Superparamagnetic Fe3O4 Nanoparticles in a Deep Eutectic Solvent: An Efficient and Recyclable Catalytic System for the Synthesis of Primary Carbamates and Monosubstituted Ureas

Article abstract of DOI:10.1002/ejoc.201800581

Superparamagnetic Fe₃O₄ nanoparticles were used to synthesize various primary carbamates as well as monosubstituted and N,N-disubstituted ureas. This efficient phosgene-free process used urea as an eco-friendly carbonyl source in the presence of a biocompatible deep eutectic solvent (DES) to provide an inexpensive and attractive route that afforded the products in moderate to excellent yields. The employed DES serves both a catalytic role and as the green reaction medium. The magnetic nanocatalyst and DES can been reused several times without a significant loss of activity.

Full text of DOI:10.1002/ejoc.201800581

A Journal of
Accepted Article
Title: Superparamagnetic Fe3O4 Nanoparticles in Deep Eutectic
Solvent: an Efficient and Recyclable Catalytic System for the
Synthesis of Primary Carbamates and Mono-Substituted Urea
Authors: Iman DindarlooInaloo, Sahar Majnooni, and Mohsen
Esmaeilpour
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201800581
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10.1002/ejoc.201800581
European Journal of Organic Chemistry
FULL PAPER
Superparamagnetic Fe3O4 Nanoparticles in Deep Eutectic
Solvent: an Efficient and Recyclable Catalytic System for the
Synthesis of Primary Carbamates and Mono-Substituted Urea
Iman Dindarloo Inaloo,*[a] Sahar Majnooni[b] and Mohsen Esmaeilpour[a]
Dedication ((optional))
Abstract: Superparamagnetic Fe3O4 nanoparticles were prepared
and tested for the synthesis of various primary carbamates and
mono- or N,N-disubstituted ureas using urea as the eco-friendly
carbonyl source in the presence of a biocompatible deep eutectic
solvent (DES). This efficient and phosgene-free process provided an
inexpensive and attractive route to synthesize the products in
moderate to excellent yields. The employed DES plays both catalytic
roles and green reaction medium for this reaction. Moreover, the
magnetic catalyst and DES have been reused several times in this
procedure without significant loss of activity.
ammonium or phosphonium salts with an organic molecule is
typically occurred by hydrogen bond donor units.[4] Up to now,
different kinds of DESs have been synthesized that present
notable advantages in organic syntheses.[3,4] Recently, an
efficient and novel DES has been formed from the reaction of
choline chloride and zinc chloride, which can be used as stable
Lewis acid and green solvent for organic syntheses.[5,6]
Compared with other DESs, the advantages of this DES are
having an easy synthetic process, low melting point, high purity,
non-toxicity, biodegradability and lower price.[6]
Transition-metal catalyzed organic reactions are often
considered to follow the principles of green chemistry because
of using minimum energy and more clean reagents or auxiliaries
as well as the minimization of wastes.[7] Nanocatalysts are
Introduction
considered to be
a bridge between heterogeneous and
homogeneous catalysts.[8] One of the attractive properties of
nanomaterials is that the active component has a high specific
surface area leading to an increase of the contact with the
reactants.[8] Also, a higher surface area gives nanomaterials
more active surface; they are hardly separable. Therefore, it is
important to design a recoverable and well-dispersed catalyst.
