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acid used, the solvolysis of cellulose would be mainly catalyzed
by sulfonic acids in the mixed-acid systems.
Notes and references
1 J. J. Bozell, L. Moens, D. C. Elliott, Y. Wang, G. G. Neuenscwander,
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Morley, J. Smith and P. A. Stevenson, WO 44960, 2005; T. Tanaka, K.
Takahashi, Y. Hotta, Y. Takeuchi and M. Konnai, U.S. Pat. 5298482,
1994.
The reaction from sugars to methyl levulinate proceeds even
at the lower temperatures. Comparison of the effects of In(OTf)3
and PTSA on the reaction of glucose at 160 ◦C showed that the
former catalyzed the formation of methyl levulinate much faster
than the latter (eqn (2)). This result also suggests that this step
should be mainly catalyzed by In(OTf)3.
2 T. Werpy and G. Petersen, ed., Top Value Added Chemicals from
Biomass: Volume 1—Results of Screening for Potential Candidates from
Sugars and Synthesis Gas, National Renewable Energy Laboratory,
Golden, CO, 2004.
3 Grote and Tollens, Ann., 1875, 175, 181.
4 B. F. McKenzie, Org. Synth., 1929, 9, 50.
(2)
5 R. W. Thomas and H. A. Schuette, J. Am. Chem. Soc., 1931, 53, 2324;
J. Dahlmann, Chem. Ber., 1968, 101, 4251; Y. Nakamura, JP Pat. S55-
87741, 1980; J. Jow, G. L. Rorrer, M. C. Hawley and D. T. A. Lamport,
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When the above In(OTf)3-catalyzed reaction of glucose was
stopped after 1 h, a trace amount of 5-methoxymethylfurfural
was also observed, which appears to be an intermedi-
ate for the methyl levulinate formation.9 Further investi-
gation on the reaction mechanism is in progress in our
laboratory.
In summary, the combination of group 13 metal triflates and
sulfonic acids synergistically catalyzes the formation of methyl
levulinate from cellulose. The reaction proceeds in two steps;
cellulose is solvolyzed to sugars, which are readily converted to
methyl levulinate. The former step is mainly catalyzed by sulfonic
acids, and the latter by the metal triflates.
6 S. W. Fitzpatrick, U.S. Pat. 5608105, 1997.
7 K. Seri, T. Sakaki, M. Shibata, Y. Inoue and H. Ishida, Bioresour.
Technol., 2002, 81, 257; L.-P. Peng, L. Lin, J. Zhang, J. Zhuang, B.
Zhang and Y. Gong, Molecules, 2010, 15, 5258; J. Hegner, K. C.
Pereira, B. DeBoef and B. L. Lucht, Tetrahedron Lett., 2010, 51, 2356.
8 General procedure for the synthesis of methyl levulinate from cellulose:
A stainless steel autoclave was charged with In(OTf)3 (Aldrich,
0.02 mmol), PTSA (Nacalai, 0.1 mmol), microcrystalline cellulose
(Aldrich, 2.5 mmol as a glucose unit), MeOH (20 mL). After the
autoclave was charged with N2 (0.5 MPa), it was heated at 180◦C
for 5 h with stirring. After the resulting solution was cooled to room
temperature, it was analyzed with HPLC.
ˇ
9 J. Horvat, B. Klaic´, B. Metelko and V. Sunjic´, Tetrahedron Lett., 1985,
26, 2111.
812 | Green Chem., 2011, 13, 810–812
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