186
J.U. Ahmad et al. / Applied Catalysis A: General 411–412 (2012) 180–187
3.6. Oxidation of other alcohols catalyzed by CuSO4/TEMPO/1
system
compounds. The ligand modified system was also highly selec-
tive as no overoxidation of aldehydes to carboxylic acids was
observed.
A series of other alcohols was selected to study the influ-
ence of different substituents on the phenyl ring. When reaction
conditions are optimized for each alcohol, in general all ben-
zylic alcohols are nearly quantitatively converted to aldehydes
without overoxidation regardless the type, position and num-
ber of the substituents (Table 4, entries 2–7). Oxidations of such
alcohols have been recently reported to be catalyzed also by a
Cu–diphenoxydiamine complex with H2O2 [5]. However, with this
of high excess of H2O2 (10 eq. to substrate). The ligand assisted
catalyst oxidizes efficiently cinnamyl alcohol to the correspond-
ing ␣,-unsaturated aldehyde without affecting the double bond
(Table 4, entry 8) unlike the CuSO4 system (see Table 2, entry
6).
Despite of successful oxidation of primary benzylic and -
activated alcohols with the ligand modified catalyst, secondary
alcohol, an example of heterocyclic alcohol, is also smoothly con-
verted to the aldehyde in moderate conversion (Table 4, entry 11).
With 2-pyridine methanol only a very low conversion is obtained
(Table 4, entry 12) due to the formation of a new complex with
overoxidized product, i.e., picolinic acid. After the oxidation with
H2O2, blue crystals suitable for X-ray crystallography measure-
ment were isolated and identified as the Cu complex of picolinic
acid (m/z 307 for C12H8CuN2O4). It is worth noting that the ligand-
assisted system is highly selective toward primary benzylic and
allylic alcohols as secondary benzylic alcohols are oxidized in poor
conversions. Primary and secondary aliphatic alcohols are barely
active or totally inactive with both systems. On the other hand,
CuSO4 system alone has high activities and selectivities toward
secondary alcohols.
Acknowledgment
The financial support of the Graduate School of Inorganic Mate-
rial Chemistry is gratefully acknowledged.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
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