Catalytic application of fluorous silica gel in Fries rearrangement

Article abstract of DOI:10.1016/j.jfluchem.2014.01.005

Commercially available fluorous silica gel (Fluoro Flash) with no further post-modification was successfully investigated and applied merely as a catalyst in Fries rearrangement of various aryl esters under solvent free conditions in 4 h and optimized temperatures. In addition to good yields and recyclability of the catalyst, toxicity of reaction medium, by-products, and wastes were minimized. Also, low catalyst loading was another advantage of this methodology.

Full text of DOI:10.1016/j.jfluchem.2014.01.005

Journal of Fluorine Chemistry 160 (2014) 77–81
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Catalytic application of fluorous silica gel in Fries rearrangement
*
Mohammad Ghaffarzadeh , Maryam Ahmadi
Chemistry and Chemical Engineering Research Center of Iran (CCERCI) , P.O. Box 14335-186, Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Commercially available fluorous silica gel (Fluoro FlashTM) with no further post-modification was
successfully investigated and applied merely as a catalyst in Fries rearrangement of various aryl esters
under solvent free conditions in 4 h and optimized temperatures. In addition to good yields and
recyclability of the catalyst, toxicity of reaction medium, by-products, and wastes were minimized. Also,
low catalyst loading was another advantage of this methodology.
Article history:
Received 27 November 2013
Received in revised form 5 January 2014
Accepted 8 January 2014
Available online 20 January 2014
ß 2014 Elsevier B.V. All rights reserved.
Keywords:
Fluorous silica gel (Fluoro FlashTM
Fries rearrangement
Aryl esters.
)
1. Introduction
Therefore, these supports can be either a potent candidate in
catalyzing the reactions. However, application of mere FSGs are
The original Fries rearrangement was published by Fries and
Finck more than 100 years ago in which p-cresyl chloroacetate was
heated to 140 8C in the presence of AlCl3 [1]. This rearrangement is a
significant synthetic strategy for the preparation of biologically and
medicinally interesting acylated scaffolds [2,3]. Fries rearrangement
has been reported with many homogenous catalysts such as
polyphosphoric acid, MeSO3H/POCl3, montmorillonite clays,
Hf(OTf)4, ZrCl4, Sc(OTf)3, and TiCl4 [4–10]. These procedures require
a prohibitively large amountof a Lewis or Brønsted acid(e.g., AlCl3 or
H2SO4) which result in larger amount of waste materials and cause
to a strong corrosion [11,12]. In addition, homogenous catalysts are
unrecoverable. To overcome this problem, much effort has been put
into developing heterogeneous catalysts in Fries rearrangement
such as solid catalysts [11–14]. Heteropolyacids (HPAs), such as
H3PW12O40 (PW), Cs2.5H0.5PW12O40 (CsPW), H-beta, and ion-
exchange resins (Amberlyst-15, Nafion-117) are examples of
heterogeneous solid acid catalysts for Fries reaction [15–17].
In recent years, fluorous silica gel [18] (FSG) has been
successfully applied as a solid support for heterogeneous catalyst
in the organic reactions such as carbon-carbon couplings [19,21],
protection [22], N-formylation [23]. However, FSG itself can be
used merely without any post-modifications due to its highly
active surface by perfluoroalkyl chains bonded to the surface of
silica gel [24]. There have been many reports which confirm the
catalytic activity of fluorous compounds such as fluorous solvents
and their roles when dispersed on silica solid supports [25–28].
only limited to extraction and separation in synthetic chemistry
[24]. In the present study, we have introduced the FSG (Fluoro
FlashTM) as a recoverable, highly active, and economical catalyst
for the Fries rearrangement.
2. Results and discussion
Over the last decade, development of FSGs applications have
been enhanced as absorbents and catalytic support [20–24,29].
Although, FSGs are suitable supports in various organic reactions
due to exceptional nature of fluorous compounds, their modifica-
tions are sometimes difficult, costly, or time consuming. These
disadvantages are drawbacks of their large scale production and
industrialization. Therefore, development of available and low cost
catalysts as potent as fluorous-tagged catalysts which are
immobilized on the FSG surface (e.g. efficiency, recyclability,
etc.) can surpass these problems. Hence, we studied and developed
the catalytic application of unmodified FSG, which is available
under the commercial name of Fluoro FlashTM, in Fries rearrange-
ment of various aryl esters. Mechanism of rearrangement when
catalyzed by FSG is not clear yet. However, it can be proposed that
silica surface due to having perfluoroalkyl chains on the surface
tends to share its fluorine atoms in hydrogen bonding which affect
on the acidity of silanol groups and cause to increase their O–H
acidity [30]. In addition, perfluoroakyl chains may directly undergo
a strong interaction with reactants (Scheme 1).
Results showed the FSG as a green, recyclable, highly efficient
and readily available catalyst in the present process. To show the
unique catalytic behavior of FSG, the non-fluorinated silica gel (SG)
and FSG were compared in Fries rearrangement by a model
*
Corresponding author.
E-mail address: mghaffarzadeh@ccerci.ac.ir (M. Ghaffarzadeh).
0022-1139/$ – see front matter ß 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2014.01.005

