Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using Sulfonic Acid Functionalized Hyper-Cross-Linked Poly(2-naphthol) as a Solid Acid Catalyst

Article abstract of DOI:10.1007/s10562-019-02811-w

Abstract: The hyper-cross-linked porous poly(2-naphthol) fabricated by the Friedel–Crafts alkylation of 2-naphthol has been functionalized with sulfonic acid to obtain a solid acid catalyst. The catalyst is applied for the protection of phenol, alcohols, thiols, amines and aldehydes with acetic anhydride at room temperature. The catalytic protection using the new solid acid is featured by achieving high yield at neat condition, needing no aqueous work-up and/or chromatographic separation, and showing excellent recycling efficiency, suggesting the potential of this sulfonated porous polymers as a new protection protocol in a wide range of sustainable chemical reactions. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02811-w

Catalysis Letters
https://doi.org/10.1007/s10562-019-02811-w
Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using
Sulfonic Acid Functionalized Hyper‑Cross‑Linked Poly(2‑naphthol)
as a Solid Acid Catalyst
Reddi Mohan Naidu Kalla1 · Sirigireddy Sudharsan Reddy1 · Il Kim1
Received: 2 January 2019 / Accepted: 4 May 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The hyper-cross-linked porous poly(2-naphthol) fabricated by the Friedel–Crafts alkylation of 2-naphthol has been function-
alized with sulfonic acid to obtain a solid acid catalyst. The catalyst is applied for the protection of phenol, alcohols, thiols,
amines and aldehydes with acetic anhydride at room temperature. The catalytic protection using the new solid acid is featured
by achieving high yield at neat condition, needing no aqueous work-up and/or chromatographic separation, and showing
excellent recycling efciency, suggesting the potential of this sulfonated porous polymers as a new protection protocol in a
wide range of sustainable chemical reactions.
Graphical Abstract
An efcient and eco-friendly method has been developed for the protection of phenols, alcohols, thiols, amines and aldehydes with acetic anhy-
dride in presence of sulfonic-acid-functionalized hyper-cross-linked poly(2-naphthol) as a solid acid catalyst.
Keywords Acylation · Crosslinked polymers · Heterogeneous catalysis · Poly(2-naphtol) · Protection · Solid acid
1 Introduction
The protection of functional group is essential throughout
the course of diferent organic transformations in multi-step
synthesis of organic compounds, particularly within the
preparation of poly functional molecules like nucleosides,
carbohydrates, and natural products [1]. Environmentally
* Il Kim
ilkim@pusan.ac.kr
1
BK21 PLUS Center for Advanced Chemical Technology,
Department of Polymer Science and Engineering, Pusan
National University, Busan 46241, Republic of Korea
Vol.:(0123456789)
1 3

R. M. N. Kalla et al.
clean protection protocol has emerged as part of immense
interest in the view of economic and environmental aspects.
Even though diferent reagents are adopted for the protec-
tion of functional groups such as phenol and alcohol [2],
thiols [3], amines [4], and aldehydes [5, 6], acetic anhydride
is most widely used, because it is cheap and easily avail-
able, and easy to deprotect [6, 7]. In general the protection
reactions were performed in the presence of either acid [8]
or base catalysts [9]. However, most of the reports to date
possess fundamental drawbacks including employing harsh
conditions with long reaction time, using harmful organic
solvents, and need tedious work-up procedures [10, 11].
The use of heterogeneous catalyst and environmentally
friendly reaction conditions can be a candidate to circum-
vent of drastic methods and hazardous solvents. Heteroge-
neous polymer functionalized materials (PFMs) have been
efciently working due to their functional availability and
efcient workup procedures [12–14]. Suitably crosslinked
PFMs are featured by their high surface areas, unique prop-
erties, and a broad range of potential uses in disciplines
including catalysis, sensing, energy storage and catalysis
support applications [15–18]. Moreover, the PFMs catalysts
show high dispersion and reactivity with a high degree of
chemical stability [19].
As a means of developing green and eco-friendly protec-
tion protocol of functional groups a crosslinked FPM has
been fabricated by the alkylation of 2-naphthol, followed
by self-crosslinking (Sch 1). The crosslinked poly(2-naph-
thol) (p2NPh–OH) was subjected to sulfonic acid function-
alization and employed the sulfonic acid-functionalized
poly(2-naphthol) (p2NPh–OSO3H) for solvent-free acyla-
tion of phenol, alcohols, thiols, amines, and aldehydes. The
p2NPh–OSO3H catalyst is featured by high efciency for
targeted protection and recyclability.
2 Experimental
2.1 General
2-naphthol (2NPh–OH), and formaldehyde dimethyl acetal
(FDA; 98%) obtained from TCI, chlorosulfonic acid and
Scheme 1 Fabrication of
sulfonic acid functionalized
poly(2-naphthol) and its appli-
cations for the protection of
phenols, alcohols, thiols, amines
and aldehydes
1 3

Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using Sulfonic Acid Functionalized…
various phenols, alcohols, thiols, amines, and aldehydes
obtained from Merck, 1,2-dichloroethane (DCE) from Dae-
jung Chem. (Seoul, Korea), anhydrous FeCl3 (98%) from
Acros were used as received. 1H and 13C NMR (400 MHz
and 100 MHz) spectra were checked by using Varian INOVA
400 NMR spectrometer at 25 °C. The chemical shift values
are quoted relative to Me4Si. Fourier transform infrared (FT-
IR) spectra were recorded at 25 °C, by Shimadzu IR Prestige
21 spectrometer using KBr disk in the range between 4500 to
500 cm−1. The x-ray difraction (XRD) study was performed
by using an automatic Philips powder difractometer with
nickel-fltered Cu Kα radiation. The difraction pattern was
collected the 2θ range in between 0 and 80° in steps of 0.02
and counting times of 2 s per step. The microstructures of
the samples were carryout using an S-3000 scanning elec-
tron microscope (SEM; Hitachi, Japan), and thermogravi-
metric analysis (TGA) was carried out using a TGA N-1000
(Scinco, Seoul, and Republic of Korea). X-ray photoelectron
spectroscopy (XPS) analysis was performed in a Theta Probe
AR-XPS system with a monochromatic Al Kα x-ray source
(1486.6 eV). The Brunauer–Emmett–Teller (BET) and den-
sity functional theory (DFT) methods (Nova 3200e system,
Quantachrome Instruments, USA) were used to examine the
BET specifc surface area and pore size distribution of the
samples.
2.3 General Procedure for Acylation Reaction
To a 10 mL reaction fask phenol/alcohol/thiol/amine/aldehyde
(1 mmol), acetic anhydride (1 mmol) and p2NPh–OSO3H
(10 mg) as a catalyst was added and the resulting mixture
stirred at 25 °C. The progress of the reaction was checked
using thin layer chromatography (TLC). After completion,
ethyl acetate (EA) was added and the catalyst was separated
from the reaction mixture by straightforward fltration. The
separated catalyst was cleaned with EA (10 mL) and then dried
in an oven for 2 h and reused for further reaction. The reac-
tion mixture was evaporated under reduced pressure to get the
products which were characterized by 1H and 13C NMR spec-
troscopy. All of the obtained products are renowned within
the literature.
2.4 Molecular Simulations of Hypercrosslinked
Poly(2‑naphthol)
Molecular models for the crosslinked polymer networks were
generated using the BIOVIA Materials Studio 5.0 software
package (Dassault Systemes, BIOVIA Corp., San Diego, CA)
with the polymer consistent force feld (COMPASS II) [20].
Molecular simulations were performed with the Forcite mod-
ule, using a time step of 1 fs, the Nosé-Hoover thermostat with
a Q ratio of 0.01, and the Andersen barostat with a time con-
stant of 1 ps. Monomers are packed into a periodic cell using
amorphous cell module in Materials Studio. The enclosed
script implemented for a crosslinking simulation using For-
cite was adapted to join monomer units via a condensation
polymerization based on a set of predetermined connectivity
rule with the removal of simple molecules. Packing mono-
mers and defning their reactive atoms and crosslinking sites,
the crosslinked structure can be generated with any degree
of crosslinking. This script is composed of three steps: (a)
initial packing of the simulation box (using amorphous cell),
(b) dynamics for initial equilibration: i.e. NVT dynamics run
followed by NPT run, (c) a cross-linking procedure until the
target degree of cross-linking is reached, and (d) dynamics for
a fnal energy minimization. Default values were used to run
the script. Close contact exclusion rules were applied during
the condensation polymerization. Close contacts were deleted
if (i) they are not between predetermined reactive atoms, (ii)
they would exceed the conversion target, and (iii) intra-topol-
ogy, meaning they would result in more than one concurrent
crosslinks to an atom.
2.2 Synthesis of Porous p2NPh–OH and Sulfonation
of p2NPh–OH
The FDA (8 mmol) was added to a solution containing
2-napthol (4 mmol) in 15 mL of DCE in a 50 mL fask, and
the mixture was stirred for 20–30 min. After that anhydrous
FeCl3 (8 mmol) was then added, and the reaction was con-
tinued for 18 h at 70 °C. After cooling, the reaction was
quenched with MeOH and the polymer was washed with
deionized water, acetone, and MeOH. The solid was addi-
tional refned by Soxhlet extraction with methanol for 24 h,
then dried beneath vacuum at 70 °C for 12 h. The polymer
was denoted as p2NPh–OH.
For the sulfonation of p2NPh–OH, 0.3 g of p2NPh–OH
in 10 mL of CH2Cl2 at 0 °C was added drop-by-drop to a
solution of chlorosulfonic acid (2.5 mL) in CH2Cl2 (10 mL)
and the resultant mixture was stirred for 2 h at 25 °C. The
black solid fltered and rinsed with CH2Cl2 and dried to
aford p2NPh–OSO3H. The concentration of acid sites of
the p2NPh–OSO3H catalysts was measured by a reverse
titration with HCl (0.337 N). 10 mL of NaOH (0.130 N)
was added to 0.1 g of catalyst and stirred for 30 min at room
temperature. The resultant mixture was fltered and washed
with deionized water. The additional amount of NaOH in
the fltrate was titrated with HCl in the presence of phenol-
phthalein as an indicator. The concentration of acid sites
was 1.14 mmol g−1.
3 Results and Discussion
Post-functionalization of the hypercrosslinked p2NPh–OH
with chlorosulfonic acid was monitored using FT-IR spec-
troscopy. The FT-IR spectra of p2NPh–OH, p2NPh–OSO3H
1 3

