N-Benzylation of primary amines using magnetic Fe3O4 nanoparticles functionalized with hexamethylenetetramine as an efficient and recyclable heterogeneous catalyst

Article abstract of DOI:10.1016/j.molstruc.2020.128583

Herein we report, a new, simple and mild procedure for N-benzylation and N,N-dibenzylation of anilines through the reaction of aniline derivatives and benzyl bromide at 60 °C in EtOH in the presence of catalytic amounts of magnetic Fe₃O₄ nanoparticles functionalized with hexamethylenetetramine (Fe₃O₄?SiO₂?Propyl-HMTA). The title compounds were formed in high purity and their structures characterized by spectral analysis. The results also showed that the magnetic nanoparticle catalyst had significant advantages including, simplicity of preparation, heterogeneity, stability and recyclability. Moreover, the catalyst was characterized by various methods, such as FT-IR, SEM, VSM, TEM, TGA and XRD, after the reaction to compare with its structure before reaction.

Full text of DOI:10.1016/j.molstruc.2020.128583

Journal Pre-proof
N‐Benzylation of primary amines using magnetic Fe O nanoparticles functionalized
3 4
with hexamethylenetetramine as an efficient and recyclable heterogeneous catalyst
Samira Noori, Ramin Ghorbani-Vaghei, Maryam Mirzaei-Mosbat
PII:
S0022-2860(20)30908-X
DOI:
https://doi.org/10.1016/j.molstruc.2020.128583
MOLSTR 128583
Reference:
To appear in: Journal of Molecular Structure
Received Date: 9 March 2020
Revised Date: 28 May 2020
Accepted Date: 1 June 2020
Please cite this article as: S. Noori, R. Ghorbani-Vaghei, M. Mirzaei-Mosbat, N‐Benzylation of primary
amines using magnetic Fe O nanoparticles functionalized with hexamethylenetetramine as an
3 4
efficient and recyclable heterogeneous catalyst, Journal of Molecular Structure (2020), doi: https://
doi.org/10.1016/j.molstruc.2020.128583.
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CRediT author statement
Samira Noori: Doing laboratory work and preparing data. Ramin Ghorbani-Vaghei: Supervisor
and presenter of research work and results analysis. Maryam Mirzaei-Mosbat: Writing and
editing

Graphical Abstract
N
‐
Benzylation of Primary Amines Using Magnetic Fe3O4 Nanoparticles Functionalized with
Hexamethylenetetramine as an Efficient and Recyclable Heterogeneous Catalyst
Samira Noori, Ramin Ghorbani-Vaghei * and Maryam Mirzaei-Mosbat
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, PO Box 65174,
Hamedan, Iran

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N Benzylation of Primary Amines Using Magnetic Fe3O4 Nanoparticles
Functionalized with Hexamethylenetetramine as an Efficient and Recyclable
Heterogeneous Catalyst
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Samira Noori, Ramin Ghorbani-Vaghei *and Maryam Mirzaei-Mosbat
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Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, 6517838695,
Hamedan, Iran
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Fax/Tel +98(813)8257407; E-mail: rgvaghei@yahoo.com
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Abstract
Herein we report, a new, simple and mild procedure for N-benzylation and N,N-dibenzylation of anilines
through the reaction of aniline derivatives and benzyl bromide at 60 °C in EtOH in the presence of
catalytic amounts of magnetic Fe3O4 nanoparticles functionalized with hexamethylenetetramine
(Fe3O4@SiO2@Propyl-HMTA). The title compounds were formed in high purity and their structures
characterized by spectral analysis. The results also showed that the magnetic nanoparticle catalyst had
significant advantages including, simplicity of preparation, heterogeneity, stability and recyclability.
Moreover, the catalyst was characterized by various methods, such as FT-IR, SEM, VSM, TEM,
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TGA and XRD, after the reaction to compare with its structure before reaction.
Keywords: magnetic Fe3O4, nanoparticles, hexamethylenetetramine, N-benzylation.