Magnetite nanoparticles (MNPs) are very promising catalytic
structures due to their large specific surface area and magnetic
properties.[9] They can be collected very easily by using a
magnet to prevent any loss of catalyst amount.[9] Recently, the
chemists have focused on the catalytic aspects of magnetite
nanoparticles of Fe3O4 (MNP-Fe3O4) to improve the protocols of
catalytic activity.[10]
In the current century, the development of simple, efficient,
green and low-cost methodologies for the synthesis of organic
compounds has been attracted scientists' attentions and
industrial interests. Although traditional methods focused mainly
on high-yield procedures in the shortest time, modern methods
are keen to improve reusability, prevent waste production, and
reduce toxicity. Obviously, hazardous reagents should be
replaced by safe resources and more green and eco-friendly
methodologies to minimize the amount of toxic byproducts.[1]
The concept of ‘‘Green Chemistry’’ refers to actions aimed to
improve the reaction efficiency using natural resources,
comprising the design and implementation of new chemical
processes and transformations that operate in a more efficient,
safe, and environmentally way.[1] Thanks to the framework of
green chemistry, solvents occupy a strategic place. To be
qualified as a green medium, the components of this solvent
must possess different criteria such as availability, non-toxicity,
recyclability, thermal stability, non-flammability, renewability, low
vapor pressure, cheap and also biodegradability.[2] Deep
eutectic solvents (DESs) are particularly attractive in organic
synthesis owing to their ability to dissolve both polar and non-
polar reactants and their facile recovery.[3-6] For the first time,
DESs were reported at the beginning of the 21st century by
Abbot and co-workers in which the combination of quaternary
Figure 1. Some biologically active carbamates and ureas.
[a]
[b]
Drs. Iman Dindarloo Inaloo, Mohsen Esmaeilpour
Chemistry Department, College of Sciences, Shiraz University,
Shiraz 71946 84795, Iran.
E-mail: iman.dindarlooinaloo@gmail.com
Sahar Majnooni
Carbamates (carbamic esters) and ureas are important industrial
intermediates for agrochemicals (i.e., herbicides, pesticides,
bactericides and antiviral agents),[11] pharmaceuticals (i.e.,
carisoprodol, methocarbamol, felbamate, zafirlukast, retigabine,
diethylcarbamazine and meprobamate),[12] organic syntheses
(i.e., synthesis of heterocyclic compounds and protection of
amino group in peptide chemistry)[13] and polymer syntheses (i.e.,
Chemistry Department, University of Isfahan, Isfahan 81746-73441,
Iran.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejoc.201800581
European Journal of Organic Chemistry
FULL PAPER
polyurethanes and peptides).[14] Some important carbamate and
urea derivatives with biological activities are depicted in Figure
1.[11-14]
Generally, the synthesis of substituted carbamates involves the
reaction of suitable amines and alcohols with phosgene (COCl2)
as a carbonyl source,[15] though, such well-established protocols
activity for the preparation of the desired product. The effect of
molar ratio of urea to 1-pentanol on this reaction was also
investigated. The best yield of 1-pentyl carbamate (C1) was
observed when the molar ratio of urea:1-pentanol be 2:1
(Table 1, entry 10). For the further corroborate of the effect of
MNP-Fe3O4 as a catalyst, the reactions were performed by some
different amount of catalyst. The desired product did not proceed
with excellent yield without using MNP-Fe3O4 (Table 1, entry 24).
To obtain the best amount of the catalyst, these conditions were
studied using different amounts of MNP-Fe3O4 (5, 10, 15 and 20
mol %). These experiments showed that the reduction of the
present some drawbacks such as insufficiency for
N-
unsubstituted (primary) carbamates, using highly toxic and
corrosive reagents, the production of massive toxic-wastes,
longer reaction time, and low efficiency and yields.[15, 16]
During past few years, great efforts have been done to explore
the environmentally benign routes that employ other carbonyl
sources including 1,1,1-trichloromethyl formate (diphosgene),[17]
catalyst amount from 10 to
5 mol% extensively made a
decrement in the reaction yield (Table 1, entry 25).
trichloroacetylchloride,[18]
1,1-carbonyldiimidazole
(CDI),[19]
Table 1. Optimization of reaction parameters for the synthesis of
1-pentyl carbamate ( 1).
carbonate esters,[20] N-acylbenzotriazoles,[21] isocyanates or
C
cyanate salts,[22] isocyanides,[23] dialkylazodicarboxylate,[24]
azides,[25] amides,[26] CO2
and CO
instead of COCl2 for
[27]
[28]
carbamate production. Despite the development of new carbonyl
sources, these processes utilize strong bases and/or toxic
metal-based catalysts, expensive ligands, multi‐step procedures
and harsh reaction conditions.