R. M. N. Kalla et al.
are shown in Fig. 1. Both p2NPh–OH and p2NPh–OSO3H
show –OH stretching frequencies at 3448 and 3456 cm−1,
respectively, and the asymmetric and symmetric stretching
bands of p2NPh–OSO3H sample at 1227 and 1058 cm−1,
correspondingly, and the S–O stretching band at 775 cm−1,
confrming the existence of the –SO3H cluster. Figure 1b
shows the XRD patterns of the sample before and after
sulfonic acid functionalization. The p2NPh–OH sample
shows a very broad peak centered at 2θ = 18.5° and the
p2NPh–OSO3H sample at 2θ=23.5°. Both samples are basi-
cally amorphous and the shift of the center is related with
the functionalization of mainly peripheral –OH groups in
p2NPh–OH to bulky –OSO3H groups.
in the molecular skeletons of p2NPh–OSO3H, (Fig. 1c).
The SEM images of p2NPh–OH and p2NPh–OSO3H in
Fig. 2a–d shows a mixed tubular and sphere morphology,
and, after sulfonation, the tubular and sphere morphology
of the polymers was retained.
Nitrogen adsorption, desorption isotherms and the tex-
tural properties of p2NPh–OH and p2NPh–OSO3H are
shown in Fig. 3. The BET surface area of p2NPh–OH,
408 m2g−1, decreases signifcantly once sulfonic acid func-
tionalization to 180 m2g−1. The large sulfonic acid groups
are grafted onto the porous surface of the p2NPh–OH,
resulting in overcrowd partial pores in p2NPh–OH. Addi-
tionally, the decrease in surface area after the functionali-
zation of the p2NPh–OH is due to the raise in the mass of
the fabric with regard to the load of weight percent of the
polymer. Furthermore, the p2NPh–OSO3H shows signif-
cantly lower mesoporous volume than that of p2NPh–OH.
These various changes within the textural properties of
p2NPh–OSO3H indicate the productive functionalization
of p2NPh–OH. The pore size distribution of p2NPh–OH
and p2NPh–OSO3H was determined by DFT, indicating
foremost pore widths of p2NPh–OH and p2NPh–OSO3H
centered at about 9.2 and 8.2 Å (Fig. 3b), respectively.
These results clearly suggest that these polymers contain
micropores as well.
The TGA curves of p2NPh–OH and p2NPh–OSO3H, are
shown in Fig. 1c. The TGA curve of the sulfonated materi-
als show the frst weight losses 6.5% at 100 °C, which cor-
respond to the loss of water molecules present in the pore
surface, followed by the loss of adsorbed water molecules
having a non-covalent interaction with the free sulfonic
acid groups. The further, weight losses of 55.4% in the
temperature range 130–280 °C could be attributed to the
loss of free sulfonic acid groups followed by the cleavage
of the organic framework beyond 530 °C. The high ther-
mal stability of the porous polymers could be attributed to
the hyper crosslinking and the rigid polymeric networks
Fig. 1 a FT-IR spectra, b XRD
patterns, and c TGA thermo-
grams of p2NPh–OSO3H
1 3

Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using Sulfonic Acid Functionalized…
Fig. 2 SEM images of
p2NPh–OH (a, b) and p2NPh–
OSO3H (c, d)
Fig. 3 a Nitrogen adsorption/
desorption isotherms and b pore
size distribution of p2NPh–OH
and p2NPh–OSO3H
For the atomic simulations [21] of p2NPh–OH the
amorphous cells were produced with 200 seed mol-
ecules, 1,6-alkylated 2-naphthol, as shown in Fig. 4. The
crosslinks were formed between atoms labelled R1 and R2 in
1,6-bis(methoxymethyl)naphthalen-2-ol monomer. For the
crosslinking close contacts are searched between R1 and R2
within threshold (here<4Å). A spring connects R1 and R2
and gradually stifer by harmonic restraint. Then, the spring
between R1 and R2 is replaced by bond. In order to ft stoi-
chiometry methoxy group on R1 and hydrogen atom on R2 is
removed as methanol molecule. After the new bond forma-
tion and the removal of methanol, atom types, charges and
charge groups in the amorphous cell are recalculated and
then repeat the same processes to achieve the target con-
version. The amorphous cells for the 200-unit cluster with
solvent accessible surfaces (blue) according to the degree of
crosslinking (X) are shown in Fig. 4b. The simulation box
size is 38.50 Å at X = 11.00% and 35.62 Å at X = 100%.
At low degree of crosslinking, both samples are essentially
nonporous, since the fexible and mobile nature of growing
polymer chains prevents pores from forming. As the degree
of crosslinking increases to a specific degree expected
micropores are formed.
Figure 4b displays the pore volumes as defned by the sol-
vent-accessible surface [22] at diferent degrees of crosslink-
ing. To compare experimental BET surface area with geo-
metric one the solvent-accessible surface area is commonly
used. Even though the geometric and BET surface areas
are fundamentally diferent and should be compared with
care, geometric surface areas obtained for p2NPh–OH
1 3

R. M. N. Kalla et al.
1 3

Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using Sulfonic Acid Functionalized…
◂Fig. 4 a 1,6-bis(methoxymethyl)naphthalen-2-ol monomer used for
sulfonic acid groups in p2NPh–OSO3H. The S(2p) peak of
the synthesis of hypercrosslinked poly(2-naphthol) networks showing
polymerization procedures and b snapshots of molecular simulation
boxes of p2NPh–OH taken at various degrees of crosslinking (X),
showing the solvent-accessible surface areas (blue areas). For amor-
phous cells construction, 200 units monomer were used. Dark blue
areas represent the micropore surface and grey balls and sticks repre-
sent newly formed crosslink sites
p2NPh–OSO3H corresponds to S(2p3/2) [24, 25], indicat-
ing the presence of SO3H within the p2NPh–OSO3H. The
reduced binding energy of the S(2p) peak is determined for
p2NPh–OSO3H (Fig. 5d), suggesting a rise within the elec-
tron density on the sulfur atoms.
The catalytic activity of p2NPh–OSO3H was investigated
for the acylation of phenols, alcohols, thiols, amines, and
aldehydes with acetic anhydride (Sch 1). To pre-optimize
the reaction conditions, a model reaction using phenol with
acetic anhydride was conducted at various conditions in the
presence of p2NPh–OSO3H catalyst. Various protic (etha-
nol, methanol, and water) and aprotic (CH2Cl2, CHCl3, and
toluene) solvents were frstly used for the acylation, resulting
in insufcient yields (50–75%) even after 3 h of reaction
(see entries 1–6 in Table 1). The acylation of phenol was
then conducted under solvent free conditions. Entry 7 in
Table 1 clearly shows the acylation of phenol gives much
better yield (97%) in much shorter reaction time (15 min)
under neat condition. The decrease of catalyst amount from
10 to 5 mg results in the decrease of yield (89%) and the
increase of catalyst amount to 15 mg showed no further
increase of yield. As expected, no products were observed
using an N2-size probe (dN2 =3.681 Å) in Materials Studio.
The surface area is found to record the maximum value,
503.88 m2g−1, at X =68.25%. Strict trend of the variation
of surface area according to the degree of crosslinking is
not observed; however, the surface area decreases as the X
value increases. Finally the surface area becomes 200.28
m2g−1 at X=100%. Considering the experimental BET sur-
face area of p2NPh–OH is 408 m2g−1, the calculated solvent-
accessible surface areas show reasonable agreement with the
experimental BET value as measured by N2 sorption. The
origination of discrepancies between BET surface area and
geometrical one have been well described in the literature
[23].
The p2NPh–OSO3H, is characterized by XPS. As shown
in Fig. 5a, peaks corresponding to oxygen, carbon, and sul-
fur are a unit clearly determined, confrming the presence of
Fig. 5 XPS spectrum of
p2NPh–OSO3H (a) and its
expanded spectra (b–d) cor-
responding to C(1 s), O(1 s) and
S(2p), respectively
1 3

