtsheim and W. Ieawsuwan, Adv. Synth.
Catal., 2006, 348, 1033–1037.
13. K. Mertins, I. Iovel, J. Kischel, A. Zapf and M. Beller, Angew.
Chem., Int. Ed., 2005, 44, 238–242.
14. K. Motokura, N. Nakagiri, T. Mizugaki, K. Ebitani and
K. Kaneda, J. Org. Chem., 2007, 72, 6006–6015.
15. B. M. Devassy, G. V. Shanbhag, F. Lefebvre, W. Bohringer,
J. Fletcher and S. B. Halligudi, J. Mol. Catal. A: Chem., 2005, 230,
113–119.
16. Y. X. Rao, M. Trudeau and D. Antonelli, J. Am. Chem. Soc.,
2006, 128, 13996–13997.
17. B. M. Choudary, R. S. Mulukutla and K. J. Klabunde, J. Am.
Chem. Soc., 2003, 125, 2020–2021.
18. K. Yamashita, M. Hirano, K. Okumura and M. Niwa, Catal.
Today, 2006, 118, 385–391.
19. S. K. Jana, Catal. Surv. Asia, 2005, 9, 25–34.
20. L. Fang, Y. Y. Shu, A. Q. Wang and T. Zhang, J. Phys. Chem. C,
2007, 111, 2401–2408.
21. T. Mizushima, K. Fukushima, H. Ohkita and N. Kakuta, Appl.
Catal., A, 2007, 326, 106–112.
22. M. J. Jones, Jr, Organic Chemistry, W. W. Norton & Company,
New York, 1997, pp. 203–204.
23. G. Pacchioni, Surf. Rev. Lett., 2000, 7, 277–306.
24. F. Cinquini, C. Di Valentin, E. Finazzi, L. Giordano and
G. Pacchioni, Theor. Chem. Acc., 2007, 117, 827–845.
25. K. K. Zhu, J. C. Hu, C. Kubel and R. Richards, Angew. Chem.,
Int. Ed., 2006, 45, 7277–7281.
In summary, we have demonstrated that nanostructured
MoO3 (MP) can efficiently catalyze the benzylation of a broad
range of arenes, with various benzylic alcohols as alkylating
agents. The catalytic reaction is clean and quick, which enables
the method to be feasible at either the bench or pilot plant
level. Further research will be devoted to broadening the
application of the catalyst into other reactions and investigat-
ing the mechanisms involved.
F. Wang would like to acknowledge the Japan Science and
Technology Agency (CREST-JST) for financial support.
26. K. A. Conners, Chemical Kinetics: The Study of Reaction Rates in
Solution, VCH Publishers, New York, 1990.
ꢀc
This journal is The Royal Society of Chemistry 2008
3198 | Chem. Commun., 2008, 3196–3198