Solventless acetylation of alcohols and phenols catalyzed by supported iron oxide nanoparticles

Article abstract of DOI:10.1016/j.catcom.2013.11.003

Supported iron oxide nanoparticles on silicate catalysts were found to be efficient and easily recoverable materials in the acetylation of alcohols and phenols to their corresponding acetyl compounds using acetic anhydride under mild and solvent-less conditions. The supported iron oxide nanoparticles could be easily recovered from the reaction mixture and reused ten times without any loss in activity.

Full text of DOI:10.1016/j.catcom.2013.11.003

Catalysis Communications 45 (2014) 129–132
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Solventless acetylation of alcohols and phenols catalyzed by supported
iron oxide nanoparticles
a, ,1
b,c
Fatemeh Rajabi ⁎ , Rafael Luque
a
Department of Science, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran
Departamento de Quimica Organica, Universidad de Córdoba, Edificio Marie Curie (C-3), Campus de Excelencia Agroalimentario CeiA3, Ctra Nnal IV-A, Km 396, E14014 Cordoba, Spain
Department of Chemical and Biomolecular Engineering (CBME), Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 August 2013
Received in revised form 10 October 2013
Accepted 5 November 2013
Available online 12 November 2013
Supported iron oxide nanoparticles on silicate catalysts were found to be efficient and easily recoverable mate-
rials in the acetylation of alcohols and phenols to their corresponding acetyl compounds using acetic anhydride
under mild and solvent-less conditions. The supported iron oxide nanoparticles could be easily recovered from
the reaction mixture and reused ten times without any loss in activity.
©
2013 Elsevier B.V. All rights reserved.
Keywords:
Supported iron oxide nanoparticles
Acetylation
Solventless reactions
Heterogeneous catalyst
1
. Introduction
acetylation of a wide range of alcohols using previously reported and
characterized supported iron oxide nanoparticles on silicate materials
(Fe/SBA-15). Basic characterization of the material is included in this
work, readers are kindly referred to previous reports from the group
for a detailed and comprehensive characterization [28–31].
Acetylation of alcohols and phenols is a frequently utilized transfor-
mation in synthetic chemistry and widely used as protecting group in
multi-step pharmaceutical synthesis and food or cosmetic industries
[
1,2]. The acetylation of alcohols and phenols has been typically
performed using acetic anhydride or acetyl chloride in the presence of
either base [3–6] or acid catalysts [7–21]. Although various acetylation
methods are available, most protocols to date possessed inherent draw-
backs including long reaction times, harsh conditions, harmful organic
solvents, and tedious work-up procedures. One of the most promising
solutions to these problems seems to be immobilization of catalysts or
using eco-friendly solvent-free conditions. Supported or solid catalyst
can be easily separated by filtration and the catalyst can be simply
recovered and recycled in the reaction, often also providing higher
selectivity to products under typically simpler work-up procedures
2. Experimental
2.1. Synthesis of iron oxide supported nanoparticles
Supported iron oxide NPs were synthesized according to our previously
reported procedure [30]. A solution of salicylaldehyde (2 mmol, 0.244 g) in
an excess of absolute MeOH was added to the aminopropyl-functionalized
SBA-15 materials (2.35 g, NH
came yellow due to imine formation. After 6 h, Fe(NO)
(1 mmol), was added to the solution, and the mixture was gently heated
at 50 °C for 24 h, until a dark red color was observed, which is due to the
formation of the metal oxide nanoparticles on the SBA-15. The final product
was washed with MeOH and water until the washings were colorless. Fur-
ther drying of the solid product was carried out in an oven at 80 °C for 8 h.
Characterization data of an analogous Fe/Al-SBA-15 material has been
exclusively included for comparative purposes.
−
1
2
loading 0.85 mmol g ). The solution be-
·9 H O,
3
2
[22–24]. These premises generally work for the use of nanomaterials
and supported nanoparticles as catalysts in various types of chemistries.
Such nanoentities provide a remarkable versatility in their use as
heterogeneous catalysts in a wide range of processes (e.g. acid, base
and redox catalysis) [25–27].
Following recent research endeavors from the groups aimed to
benign by design protocols for nanomaterials synthesis and heteroge-
neously catalyzed applications, this work reports the solventless
2.2. Materials characterization
Nitrogen adsorption measurements were carried out at 77 K using an
ASAP 2000 volumetric adsorption analyzer from Micromeritics. The sam-
ples were outgassed for 24 h at 100 °C under vacuum (p b 10 Pa) and
⁎
Corresponding author.
E-mail addresses: f_rajabi@pnu.ac.ir, rafaluque@ust.hk (F. Rajabi), rafaluque@ust.hk
−
2
(
R. Luque).
1
Tel.: +98 2813336366; fax: +98 2813344081.
subsequently analyzed. The linear part of the BET equation (relative
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.11.003

130
F. Rajabi, R. Luque / Catalysis Communications 45 (2014) 129–132
Table 2
pressure between 0.05 and 0.30) was used for the determination of the
Acetylation of various alcohols to their corresponding products using supported iron oxide
nanoparticles as catalysts.
specific surface area. Mean pore size diameter (DBJH) and pore volumes
(VBJH) were obtained from porosimetry data.
Fe content in the materials was determined using Inductively
Coupled Plasma (ICP) in a Philips PU 70000 secuential spectrometer
equipped with an Echelle monochromator (0.0075 nm resolution)
3
and couple to Mass Spectrometry. Samples were digested in HNO and
subsequently analyzed by ICP at the SCAI of Universidad de Cordoba.
Pyridine (PY) and 2,6-dimethylpyridine (DMPY) titration experi-
ments were conducted at 200 °C via gas phase adsorption of the basic
probe molecules utilizing a pulse chromatographic titration methodolo-
gy.20,21 Briefly, probe molecules (typically 1–2 mL) were injected in
very small amounts (to approach conditions of gas-chromatography
linearity) into a gas chromatograph through a microreactor in which
the solid acid catalyst was previously placed. Basic compounds are
adsorbed until complete saturation from where the peaks of the probe
molecules in the gas phase are detected in the GC. The quantity of
probe molecule adsorbed by the solid acid catalysts can subsequently
be easily quantified. In order to distinguish between Lewis and Bronsted
acidity, the assumption that all DMPY selectively titrate Bronsted sites
(
methyl groups hinder coordination of nitrogen atoms with Lewis
acid sites) while PY titrates both Bronsted and Lewis acidity in the
materials was made. Thus, the difference between the amounts of
PY (total acidity) and DMPY (Bronsted acidity) adsorbed should
correspond to Lewis acidity in the materials.
2
.3. General procedure for the acetylation of alcohols and phenols
To a solution of substrate (1 mmol) and acetic anhydride (1.5 mmol)
was added supported iron catalyst (Fe/SBA-15) (0.005 mmol, 0.085 g)
and the mixture was stirred at 40 °C. After completion of the reaction
(
TLC), the reaction mixture was filtered and the catalyst rinsed with
ethyl acetate and heated at 70 °C prior to its reuse in the next reaction.
The organic layer was washed with saturated NaHCO and water, and
3
dried over anhydrous sodium sulfate. The product was obtained after
removal of the solvent.
3
. Results and discussion
The preparation and characterization of supported iron oxide nano-
particles on mesoporous SBA-15 have been previously reported. The Fe-
containing catalyst featured similar textural and structural properties as
compared to its parent silicate in terms of high surface area (650 vs.
20 m2
g
−1
), narrow pore size within the mesoporous range
6
(
(
3
−1
4.8 nm), a relatively high pore volume (0.7 cm g ) and both Lewis
mostly) and minor Bronsted acidity as measured by a gas chromatog-
raphy method using pyridine (PY) and 2,6-dimethyl pyridine (DMPY)
as probe molecules (Table 1) [32]. The iron content was ca. 0.62 wt.%
(
2 3
as measured by ICP/MS) and the hematite Fe O phase was found to
be the active phase in the material [28–30,33]. Due to such acidity,
such materials as well as analogously synthesized aluminosilicates
(
Table 1, last entry, included as comparison) have been previously
utilized as catalyst in a range of acid-catalyzed processes [33,34].
Table 1
Textural and acidic properties of Fe/SBA-15 materials.
Catalyst
S
(
BET
Pore size Fe content Surface acidity at 300 °C
m2 g−1
)
(nm)
(wt.%)
(μmol g
−1
)
PY
DMPY
(total acidity) (Bronsted acidity)
SBA-15
Fe/SBA-15
Fe/SBA-15
650
620
598
4.9
4.8
4.6
–
–
–
0.62
0.60
58
51
12
9
(
5th reuse)
a
Isolated yields. b 3 eq of acetic anhydride. c 4.5 eq of acetic anhydride.
Fe/Al-SBA-15 688
7.8
0.63
104
88

F. Rajabi, R. Luque / Catalysis Communications 45 (2014) 129–132
131
1
00
Fe/Al-SBA-15 (included as comparison), Fe/SBA-15 was able to simply
promote the proposed acetylation process.
9
0
0
0
0
0
0
0
0
0
Our protocol was compared to a recent literature work [35] for the
particular case of a challenging molecule such as glycerol for triacetin
production. Very similar results (94% yield, 25 min reaction at 40 °C
for this work vs. 100% yield after 20 min reaction at 60 °C using beta-
zeolite or K-10 montmorillonite) were recorded for the same reaction
using acetic anhydride as acetylating agent. In fact, Silva et al. showed
poor triacetin yields were generally obtained when acetic acid was
employed as acetylating agent, in good agreement with our findings
8
7
6
5
4
3
2
1
(
results not shown). With regard to phenolic-derived compounds,
comparative data on Table 3 clearly demonstrates the advantages of
the proposed methodology as compared to similar processes catalyzed
by various materials ranging from ZnO to less environmentally friendly
and not reusable bismuth, ruthenium and indium chlorides as well as
magnesium perchlorate (Table 3).
0
1st
2nd
3rd
4th
5th
6th
7th
8th
9th
10th
Fig. 1. Reusability of Fe/SBA-15 catalyst in acetylation of phenol. Reaction conditions:
mmol phenol, 1.5 mmol acetic anhydride, supported iron catalyst (0.005 mmol,
.085 g), 40 °C, 15 min reaction.
1
0
4. Conclusions
In this work, the acetylation of a series of alcohols including phenols,
naphthols, hydroxyl-substituted chromenones and polyols (e.g. glycerol)
has been conducted under mild conditions, typically 15–30 min reaction
and 40 °C. Acetic anhydride was utilized as acetylating agent instead of
the corrosive acetyl chloride. Table 2 summarizes the main relevant
results of this work. Blank reactions (in the absence of catalyst as well
as with the SBA-15 support) provided negligible conversion in the
selected reaction even for the simplest substrates (e.g. phenol). Compa-
rably, supported iron oxide nanoparticle systems were able to convert a
wide range of substrates into their corresponding acetylated products. A
number of relevant compounds could be produced in high yields
Supported iron oxide nanoparticles on porous silicates have been
proved to be highly active and stable catalysts for the acid-catalyzed
acetylation of a series of alcohols and phenols in excellent yields to
products. These included the transformation of relevant biomass-
derived platform chemicals (e.g. glycerol). Reactions could efficiently af-
ford the target product at short times of reaction (typically 15–30 min)
under mild reaction conditions. The catalyst was found to be highly
reusable under the investigated conditions which prove the usefulness
of supported transition metal oxide nanoparticle systems in heteroge-
neously catalyzed processes.
(
N90%) in a short time of reaction, typically 15–30 min. The protocol
was amenable to all types of substituted phenols with electron donating
and electron withdrawing groups, naphthols, benzyl alcohol and
cinnamyl alcohol as well as other biomass-derived relevant molecules
including glycerol, propanediol and cylohexanol (Table 2).
Acknowledgments
F. R. is grateful to Payame Noor University for support of this work.
R.L. gratefully acknowledges Ministerio de Ciencia e Innovación,
Gobierno de España for the concession of a Ramon y Cajal contract
To test the heterogeneity of the catalytic system, the catalyst was
filtered after half of reaction time for acetylation of phenol during the
reaction and the filtrate was allowed to react further. We found that
after filtration of the supported iron catalyst, the filtration liquor did
not further react. AAS confirmed that no Fe could be detected in the
solution phase upon catalyst filtration after the end of the reaction.
Reuse reactions were carried out under similar conditions. The cata-
lyst showed excellent recoverability and reusability over 10 successive
runs under the same conditions to the first run (Fig. 1). No detectable
metal traces in solution (b0.5 ppm) were determined by ICP of the
final reaction mixture, confirming the strong coordination and stability
of iron in the catalyst that prevented metal leaching during/after the
reaction, something somehow expected from the mild reaction
conditions (40 °C) and short times of reaction (typically minutes).
Reaction conditions: 1 mmol substrates, 1.5 mmol acetic anhydride,
supported iron catalyst (0.005 mmol, 0.085 g), 40 °C (unless otherwise
stated).
(
ref. RYC 2009-04199) and funding under project CTQ2011 28954-
C02-02 as well as Consejeria de Ciencia e Innovación, Junta de Andalucía
for funding under project P10-FQM-6711.
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