1. Introduction
As the carbon-nitrogen bond is of great importance in pharmaceutical and bioactive compounds
[1], many researchers have been recently engaged in designing C-N bond formation protocols as
new strategies in organic synthesis [2,3]. Recently, the synthesis of amines has attracted
considerable attention because amines and their derivatives are major functionalities in various
natural products and important synthetic targets. They have been greatly used as solvents, fine
chemicals, fluorescence probes, pharmaceuticals, agrochemicals, catalysts for polymerization
and in synthetic dyes [4,5]. Consequently, various research groups aimed at developing novel
methods in order to prepare the mentioned compounds. It should be noted that N-benzylation of
amines with alkyl halides can be regarded as a significant synthetic tool for the preparation of
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mono- and di-N-benzylated derivatives. However, running such reactions in the presence of a
base, has its own drawbacks; e.i. long reaction times, high temperatures and low yields of desired
products [6,7]. Therefore, it is necessary for the protocol to be significantly improved. A greatly
advisable solution is to replace a homogenous catalytic process by a heterogeneous one [8].
Based on such a strategy, there have been different reports for the N-alkylation of amines with
excellent yields; for example Marzaro et al have announced the selective N-alkylation of amines
using alkyl halides in an aqueous NaOH medium under microwave irradiation [9]. Though this
procedure led to satisfactory results, it required using specialized microwave equipment [10-12].
In another attempt, Zhao et al have successfully run N-alkylation reaction of amines in the
presence of catalytic amounts of iron (III) bromide, dl-pyroglutamic acid and 1,2,3,4,5-
pentamethylcyclopenta-1,3-diene at 160 °C under an Ar atmosphere [13]. Zhang et al reported
excellent yields using Fe2O3–supported palladium catalyst for the N-alkylation of amines with
alcohols at 140 °C or 160 °C [14]. Notably, the last mentioned method needs argon atmosphere
and relatively high temperature in order to achieve acceptable yields. To find a way out of this
problem, we were prompted to investigate the use of magnetic nanoparticles (MNPs) for the N-
alkylation of anilines.
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In the past few decades, novel catalysts such as: M(Fe, Co, Mn, Cu)-doped ZrO2 tetragonal
nanoparticles [15-18], Au@TiO2 yolk-shell NPs [19], (Y, Cu) codoped a-Fe2O3 nanostructure
[20], Gadolinium Substituted BiFeO3 Nanoparticles [21] carbon quantum dots (CQDs) [22] and
carbon nanotubes-titania quantum dots (FCNT-TQDs) [23] have been introduced as catalysts
developed with their catalytic activities. Because of their high surface area, facile preparation
route, high activity and selectivity, easy separation from the reaction medium, recyclability and
reusability have been developed as suitable replacements for conventional heterogeneous
catalysts. In this article, we also introduce a new catalyst.
One of the major problems in using homogeneous catalysts is their separation from the reaction
medium. Though the use of heterogeneous catalysts solves this problem, the unavailability of all
active sites remains as the main problem of such catalysts. Nanocatalysts are the bridge between
homogeneous and heterogeneous catalysts due to their high surface area, causing a significant
contact between the reactants and the catalyst. In this aspect, nanocatalysts are similar to
homogeneous ones but are as well easy to separate from the mixture. Magnetic nanoparticles are
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considered as broadly applied nanocatalysts which can be separated by an external magnet and
reused several times [24-28].
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Different organic and inorganic compounds, for example ionic liquids (ILs), have been used to
modify MNPs [29, 30]. The negative properties of ILs, i.e. their high viscosity, can be decreased
by immobilizing functional ILs on a surface. Herein, report the use of silica‐coated MNPs
surface modified by hexamethylenetetramine is reported [31].
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In the presented study, the synthesis of mono-N- and N,N-dibenzylation of primary amines
(Scheme 1) under mild conditions is described. Low reaction temperature, good yields of
products, green method, and no need for inert atmosphere and metal can be cited as other
important advantages of this protocol.
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Scheme 1. General approach of N,N-dibenzylation of primary amines
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2. Experimental Section
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2.1. General Remarks
All chemicals were purchased from commercial suppliers (Merck and Fluka companies). Proton
Nuclear Magnetic Resonance NMR (1H NMR) spectra and carbon nuclear magnetic resonance
(13C NMR) spectra were run on Bruker BioSpin GmbH 250 MHz FT NMR spectrometers.