Pursuing our interest in the development of eco-friendly
approaches to find carbamate derivatives bearing remarkable
applications in pharmaceuticals and agrochemistry, the use of
urea and polyurea as safe and green carbonyl sources is being
considered.[29]
As part of our interest in the development of simple, efficient and
eco-friendly protocols for the synthesis of useful organic
compounds, we recently reported the synthesis of primary
carbamates under solvent-free conditions.[30] In continues, we
report an experimentally and environmentally convenient one-
pot process for the synthesis of primary carbamates by using
urea as a safe carbonyl source via MNP-Fe3O4 and choline
chloride:Zinc (II) chloride [ChCl][ZnCl2] as recoverable catalyst
and solvent, respectively (Scheme 1).
Entry
Molar ratio
Phenol:Urea
Solvent
Cat
(mol %)
Temp
[oC]
Yield
(%)a
1
2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
None
ClCH2CH2Cl
CH3CN
10
10
10
10
10
10
10
10
10
10
10
130
130
130
130
130
130
130
130
130
130
130
23
43
44
41
46
40
38
42
78
93
81
3
4
Toluene
5
DMF
6
DMSO
7
PEG 400
ChCl:urea (1:2)
8
9
ChCl:FeCl3 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:SnCl2 (1:1)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:1
1:1.5
1:2.5
1:3
1:2
1:2
1:2
1:2
1:2
1:2
ChCl:AlCl3 (1:1)
ChCl:NiCl2 (1:1)
ChCl:CuCl2 (1:1)
ChCl:CoCl2 (1:1)
ChCl:LaCl3 (1:1)
ChCl:CrCl3 (1:1)
ChCl:MnCl2(1:1)
ChCl:CaCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
ChCl:ZnCl2 (1:1)
10
10
10
10
10
10
10
10
10
10
10
10
None
5
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
130
110
150
61
65
57
62
73
81
72
69
72
81
91
92
15
63
91
89
71
92
Scheme 1. Primary carbamates synthesis (C) via urea.
Results and Discussion
In an initial endeavor to determine the best conditions, the
reaction of 1-pentanol (A1) and urea (B) was chosen as a model
reaction in the presence of MNP-Fe3O4. Firstly, a series of
common solvents and choline chloride-based DESs including
[ChCl][MCl]2 (M = Fe, Zn, Sn, Al, Ni, Cu, Co, La, Cr, Mn and Ca)
were selected to study their performance on the synthesis of
1-pentyl carbamate (C1). The activity of these solvents was
evaluated using the calculated yield of synthesized
1-pentyl carbamate (C1) and obtained results were summarized
in Table 1. As shown in which, DES originated from choline
chloride and Zinc (II) chloride [ChCl][ZnCl2] had the highest
15
20
10
10
[a] Isolated yield.
However, using larger values (15 and 20 mol %) exhibited no
significant enhancement in the reaction yield (Table 1, entries 26
and 27). The yield of 1-pentyl carbamate (C1) was also checked
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10.1002/ejoc.201800581
European Journal of Organic Chemistry
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out by temperature. These results showed that the better yield of
the desired product was obtained when the reaction temperature
and the reaction time were 130 oC and 6 h, respectively.
As a part of our interests to find the best and the greenest
conditions for the synthesis of primary carbamates, the effect of
Lewis acids such as MNP-MFe2O4 (M = Ni, Co, Mn, Cu, Zn and
Sn), bulk Fe3O4, Fe2O3, FeCl3, FeBr2, Fe(OAc)2, Cu(OAc)2, AlCl3,
CoCl2, ZnCl2, SnCl2, NiCl2 and TiO2 was explored instead of
MNP-Fe3O4 on the model reaction. On the basis of results
exhibited in Table 2, the reaction was led to the desired product
in the presence of all checked catalysts but lower yields were
received after 6 h at 130 oC.
