Paper
RSC Advances
ether was less than 2% under a nitrogen atmosphere or in the Strategic Priority Research Program of Chinese Academy of
absence of a catalyst (Table 1, entries 2 and 3). In addition, Sciences (XDB17020300).
phenyl benzoate was also made to serve as a substrate. Unex-
pectedly, the percent conversion in this case was much lower
(16%) than that of benzyl phenyl ether. What is more, there was
no benzaldehyde product, and only very small amounts (<2%) of
Notes and references
benzoic acid, phenol and phenyl salicylate were detected (Table
1, entry 4). This result suggested that phenyl benzoate was not
likely the intermediate during the oxidation of benzyl phenyl
ether. In the reaction, the aromatic ring of the benzyl phenyl
ether substrate might have interacted with Lewis acid sites of
the vanadium catalyst21 and thus have had an orienting effect
even when the acid–aromatic interaction was not the dominant
effect.22 The a-carbon–ether linkage of benzyl phenyl ether was
therefore more likely susceptible to being oxidatively than
under other systems.
In addition, an oxidation reaction in a mixture of acetic acid
and acetic anhydride was conducted. Aer 1 h of reaction,
a hemiacetal acetate-like (a-phenoxybenzyl acetate) structure
was detected using GC-MS (ESI, Fig. S9†). This interesting
result of the same presence of benzaldehyde and the discus-
sions above allowed us to propose a reasonable reaction
pathway. That is, in the oxidation of benzyl phenyl ether, the
Ca–H bond of the phenyl ether was the bond preferentially
subjected to oxidative hydroxylation. A hemiacetal structure
was obtained, and then further C–O bond cleavage proceeded
smoothly. This result for the oxidation of benzyl phenyl ether
was in good accordance with the strategy we proposed above.
Formation of a hemiacetal-like structure via oxidation of the
Ca–H bond of aralkyl aryl ethers could promote the aryl ether
bond cleavage. Furthermore, we also studied the catalytic
oxidation of the b-O-4 model [1-(3,4-dimethoxyphenyl)-2-(2-
methoxyphenoxy)propane-1,3-diol] with the VO(acac)2/CH3-
COOH system. The corresponding benzaldehyde (3,4-dime-
thoxybenzaldehyde) was indeed detected among the cleavage
products. A more detailed study of the oxidative degradation of
actual lignin is underway.
1 C. O. Tuck, E. Perez, I. T. Horvath, R. A. Sheldon and
M. Poliakoff, Science, 2012, 337, 695–699.
2 R. D. Perlack and B. J. Stokes, U.S. Billion-Ton Update:
Biomass Supply for a Bioenergy and Bioproducts Industry,
Oak Ridge National Laboratory, Oak Ridge, TN, 2011, pp.
1–227.
3 (a) A. L. Marshall and P. J. Alaimo, Chem.–Eur. J., 2010, 16,
4970–4980; (b) K. Y. Chen, M. Tamura, Z. L. Yuan,
Y. Nakagawa and K. Tomishige, ChemSusChem, 2013, 6,
613–621; (c) Y. Nakagawa, S. B. Liu, M. Tamura and
K. Tomishige, ChemSusChem, 2015, 8, 1114–1132; (d)
R. A. Sheldon, Chem.–Eur. J., 2016, 22, 1–17; (e) X. Chen,
B. Zhang, Y. Z. Wang and N. Yan, Chimia, 2015, 69, 120–
124; (f) Y. Z. Wang, S. De and N. Yan, Chem. Commun.,
2016, 52, 6210–6224; (g) M. Besson, P. Gallezot and
C. Pinel, Chem. Rev., 2014, 114, 1827–1870.
4 (a) J. Zakzeski, P. C. Bruijnincx, A. L. Jongerius and
B. M. Weckhuysen, Chem. Rev., 2010, 110, 3552–3599; (b)
C. Z. Li, X. C. Zhao, A. Q. Wang, G. W. Huber and
T. Zhang, Chem. Rev., 2015, 115, 11559–11624; (c)
J. E. Holladay, J. F. White, J. J. Bozell and D. Johnson, Top
Value-Added Chemicals from Biomass-Volume II—Results of
Screening for Potential Candidates from Biorenery Lignin.
PNNL-16983, Pacic Northwest National Laboratory,
Richland, WA, 2007; (d) F. G. Calvo-Flores and
J. A. Dobado, ChemSusChem, 2010, 3, 1227–1235; (e)
J. J. Bozell, Top. Curr. Chem., 2014, 353, 229–255; (f)
C. P. Xu, R. A. Arancon, J. Labidi and R. Luque, Chem. Soc.
Rev., 2014, 43, 7485–7500.
5 (a) J. M. Nichols, L. M. Bishop, R. G. Bergman and
J. A. Ellman, J. Am. Chem. Soc., 2010, 132, 12554–12555; (b)
M. V. Galkin, S. Sawadjoon, V. Rohde, M. Dawange and
J. S. M. Samec, ChemCatChem, 2014, 6, 179–184; (c)
Y. S. Kim, H.-m. Chang and J. F. Kadla, Holzforschung,
2008, 62, 38–49; (d) J. K. Mobley, S. G. Yao, M. Crocker and
M. Meier, RSC Adv., 2015, 5, 105136–105148.
6 (a) A. Rahimi, A. Ulbrich, J. J. Coon and S. S. Stahl, Nature,
2014, 515, 249–252; (b) W. P. Deng, H. X. Zhang, X. J. Wu,
R. S. Li, Q. H. Zhang and Y. Wang, Green Chem., 2015, 17,
5009–5018; (c) J. Mottweiler, M. Puche, C. Rauber,
T. Schmidt, P. Concepcion, A. Corma and C. Bolm,
ChemSusChem, 2015, 8, 2106–2113; (d) Y. J. Gao,
J. G. Zhang, X. Chen, D. Ma and N. Yan, ChemPlusChem,
2014, 79, 825–834; (e) R. Zhu, B. Wang, M. S. Cui, J. Deng,
X. L. Li, Y. B. Ma and Y. Fu, Green Chem., 2016, 18, 2029–
2036.
Conclusions
In summary, benzaldehyde was found to form during the
vanadium-catalyzed oxidative cleavage of 2-phenoxy-1-
phenylethanol (1) in acetic acid, and various aspects of this
result have been discussed. A new strategy for catalytic oxida-
tion cleavage of aryl ethers in aralkyl aryl ethers involving
a hemiacetal-like structure was proposed. Prior formation of
hemiacetal-like structures via oxidation of the Ca–H bond in
aralkyl aryl ethers would facilitate aryl ether bond cleavage
under mild reaction conditions. This work should contribute to
a better understanding and design of novel catalytic oxidative
strategies for the specic cleavage of dened linkages in lignin
models or even lignin itself.
7 (a) P. Ferrini and R. Rinaldi, Angew. Chem., Int. Ed., 2014, 53,
8634–8639; (b) Q. Song, F. Wang, J. Y. Cai, Y. H. Wang,
J. J. Zhang, W. Q. Yu and J. Xu, Energy Environ. Sci., 2013,
6, 994–1007; (c) J. G. Zhang, J. Teo, X. Chen, H. Asakura,
T. Tanaka, K. Teramura and N. Yan, ACS Catal., 2014, 4,
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21473184 and 21233008) and the
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 110229–110234 | 110233