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J. Chem. Sci. Vol. 127, No. 8, August 2015, pp. 1485–1489. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0902-2
Silica functionalized Cu(II) catalysed selective oxidation of benzyl
alcohols using TEMPO and molecular oxygen as an oxidant
MANJULLA GUPTA, PANKAJ SHARMA, MONIKA GUPTA∗ and RAJIVE GUPTA
Department of Chemistry, University of Jammu, Jammu-180 006, India
e-mail: monika.gupta77@rediffmail.com
MS received 11 March 2015; revised 20 June 2015; accepted 21 June 2015
Abstract. A general scheme for the oxidation of benzyl alcohols catalyzed by silica functionalized copper
(II) has been designed. TEMPO, a free radical, assists this oxidation that was initiated by molecular oxygen
which converts it to a primary oxidant. This catalytic combination i.e. SiO2-Cu(II) in presence of TEMPO and
oxygen provides excellent results in terms of yields and reaction time. SiO2-Cu(II) was very well characterized
by different spectroscopic techniques such as FTIR, XRD, TGA, XPS, EDAX, SEM, TEM and AAS and is
recyclable upto five times which makes it economically beneficial.
Keywords. Oxidation; copper(II); aminopropyl silica; recyclability; TEMPO; molecular oxygen.
1. Introduction
oxidantsandsolvents,lowyieldsofproducts,useofstrong
bases, less tolerance of functional groups, etc. Keeping
in view of the above said disadvantages of other copper
catalytic systems, we have extended our study for the
oxidation capability of silica functionalized copper (II)
catalyst towards the TEMPO mediated selective oxida-
tion of benzyl alcohols using oxygen as an oxidant.
This catalytic system i.e. SiO2-Cu(II)/TEMPO/O2
proves to be very efficient for the selective synthesis of
aldehydes from benzyl alcohols.
The selective and catalytic oxidation of benzyl alcohols
is a decisive functional group transformation in modern
organicsynthesis and in industrial processes.The signif-
icance of this reaction lies in the fact that aldehydes are
the important key intermediates for the synthesis of other
are also important moieties in plastic additives; process-
ing of perfume and flavouring compounds and for the pre-
paration of aniline dyes in the textile industry.2 In earlier
times, oxidation of alcohols has been carried out using
stoichiometric amounts of chromium (VI) and manga-
nese (VII)3,4 but these methodologies require costly and
toxicsolvents.5 andproducedlargeamountofheavymetal
wastes6 thus making these methods highly undesirable.
In this regard, non-waste producing oxidants like air,
oxygen, hydrogen peroxide are more appealing as they
are environmental friendly and cheap but these oxidants
need to be activated by some cocatalyst.7 Several cata-
lytic systems using transition metal complexes and ter-
minal oxidants are well known.8 The use of persistent
(TEMPO– 2,2,6,6-tetramethylpiperidinyl-1-oxyl, and its
derivatives) or non-persistent (PINO– phthalimide-N-
oxyl)nitroxylradicalsinoxidationreactionsprovestobe
a better solution for various transition metal catalytic
systems.9 Copper as a catalyst is highly selective (which
is the key feature of the reaction) and the uses of copper
catalyticsystemsforthisorganictransformationare very
well known.10 But the use of these systems for oxidation
of alcohols require large reaction times, use of toxic
In this research work, we have used silica function-
alized copper (II) for the aerobic oxidation of benzyl
alcohols using TEMPO as a co-catalyst.
2. Experimental
2.1 Materials and Methods
Silica gel was purchased from ACROSS Organics and
3-aminopropyl(trimethoxy) silane and salicylaldehyde
werepurchasedfrom Sigma Aldrichandwereusedwith-
out further purification. IR spectra of the catalyst and
the synthesized compounds were recorded in the range
of 4,000–300 cm−1 on a Shimadzu Prestige-21 spec-
trophotometer. TGA of the catalyst was obtained on a
Linesis Thermal Analyser. X-ray diffractograms were
recorded in 2 h range of 10–80 on a Panalyticals X’pert
Pro X-ray diffraction spectrometer using CuKα radi-
ation. XPS spectra of the catalyst were recorded on
KRATOS ESCA model AXIS 165 (Resolution). SEM was
recorded on JSM-7600F and TEM was recorded on
Hitachi (H-7500) 120 kV with CCD camera. The atomic
∗For correspondence
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