Table 3.Substrate scopes.a
O
O
NH2
C1, (93%)b
C2, (92%)b
C3, (94%)b
C5, (88%)b
C4, (90%)b
O
O
Table 2. Results of 1-pentyl carbamate (C1) from 1-pentanol (A1) and
O
urea (B
) over different catalysts.a
O
NH2
O
NH2
O
NH2
C8, (88%)b
C6, (90%)b
C7, (90%)b
O
O
O
Entry
Catalyst
Yield (%)b
Ph
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
MNP-Fe3O4
Bulk-Fe3O4
MNP-NiFe2O4
MNP-CoFe2O4
MNP-MnFe2O4
MNP-CuFe2O4
MNP-ZnFe2O4
MNP-SnFe2O4
Fe2O3
FeCl3
FeBr2
Fe(OAc)2
Cu(OAc)2
AlCl3
93
81
81
86
82
87
89
88
79
83
82
86
74
71
79
69
81
70
73
O
C10, (88%)b
O
NH2
O
NH2
O
NH2
C9, (69%)b
C11, (82%)b
O
NH2
C12, (80%)b
C13, (90%)b
C14, (92%)b
O
O
NH2
CoCl2
ZnCl2
SnCl2
NiCl2
Cl
C15, (87%)b
C16, (86%)b
C19, (44%)b
C17, (79%)b
C20, (47%)b
TiO2
[a] Reaction conditions: 1-pentanol (1 mmol), urea (2 mmol), [ChCl][ZnCl2]
(3 mL), catalyst (10 mol %), 130 oC, 6 h. [b] Isolated yield.
C18, (87%)b
Under these optimized conditions, the scope and generality of
this protocol were pursued using various alkyl and aryl alcohols
and the results are summarized in Table 3.
C21, (45%)b
C24, (51%)b
C27, (53%)b
C30, (16%)b
C22, (41%)b
C25, (44%)b
C28, (52%)b
C31, (18%)b
C23, (40%)b
C26, (50%)b
C29, (15%)b
C32, (19%)b
The reaction of alkyl alcohols with urea gave the corresponding
primary carbamates in good to excellent yields (Table 3, entries
C1-12). Interestingly, alkyl alcohol like tert-butyl alcohol with
steric hindrance was also reactive in this method and procreated
a product in 69% yield (Table 3, entry C9). As expected, allyl
alcohol and benzyl alcohol derivatives presented the desired
products in excellent yields even in the presence of electron-
withdrawing groups in which no reduction in the efficiency was
observed (Table 3, entries C13-19). However, lower yield was
beholden for 1-phenylethanol, which suffers from steric
hindrance (Table 3, entry C18). Moreover, the same results
were apperceived for different phenols that are substituted by
nucleophiles. The use of phenols and their derivatives bearing
electron-rich substitutions afforded the desired products in
moderate yields (Table 3, entries C20-28). Unfortunately, using
phenols with halogen substitutions as nucleophile led to a
drastic decrease in reaction conversion and the reaction will be
quenched in low yields (<20%) (Table 3, entries C29-32).
[a] Reaction conditions: Phenol or alcohol (1 mmol), urea (2 mmol),
[ChCl][ZnCl2] (3 mL), MNP-Fe3O4(10 mol %), 130 oC, 6 h. [b] Isolated yield.
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Apparently, phenol derivatives do not have enough nucleophilic
properties to provide the primary O-aryl carbamates with
excellent efficiency. It should be noted that in the case of L-(-)-
menthol, the reaction can produce the corresponding L-(-)-
menthyl carbamate without any epimerization (Table 3, entry
C12).