R. M. N. Kalla et al.
Table 1 Optimization of the acylation of phenol in the presence of
Table 2 Acylation of phenols, alcohols, thiols, amines and aldehydes
with acetic anhydride below neat conditions in presence of p2NPh–
OSO3H
p2NPh–OSO3H catalyst
Entry Solvent Catalyst amount (mg) Time (min) Yield (%)a
Compd
Substrate
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
EtOH
MeOH
H2O
CH2Cl2 10
CHCl3 10
Toluene 10
Neat
Neat
Neat
Neat
10
10
10
180
180
180
140
180
180
15
32
15
180
63
58
50
75
65
64
97
89
97
0.0
1
2
3
4
5
6
7
8
C6H5OH
C6H5CH2OH
4-Br-C6H4CH2OH
4-Cl-C6H4CH2OH
C6H5(CH2)2OH
C10H7OH
C10H7SH
SHC2H4OH
SHC2H4SH
C12H25SH
20
14
10
12
15
16
50
45
60
70
8
12
10
12
11
15
12
10
12
15
9
10
8
5
4
4
3
4
3
6
97
95
96
93
92
93
89
94
93
91
97
93
94
95
94
92
92
93
91
88
96
95
84
95
97
98
97
98
98
96
95
96
98
97
98
75
79
10
5
15
9
Catalyst free
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Reaction conditions: phenol (1 mmol), acetic anhydride (1 mmol),
and solvent (4 mL)
C6H5NH2
2-Me-C6H4NH2
3-Me-C6H4NH2
2,4-Me-C6H3NH2
2,5-Me-C6H3NH2
2,6-Me-C6H3NH2
3,5-Me-C6H3NH2
2,4,6-Me-C6H2NH2
2,6-Et-C6H3NH2
2,6-iPr-C6H3NH2
2-Cl-C6H4NH2
2-Cl-3-Me-C6H3NH2
C4H9NH2
aIsolated yields
in the absence of catalyst even after a prolonged reaction
time (entry 10 in Table 1).
Having the optimized conditions, we further examined
for the acylation of varied phenols and benzylic alcohols.
As shown in Table 2, all phenols and benzylic alcohols
were under gone smoothly to the resultant acetates in sen-
sible yields. The benzylic alcohols bearing electron-releas-
ing groups resulted in better yields with shorter reaction
times than aromatic substrates bearing electron-withdraw-
ing groups (entries 3 and 4). The acylations of a range of
thiols, amines and aldehydes were also attempted to con-
frm the potential of the solid acid catalyst. The acylations
of phenols and thiols were proceeded slowly, comparing
to amines and aldehydes. Specifcally high activities were
achieved for the acylations of varied substituted aromatic
amines and substituted aldehydes. No chemo-selectivity
was observed for compounds with two diferent functional
groups like –SH and –OH in a molecule (entry 8, Table 2).
However, the p2NPh–OSO3H catalyst showed very good
substrate selectivity between the phenol and benzyl alco-
hol: i.e. it gave predominantly acylated product of benzylic
alcohol. In the case of ethane-1,2-dithiol and salicylalde-
hydes the corresponding diacetates and triacetates were
formed.
C6H5CH2NH2
C6H5CHO
2-Cl-C6H4CHO
2-Br-C6H4CHO
3-Br-C6H4CHO
4-Br-C6H4CHO
4-NO2-C6H4CHO
4-Me-C6H4CHO
2-OH-5-Br-C6H3 CHO
2-OH-3,5-C-C6H2CHO
2-furfural(C4H3OCHO)
C14H9CHO
4
4
5
4
4
6
8
CH(CH3)2CHO
C5H13CHO
Reaction conditions: substrate (1 mmol), acetic anhydride (1 mmol)
and catalyst (10 mg) at 25 °C under neat conditions
Based on the obtained results, the following reaction
mechanism might be proposed for the acylation of phenols,
alcohols, thiols, amines in the presence of p2NPh–OSO3H
(Sch 2). The mechanism involves the protonation of the
carbonyl group of acetic anhydride by p2NPh–OSO3H
catalyst. Then the nucleophilic addition of various sub-
strates on the electron defcient carbonyl carbon results in
the corresponding acylated products.
aIsolated yields
summarized in Table 3. The polydopamine sulfamic acid-
functionalized magnetic Fe3O4 nanoparticles (Fe3O4@
PDA–SO3H) showed high activity at neat condition [26].
However, it needs tedious multi-step procedures to pre-
pare the catalyst, which makes commercially trouble-
some. In situ generated Ph3P(OAc)2 acted as reasonable
organo-catalyst for the protection of alcohols and thiols
For the comparison of the catalyst performance, the
acylation of benzyl alcohol with acetic anhydride was
1 3