78
M. Ghaffarzadeh, M. Ahmadi / Journal of Fluorine Chemistry 160 (2014) 77–81
Scheme 1. Proposed mechanism for surface interaction of FSG with reactant.
reaction (Entry 1) under the similar conditions. The results showed
no reaction when catalyzed by SG (Scheme 2). After sufficient
studies, the optimal conditions for each substrate and the
rearranged product are shown in Table 1. During the synthesis
of diverse derivatives of aryl esters, diacylated biphenols showed a
different behavior in Fries rearrangement and only one of the acyl
groups underwent migration and another acetyl group hydrolyzed
(Entry 9–11) [31].
Scheme 2. Fries rearrangement of aryl ester in the presence SG and FSG.

M. Ghaffarzadeh, M. Ahmadi / Journal of Fluorine Chemistry 160 (2014) 77–81
79
Table 1
Optimal conditions for Fries rearrangement of aryl esters catalyzed by FSG.
O
OH
R'
O
O
i
FSG, neat
4 h
R
+
Ph
O
Cl
R'
solventless
R
1-11a
OH
74-90%
1-11b
Entrya
1
R0
R
Product
Yield (%)
80
Temperature (8C)
Ph
H
80
O
HO
2
3
Ph
Ph
4-Me
85
85
80
80
O
H3C
OH
O
4-Cl
Cl
OH
4
Ph
4-NO2
–
80–120
OH
O
NO2
5
6
b
-naphtyl
H
H
75
85
80
80
HO
O
Me
Me
HO
O
O
7
8
4-Cl
90
74
80
80
Cl
HO
HO
Me
4-Me
O
O
9
Me
Me
3-OH
2-OH
77
77
80
80
HO
HO
OH
O
10
OH

