Synthesis of phenols by using aryldiazonium silica sulfate nanocomposites

Article abstract of DOI:10.1016/j.tet.2017.10.057

The hydrolysis of a new type of diazonium salt immobilized on the surface of silica sulfuric acid was studied in this work. By using diazonium salt nanocomposites, a number of phenol derivatives were synthesized in good yields. In contrast to the previous works, the present procedure was conveniently carried out under mild and solvent-free conditions. The effects of solvent and temperature were studied on the dediazoniation products. The notable advantages of this methodology were operational simplicity, availability of reactants, short reaction time and easy work-up.

Full text of DOI:10.1016/j.tet.2017.10.057

Accepted Manuscript
Synthesis of phenols by using aryldiazonium silica sulfate nanocomposites
Amin Zarei, Leila Khazdooz, Hamidreza Aghaei, Mohammad Mehdi Gheisari,
Shahrzad Alizadeh, Laleh Golestanifar
PII:
S0040-4020(17)31094-3
10.1016/j.tet.2017.10.057
TET 29060
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 16 August 2017
Revised Date: 16 October 2017
Accepted Date: 20 October 2017
Please cite this article as: Zarei A, Khazdooz L, Aghaei H, Gheisari MM, Alizadeh S, Golestanifar L,
Synthesis of phenols by using aryldiazonium silica sulfate nanocomposites, Tetrahedron (2017), doi:
10.1016/j.tet.2017.10.057.
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Graphical Abstract
Synthesis of phenols by using aryldiazonium silica sulfate
nanocomposites
Leave this area blank for abstract info.
a
,
b
c
Amin Zarei, ∗ Leila Khazdooz, Hamidreza Aghaei,
b
c
Mohammad Mehdi Gheisari, Shahrzad Alizadeh
c
and Laleh Golestanifar
a
Department of Science, Fasa Branch, Islamic Azad University, PO Box No. 364, Fasa 7461713591, Fars.
Department of Science, Isfahan (Khorasgan)) Branch, Islamic Azad University, Isfahan 81595-158, Iran.
Department of Chemistry, Shahreza Branch, Islamic Azad University, Shahreza 311-86145, Isfahan, Iran.
b
c
ONa
ON Ar
2
ONa
OH
S
O
S
O
O
S
O
O
S
O
O
O
O
O
O
O
O
O
O
O
HO
HO
1
5-60 min
Si
Si
Si
Si
+ H O
2
Si
Si
Si
Si
+
ArOH
O
O
O
o
60-110 C
O
O
O
Aryldiazonium silica sulfates
2

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Synthesis of phenols by using aryldiazonium silica sulfate nanocomposites
a
,
b
c
b
c
Amin Zarei, ∗ Leila Khazdooz, Hamidreza Aghaei, Mohammad Mehdi Gheisari, Shahrzad Alizadeh
c
and Laleh Golestanifar
a
Department of Science, Fasa Branch, Islamic Azad University, PO Box No. 364, Fasa 7461713591, Fars.
Department of Science, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan 81595-158, Iran.
Department of Chemistry, Shahreza Branch, Islamic Azad University, Shahreza 311-86145, Isfahan, Iran.
b
c
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Type your Abstract text here
2
009 Elsevier Ltd. All rights reserved.
The hydrolysis of a new type of diazonium salt immobilized on the surface of silica sulfuric
acid was studied in this work. By using diazonium salt nanocomposites, a number of phenol
derivatives were synthesized in good yields. In contrast to the previous works, the present
procedure was conveniently carried out under mild and solvent-free conditions. The effects of
solvent and temperature were studied on the dediazoniation products. The notable advantages of
this methodology were operational simplicity, availability of reactants, short reaction time and
easy work-up.
Available online
Keywords:
Phenols
Nanocomposite
Hydrolysis
Aryldiazonium silica sulfate
Solvent-free conditions
1
. Introduction
In comparison with aryl halides and triflates, arenediazonium
arenediazonium tetrafluoroborates are much used because of their
5
stability and availability. Moreover, aryldiazonium salts with
6
7
8
disulfonimides, carboxylates, tosylates, and tetrachloroaurate
+
-
salts (ArN X ) have a greater reactivity and wider availability
from inexpensive aromatic amines. Therefore, these salts have
been prepared and studied as useful intermediates in classical and
9
2
counterions have been synthesized and reported to good
stability. Diazotization reactions of these anhydrous aryl
diazonium salts are carried out in an appropriate organic solvent,
1
modern organic synthesis. Moreover, arenediazonium salts are
and it is necessary to add Et O into the reaction mixture to
2
used for the modification of conducting surfaces in materials
science, which has led to a wide range of applications in
biochemical sensors, microelectronics and in the biomedical
industry. These salts have been prepared by a wide variety of
methods. One of the oldest and commonly used methods involves
the diazotization of aromatic amines with sodium nitrite in a
highly acidic aqueous solution. Moreover, diazonium salts can
be formed in organic solvents by the reaction between aromatic
amines and an alkyl nitrite in the presence of an acid. It is notable
that the counterion (X ), determined by the choice of the acid, has
an important role for both stability and reactivity of the
precipitate the corresponding diazonium salt. Also, in most of
these procedures, it is required to control the reaction at low
temperatures. Recently, diazonium ions have been immobilized
2
10
on silica nanoparticles (Figure 1).