Infrared (IR) spectra were taken using a Shimadzu 435-U-04 FT spectrophotometer using KBr
tablets. IR data are represented as frequency of absorption (cm-1). Melting points were measured
on a BUCHI 510 apparatus in open capillary tubes. Scanning electron microscopy (SEM) was
fulfilled med on EM3200 instrument operated at 30 kV accelerating voltage. The magnetic
measurements were performed with VSM at room temperature.
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2.2. Preparation of Fe3O4 MNPs
To a 100 mL of deionized water, FeCl3⋅6H2O (11.3 g, 0.0418 mol) and FeCl2⋅4H2O (5.648 g,
0.020 mol) were added and dissolved and stirred at 85 °C for 30 min. 25 mL of ammonia (28%
aqueous solution) was then rapidly injected into the reaction mixture. In order to afford Fe3O4
nanoparticles, the reaction was stirred for another 30 min at 85 °C. The suspended Fe3O4
nanoparticles were isolated by an external magnet. Finally, the product was washed subsequently
with distilled water and ethanol, dried at 80 °C in an oven.
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2.3. Preparation of MNPs coated by silica (Fe3O4@SiO2 MNPs)
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A modified Stöber method was applied in order to prepare Fe3O4@SiO2 core-shell nanoparticles.
To a mixture of 80 mL of deionized water, 20 mL of EtOH and 2 mL of ammonia (28 wt%),
1.0g of the naked Fe3O4 was dispersed and 2.0 mL of tetraethyl orthosilicate (TEOS) was then
added. The core-shell MNPs (Fe3O4@SiO2MNPs) were vigorously stirred at room temperature
for 2 h and separated using an external magnet in order to remove the unbound silica particles.
Then nanoparticles were washed subsequently with deionized water, EtOH and acetone, and
finally dried at room temperature.
2.4. Preparation of HMTA containing silane (Ionic liquid)
3-Chloropropyltrimethoxysilane (2.0 g, 10 mmol) was added to a solution of HMTA (1.4 g, 10
mmol) in toluene (30 mL). The resulting precipitate was refluxed under nitrogen atmosphere for
24 h which was then isolated and washed with EtOH.
2.5. Preparation of Fe3O4@SiO2@Propyl-HMTA
To a dispersed solution of Fe3O4@SiO2 MNPs (2.0 g) in dry toluene (30 mL), it was added
HMTA containing silane (0.5 g) and sonically irradiated in an ultrasonic bath for 30 min. The
mixture was then refluxed for 48 h under Nitrogen atmosphere. An external magnet was applied
in order to separate the Fe3O4@SiO2@Propyl-HMTA. Finally, the product was washed with
EtOH for several times and dried within 6 h in an oven.
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2.6. General procedure for N-benzylation and N,N-dibenzylation of primary amines
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A mixture of aniline (1eq), benzyl bromide (2.2 eq) and 0.06 g Fe3O4@SiO2@Propyl-HMTA in
EtOH (5 mL) was heated at 60 . After completion of the reaction, as indicated by the TLC (n-
hexane/acetone 10:3), the reaction mixture was cooled to room temperature and the nanocatalyst
was separated using an external magnet. The crude product washed with ethanol and purified by
hot ethanol. The products were characterized using physical and spectroscopic (IR, NMR, MS)
data.
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N,N-dibenzyl-4-chloroaniline 4a:
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White solid; Yield: 93%; M.p. 104-105 °C; H NMR (250 MHz, CDCl3): δ 4.65 (s, 4H, CH2),
6.64-6.67 (d, J= 7.5, 2H, ArH), 7.10-7.13 (d, J= 7.5, 2H, ArH), 7.23-7.39 (m, 10H, ArH); 13C
NMR (62.5 MHz, CDCl3): δ 54.5, 113.7, 121.6, 126.6, 127.1, 128.8, 129.0, 138.1, 147.7; MS
(m/z): 307 (M+, 100%), 215.9, 179.9, 137.9, 91.2, 65.0.
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N,N-dibenzyl-4-bromoaniline 4b:
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White solid; Yield: 94%; M.p. 125-126 °C; H NMR (250 MHz, CDCl3): δ 4.69 (s, 4H, CH2),
6.63-6.67 (d, J= 7.5, 2H, ArH), 7.29-7.37 (m, 12H, ArH); 13C NMR (62.5 MHz, CDCl3): δ 54.4,
108.6, 114.2, 126.5, 127.1, 128.8, 131.9, 138.0, 148.1; ; MS (m/z): 351.06 (M+, 100%), 274.0,
260.0, 180.9, 91.2, 65.0.
