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10.1002/asia.201700846
Chemistry - An Asian Journal
FULL PAPER
Phosphorylated Polyacrylonitrile Fiber as an Efficient and
Greener Acetalization Catalyst
Gang Xu,[a] Jian Cao,[a] Yali Zhao,[a] Lishuo Zheng,[a] Minli Tao*[a] and Wenqin Zhang*[a,b]
Abstract: A novel solid acid catalyst (PANEAPF) was developed by
immobilization of phosphoric acid on polyacrylonitrile fiber via
covalent bond. Various characterization techniques such as
elemental analysis (EA), X-ray photoelectron spectroscopy (XPS),
Fourier transform infrared spectroscopy (FTIR), etc. were utilized to
confirm the successful grafting and the stability of the fiber catalysts
during application. The PANEAPF showed high catalytic activity in the
acetalization of aldehydes due to the high utilization efficiency of its
functionalized acid sites. Besides, the strong polarity micro-
environment in the surface layer of the PANEAPF make it highly
suitable for catalytic application no matter in water or alcohol.
Furthermore, the fiber catalyst can be applied to acetalization of
aldehydes in a continuous flow process at room temperature, and
shows excellent reactivity and superior recyclability (over 20 times).
In a word, many advantages of the PANEAPF such as simple
preparation, convenient acid amount regulatability, high durability,
and eco-friendly process make it very attractive for fixed-bed
reactors in chemical industry.
basis of functionalized materials based on different supports,
there are still many obstacles to restrict its commercial process.
For example, porous materials are more suitable for gas phase
adsorption, but it is difficult for organic phase in aqueous
solution to enter the aperture, which is a limitation during its
application process. Carbon materials such as graphene have
huge potential applications, but the cost is too expensive and the
recycling operation is inconvenient. Besides, the catalytically
active species are immobilized on the surface of silica gel,
leading to a low catalyst loading, which would affect the catalytic
efficiency. Hence, the application of new supports which is more
suitable for green industrial production has acquired increasingly
attention but still remains challenging.
Textiles fiber have been integral to people’s daily life, but the
research in catalysis area is not enough ever. Recently, we
have been interested in employing inexpensive and
commercial synthetic fiber as an excellent support.[10] For
example, in 2011, amine-functionalized polyacrylonitrile fiber
(PANF) was first reported to achieve excellent results in
promoting Knoevenagel condensations.[10a] Then ionic liquids
modified polypropylene fiber (PPF) was applied for the
conversion of fructose to 5-hydroxymethylfurfural.[10b]
Particularly, in 2013, Benjamin List and co-workers reported
that textile nylon-immobilized organocatalysts showed
distinctive stability, activity, and recyclability in many
asymmetric organic transformations.[11] All of these positive
results indicate that textiles are good candidate as catalyst
supports. And as one of the most common synthetic materials,
PANF is a more promising one because of its eminent
properties such as simple preparation, large surface area, low
density and high mechanical intensity. Besides, PANF contains
abundant nitrile groups that can be easily transformed into
various functional moieties (carboxyl, amide, amidoxime,
etc.).[12] Furthermore, textile fibers are easily woven into the
shapes that we need, which can be applied to the current
mainstream of the continuous-flow reactors.[13]
Among various supported catalysts, acid-functionalized solid
catalysts[14] are of great interest because they have many
advantages over their small-molecule counterparts. And they
are much less corrosive and cause fewer disposal problems,
offering an environmentally benign and economical pathway
for the synthesis of chemicals. As a powerful and versatile
metal-free catalyst, phosphoric acid group bear both a Lewis
basic site (P=O) and a Brønsted acidic (P-OH) that can react
cooperatively. To date, chiral phosphoric acid is widely used as
a powerful metal ligand.[15] However, only a few literatures
report the application of phosphoric acid supported materials
as acid catalysts in organic catalysis,[16] and some of the
catalysts present several drawbacks of easy leaching out of
catalytically active centers, rough preparation, and high cost.
Especially, higher acid loading on solid support is still
demanding. Based on these observations and in continuation
of our interest in fiber catalysts, we demonstrate here a simple
Introduction
Small-molecule organocatalysts have the advantages of
accessible catalytic sites, distinct reactivity, and high
selectivity.[1] Nevertheless, further application of small-molecule
organocatalysts in industry is always limited because of the
difficulty associated with separating the catalysts from the
reaction medium, which will cause catalyst loss and
environmental problems.[2] Recently, the immobilization of
organocatalysts on solid supports via robust covalent bonds has
become a very attractive solution with minimum production
waste and maximum catalytic efficiency. It also exhibits many
other merits, such as easy separation and recovery from
reaction system, excellent recycling potential, good stability and
straightforward operation etc.[3] Currently, both established and
emerging solid supports, such as silicas,[4] polymers,[5] zeolites,[6]
metal nanoparticles,[7] graphenes,[8] and metal–organic
frameworks (MOFs)[9] etc. have been applied to meet the
demands of sustainable development and green chemistry.
Although fruitful advancements have been discovered on the
[a]
[b]
Dr. G. Xu, Dr. J. Cao, Ms. Y. Zhao, Mr. L. Zheng, Dr. M. Tao, Prof.
Dr. W .Zhang
Department of Chemistry, School of Science
Tianjin University
Tianjin, 300072, P. R. China.
E-mail: mltao@tju.edu.cn,zhangwenqin@tju.edu.cn
Prof. Dr. W. Zhang
Department of Chemistry, School of Science
Collaborative Innovation Center of Chemical Science and
Engineering.
Tianjin, 300072, P. R. China.
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