Although these
nanocomposites are suitable for deposition on a metal surface,
they are not useful for consequent organic syntheses because
diazonium groups are directly linked to the surface of the SiO2.
Moreover, the synthesis of these kinds of diazonium salts is time-
consuming and expensive.
3
-
+
N
2
BF
4
O
4
+
-
H
diazonium salt. For example, aryldiazonium chlorides (ArN Cl
)
2
O
N
SiO
2
N
are usually unstable above 0 °C and some of them are
H
O
explosive. Furthermore, because of this instability, subsequent
reactions with diazonium salts must be carried out under the
same conditions that these salts are formed. Thus, aryldiazonium
salts with higher stability and versatility that are not explosive are
desirable and necessary. Recent developments have shown that
the stability of the aryldiazonium cation can be modulated by
changing its counterion. Among arenediazonium salts,
Figure 1. Silica nanoparticles functionalized with diazonium
groups.
Recently, we have reported a new method for the preparation
of anhydrous and stable aryldiazonium ions on the surface of
—
——
∗
Corresponding author. Tel: +989171302528, Fax: +983132289113, Email: aj_zarei@yahoo.com, aminzarei@iaufasa.ac.ir

2
Tetrahedron
silica sulfuric acid (SSA), named aryldiazon
A
ium
C
s
C
ili
E
ca
P
s
T
ul
E
fa
D
tes MA2.
NU
R
esu
S
lt
C
s a
R
n
I
d discussion
P
T
+-
(ArN2 OSO -SiO ). These aryldiazonium salts are easily
3
2
As mentioned, modification of surfaces using diazonium salts
is an ongoing area of research in materials and organic
synthesized by using aromatic amines, sodium nitrite and silica
sulfuric acid as an inexpensive and safe solid acid (Scheme 1).
11
2,16
chemistry. Therefore, the synthesis of aryldiazonium salts with
good stability is necessary to follow this purpose. In this area of
research, aryldiazonium silica sulfates can be introduced as one
of the most important classes of the stable aryldiazonium salts
with the simplest synthesis procedure. In the present work, we
study the reasons of the stability of aryldiazonium silica sulfates
by surface study of 4-nitrophenyl diazonium silica sulfate as a
model (Scheme 3).
It is notable that these reactions are carried out in a few minutes
under solvent-free conditions. Contrary to the reported methods,
diazotization reactions of these salts are conducted at room
temperature in one step and there is no need to maintain the
reactions at low temperatures.
OH
S
OH
S
ONa
ON
S
2
Ar
O
O
O
O
O
S
O
O
O
O
O
O
O
O
O
O
O
HO
+
HO
r.t., grinding
0-20 min
ArNH
2
+ NaNO
2
Si
Si
Si
Si
Si
Si
Si
Si
+ 2H
2
O
ONa
ON
S
2
NO
2
1
O
O
O
O
O
O
O
S
O
O
O
Silica sulfuric acid
Aryldiazonium silica sulfates
O
O
O
O
HO
Scheme 1. Immobilization of aryldiazonium ion on SSA.
Si
Si
Si
Si
O
O
O
Scheme 3. 4-nitrophenyl diazonium silica sulfate.
By using these new arenediazonium salts, a number of
compounds can be synthesized efficiently under mild and
11
First, to demonstrate the formation of the arenediazonium ion
on the surface of silica sulfuric acid, The FT-IR spectrum of 4-
nitrophenyl diazonium silica sulfate was studied and compared
with the spectrum of silica sulfuric acid (Figure 2). Two spectra
heterogeneous conditions. It is noteworthy that some of these
syntheses are easily carried out under solvent-free conditions and
11
the corresponding products are isolated by simple extraction.
Moreover, in some of these reactions, the used solid support can
be recycled after completion of the reaction. These significant
capabilities of aryldiazonium silica sulfates are in accordance
with the green chemistry principles, and make them more
attractive than the other arenediazonium salts.
show a broad stretching vibration of the hydroxyl groups around
-1
3
400 cm . The other broad peaks that are almost common
between the two spectra refer to asymmetric and symmetric
-1
O=S=O stretching from 1300-1000 cm that overlap with the
17
asymmetric and symmetric stretching bands of Si-O-Si.
-
1
Phenols and their derivatives are widely used as intermediates
in organic chemistry, and are found in natural products,
Moreover, the S-O stretching bands around 581 cm are almost
17
alike between the two spectra. It is notable that the main peaks
that can support the formation of the 4-nitrophenyl diazonium
group on the surface of silica sulfuric acid are clearly observed at
12
polymers, materials, and biological and medicinal compounds.
Functional phenols are commonly prepared by direct
hydroxylation of aryl halides with strong basic hydroxide salts, or
-
1
2292, 1545 and 1354 cm . These stretching bands are
13
+
by metal-catalyzed hydroxylation of aryl halides. Thermal
decomposition of aryldiazonium salts in a highly acidic aqueous
solution or copper-catalyzed transformation of aryldiazonium
salts can be the other routes for the preparation of phenol
respectively attributed to N≡N , and the asymmetric and
10,17
symmetric vibrations of NO
.
It should be mentioned that the
2
adsorbed water band overlapping with aromatic C=C stretching
-
1
-1
band appears at 1635 cm . Also, a peak at 851 cm is observed
which is corresponding to the C-H bending vibrations in the para
14
derivatives. Recently, the synthesis of phenols has been
15
17
followed by oxidative hydrolysis of aryl boronic acids.
substitution of aromatic ring.
Although some of these methods have convenient protocols with
good to high yields, the majority of these methods are associated
with limitations such as: the use of strong basic and acidic
reaction conditions, high reaction temperature, long reaction
time, low yield of the product, using excess amount of expensive
reagents, using toxic solvents and the use of expensive catalysts
and additives. Therefore, the introduction of an efficient,
convenient and cost-effective method for the synthesis of phenols
under mild and neutral conditions is desirable.
To further study the formation of the diazonium salt on the
surface of silica sulfuric acid, X-Ray Photoelectron Spectroscopy
(XPS) data of 4-nitrophenyl diazonium silica sulfate were
considered. As shown in Figure 3, the presence of Si, S and O are
demonstrated by appearance of three peaks at ~103, ~164 and
2
~
533 eV respectively. There are two main peaks which are
indicative of the formation of the 4-nitrophenyl diazonium ion on
SSA. The first peak that appears at ~285 eV is attributed to the C
2
1
s XP spectrum, because of the presence of a phenyl group in
In continuation of our ongoing program to develop
environmentally benign methods in organic synthesis, herein we
report an efficient method for the synthesis of phenol derivatives
by using aryldiazonium silica sulfates under mild, heterogeneous
and solvent-free conditions (Scheme 2).
the structure of 4-nitrophenyl diazonium silica sulfate. The
+
second XP spectrum assigned to N≡N and NO appears at ~406
2
2
eV as a small peak (N1s). Moreover, the presence of the Na 1s
XP spectrum at ~1073 eV indicates that the protons of SSA have
been exchanged with sodium cations of NaNO
diazotization process.
during the
2
ONa
2
ON Ar
ONa
OH
S
O
S
O
O
S
O
O
S
O
After the formation of the 4-nitrophenyl diazonium salt on the
surface of silica sulfuric acid, the morphology of this salt was
studied and compared with SiO2 and SSA. It should be
mentioned that silica sulfuric acid is synthesized by using
O
O
O
O
O
O
O
O
O
O
HO
HO
15-60 min
Si
Si
Si
Si
+ H
2
O
Si
Si
Si
Si
+
ArOH
O
O
O
0-110 o
O
O
O
6
C
Aryldiazonium silica sulfates
18
amorphous silica according to our previous works. In order to
study the surface of these materials, the XRD spectra of SiO2,
SSA and 4-nitrophenyl diazonium silica sulfate were compared.
As shown in Figure 4, both silica and silica sulfuric acid indicate
similar amorphous peaks centered at 2Ɵ = 23° (Figure 4, (a, b)).
Scheme 2. Synthesis of phenols by using aryldiazonium silica
sulfates.
It means that by modification of the amorphous SiO surface with
2

3
ACCEPTED MANUSCRIPT
Figure 2. (a) FT-IR spectra of SSA. (b) FT-IR spectra of 4-nitrophenyl dizonium silica sulfate.
Figure 4. (a) XRD pattern of amorphous silica. (b) XRD pattern of silica
sulfuric acid. (c) XRD pattern of 4-nitrophenyl diazonium silica sulfate.
Figure 3. XPS spectra of 4-nitrophenyl diazonium silica sulfate.
To better illustrate the morphology of the present diazonium
salt, the TEM images of 4-nitrophenyl diazonium silica sulfate
were studied. As shown in Figure 6, 4-nitrophenyl diazonium
ions are agglomerated on the surface of silica sulfuric acid in
various nanometer sizes. It should be mentioned that by
increasing the nano phases of the diazonium salts on SSA, the
active sites of the present nanocomposite increase so that the next
reactions c1an easily be carried out under solvent-free
SO H, no change in its morphology is observed. However, the
3
XRD pattern of 4-nitrophenyl diazonium silica sulfate shows the
crystalline phases specially at 2Ɵ = 22°, 24°, 28°, 31°, 33°, 35°
and 48° (Figure 4, (c)). We think that by immobilization of the
corresponding diazonium salt on SSA, the ionic structures and
crystalline phases on the surface increase.
To further investigate the morphology of the present materials,
1
the SEM images of amorphous SiO , SSA and 4-nitrophenyl
conditions.
2
diazonium silica sulfate were studied (Figure 5). The findings
demonstrate that no substantial difference was observed between
the morphology of silica and silica sulfuric acid (Figure 5, (a, b)).
These results are in agreement with the XRD patterns of these
materials. It is notable that the SEM images of 4-nitrophenyl
diazonium silica sulfate indicate the new phases of the
corresponding diazonium ions which are irregularly formed on
the surface of SSA (Figure 5, (c)). In the present procedure the
diazotization process is carried out under solvent-free conditions,
therefore the particle size distribution of these new phases is
different (Figure 5, (d-f)).
It is known that one of the most important restrictions when
using diazonium salts is their instability at room temperature.
However, by immobilization of these salts on the surface of silica
sulfuric acid, their stabilities increase so that some of these salts
can be kept at ambient conditions for days. In the present work,
for the first time, we examined the stability of these salts at
higher temperature by studying the thermal gravimetric analysis
(
TGA) and differential scanning calorimetry (DSC) of 4-
nitrophenyl diazonium silica sulfate nanocomposite (Figure 7, 8).
The TGA curve indicates that the decomposition of the present
nanocomposite with 30% of the total weight loss is done in
several steps (Figure 7).

4
Tetrahedron
ACCEPTED MANUSCRIPT
Figure 5. (a) SEM image of amorphous SiO
2
in 200 µm scale. (b) SEM image of SSA in 200 µm scale. (c) SEM image of 4-nitrophenyl
diazonium silica sulfate in 200 µm scale. (d) SEM image of 4-nitrophenyl diazonium silica sulfate in 50 µm scale. (e) SEM image of 4-
nitrophenyl diazonium silica sulfate in 10 µm scale. (f) SEM image of 4-nitrophenyl diazonium silica sulfate in 2 µm scale.
temperature but also at higher temperature so that its
decomposition point is almost at 145 °C. Moreover, by knowing
the decomposition point of each aryl diazonium silica sulfate, we
are able to adjust the best temperature for the progress of the
reaction without decomposition of the corresponding diazonium
salt.
After studying the morphology of these types of diazonium
salts immobilized on the surface of silica sulfuric acid, their
application for the synthesis of functional phenols was studied.
As cited in the literature, the usual method for the conversion of
an aryldiazonium salt to the corresponding phenol is thermal
decomposition of the diazonium salt in a highly acidic aqueous
14a
solution.
It should be mentioned that the use of high acidity
conditions is required to prevent the ionization of the resulting
phenol to phenoxide which couples easily with unreacted
diazonium ion to form the azo compound. Another side reaction
encountered during thermal decomposition of a diazonium ion is
the reaction of an aryl cation (formed by losing N from an
2
aryldiazonium ion) with the phenolic product to produce an
14a
arylphenol or a diaryl ether. Moreover, to obtain a high yield of
phenol uncontaminated with azo compound, addition of a
solution of the diazonium salt to a boiling sulfuric acid solution
with simultaneous removal of the phenol product by steam
Figure 6. (a) TEM images of 4-nitrophenyl diazonium silica sulfate in
200 nm scale. (b) TEM images of 4-nitrophenyl diazonium silica sulfate
in 50 nm scale.
14a
distillation is usually required.
In this work, these difficulties were reduced by thermal
decomposition of aryldiazonium silica sulfates under neutral and
solvent-free conditions. First, the synthesis of phenol was studied
At first, the physically absorbed water is removed from the
nanocomposite in the range of 37-108 °C. At higher temperature
(148-157 °C), decomposition of the diazonium salt takes place by
+-
by using phenyldiazonium silica sulfate (PhN2 OSO -SiO )
3
2
exhaust of N molecule from the surface of the nanocomposite.
2
under different conditions (Table 1). The completion of the
reactions was monitored by the 2-naphtholate test (absence of azo
coupling with 2-naphtholate). It should be mentioned that the
reactions carried out at 25 and 35 °C were not complete after the
time specified in Table 1. But, the corresponding reactions
carried out at 50 and 60 °C were complete after the time
indicated in Table 1. By comparison of the findings, the best
result was obtained when the reaction was carried out at 60 °C
under solvent-free conditions (Table 1, entry 5). In all reactions
carried out in water, the phenol product was isolated by an acidic
This step is in agreement with the DSC analysis by appearance of
an exothermic peak at ~145 °C (Figure 8). By increasing the
temperature (231-276 °C), the support (SSA) is decomposed and
converted to silica by exhaust of SO from the surface of silica
3
19
sulfuric acid. The result completely coincides with the DSC
measurement by emergence of an exothermic peak at ~250 °C
(
°
Figure 8). Finally, the last peak appears in the range of 300-311
C (Figure 7). It may be due to the decomposition of the phenyl
group of 4-nitrophenyl diazonium silica sulfate. As a whole, the
present diazonium salt nanocomposite is stable not only at room

5
ACCEPTED MANUSCRIPT
Figure 7. TGA and dTG curves of 4-nitrophenyl diazonium silica sulfate.
Figure 8. DSC curve of 4-nitrophenyl diazonium silica sulfate.
work-up using EtOAc as the solvent. However, when the reaction
was carried out under solvent-free conditions, the phenol product
was isolated by simple extraction with EtOAc. Due to the phenol
solubility in water, the yield of the isolated product by acidic
work-up is less than that by simple extraction. It should be cited
that no by-product was observed when the reaction was carried
out under solvent-free conditions at 60 ° C. However, by
increasing the temperature to 70 ° C, diphenyl ether, as a side
product, was obtained in 7% yield (based on GC-MS). Therefore,
the best reaction conditions for the hydrolysis of
phenyldiazonium silica sulfate were determined by conducting
the reaction under solvent-free conditions at 60 ° C.
Table 1. Optimization of the reaction conditions for the
synthesis of phenol using phenyldiazonium silica sulfate
a
b
Entry
Solvent
Temperature (° C)
Time
Yield (%)
1
2
3
4
5
H
2
2
O
O
25
35
50
60
60
6 h
trace
30
H
3 h
2
H O
1 h
68
H
2
O
25 min
15 min
70
Solvent-free
81
a
Reaction conditions: phenyldiazonium silica sulfate (1 mmol), solvent (5
mL).
b
The yields refer to the isolated pure products.

6
Tetrahedron
a
Table 2. Synthesis of phenol derivatives by
A
us
C
in
C
g a
E
ry
P
ld
T
ia
E
zo
D
niu
MANU
m
sil
ica
su
S
lf
C
at
R
es
I
under solvent-free conditions.
P
T
Entry
Diazonium salt
Product
Temp. (°C)
Time (min)
Yield (%)
+
-
1
2
3
4
5
6
7
8
9
PhN
2
OSO
3
-SiO
2
Phenol
60
60
60
70
80
85
80
80
80
80
110
15
25
25
25
30
30
30
30
30
30
60
81
83
78
82
74
73
80
75
+
-
4-MeC
2-MeC
6
6
H
4
4
N
2
2
OSO
3
3
-SiO
2
2
4-Methylphenol
2-Methylphenol
Biphenyl-4-ol
+
-
H
N
OSO
-SiO
+
-
4-PhC
4-BrC
3-ClC
6 4 2 3 2
H N OSO -SiO
+
-
6
H
4
N
2
OSO
3
-SiO
2
4-Bromophenol
3-Chlorophenol
+
-
6
H
4
N
2
OSO
3
-SiO
2
+
-
3-MeCOC
4-MeCOC
6
6
H
4
4
N
2
2
OSO
3
3
-SiO
2
2
3-Hydroxyacetophenone
4-Hydroxyacetophenone
2-Hydroxybenzophenone
4-Hydroxybenzoicacid
3-Nitrophenol
+
-
H
N
OSO
-SiO
+
2
-
b,c
2-PhCOC
4-HOOCC
3-NO
6
H
4
N
OSO
3
-SiO
2
20
+
2
-
1
1
0
1
6
H
4
N
OSO
3
-SiO
2
71
67
+
2
-
2
C
6
H
4
N
OSO
3
-SiO
2
a
1
The yields refer to the isolated pure products which were identified by FT-IR and HNMR spectroscopy and GC-MS and compared with standard samples.
b
c
Determined by GC-MS analysis.
9
-Fluorenone was determined in 80% yield by GC-MS analysis.
After optimization of the reaction conditions, the generality of
extremely reactive intermediate. The homolytic solvolysis of
arenediazonium salts takes place in solvents with better
the present method was studied by the synthesis of various
functionalized phenols. As shown in Table 2, a number of
aryldiazonium silica sulfates possessing electron-withdrawing or
electron-donating groups were easily converted into the
corresponding phenols in good yields and short reaction time. All
reactions were carried out under thermal and solvent-free
conditions. In comparison with the electron-donating groups, the
electron-withdrawing groups on the aromatic rings of these
diazonium salts decreased the reaction rate, meaning that the
reaction should be carried out at higher temperatures. In contrast
to the traditional methods, in the present work, all products were
isolated from the surface of silica by simple extraction without
using tedious work-up. Moreover, the primary solid support was
21
nucleophilicity such as pyridine or HMPT. The formation of an
aryl radical intermediate is characteristic of this pathway. MeOH,
EtOH and DMSO are introduced as borderline solvents in which
21
both mechanisms may be observed simultaneously. It should be
stated that electron-withdrawing substituents on the aromatic
rings of arenediazonium ions make them more prone to
21
homolytic dediazoniation.
OS
+
SOH
N2+
G
SOH
-N
Heterolytic pathway
11b
2
G
recovered according to the previous work. Contrary to the
traditional methods, the azo-coupled side-products were not
observed during the course of the reactions. Although
SOH
G
N
N
OS
G
+
-
arenediazonium
tetrafluoroborates
(ArN BF )
and
2
4
+
-
Homolytic pathway -N2
arenediazonium chlorides (ArN Cl ) are the most common
2
diazonium salts used for the thermal decomposition of these salts
in solution, arylfluorides and arylchlorides, as side products, are
formed during the course of the reactions. In the present work,
by immobilization of the arenediazonium salts on the surface of
silica sulfuric acid, this limitation obviously decreased. It should
be noted that, when 2-benzoylphenyl diazonium silica sulfate
20
G
H
G
was
hydrolyzed
by
the
present
procedure,
2-
G
G
hydroxybenzophenone was obtained in 20% yield and 9-
fluorenone, as a side product, was formed in 80% yield (Table 2,
entry 9).
Scheme 4. Heterolytic and homolytic pathways for the
solvolysis of arenediazonium ions.
We changed the reaction conditions by using water as the
solvent under the same reaction time and temperature. By
employing these conditions, 2-hydroxybenzophenone was
formed in 4% yield and 9-fluorenone was obtained in 96% yield
In the present work the hydrolysis of these immobilized
arenediazonium ions was easily carried out under solvent-free
conditions, and the phenol derivatives were obtained in good
yields. Products analysis (based on GC-MS analysis) did not
identify the presence of products from the homolytic pathways
(based on GC-MS).
(
e.g. ArH or biaryls) using the present procedure. Therefore, a
Mechanistic proposals relating to the decomposition of
arenediazonium salts have been described in earlier studies.
7,14a,21
heterolytic mechanism seems most probable.
The results demonstrate that the solvolysis of arenediazonium
ions occurs through two main mechanisms: heterolytic and
It is known that the thermal decomposition of the diazonium
salts derived from 2-aminobenzophenone in aqueous solution
gives 9-fluorenone as the major product and 2-
hydroxybenzophenone as the minor product. The formation of
9-fluorenone and 2-hydroxybenzophenone occur readily under
7,21
homolytic pathways (Scheme 4). The heterolytic solvolysis is
generally carried out in solvents (SOH) with low nucleophilicity
22
21
such as water or trifluoroethanol. This dediazoniation is
specified by losing N and formation of an aryl cation as an
2

7
2
2
acidic conditions by a heterolytic mechanism
A
(S
C
ch
C
em
E
e
P
5
T
).
E
B
D
y
MA3.
N
C
U
on
S
clu
C
si
R
on
I
s
PT
following this mechanism, the ring closure reaction is carried out
by an intramolecular arylation, competing with water
intermolecular nucleophilic attack. It is well known that the
closure of a five-membered ring usually occurs much more
In summary, we have developed a fast, efficient and
convenient method for the synthesis of phenols in good yields.
Using the present method, a number of aryldiazonium silica
sulfate nanocomposites were hydrolyzed to the corresponding
phenol derivations under mild and solvent-free conditions. The
notable advantages of this methodology were operational
simplicity, availability of reactants, short reaction time and easy
work-up.
2
2
readily than the other intermolecular competitive reactions.
O
O
O
-N
2
-H
+
4
. Experimental
+
+
N
2
major product
-H+
2
H O
4.1. General
All reagents were purchased from Merck and Aldrich and
used without further purification. All yields refer to isolated
products after purification. Silica sulfuric acid was synthesized
according to the previous works with 4.4 mmol H+/g capacity.18
The products were characterized by comparison of physical data
with those of known compounds and by spectroscopic data (FT-
IR, 1HNMR and GC-MS). IR spectra were reordered on a
JASCO FT-IR-680 PLUS spectrometer. 1HNMR spectra were
recorded with a Bruker Avance 400 (400 MHz). The results of
GC-MS were obtained by using an Agilent 7890AGC 5975C
inert XLEI/CIMSD instrument. The morphology and particle size
of the nanocomposite were measured by using transmission
electron microscopy (TEM, Philips CM30) at 200 kV and by a
scanning electron microscope (SEM, Philips XL30) operated at
an acceleration voltage of 20 kV. X-ray photoelectron
spectroscopy (XPS) signals were acquired by using a BESTEC
O
OH
minor product
Scheme 5. Proposed heterolytic mechanism for the
hydrolysis of diazonium cation derived from 2-
aminobenzophenone
.
As discussed, by hydrolysis of 2-benzoylphenyl diazonium
silica sulfate, 9-fluorenone was formed in 80% yield and 2-
hydroxybenzophenone was obtained in 20% yield at 80 °C under
solvent-free conditions. By using H O as the solvent, 9-
2
fluorenone was obtained in 96% yield and 2-
hydroxybenzophenone was formed in 4% yield at 80 °C. We
think that by employing water as the solvent, the concentration of
H which is generated during the course of the reaction decreases
and subsequently the nucleophilicity of H O increases. Moreover,
the existence of a carbonyl group, as an electron-withdrawing
group, in the structure of the corresponding diazonium salt makes
it prone to partially homolytic hydrolysis according to the
Scheme 6. In this mechanism, a diazohydroxide intermediate is
formed by addition of water to the corresponding diazonium
cation. Because of the instability of diazohydroxide group, it can
undergo homolytic fragmentation to give the corresponding aryl
Then, the closure of the five-membered ring occurs
readily due to the proximity of the radical to the potential
reaction site. Finally, 9-fluorenone is formed by losing a
hydrogen radical. As a whole result, by employing water as the
solvent, the hydrolysis reaction of 2-benzoylphenyl diazonium
silica sulfate is carried out, not only by a heterolytic mechanism
but, also may be followed by a homolytic pathway. We think that
the simultaneous occurrence of heterolytic and homolytic
mechanisms may be a logical reason for the increase of 9-
fluorenone yield in water.
8
025 system fitted with a microfocused and monochromatic Al
+
Kα X-ray source (1486.6 eV). Phase structure analyses were
determined by X-ray diffractometer (XRD, Philips Xpert) using
the Ni-filtered CuKα (λCuKα=0.1542 nm, radiation at 40 kV and
2
3
9
0 mA). The data were collected over the 2θ range from 10° to
0° (time per step was 2.5 s and step size was 0.021°).
Thermogravimetric analyses were performed in a SETARAM
LABSYS instrument (SETARAM, Caluire, France) under argon
atmosphere with 10°C/min heating rate.
4
.2. Typical procedure for the preparation of phenyl diazonium
21,22
radical.
silica sulfate
Aniline (1 mmol, 0.095 mL), silica sulfuric acid (0.75 g) and
sodium nitrite (1.7 mmol, 0.12 g) were ground in a mortar witha
pestle for a few minutes to obtain a homogeneous mixture. Then,
four drops of water were gradually added and the mixture was
ground for 10 min to give phenyl diazonium silica sulfate.
22
4
.3. Typical procedure for the synthesis of phenol by using
phenyl diazonium silica sulfate
Five drops of water were added to phenyl diazonium silica
sulfate (1 mmol) and the resulting mixture was simply blended
and then placed into a covered petri dish. Then, the petri dish was
placed in an oven at 60 °C for 15 minutes. After that, the reaction
mixture was diluted with EtOAc (15 mL) and filtered after
vigorous stirring. The residue was extracted with EtOAc (2× 10
mL) and the combined organic layer was dried over anhydrous
Na2SO4. The solvent was evaporated under reduced pressure to
afford the crude product. Further purification was performed by
flash column chromatography and the pure phenol was obtained
in 81% (0.076 g).
O
O
O
2
H O
H+
-
+
N
2
N
N
HO
O
O
-H
H
Scheme 6. Proposed homolytic mechanism for the formation
of 9-fluorenone by hydrolysis of diazonium cation derived
from 2-aminobenzophenone.
Acknowledgments

8
Tetrahedron
or MANUSCRIPT
M.; Plessis, M. D.; Tonder, J. H. V.; Bezuidenhoudt, B. C. B.
We gratefully acknowledge the funding su
A
pp
C
or
C
t r
E
ec
P
eiv
TED
e
d f
Tetrahedron Lett. 2014, 55, 2082. (k) Matsui, K.; Ishigami, T.;
Yamaguchi, T.; Yamaguchi, E.; Tada, N.; Miura, T.; Itoh, A.
Synlett 2014, 2613. (l) Paul, A.; Chatterjee, D.; Rajkamal, Haider,
T.; Banerjee, S.; Yadav, S. Tetrahedron Lett. 2015, 56, 2496. (m)
Yang, D. S.; An, B. J.; Wei, W.; Jiang, M.; You, J. M.; Wang, H.
Tetrahedron 2014, 70, 3630. (m) Chatterjee, N.; Goswami, A.
Tetrahedron Lett. 2015, 56, 1524. (n) Begum, T.; Gogoi, A.;
Gogoi, P. K.; Bora, U. Tetrahedron Lett. 2015, 56, 95. (o)
Mahanta, A.; Adhikari, P.; Bora, U.; Thakur, A. J. Tetrahedron
Lett. 2015, 56, 1780. (p) Gupta, S.; Chaudhary, P.; Seva, L.;
Sabiah, S.; Kandasamy, J. RSC Adv. 2015, 5, 89133. (q) Gupta, S.;
Chaudhary, P.; Srivasava, V.; Kandasamy, J. Tetrahedron Lett.
this project from the Islamic Azad University, Fasa Branch and
Khorasgan Branch.
References
1
2
.
Roglans, A.; Pla-Quintana, A.; Moreno-Manas, M. Chem. Rev.
006, 106, 4622.
2
. (a) Chehimi, M. M. Aryl Diazonium Salts: New Coupling Agents in
Polymer and Surface Science, Wiley-VCH Verlag & Co. KGaA,
Boschstr. Weinheim, Germany, 2012. (b) Polsky, R.; Harper, J. C.;
Dirk, S. M.; Arango, D. C.; Wheeler, D. R.; Brozik, S. M. Langmuir
2
016, 57, 2506.
2
007, 23, 364. (c) Harper, J. C.; Polsky, R.; Wheeler, D. R.; Brozik,
1
1
6. Belanger, D.; Pinson, J. Chem. Soc. Rev. 2011, 40, 3995.
7. Silverstein, R. M.; Webster, F. X.; Kiemle, D. J.; Bryce, D. L.
Spectrometric Identification of Organic Compounds, 8th. Edition,
Wiley, John & Sons Publisher, 2014.
8. Hajipour, A. R.; Zarei, A.; Khazdooz, L.; Mirjalili, B. B. F.;
Sheikhan, N.; Zahmatkesh, S.;. Ruohoa, A. E Synthesis 2005,
S. M. Langmuir 2008, 24, 2206. (d) Hansen, M. N.; Farjami, E.;
Kristiansen, M.; Clima, L.; Pedersen, S. U.; Daasbjerg, K.;
Ferapontova, E. E.; Gothelf, K. V. J. Org. Chem. 2010, 75, 2474.
Zollinger, H. Diazo chemistry I, aromatic and heteroaromatic
compounds, Weinheim: Wiley VCH, 1994.
Felpin, F. X.; Hardy, L. N.; Callonnec, F. L.; Fouquet, E.
Tetrahedron 2011, 67, 2815.
Taylor, J. G.; Moro, A. V.; Correia, C. R. D. Eur. J. Org. Chem.
3
.
1
4
5
6
.
.
.
3
644.
9. Shaterian, H. R.; Ghshang, M.; Feyzi, M. Appl. Catal. A: Gen.
008, 345, 128.
1
2
2
2
011, 1403.
0. (a) Canning, P. S. J.; Maskill, H.; McCrudden, K.; Sexton, B. Bull.
Chem. Soc. Jpn. 2002, 75, 789. (b) Canning, P. S. J.; McCrudden,
K.; Maskill, H.; Sexton, B. Chem. Commun. 1998, 1971.
1. (a) Pazo-Liorente, R.; Bravo-Diaz, C.; Gonzalez-Romero, E. Eur.
J. Org. Chem. 2004, 3221. (b) Pazo-Liorente, R.; Bravo-Diaz, C.;
Gonzalez-Romero, E. Eur. J. Org. Chem. 2003, 3421.
Barbero, M.; Crisma, M.; Degani, I.; Fochi, R.; Perracinoa, P.
Synthesis 1998, 1171.
Colas, C.; Goeldner, M. Eur. J. Org. Chem. 1999, 1357.
Filimonov, V. D.; Trusova, M.; Postnikov, P.; Krasnokutskaya, E.
A.; Lee, Y. M.; Hwang, H. Y. Org. Lett. 2008, 10, 3961.
Overton, A. T.; Mohamed, A. A. Inorg. Chem. 2012, 51, 5500.
7
8
.
.
2
2
9
1
1
.
2. DeTar, D. F. Org. React. 1957, 9, 409.
0. Joselevich, M.; Williams, F. J. Langmuir 2008, 24, 11711.
1. (a) Zarei, A.; Hajipour, A. R.; Khazdooz, L.; Mirjalili, B. B. F.;
Najafichermahini, A. Dyes Pigments 2009, 81, 240. (b) Zarei, A.;
Hajipour, A. R.; Khazdooz, L. Synthesis 2009, 941. (c) Zarei, A.;
Hajipour, A. R.; Khazdooz, L.; Aghaei, H. Tetrahedron Lett.
2
009, 50, 4443. (d) Zarei, A.; Hajipour, A. R.; Khazdooz, L.;
Aghaei, H. Synlett 2010, 1201. (e) Zarei, A.; Khazdooz, L.;
Hajipour, A. R.; Aghaei, H. Dyes Pigments 2011, 91, 44. (f) Zarei,
A.; Khazdooz, L.; Pirisedigh, A.; Hajipour, A. R.; Seyedjamali,
H.; Aghaei, H. Tetrahedron Lett. 2011, 52, 4554. (g) Zarei, A.;
Khazdooz, L.; Hajipour, A. R.; Rafiee, F.; Azizi, G.; Abrishami,
F. Tetrahedron Lett. 2012, 53, 406. (h) Pirisedigh, A.; Zarei, A.;
Seyedjamali, H.; Khazdooz, L.; Hajipour, A. R. Monatsh. Chem.
2
012, 143, 791. (i) Zarei, A.; Khazdooz, L.; Hajipour, A. R.;
Aghaei, H.; Azizi, G. Synthesis 2012, 3353. (j) Zarei, A.;
Khazdooz, L.; Hajipour, A. R.; Aghaei, H.; Azizi, G.;
Najafichermahini, A.; Hajipour, A. R. Dyes Pigments 2014, 101,
2
95.
1
1
2. (a) Rappoport, Z. The Chemistry of Phenol, Wiley-VCH:
Weinheim, 2003. (b) Tyman, J. H. P. Synthetic and Natural
Phenols, Elsevier, New York, 1996.
3. (a) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. J.
Am. Chem. Soc. 2006, 128, 10694. (b) Schulz, T.; Torborg, C.;
Schaffner, B.; Huang, J.; Zapf, A.; Kadyrov, R.; Borner, A.;
Beller, M. Angew. Chem., Int. Ed. 2009, 48, 918. (c) Sergeev, A.
G.; Schulz, T.; Torborg, C.; Spannenberg, A.; Neumann, H.;
Beller, M. Angew. Chem., Int. Ed. 2009, 48, 7595. (d) Zhao, D.;
Wu, N.; Zhang, S.; Xi, P.; Su, X.; Lan, J.; You, J. Angew. Chem.,
Int. Ed. 2009, 48, 8729. (e) Tlili, A.; Xia, N.; Monnier, F.;
Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 8725. (f) Paul, R.;
Ali, M. A.; Punniyamurthy, T. Synlett 2010, 4268. (g) Song, G. L.;
Zhang, Z.; Da, Y. X.; Wang, X. C. Tetrahedron 2015, 71, 8823.
(
h) Tan, B. Y. H.; Teo, Y. C. Synlett 2016, 1814.
4. (a) Cohen, T.; Dietz, A. G.; Miser, J. R. J. Org. Chem. 1977, 42,
053. (b) Mo, F.; Dong, G.; Zhang, Y.; Wang, J. Org. Biomol.
Chem. 2013, 11, 1582.
5. (a) Prakash, G. K. S.; Chacko, S.; Panja, C.; Thomas, T. E.;
Gurung, L.; Rasul, G.; Mathew, T.; Olah, G. A. Adv. Synth. Catal.
1
1
2
2
009, 351, 1567. (b) Xu, J. M.; Wang, X. Y.; Shao, C. W.; Su, D.
Y.; Cheng, G. L.; Hu, Y. F. Org. Lett. 2010, 12, 1964. (c) Hosoi,
K.; Kuriyama, Y.; Inagi, S.; Fuchigami, T. Chem. Commun. 2010,
1
284. (d) Mulakayala, N.; Ismail, Kumar, K. M.; Rapolu, R. K.;
Kandagatla, B.; Rao, P.; Oruganti, S.; Pal, M. Tetrahedron Lett.
2
2
012, 53, 6004. (e) Zhu, C.; Wang, R.; Falck, J. R. Org. Lett.
012, 14, 3494. (f) Gogoi, A.; Bora, U. Synlett 2012, 1079. (g) Qj,
H. L.; Chen, D. S.; Ye, J. S.; Huang, J. M. J. Org. Chem. 2013, 78,
482. (h) Zou, Y. Q.; Chen, J. R.; Liu, X. P.; Lu, L. Q.; Davis, R.
L.; Jorgensen, K. A.; Xiao, W. J. Angew. Chem., Int. Ed. 2012, 51,
84. (i) Chen, D. S.; Huang, J. M. Synlett 2013, 499. (j) Gohain,
7
7