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N,N-dibenzyl-4-methoxyaniline 4c:
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Light yellow solid: 91%; M.p. 85-87 °C; H NMR (250 MHz, , DMSO-d6):): δ 4.55 (s, 4H,
CH2), 6.59-6.70 (q, 4H, ArH), 7.21-7.31 (m, 10H, ArH); 13C NMR (62.5 MHz, DMSO-d6): δ
29.0, 55.4, 114.9, 127.0, 127.3, 128.8, 139.7, 143.1, 151.6; MS (m/z): 303.16 (M+, 100%), 287.1,
210.2, 196.1, 91.1, 77.1, 65.1.
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N,N-dibenzylaniline 4d:
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Light green solid; Yield: 94%; M.p. 85-87 °C; H NMR (250 MHz, DMSO-d6): δ 4.69 (s, 4H,
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CH2), 6.67-7.44 (m, 15H, ArH); C NMR (62.5 MHz, DMSO-d6): δ 56.0, 122.7, 123.8, 127.6,
128.1, 128.5, 128.8, 129.4, 129.8, 130.0, 130.5; MS (m/z): 273.15 (M+, 100%), 196.1, 182.1,
104.1, 91.1, 77.1, 65.1.
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tribenzylamine 4e:
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Light yellow solid; Yield: 93%; M.p. 90-92 °C; H NMR (250 MHz, CDCl3): δ 4.14 (s, 6H,
CH2), 7.24-7.66 (m, 15H, ArH); 13C NMR (62.5 MHz, CDCl3): δ 55.9, 128.7, 129.3, 129.8,
131.3; MS (m/z): 287.17 (M+, 100%), 210.1, 196.1, 181.1, 91.1, 65.1
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N,N-dibenzyl-2,4-dimethylaniline 4g:
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Light yellow solid; Yield: 92%; M.p. 144-146 °C; H NMR (250 MHz, DMSO-d6): δ 2.26 (s,
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3H, CH3), 2.32 (s, 3H, CH3), 4.41 (s, 4H, CH2), 7.07-7.29 (m,13H, ArH); C NMR (62.5 MHz,
DMSO-d6): δ 18.5, 20.8, 40.4, 122.8, 127.4, 128.5, 131.9, 133.3; MS (m/z): 301.18 (M+, 100%),
224.1, 210.1, 194.1, 122.1, 91.1, 77.1, 65.1.
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N-benzyl-4-nitroaniline3h:
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Yellow solid; Yield: 91%; M.p. 84-86 °C; H NMR (250 MHz, CDCl3): δ 4.43 (s, 2H, CH2),
4.85 (s, 1H, NH), 6.55-6.58 (d, J= 7.5 Hz, 2H, ArH), 7.20-7.34 (m, 5H, ArH), 8.06-8.09 (d, J=
7.5 Hz, 2H, ArH); 13C NMR (62.5 MHz, CDCl3): δ 47.6, 111.3, 126.4, 127.3, 127.8, 128.9; MS
(m/z): 228 (M+, 100%), 180.9, 91.0, 65.0
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N-benzyl-2-methyl-4-nitroaniline 3i:
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Yellow solid; Yield: 93%; M.p. 104-105 °C; H NMR (250 MHz, CDCl3): δ 2.22 (s, 3H,
CH3)4.50 (s, 2H, CH2), 4.67 (s, 1H, NH), 6.52-6.55 (d, J= 7.5 Hz, 1H, ArH), 7.35-7.41 (m, 5H,
ArH), 8-8.03 (d, J= 7.5 Hz, 2H, ArH); 13C NMR (62.5 MHz, CDCl3): δ 17.3, 47.7, 108.2, 121.1,
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124.6, 126.0, 127.3, 127.8, 128.9, 137.4, 137.8, 151.3; MS (m/z): 242.1 (M+, 100%), 194.1,
165.1, 91.1, 65.1
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N-benzyl-2,6-dimethylaniline 3j:
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Light yellow solid: 87%; M.p. 124-126 °C; H NMR (250 MHz, CDCl3): δ 2.40 (s, 6H, CH3),
4.64 (s, 2H, CH2), 6.98 7.22 (m, 8H, ArH), 10. 93 (s, 1H, NH), ArH; 13C NMR (62.5 MHz,
CDCl3): δ 19.6, 53.5, 128.5, 129.2, 129.6, 129.9, 131.4, 132.1, 133.5; MS (m/z): 211.2 (M+,
100%), 120.1, 91.2, 77.1, 65.1
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3. Result and discussion
In this project Fe3O4@SiO2@Propyl-HMTA was synthesized and used to develop the convenient