Acylation of Phenols, Alcohols, Thiols, Amines and Aldehydes Using Sulfonic Acid Functionalized…
Scheme 2 Proposed mecha-
nism for the p2NPh–OSO3H-
catalyzed acylation of phenols,
alcohols, thiols, and amines
Table 3 Comparison of the acylation of benzyl alcohol with acetic
at mild conditions [27]. Harmful polar solvent like ace-
anhydride using various catalysts
tonitrile was used to achieve 87% yield in 120 min for
the acylation of benzyl alcohol. Sodiumacetate trihydrate
(NaOAc·3H2O) was also used for the acylation of benzyl
alcohol, needing laborious workup procedure [28]. Bro-
modimethylsulfonium bromide (Me2S+Br Br−) was used
as a catalyst for the protection of phenols, alcohols, thiols,
amines and aldehydes [29]. For the acylation of 1 mmol
of benzyl alcohol large amount of catalyst (111 mg) and
2 mmol of acetic anhydride were used to achieve 90%
yield in 25 min.
Entry Catalyst (mol% or mg)
Solvent Time
(min)/
References
yield(%)
1
2
3
4
5
Fe3O4@PDA–SO3H (30) Neat
30/96
[26]
[27]
[28]
[29]
Ph3P(OAc)2 (1.25)
NaOAc·3H2O (10)
Me2S+Br Br− (111)
p2NPh–OSO3H (15)
CH3CN 20/91
Neat
Neat
Neat
10/95
25/90
14/96
This work
The reusability of p2NPh–OSO3H was also examined for
the preparation of acylation of phenol, from the reaction of
phenol with acetic anhydride. The catalyst was easily recov-
ered by adding EA to the reaction mixture; the insoluble
p2NPh–OSO3H was separated by simple fltration, washed
twice with EA (15 mL), and fnally dried under vacuum. The
catalyst displayed good reusability after 10 runs (Fig. 6).
4 Conclusions
Hyper-cross-linked and porous poly(2-naphthol) was pre-
pared by using Friedel–Crafts alkylation-induced polym-
erization of 2-naphthol and was acid-functionalized to get
solid acid p2NPh–OSO3H catalyst (1.14 mmol –OSO3H
g−1). The catalyst showed excellent activities for the acyla-
tion of phenols, alcohols, thiols, amines, and aldehydes at
eco-friendly reaction conditions. The catalyst also showed
perfect chemo-selectivity for the acylation of phenol and
alcohol. In addition the catalyst retained its activity up
Fig. 6 Efect of p2NPh–OSO3H recycling on the yield of the com-
pound 1
1 3

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Acknowledgements This work was supported by the Basic Science
Research Program of the National Research Foundation of Korea
(2018R1D1A1A09081809). The authors are also grateful to the BK21
PLUS Program for partial fnancial support.
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(2018) Chem Commun 54:2796–2799
Compliance with Ethical Standards
20. Bennett AE, Rienstra CM, Auger M, Lakshmi KV, Grifn RG
(1995) J Chem Phys 103:6951–6958
Conflict of interest The authors declare that they have no confict of
21. Trewin A, Willock DJ, Cooper AI (2008) J Phys Chem C
112:20549–20559
interest.
22. Duren T, Millange F, Fe´rey G, Walton KS, Snurr RQ (2007) J
Phys Chem C 111:15350–15356
23. Hart KE, Abbott LJ, Colina CM (2013) Mol Simul 39:397–404
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Barreca F, Mafra L, Pillinger M, Pinna N, Valente AA (2014) J
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