Silica-supported 4-OH-TEMPO/NOx: A novel and efficient catalyst for aerobic oxidation of alcohols

Article abstract of DOI:10.1080/00397911.2013.827207

Silica-supported 4-OH-2,2,6,6-tetramethylpiperidyl-1-oxy/NO_x (4-OH-TEMPO was immobilized on the surface of silica using the sol-gel method, and then it adsorbed NO_x), as a heterogeneous catalyst, has exhibited good catalytic performance in alcohol oxidation. A broad range of alcohols were oxidized to their corresponding aldehydes or ketones with more than 99% selectivity and 99% conversion rate by such a catalyst system at room temperature in air. NO_x not only acted as an electron bridge between O₂ and 4-OH-TEMPO but also were conducive to the formation of the aldehydes as active component. A possible mechanism for oxidation of alcohols promoted by silica-supported 4-OH-TEMPO/NO_x was supposed. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.] Copyright

Full text of DOI:10.1080/00397911.2013.827207

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
This article was downloaded by: [Washington University in St Louis]
On: 07 October 2014, At: 12:43
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Silica-Supported 4-OH-TEMPO/NOx: A
Novel and Efficient Catalyst for Aerobic
Oxidation of Alcohols
Hua Zhang a & Luoling Fu b
a Dalian University of Technology, State Key Laboratory of Fine
Chemicals , Dalian , China
b Dalian University of Technology , Dalian , China
Accepted author version posted online: 28 Oct 2013.Published
online: 27 Dec 2013.
To cite this article: Hua Zhang & Luoling Fu (2014) Silica-Supported 4-OH-TEMPO/NOx: A
Novel and Efficient Catalyst for Aerobic Oxidation of Alcohols, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 44:5, 610-619, DOI:
10.1080/00397911.2013.827207
To link to this article: http://dx.doi.org/10.1080/00397911.2013.827207
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Synthetic Communications1, 44: 610–619, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.827207
SILICA-SUPPORTED 4-OH-TEMPO/NOX: A NOVEL AND
EFFICIENT CATALYST FOR AEROBIC OXIDATION OF
ALCOHOLS
Hua Zhang1 and Luoling Fu2
1Dalian University of Technology, State Key Laboratory of Fine Chemicals,
Dalian, China
2Dalian University of Technology, Dalian, China
GRAPHICAL ABSTRACT
Abstract Silica-supported 4-OH-2,2,6,6-tetramethylpiperidyl-1-oxy/NOx (4-OH-TEMPO
was immobilized on the surface of silica using the sol-gel method, and then it adsorbed NOx),
as a heterogeneous catalyst, has exhibited good catalytic performance in alcohol oxidation.
A broad range of alcohols were oxidized to their corresponding aldehydes or ketones with more
than 99% selectivity and 99% conversion rate by such a catalyst system at room temperature
in air. NOx not only acted as an electron bridge between O2 and 4-OH-TEMPO but also
were conducive to the formation of the aldehydes as active component. A possible mechanism
for oxidation of alcohols promoted by silica-supported 4-OH-TEMPO/NOx was supposed.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords Alcohol oxidation; molecular oxygen; NOx; sol-gel; TEMPO
INTRODUCTION
The selective oxidation of alcohols to the corresponding carbonyl compound
is a fundamental transformation in organic synthesis reactions.[1–3] Traditionally,
numerous stoichiometric amounts of chromium and manganese reagents[4] have been
Received June 8, 2013.
Address correspondence to Hua Zhang, State Key Laboratory of Fine Chemicals, Dalian 116012,
China. E-mail: zhanghua@dlut.edu.cn
610

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
AEROBIC HETEROGENEOUS OXIDATION OF ALCOHOLS
611
Scheme 1. Alcohol oxidation with silica-supported 4-OH-TEMPO=NOx system.
employed to accomplish this transformation. However, along with these processes,
considerable problems, such as use of expensive reagents and serious effluent dis-
posal problem, appear. To resolve these problems, molecular oxygen as the terminal
oxidant for alcohol oxidation has attracted much attention in recent years.[5–7]
Many highly efficient catalysts for the aerobic oxidation of alcohols using transition
metals (such as copper salts, palladium, and ruthenium complexes)[8–12] have been
developed recently. Furthermore, catalytic systems consisting of 2,2,6,6-
tetramethylpiperidyl-1-oxy (TEMPO) for the selective aerobic oxidation of alcohols
under mild conditions proved more efficient.
In the past two decades, many impressive in the combinations of diversified
cocatalysts[13] with TEMPO in alcohol oxidation have been reported. The cocatalysts
can be divided into two groups: transition-metal compounds [Fe(NO3)3, FeCl3, Cu
(I) salts, Cu (II) salts, Ru complexes, etc.] and non-transition- metal compounds
(NaNO2, t-BuONO, m-CPBA).[14,15] These catalysts have several advantages, such
as good selectivity. However, they still suffer from drawbacks, such as multistep
synthesis, tedious workup procedure for the recovery of the final products, due to
homogeneous complex catalysts, and generation of copious amounts of toxic
heavy-metal or halogen waste. Compared to homogeneous catalysts, heterogeneous
catalysts have inherent advantages: easy separation and easy handling properties.
There were also some reports on immobilized TEMPO (TEMPO immobilized on
MCM-41, SBA-15, etc.), which combined with electron transfer compounds [such
as tert-butyl nitrite (TBN), 1,3-dibromo-5,5-dimethylhydantoin (DBDMH), etc.]
and exhibited good performance in selective oxidation of alcohols.[16–24] Hence, in
view of atom economy, development of an efficient and selective heterogeneous
catalyst that could utilize molecular oxygen as oxidant in alcohol translation under
mild conditions is highly desirable.
Our previous work reported on the PSB-TEMPO-NOx system,[25] and we herein
focus on developing catalysis system (silica-supported 4-OH-TEMPO=NOx), in
which 4-OH-TEMPO was immobilized on the surface of silica by using the sol-gel
method and then absorbing molecular nitrogen oxide (NOx), with activated molecu-
lar oxygen as oxidant in alcohol oxidation. In the presence of silica supported
4-OH-TEMPO=NOx, many benzylic alcohols and secondary alcohols can be oxidized
to their corresponding aldehydes or ketones in 7 h with more than 99% conversion
and about 99% selectivity just at room temperature in an air atmosphere (Scheme 1).
RESULTS AND DISCUSSION
Characterization of Catalyst
The degree of functionalization of silica-supported 4-OH-TEMPO was calcu-
lated on the basis of the nitrogen content in the catalyst (Table 1, entry 1), the final