methods for N,N-dibenzylation of anilines [32]. For this purpose, after preparing the Fe3O4
nanoparticles [33] silica was used as a protecting shell to form the core-shell structure
(Fe3O4@SiO2) [34-36]. On the other hand, and in order to synthesize the ionic liquid, HMTA
was treated with triethoxy-3-(chloropropyl)-silane in dry toluene and refluxed for 24 h. As the
mole ratio of reactants were chosen to be 1:1, it is reasonable to assume that only one nitrogen
atom has reacted with triethoxy-3-(chloropropyl)-silane. As a final step, Fe3O4@SiO2@Propyl-
HMTA catalyst (figure 1) was prepared by coating MNPs (Fe3O4@SiO2) with the ionic liquid.
Afterwards, Fe3O4@SiO2@Propyl-HMTA was investigated for its effect on N-benzylation and
N,N-dibenzylation of anilines.
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Figure 1. The structures of Fe3O4@SiO2@Propyl-HMTA
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At first, the catalytic activity of Fe3O4@SiO2@Propyl-HMTA was compared with those of other
catalysts reported in literature, the results of which are shown in Table 1. Based on these data, the
Fe3O4@SiO2@Propyl-HMTA is one of the most effective catalysts for N,N dibenzylation of
anilines. It is assumed that, owing to the presence of nitrogen atoms in the HMTA moiety of the
catalyst, it acts as a Lewis base and hence, prevents the deactivation of aniline.
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Table 1: Comparison of various catalysts for the N-benzylation and N,N-dibenzylation of primary amines
Entry
1
Catalyst
K10–ZnO
T (℃)
70
Time (min)
720
Yield (%)
86
Ref
[8]
2
3
4
5
6
SiO2-Cu2O
SiO2-CuI
100
15
480
240
1440
4
50
75
60
97
94
[38]
[39]
I2
120
150
60
[37]
Microflow Reactor
Fe3O4@SiO2@PropylHMTA
[40]
240
This work
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In order to optimize the reaction conditions, the reaction of aniline (1eq) and benzyl bromide
(2.2eq) was chosen as the model one. Conducting the model reaction in the absence of any
catalyst revealed that it did not produce the desired product (Table 2, entry 1). Table 2 illustrates
that 0.06 g of the catalyst is optimal amount (entries 11-12). It should be noted that the yield of
reaction in the presence of either MNPs or MNPs@SiO2, is much less than that of
MNPs@SiO2‐@Propyl-HMTA (Table 2, entries 13-14). Running the reaction in different
solvents (Table 2, entries 2–6) revealed that EtOH was the best choice. It was also found that the
optimal temperature for this reaction was 60 °C (Table 2, entry 8). Consequently, the best
reaction conditions are the ones mentioned in entry 10 of Table 2. It is worth noting that the
products were characterized by FT-IR, 1H NMR, 13C NMR and Mass spectroscopic data.
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Table 2: Optimization of reaction conditionsa
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Entry
1
Catalyst
-
Solvent
EtOH
Time [min]
720
Temperature
reflux
Yieldb(%)
-
2
3
0.1
0.1
H2O
H2O/EtOH
CH3CN
Solvent-free
EtOH
720
480
480
720
720
240
240
240
240
360
480
720
720
100
100
reflux
100
r.t
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43
74
67
65
84
86
90
94
82
63
12
22
4
0.1
5
0.1
6
0.1
7
0.1
EtOH
reflux
60
8
0.1
EtOH
9
0.08
EtOH
60
10
11
12
13
14
0.06
EtOH
60
0.05
EtOH
60
0.03
EtOH
60
Fe3O4
EtOH
reflux
Fe3O4@SiO2
EtOH
reflux
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aReaction conditions: aniline (1 mmol), benzyl bromide (2.2 mmol), catalyst, solvent (5 mL). bIsolated yield.