In the next step, to enhance the utility of this methodology and to
extend the scope and the generality of which, we explored the
reaction for the synthesis of mono-substituted ureas and
1,1-disubstituted ureas under similar reaction conditions were
used for the synthesis of primary carbamates.
bearing halogen substitutions like 4-chloroaniline and 3-
bromoaniline (Table 4, entries E11-12). Unfortunately, anilines
with strong electron-withdrawing (CN and NO2) and
heteroaromatic amine such as pyridin-2-amine failed to carry out
the reaction under optimized experimental conditions (Table 4,
entries E13-15). Most likely these functional groups decrease
the nucleophilicity of the aryl amin nitrogen atom for effective
attack. On the other hand, when N-methylaniline was used as a
nucleophile, the desired product was formed in low yield (Table
4, entry E17). However, no products were formed in the case of
diphenylamine, which was probably due to steric effects and low
nucleophilicity of diphenylamine compared with other amines
(Table 4, entry E18). An increasing in reaction time and
temperature did not improve the efficiency of these reactions.
Encouraged by this success, the preparation of primary
S-thiocarbamates from alkyl or aryl mercaptans and urea has
been examined under the same conditions. Unfortunately, the
desired products were not produced in all cases. An increasing
in the reaction temperature up to 200 oC did not show any
positive effect on the formation of S-thiocarbamate derivatives.
To show the versatility of this protocol, we tested different
electrophiles in the reaction conditions with 1-pentanol. Initially,
we chose mono-substituted and 1,1- disubstituted ureas to study
the potential formation of primary 1-pentyl carbamate.
Unfortunately, the reaction of 1-pentanol (1 mmol) with phenyl
urea (2 mmol) in the presence of the MNP-Fe3O4 catalyst (10
mol %) and [ChCl][ZnCl2] (3 mL) at 130 oC created the
corresponding product in 65% yield after 6 h (Table 5, entry 1).
However, when benzyl urea and 1,1-dibenzyl urea were used as
the electrophile, the desired primary carbamate was obtained in
88% and 89% yields (Table 5, entries 2 and 3).
Table 4.Substrate scopes.a
E2, (79%)b
E1, (83%)b
E3, (73%)b
E4, (74%)b
E7, (48%)b
E5, (63%)b
E8, (50%)b
E6, (86%)[b]
E9, (53%)b
E12, (40%)b
E11, (38%)b
E14, (11%)b
E10, (51%)b
E13, (13%)b
Table 5. Investigation of the reaction between 1-pentanol and various
substituted of ureas, thioureas and selenoureas.a
E15, (0%)b
Entry
Electrophile
structure
R
Product
structure
Yield
(%)b
R1
R2
H
Ph
1
2
3
4
5
6
7
8
9
65
88
Bn
Bn
H
H
Bn
H
E17, (13%)b
E16, (85%)b
E18, (0%)b
89
[a] Reaction condition: Aniline or amine (1 mmol), urea (2mmol), [ChCl][ZnCl2]
(3 mL), MNP-Fe3O4 (10 mol %), 130 oC, 6 h. [b] Isolated yield.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
Bn
Bn
H
H
It has been observed that the reaction of primary alkyl amines
with urea results higher yields for mono-substituted urea (Table
4, entries E1-2 and E16). In the case of secondary alkyl amines,
the desired products were formed with lower yields, which
probably were related to steric effects (Table 4, entries E3-5).
Also, benzylamine showed a reactivity as same as the aliphatic
amine (compare entries E1-2 with entry E6). Aromatic amines
have less reactivity than aliphatic amines and this difference in
reactivity can be attributed to low nucleophilicity of aromatic
amines. Therefore, aniline and the electron-rich arylamines such
as 4-methylaniline, 4-methoxyaniline and 4-(dimethylamino)
aniline gave moderate yields (Table 4, entries E7-10), but very
low yields were obtained from the reactions of anilines with
Bn
H
Bn
Bn
H
Bn
[a] Reaction conditions: 1-pentanol (1 mmol), ureas or thioureas or
selenoureas (2 mmol), [ChCl][ZnCl2] (3 mL), MNP-Fe3O4 (10 mol %), 130 oC,
6 h. [b] Isolated yield.
n.d.: not detected.
Furthermore, we investigated the synthesis of primary O-alkyl
thiocarbamates and primary O-alkyl selenocarbamates, but the
reaction of 1-pentanol with thiourea and selenourea showed no
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10.1002/ejoc.201800581
European Journal of Organic Chemistry
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conversion (Table 5, entries 4 and 7). Also, the used of 1-benzyl
or 1,1-dibenzyl thiourea and selenoureas as the electrophile
showed no benign products (Table 5, entries 5, 6, 8 and 9).
Apparently, in these cases, the reaction conditions can't activate
4-chlorophenol and 4-chlorothiophenol as leaving group gave
excellent yields (Table 6, entries 3 and 6), but good yields were
obtained from the reactions in which leaving groups are
electron-rich aryl alcohols and thiols including 4-methylphenol
the electrophile by coordination to the sulfur and selenium atoms. and 4-methylthiophenol (Table 6, entries 2 and 5). As expected,
In addition, different substituted primary O-aryl carbamates,
S-aryl thiocarbamates, O-aryl thiocarbamates and S-aryl
dithiocarbamates were employed in the model reaction to
confirm more versatility of which. As shown in Table 5, these
reaction conditions are unable to activate sulfur atom.
S-aryl thiocarbamates showed better performance than primary
O-aryl carbamates (compare entries 1-3 with entries 4-6).
The role of MNP-Fe3O4 and [ChCl][ZnCl2] are shown in the
proposed mechanism in Scheme 2. The results implied that the
MNP-Fe3O4 and [ChCl][ZnCl2] act as Lewis acid and activate the
urea to improve the nucleophilic addition. On the other hand,
[ChCl][ZnCl2] has multiple roles in this reaction: solvent,
hydrogen bond catalyst and stabilizer for the stabilization of
MNP-Fe3O4. However, more researches will be required to
postulate the exact reaction mechanism.
Table 6. Investigation of the reaction between 1-pentanol with varies
substituted primary aryl carbamates, aryl thiocarbamates and aryl
dithiocarbamates.a
Entry
Electrophile
structure
R
Product
structure
Yield
(%)b
H
CH3
Cl
1
2
88
82
3
90
H
4
91
CH3
Cl
5
86
6
95
H
7
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
CH3
Cl
8
9
H
10
11
12
CH3
Cl
[a] Reaction condition: 1-pentanol (1 mmol), ureas or thioureas or selenoureas
(2 mmol), [ChCl][ZnCl2] (3 mL), MNP-Fe3O4 (10 mol %), 130 oC, 6 h. [b]
Isolated yield.
n.d.: not detected.
Scheme 2. Proposed mechanism for the synthesis of primary carbamates and
mono-substituted ureas catalyzed by MNP-Fe3O4 and [ChCl] [ZnCl2].
Therefore,
using
O-aryl
thiocarbamates
and
S-aryl
dithiocarbamates as electrophile did not lead to the production of
the desired product (Table 6, entries 7-12). Fortunately, the
Fe3O4-catalyzed transcarbamoylation reaction using different
The recovery and reusability of catalyst and DES are necessary
for economic and environmental aspects. Therefore, at the final
step of this study, the operational stability (recycle-ability) of the
MNP-Fe3O4 and [ChCl][ZnCl2] has been explored in the model
reaction. After the completion of the model reaction, diethyl ether
(20 mL) was added to the reaction mixture for extraction the 1-
pentyl carbamate as desired product. Then water (5 mL) was
added to the magnetic DES and MNP-Fe3O4 was extracted with
the external magnet. DES was recovered with evaporation
process of the aqueous layer. The recycled catalysts (MNP-
Fe3O4 and DES) used for six consecutive runs. The data
presented in figure 2a show that the yield of the product
decreased slightly after each run. Therefore, these results are
useful for future industrial applications and environmental
protection.
substituted
primary
O-aryl
carbamates
and
S-aryl
thiocarbamates works well (Table 6, entries 1-6). However, this
method did not work for the synthesis of primary O-aryl
carbamates or primary N-aryl urea as efficient as O-alkyl
carbamates and primary N-alkyl ureas. Obviously, primary
O-aryl carbamates and S-aryl thiocarbamates showed great
efficiency as electrophoresis in the synthesis of primary O-alkyl
carbamates. In this case, a competitive substitution reaction
between alcohol as the precursor and the leaving group can
occur, but 1-pentanol was shown to be more reactive in all
examples.
The electronic effect of the leaving group in O-aryl carbamates
and S-aryl thiocarbamates showed an interesting influence on
the reaction. Electron-deficient aryl alcohols and thiols such as
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10.1002/ejoc.201800581
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(d) TEM images of the MNP-Fe3O4 before reaction and after six cycles of
reactions; (e) DLS image of MNP-Fe3O4 after six reaction cycles.
Conclusions
In conclusion, we have demonstrated an efficient, green and
simple method for the preparation of primary carbamates and N-
mono substituted ureas with good to excellent yields. Compared
with traditional methods, this new method has following
advantages: (a) starting materials are green, inexpensive and
commercially available; (b) the preparation of DES [ChCl][ZnCl]2
is very easily operated, the cost is rather low and it can be
reused directly with the initial activity; (c) the MNP-Fe3O4 catalyst
was easily separated from the reaction mixture by an external
magnet and reused, which made the protocol economic and
sustainable; (d) the separation and purification process is very
simple and convenient. All of these facts pointed out the
possibility of carrying out this green protocol facilitates the
access of these appropriate compounds for biological studies
and designing new drugs.
Figure 2. (a) Recyclability of a magnetic DES; (b) Reaction mixture
containing MNP-Fe3O4 and magnetic separation after the reaction.
Along with high catalytic capacity and stability, a noticeable
feature of catalyst is that it can be easily removed by magnetic
separation after reaction. As shown in Figure 2b, MNP-Fe3O4
was concentrated in 10 s by applying an external magnet to the
side wall of sealed vessel.
In order to further affirmation of the catalyst structure, the FT-IR
spectrum was recorded at room temperature, which is illustrated
in Fig. 3a. The FTIR spectrum of the MNP-Fe3O4 catalyst
demonstrated that no obvious changes occur after recovery on
the magnetite nanoparticles.
The XRD technique is an effective tool to determine the phase
and purity of prepared samples under various conditions. The
representative XRD patterns of fresh and recovered
nanoparticles perfectly matches with the expected cubic spinel
structure of MNP-Fe3O4 (Fig .3b).The position and relative
intensities match well with those from JCPDS card (19-0629) for
Fe3O4.Thus, the magnetite nanocatalyst is stable during the
synthesis of carbamates in eutectic solvent.
Furthermore, to investigate the MNP-Fe3O4 better, TEM images
of the fresh and reused catalyst (after the sixth recycling) have
been represented in Fig. 3c and d. As shown in Fig. 3, there was
no significant change in the morphology and dispersion of the
particles. Also, TEM images indicated that the magnetite NPs
were present as uniform nanospheres and the size of the
nanospheres was about 15 nm. Moreover, as shown in Fig. 3e,
a narrow size distribution of MNP-Fe3O4 after the six recycle was
obtained with a mean size of around 15 nm, which is in
accordance with the XRD and TEM results.
Experimental Section
General experimental:
All chemicals were purchased from the Merck, Flucka and
Aldrich Chemical Companies in high purity. The products were
characterized by comparison of their spectral and physical data
such as NMR, FT-IR, MS, CHNS and melting point with
available literature data. 1H and 13C NMR spectra were recorded
with Bruker Avance DPX 250MHz instruments with Me4Si or
solvent resonance as the internal standard. Fourier transform
infrared (FTIR) spectra were obtained using a Shimadzu FT-IR
8300 spectrophotometer. Powder X-ray diffraction (XRD)
patterns were recorded in a Bruker AXS D8-advance X-ray
diffract to meter using Cu
K
α
radiation (λ= 1.5418).
Transmission electron microscopy (TEM) images were taken on
a Philips EM208 microscope with an accelerating voltage of 100
kV. The hydrodynamic size of the particles was measured by
dynamic light scattering (DLS) techniques, using a HORIBA-
LB550 particle size analyzer. Palladium loading and leaching
test were carried out with an inductively coupled plasma (ICP)
analyzer (Varian, vista-pro). Determination of the purity of the
substrate and monitoring of the reactions was accomplished by
thin-layer chromatography (TLC) on
a silica-gel polygram
SILG/UV 254 plates.
Preparation of [ChCl][ZnCl2] as deep eutectic solvent:[31]
For the preparation of this deep eutectic solvent, a mixture of
choline chloride (10 mmol, 1.39 g) and zinc(II) chloride (10 mmol,
1.36 g) was heated to 100 oC until a clear colorless liquid
appeared, then allowed to cool at room temperature and used
without further purification.
General procedure for preparation of MNP-Fe3O4:
Figure 3. (a) FT-IR spectra of fresh and recovered Fe3O4; (b) XRD
patterns of fresh and recovered MNP-Fe3O4 after six recoveries; (c) and
The Fe3O4 nanoparticles were prepared using a chemical co-
precipitation method.[32] Firstly, 0.9 g of FeCl2.4H2O (4.5 mmol),
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800581
European Journal of Organic Chemistry
FULL PAPER
1.3 g of FeCl3.6H2O (4.8 mmol) and 1 g of poly (vinyl alcohol)
(PVA 15000) as a surfactant were added to 30 mL of water
followed by ultrasonication for 5 min. The mixture solution was
then heated to 80oC for 30 min. The pH was adjusted to 10 by
the dropwise addition of hexamethylenetetramine (1.0 mol l-1)
solution. The reaction mixture was then continually stirred for 2 h
at 60 oC. The black precipitated nanoparticles were magnetically
separated and washed several times with deionized water and
ethanol until the pH reached 7, and then dried under vacuum at
80 oC for 10 h.
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separated from MNP-Fe3O4 and [ChCl][ZnCl]2 by multiple
dilutions with diethyl ether (10 × 5 mL). Then, all starting
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the final product. Finally, by recrystallization from the CH2Cl2
pure product was obtained.
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Authors gratefully acknowledge the financial support of this work
by the research council of Shiraz University.
Keywords: Deep eutectic solvent (DES) • Fe3O4 • Nano catalyst
• Primary carbamates • Urea
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10.1002/ejoc.201800581
European Journal of Organic Chemistry
FULL PAPER
FULL PAPER
Iman Dindarloo Inaloo *, Sahar
Majnooni and Mohsen Esmaeilpour
In this work, superparamagnetic
Fe3O4 nanoparticles were prepared
and tested for the synthesis of various
primary carbamates and mono- or
N,N-disubstituted ureas using urea as
the eco-friendly carbonyl source in the
presence of a biocompatible deep
eutectic solvent (DES). This efficient
and phosgene-free process provided
an inexpensive and attractive route to
synthesize the products in moderate
to excellent yields.
Page No. – Page No.
Superparamagnetic Fe3O4
Nanoparticles in Deep Eutectic
Solvent: an Efficient and Recyclable
Catalytic System for the Synthesis of
Primary Carbamates and Mono-
Substituted Urea
This article is protected by copyright. All rights reserved.