80
M. Ghaffarzadeh, M. Ahmadi / Journal of Fluorine Chemistry 160 (2014) 77–81
Table 1 (Continued )
O
OH
R'
O
O
i
FSG, neat
4 h
R
+
Ph
O
Cl
R'
solventless
R
1-11a
OH
74-90%
1-11b
Entrya
11
R0
Me
R
Product
Yield (%)
80
Temperature (8C)
4-OH
80
OH
O
OH
a
Reaction conditions: (i) Catalyst free, 30 min, (ii) 10 mmol substrate and 1 g FSG was reacted in solvent free conditions in 4 h.
Table 4
Recyclability studies based on the yield of model reaction (Entry
Temperature optimization of Fries rearrangement.
1) was achieved. As shown in Table 2, this catalyst has been
recycled and used at least for six times with low decrease in the
yield.
Temperature (8C)
Yield
Rt
64
66
70
80
80
80
Solvent effect on the reaction was also studied. Several solvents
such as THF, n-hexane, ethanol, water, and dioxane were tested
with one model reaction under the same conditions (Entry 1). In
this case, the reaction conditions were the same as discussed in 4.2
except that FSG was suspended with 2 mL of every solvent and
then added to the mixture of reaction. Due to the fact that the most
efficient solvent yield was close to neat conditions, therefore
solvent free method was selected as optimal conditions (Table 3).
Obtained results from GC chromatography showed that when
water was used as the solvent, the major amount (ꢀ>97) of aryl
esters convert to product with good yield and remaining substrate
to hydrolyzed form of corresponding acid and phenol, and only few
amount of substrate stayed unreacted. However, when neat
approach was incorporated into Fries rearrangement, no more
hydrolysis occurred and therefore unreacted substrate remained
intact. It was one of our reasons for selecting neat conditions.
Temperature was optimized by the model reaction under the
similar conditions for Fries rearrangement. According to this
50
60
80
90
100
investigation, 80 8C was optimized temperature for Fries rear-
rangement (Table 4).
3. Conclusion
According to recent advances in the properties of fluorinated
materials such as their solvents and fluorous supports, etc., the
present work features the potential catalytic activity of unmodified
FSG in Fries rearrangement. In addition, simplicity, reusability, low
cost of preparation, and high efficiency of this catalyst led to
unique catalyst among the other similar catalysts. It can also be
concluded that discovering catalytic activity of FSG may be an
impact in studying it for further similar organic reactions.
Table 2
4. Experimental
Results of 8 times recycle for Fries rearrangement.
4.1. Chemicals and apparatus
Number of recycles
Yield (%)
1
2
3
4
5
6
7
8
80
80
80
80
79
79
75
75
All reagents were obtained from Merck (Germany) and Fluka
(Switzerland) and were used without further purification. Melting
points were measured by an Electrothermal 9100 apparatus.
Progress of reactions was monitored by thin layer chromatography
(TLC). IR spectra were recorded on Bruker, Vector 22 spectrometer;
absorbance is reported in cmꢁ1 1H NMR spectra were run on
.
Bruker DRX-500 AVANCE spectrometer at 500 MHz in CDCl3. Mass
analyses were achieved by Fison Instruments TIRO 1000-GC 8000-
GC/MS.
Table 3
Solvent effect study on the Fries rearrangement.
4.2. General procedure for Fries rearrangement and catalyst
preparation
Solvent
Yield
THF
64
12
55
75
51
68
80
n-Hexane
Diethylether
Ethanol
Water
Catalyst (FSG) was purchased from Fluorous Technologies Inc.
and used without further purification. Its synthesis procedure is
reported by Curran et al. [24]. General procedure for Fries
rearrangement was done by adding FSG to aryl ester at the ambient
temperatures. Before adding FSG to reaction mixture, aryl esters
Dioxane
–

M. Ghaffarzadeh, M. Ahmadi / Journal of Fluorine Chemistry 160 (2014) 77–81
81
were obtained by in situ formation through the reaction of acyl
chloride derivatives and phenol derivatives. Thus, to a 100 ml round
bottom flask stirring by a magnetic bar 10 mmol of phenols was
added and then, 10 mmol of acyl chloride derivatives (for catechols
20 mmol) was added dropwise and allowed to react at room
temperature. After 30 min, temperature was raised to remove HCl
fromreactionmixture.Then1 gofFSGwasaddedtoreactionmixture
at ambient temperature. After 4 h heating at appropriate tempera-
tureinoilbath,thereactionmixturewascooledtoroomtemperature
and washed with dichloromethane. The catalyst was separated by
filtration. The solvent was removed by rotary evaporator and
resulting mixture was separated by column chromatography
(stationary phase: silica-gel, eluent:hexane:ethyl acetate) and
purified by recrystallization. All isolated products successfully gave
related spectral data of IR, NMR, and mass spectrometers.
J = 8.90 Hz), 7.06 (dd, 1H, J1 = 8.90 Hz, J2 = 2.94 Hz), 7.20 (d, 1H,
J = 2.94 Hz), 11.75 (s, 1H); IR (KBr,
, cmꢁ1): 3246, 3057, 2850,
1616, 1577; MS, m/z: 152 (M+), 137, 136, 109, 77, 42, 28, 15.
y
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