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In final step of this project, we turned our attention toward the substrates reactivity (benzyl
halides and anilines). The reaction of aniline with benzyl bromide and benzyl chloride at
different temperatures shows that benzyl bromide is more reactive than benzyl chloride (Table
3).
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Table 3: Reactivity of substrates
Entry
1
Catalyst
0.06
Substrate
BnBr
Time (min)
240
T (℃)
reflux
Yield (%)
86
2
3
4
0.06
0.06
0.06
BnBr
BnCl
BnCl
240
360
360
60
reflux
60
94
72
76
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On the other hand, different substituted anilines were chosen to test the effect of electron-
withdrawing or electron-releasing groups on mono N‐benzylation and N,N-dibenzylation reaction
(Table 4). Simple aniline was converted into N,N-dibenzylated product with 94% yield in 4 h
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(Table 4, entry 4d). Interestingly, 4-nitroaniline derivatives provided mono-N-benzylated anilines
under selected conditions due to the electron-withdrawing effect of the nitro group and
subsequent reduction in nucleophilicity aniline (Table 4, entries 3h–3i). And finally, the hindered
aniline 2,6-dimethylaniline, just yielded the corresponding mono-N-benzylated product in
reaction with benzyl bromide (entry 3j).
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Table 4 N-benzylation and N,N-dibenzylation of primary amines using Fe3O4@SiO2@Propyl-HMTA as a catalysta
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N
N
N
N
OCH3
Br
Cl
4b (240 min-94%)
4a(240 min-93%)
4c (207 min-91%)
4d (240 min-94%)
N
N
N
H3C
COOH
CH3
4e (207 min-93%)
4g (270 min-92%)
4f (300 min-89%)
HN
HN
HN
H3C
H3C
CH3
NO2
3h (324 min-91%)
NO2
3i (300 min-93%)
3j (324 min-87%)
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10
11
12
aReaction conditions: aniline (1 mmol), benzyl bromide (2.2 mmol), Fe3O4@SiO2@Propyl-HMTA (0.06 g), EtOH
(5 mL), reflux
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To account for the effect of Fe3O4@SiO2@Propyl– HMTA in N,N-dibenzylation of primary amines
the following mechanism is proposed (Scheme 2). At first, aniline attacks to the electron-deficient
center of benzyl bromide (the released proton is scavenged by HMTA moiety of the catalyst) [41,
42]. In the next step, N,N-dibenzylation of primary amines is accomplished by another nucleophilic
reaction and elimination of the second proton of aniline. In comparison with HMTA as a
catalyst, the application of Fe3O4@SiO2@Propyl-HMTA nanomagnetic catalyst provides higher
reactivity and catalytic power due to its enhanced surface area [43, 44].
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Scheme 2. Suggested mechanism for the N,N-dibenzylation of primary amines
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The mode reaction was also used to assess the recyclability of the catalyst. In each cycle the
catalyst was separated, washed with hot ethanol, dried and reused in the next cycle. Figure. 2
illustrates the results and confirming the recyclability of the nanocatalyst.
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Figure 2. Recyclability of the Fe3O4@SiO2@Propyl-HMTA (MNPs)
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Various methods were used in order to analyze the catalyst i.e. Fourier transform infrared (FT-
IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy
(TEM), thermogravimetry analysis (TGA), X-ray diffraction (XRD) and vibrating sample
magnetometer (VSM). It was clarified the successful synthesis of Fe3O4@SiO2@Propyl– HMTA
[31].
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Figure 3 shows the SEM images of the catalyst before and after N-benzylation reaction which
reveal the maintenance of the morphology of nearly spherical nanoparticles with nanometric
dimensions after the reaction.
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Figure 3. SEM images of the Fe3O4@SiO2@Propyl-HMTA (MNPs) before(a) and after(b) the reaction
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The structure of the catalyst before and after reaction was also investigated by FT IR
spectroscopy (Figure 4). As is seen, the characteristic bands attributed to (Fe-O), (Si-O-Si) and
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(O-H) stretching vibrations, that is, (540 cm-1), (802 and 1103 cm-1) and (3444 cm-1)
respectively, did not change after running the reaction.
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Figure 4. FT‐IR spectra of Fe3O4@SiO2@Propyl-HMTA (MNPs) before (a) and after (b) the reaction.
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The X‐ray diffraction analysis of the catalyst before and after the reaction is shown in Figure 5.
As seen from images, the positions and relative intensities of all characteristic diffractions are
almost same implying that the original structure of Fe3O4@SiO2@Propyl-HMTA has preserved
after the reaction (2θ= 30°, 35.5°, 42.5°, 57°and 62°). A strong peak in curves observed at
2θ=35.5 is attributed to the pure Fe3O4. Regarding the position and severity of the peaks, it could
be inferred that the manipulations performed in this study could not alter the Fe3O4 phase.
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Figure 5. XRD pattern of Fe3O4@SiO2@Propyl-HMTA (MNPs) before (a) and after (b) the reaction.
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The magnetic properties of catalyst were evaluated by vibrating sample magnetometer (VSM)
analysis (Figure 6). This figure shows that the magnetic behavior of the catalyst is almost
identical before and after the reaction, illustrating no obvious alteration of the catalyst structure
during the reaction. According to Figure 6, the mass manetization of Fe3O4@SiO2@Propyl-
HMTA (MNPs) is about 10 emu/g. As is observed in these curves there are no hysteresis loops
for the nanoparticles and the Fe3O4@SiO2@Propyl-HMTA (MNPs) exhibit the
superparamagnetic qualities as that of Fe3O4 (MNPs).
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Figure 6. Magnetic curves of the Fe3O4@SiO2@Propyl-HMTA (MNPs) before and after the reaction.
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TEM image of the Fe3O4@SiO2@Propyl-HMTA is represented in Figure 7. Image of the
silica‐coated MNPs display a dark MNP core surrounded by an amorphous silica shell. Figure 7
shows that iron oxide nanoparticles are entrapped successfully in the silica shell
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Figure 7. TEM Image of the Fe3O4@SiO2@Propyl-HMTA.
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In order to evaluate the thermal stability of Fe3O4@SiO2@Propyl-HMTA catalyst,
thermogravimetry analysis (TGA) was applied. As shown in Figure 8, three massloss regions
were detected within the curves. The first region, situated below 200 °C, displays a mass loss
that is attributed to the loss of water or other solvent in the catalyst. In addition, the second
fracture appeared at 200–400°C, which could be due to the decomposition of propyl-HTMA. In
the last step, after 400°C, the cleavage and decomposition of other organic molecules in the
catalyst have begun to occur. Thus, the catalyst is stable up to 200 °C.
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Figure 8. TGA curve for Fe3O4@SiO2@Propyl-HMTA.
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Additionally, Fe, Si, O, C and N elements were observed in the energy‐ dispersive X‐ray (EDX)
analysis of the Fe3O4@SiO2@HMTA MNPs (Figure 9). The presence of nitrogen indicates the
HMTA loading on the catalyst surface.
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Figure 9. EDX analysis of Fe3O4@SiO2@Propyl-HMTA.
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4. Conclusion
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In short, a highly efficient and cost-effective method has been introduced for the N-benzylation,
and N,N-dibenzylation of primary amines in the presence of the Fe3O4@SiO2@Propyl-HMTA
catalyst. Significant advantages, such as mild reaction conditions, excellent yields of products,
simplicity of workup, and recyclability of the catalyst causes the present method to be proposed
as a useful strategy for the synthesis of N-substituted secondary and tertiary amines.
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Acknowledgment
The authors wish to thank Bu-Ali Sina University, Center of Excellence Developmental of
Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for financial support
to carry out this research.
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Highlights
•
Efficient, simple and mild synthesis of N‐Benzylation derivatives using
Fe3O4@SiO2@Propyl-HMTA.
•
•
New derivatives of N‐Benzylation was synthesized by Fe3O4@SiO2@Propyl-HMTA.
Easy recovery and reuse of this catalyst without notable change in activity

Declaration of interests
☐The authors declare that they have no known competingfinancial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be
considered as potential competing interests: