Magnetically recoverable ferromagnetic 3D hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres as an efficient and ligand-free catalyst for C–S bond formation in poly (ethylene glycol)

Journal of Sulfur Chemistry

ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20

Magnetically recoverable ferromagnetic 3D

hierarchical core-shell Fe₃O₄@NiO/Co₃O₄

microspheres as an efficient and ligand-free

catalyst for C–S bond formation in poly (ethylene

glycol)

Ahad Vatandoust Namanloo, Batool Akhlaghinia & Arezou

Mohammadinezhad

To cite this article: Ahad Vatandoust Namanloo, Batool Akhlaghinia & Arezou Mohammadinezhad

(2020): Magnetically recoverable ferromagnetic 3D hierarchical core-shell Fe₃O₄@NiO/Co₃O₄

microspheres as an efficient and ligand-free catalyst for C–S bond formation in poly (ethylene

glycol), Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2020.1753743

To link to this article: https://doi.org/10.1080/17415993.2020.1753743

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Published online: 04 May 2020.

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JOURNAL OF SULFUR CHEMISTRY

https://doi.org/10.1080/17415993.2020.1753743

Magnetically recoverable ferromagnetic 3D hierarchical

core-shell Fe₃O₄@NiO/Co₃O₄microspheres as an efficient and

ligand-free catalyst for C–S bond formation in poly (ethylene

glycol)

Ahad Vatandoust Namanloo, Batool Akhlaghinia and Arezou Mohammadinezhad

Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

ABSTRACT

ARTICLE HISTORY

Received 5 December 2019

Accepted 6 April 2020

A simple and efficient protocol for the synthesis of diaryl thioethers

from the reaction of thiourea with a wide variety of aryl halides,

including aryl iodides, aryl bromides and aryl chlorides in the pres-

ence of 3D hierarchical core-shell Fe₃O₄@NiO/Co₃O₄microspheres

has been described. This reaction enables the one-pot synthesis

of diaryl thioethers in good to high yields using a non-toxic and

magnetically separable catalyst in PEG-400 as an eco-friendly, safe,

inexpensive and thermally stable solvent. Magnetic separation and

reusability of catalyst for eight times without any significant loss

of activity, the use of a commercially available, eco-friendly, cheap

and chemically stable sulfur transfer agent and solvent, operational

simplicity, environmentally benign, easier work-up procedure and

cost efficiency make this method a promising candidate for potential

applications in some organic reactions.

KEYWORDS

3D hierarchical core-shell

Fe₃O₄@NiO/Co₃O₄

microspheres; C–S bond

formation; heterogeneous

catalyst; aryl halides;

thiourea

The catalytic activity of Fe₃O₄@NiO/Co₃O₄as a novel and inex-

pensive catalyst was investigated in the C-S cross coupling reaction.

CONTACT Batool Akhlaghinia

akhlaghinia@um.ac.ir

Department of Chemistry, Faculty of Science, Ferdowsi

University of Mashhad, Mashhad 9177948974, Iran

This article makes reference to supplementary material available on the publisher’s website at

https://doi.org/10.1080/17415993.2020.1753743

2

A. VATANDOUST NAMANLOO ET AL.

1. Introduction

Today, among the carbon-heteroatom bond-forming reactions, carbon–sulfur bond for-

mation is one of the signiﬁcant organic transformations and powerful tools in making var-

ious arrangements of target compounds including pharmaceutical to biological molecules

[1–4 ] and novel precursors in the material science as well [5 ,6 ]. Sulfur-containing organic

molecules particularly, diaryl thioethers and their derivatives have been recognized in

numerous drugs, which are used for the cure of some diseases such as Diabete, A lz heimer,

cancer, Parkinson, HIV, and inﬂammatory and microbial diseases as well. [3 ,4 ,7 ,8] Even

though, several methodologies have been designed for the C–S bond formation (including

reaction of aryl diazoniumﬂ uoroborate with diaryl disulﬁdes [9], coupling of aryl or alkyl

thiols with aryl halides [10 ,11], cross-coupling reaction of aryl halides and ethyl potassium

xanthogenate [12], reaction of phenolic esters such as acetates, triﬂates, tosylates and phos-

phonates with alkyl halides by using thiourea as a sulfur source [13], reaction of aryl halides

with aminothiourea [14], oxidative sulﬁdation of diaryl disulﬁdes with aryltrimethoxysi-

lanes [15], reduction of aryl sulfones or aryl sulfoxides [16,17] and reaction of thiourea

with aryl halides [18–28 ]), most of them require drastic reaction conditions such as strong

bases, elevated temperatures, strong reducing agents, direct use of volatile, hazardous, and

foul-smelling thiols, toxic and expensive organic solvent, stoichiometric amounts of the

catalyst as well as expensive ligands together with highly toxic metals. Furthermore, it

should be noted that most of the previous methods using homogeneous catalysts (that

cannot be separated and recovered simply), which represent more obstacles for the utility

of this chemistry in parallel synthesis and in the industry. Today, with respect to the impor-

tance of green chemistry legislations, researches in this ﬁeld of science should be moving

further towards economical, eﬃcient, beneﬁcial and eco-friendly methods and cheap and

safe resources for C–S bond generation.

Metal oxides which are involved in many petrochemicals, intermediates, ﬁne and phar-

maceutical chemicals were found to be one of the most important heterogeneous catalysis

which catalyzed a wide variety of reactions [29,30]. Amongst them, NiO and Co₃O₄

have possessed increasing consideration due to their commercial and potential applica-

tions in various ﬁelds, including catalysis electrode materials, solid-state sensors and super

capacitors [31].

Very recently, due to our interest towards the extension of environmentally friendly

synthetic methods [19 ,32], the successfully synthesized 3D hierarchical core-shell

Fe₃O₄@NiO/Co₃O₄microspheres (Scheme 1) was eﬃciently used in the C-P cross-

coupling reaction under mild conditions without using toxic solvent [31]. In the present

study, based on our previous experience for the synthesis of diaryl thioethers [19], we

sought to explore the synthesis of diaryl thioethers from the reaction of aryl halides

with thiourea (as a solid, stable, cheap and odorless sulfur transfer agent) in the pres-

ence of 3D hierarchical core–shell Fe₃O₄@NiO/Co₃O₄microspheres as a magnetically

separable nanostructured heterogeneous catalyst in the absence of an inert atmosphere

(Scheme 2).

JOURNAL OF SULFUR CHEMISTRY

3

Scheme 1. The synthetic route for the preparation of 3D hierarchical core-shell Fe₃O₄@NiO/Co₃O₄

microspheres (III).

4

A. VATANDOUST NAMANLOO ET AL.

Scheme 2. C–S coupling reaction in the presence of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres

(III).

2. Results and discussion

To obtain the standard reaction conditions, at the ﬁrst, a series of experiments were

performed with variation of reaction parameters such as solvent, base, temperature and

catalyst loading (Table 1). Initially, our studies began with the reaction between iodoben-

zene (1.0 mmol) and thiourea (0.5 mmol) in PEG-400 at 110°C under normal atmospheric

conditions. Adjusting the reaction mixture in the absence of catalyst and base/or in the

absence of catalyst /or in the absence of base showed that no product was formed even

after a long reaction time (Table 1, entries1–3). The desired product was obtained in 95%

yield using 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres and KOH (Table 1, entry 4).

We then carried out our investigations to identify the best solvent for this reaction. Among

the various solvents screened (PEG, DMF, DMSO, toluene, H₂O, THF, EtOH, and solvent

free conditions), PEG-400, with negligible vapor pressure (as an inexpensive, thermally

stable, recoverable, and non-toxic media for environmentally friendly and safe chemical

reactions) was shown to be the best solvent for C–S coupling reaction in the presence of

3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres and this was then used as a standard

for the optimization of other parameters (Table 1, entries 5–11) [33]. It was evident that

the coupling product could be obtained in DMF, DMSO, and H₂O but in lower yield or

after a prolonged reaction time, and a trace amount of product could be detected when

the reaction was carried out in toluene, THF, EtOH and solvent free conditions. Because

of the essential role of base in the C−S coupling reaction, diﬀerent bases were tested for

this transformation (Table 1, entries 12–15). According to the obtained results, KOH was

speciﬁed to be the most eﬃcient base in C−S coupling reaction in the presence of 3D hier-

archical Fe₃O₄@NiO/Co₃O₄microspheres. It was further observed that 4 equivalents of

KOH resulted in the best yield in 20 min at 110°C (Table 1, entries 16–18). Screening was

also performed at diﬀerent temperatures. (Table 1, entries 19–21) Ultimately, the ideal tem-

perature for the reaction was found to be 100°C. Finally, the eﬀect of catalyst loading on

the yield and reaction rate was also examined (Table 1, entries 22–23). Obtained results

revealed that the amount of catalyst inﬂuenced the outcome of C–S coupling reaction and

the higher yield was attained in the presence of 0.01 g (3.2: 2.8 mol% ratio of Ni:Co) of

3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres. To probe more fully the role of 3D

hierarchical Fe₃O₄@NiO/Co₃O₄microspheres in the C–S coupling reaction, a series of

JOURNAL OF SULFUR CHEMISTRY

5

Table 1. Synthesis of diphenyl sulﬁde from the reaction of iodobenzene with thiourea catalyzed by 3D

hierarchical core-shell Fe₃O₄@NiO/Co₃O₄microspheres under diﬀerent reaction conditions.

Molar ratio of

iodoben-

zene/base

Catalyst (mol%

ratio of Ni:Co)^a

Temperature

(°C)

Time

(h)

Isolated

yield (%)

Entry

Base

Solvent

1

2

3

4

5

6

7

8

–

1/0

1/2

1/0

1/2

1/5

1/4

1/3

1/4

–

KOH

–

PEG-400

DMF

DMSO

Toluene

H₂O

110

24

1

3

4

5

1.5

3

–

95

60

95

Trace

95

Trace

95

60

20

95

85

95

80

3.2: 2.8

4.4: 3.9

1.92: 1.68

0.01 (g)

3.2

KOH

K₃PO₄

K₂CO₃

NaHCO₃

Li₂CO₃

KOH

110

Reﬂux

110

120

100

90

100

9

THF

EtOH

-

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24^b

25^c

26^d

PEG-400

2

45 (min)

20 (min)

2.5

95

85

Trace

60

70

100

1.5

2.8

^aThe mol% result was obtained from ICP-OES analysis.

^bReaction was performed in the presence of Fe₃O₄@MAA NPs.

^cReaction was performed in the presence of Fe₃O₄@Co₃O₄NPs as catalyst.

^dReaction was performed in the presence of Fe₃O₄@NiO NPs as catalyst.

controlled experiments in the presence of Fe₃O₄@MAA NPs (I), Fe₃O₄@Co₃O₄NPs and

Fe₃O₄@NiO NPs, were carried out (Table 1, entries 24-26). It can be seen that trace amount

of desired product was produced after long reaction time using Fe₃O₄@MAA NPs. Also, in

the presence of Fe₃O₄@Co₃O₄NPs and Fe₃O₄@NiO NPs, the C–S coupling reaction was

sluggish and gained lower yield of desired product. The results, therefore, suggests that 3D

hierarchical Fe₃O₄@NiO/Co₃O₄microspheres is essential to the success of the reaction.

Next, to explore the scope of the C–S coupling reaction via this modiﬁed procedure

(Table 1 , entry 20), the reaction of various aryl halides with thiourea (as a commercial

available and economic aﬀordable reagent for the synthesis of aryl sulﬁdes) was studied.

(Table 2) As summarized in Table 2, the electronic nature of substitution played a major

role in governing the reactivity of the aryl halides. Generally, synthesis of aryl thioethers

with electron-withdrawing groups requires shorter reaction time than electron-donating

ones. (Table 2, entries 2–4 vs. entries 5–6, entry 8 vs. entry 9 and entries 13–14 vs. entries

6

A. VATANDOUST NAMANLOO ET AL.

15–16) Our results reveal that aryl chlorides were not as reactive as aryl bromides and aryl

iodides. (Table 2, entries 1–2 and 7–8 vs. entries 12–13) In these cases, the observed yields

are less and there was no improvement in the yields even after prolonged reaction time. As

Table 2. Synthesis of diaryl sulﬁdes from the coupling reaction of aryl halides with thiourea catalyzed

by 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres.

Entry

1

Aryl halide

Product

Time (min)

20

Isolated yield (%)

95

2

3

20

15

95

4

5

6

7

8

80

60

80

60

45

75

70

80

9

100

70

10

4.5 (h)

75

(continued).

JOURNAL OF SULFUR CHEMISTRY

7

Table 2. Continued.

Entry

11

Aryl halide

Product

Time (min)

6.5 (h)

Isolated yield (%)

65

12

13

2.5 (h)

60

65

14

2.5/7 (h)

15/15

15

16

3.5 (h)

4 (h)

55

45

17

24 (h)

Trace

can be seen, the reaction rate is sensitive to steric eﬀects of the aryl halides. A sterically

hindered ortho-substituted aryl halide proved to be problematic in the presence of 3D

hierarchical core-shell Fe₃O₄@NiO/Co₃O₄microspheres, and no cross-coupled product

was detected even after 24 h (Table 2, entries 16–17). In the case of naphthyl and hetero-

cyclic halides, the reaction time is high to obtain a reasonable yield of the corresponding

symmetrical thioethers (Table 2 , entries 10–11). To investigate the chemoselectivity of the

present method, the reaction of 1-chloro-4-iodobenzene (as dihalogenated aryl halide)

with thiourea was also tested which the iodide showed more reactivity (Table 2 , entry 4).

This fact was conﬁrmed by the mass spectrometry (Figure 9, Supporting Information ﬁle).

In the present study, the progress of the reaction was monitored by disappearance of

aryl halides and formation of C–S coupled product on TLC. All the prepared products were

known compounds and isolated, puriﬁed and initially identiﬁed by mass spectrometry and

comparison of their melting points with those reported previously or with authentic sam-

ples prepared by the conventional methods. Additionally, the structure of some selected

products was further deduced from ¹HNMR and ¹³CNMR spectral data. The spectral data

of all products are given in ‘Supporting Information’ ﬁle.

8

A. VATANDOUST NAMANLOO ET AL.

Scheme 3. Proposed mechanism for synthesis of diaryl thioethers by the reaction of aryl halides with

thiourea in the presence of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres.

Based on the reported pathway in literature and also according to our previous expe-

rience [19,21], a proposed reaction mechanism for C–S coupling reaction of aryl halides

with thiourea in the presence of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres is pre-

sented in Scheme 3. At the outset, through an oxidative addition reaction, the active sites

of catalyst (Ni and Co) inserts into the C-X bond of aryl halide aﬀorded intermediate (I).

Subsequently, upon the reaction of thiourea with intermediate (I) followed by reductive

elimination step, intermediate (II) and intermediate (III) were produced respectively along

with the catalyst. In alkaline media, thiol moiety was generated smoothly and reacted with

the intermediate (I) (which is produced in the oxidative addition step) to aﬀord intermedi-

ate (IV). Finally, the desired C–S coupled product was obtained via a reductive elimination

manner and the catalyst enters the next cycle. The results obtained from Table 1, entries

25–26, revealed that Ni and Co together in the MOF structure enhance the catalytic activ-

ity of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres which accelerate the C–S coupling

reaction.

Particularly, according to the green chemistry viewpoint, the separation of catalyst

using an external magnetic ﬁeld from the reaction mixture is a very convenient and

eﬃcient process in modern catalysis researches. Magnetic separation of the catalyst as

an attractive alternative to ﬁltration or centrifugation prevents loss of the catalyst and

JOURNAL OF SULFUR CHEMISTRY

9

Figure 1. Reusability of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres in the C–S coupling reaction

under the optimized reaction conditions.

Figure 2. FT-IR spectra of (a) fresh 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres (b) and 8th reused

3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres.

increases its reusability. Due to paramagnetic property, the magnetite Fe₃O₄particles

are amenable to magnetic separation. To demonstrate the consistency of 3D hierarchi-

cal Fe₃O₄@NiO/Co₃O₄microspheres in terms of activity and eﬃciency, the recovery and

reusability of catalyst was studied in model reaction under the optimized reaction con-

ditions. After the completion of the reaction, spent 3D hierarchical Fe₃O₄@NiO/Co₃O₄

microspheres was easily separated from the reaction mixture using an external magnetic

ﬁeld, followed by washing with EtOH (3 × 10 mL), and then dried at 70˚C overnight for the

10

A. VATANDOUST NAMANLOO ET AL.

next run without considerable decrease of its catalytic activity. (Figure 1 ) As can be seen in

Figure 1 no signiﬁcant changes in yield of desired product were observed after regeneration

until the 8th cycle.

Fourier transform infrared (FT-IR) spectroscopy was utilized to authenticate the struc-

ture of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres (III) and the 8th recovered

nanocatalyst (Figure 2 (a,b)). As it is evident from Figure 2 (a), two characteristic absorption

bands at 654 and 593 cm⁻¹were related to Co₃O₄, NiO and Fe₃O₄stretching vibrations,

respectively [32,34,35]. Furtheremore, the stretching frequencies of hydroxyl groups on

the surface of Fe₃O₄NPs and asymmetric and symmetric stretching vibrations of Fe-O-H

bond appeared as broad absorption bands at 3396, 1125 and 864 cm⁻¹, respectively [36],

conﬁrming the structure of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres (III). It is

interesting to note that the shapes, positions, intensities and frequencies of the distinctive

absorption bands are well preserved even after eight recycle runs, as can be seen in Figure

2(b). As well, the obtained ICP-OES results showed that the exact amount of metal ions (Co

and Ni) are 3.2 and 3.2 mmol of cobalt as well as 2.8 and 2.7 mmol of nickel in 1.000 g of the

fresh and the 8th reused 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres, respectively.

The catalytic eﬃciency of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres was com-

pared with some selected previously reported catalysts in preparation of diaryl thioethers

from the reaction of aryl halides with thiourea. (Table 3) It is evident from Table

3 that the reaction of iodobenzene with thiourea in the presence of 3D hierarchical

Fe₃O₄@NiO/Co₃O₄microspheres was completed more quickly than the other catalysts.

More importantly, compared with other catalysts, 3D hierarchical Fe₃O₄@NiO/Co₃O₄

microspheres can be easily separated from the reaction mixture by means of a magnetic bar

(Table 3, compare with entries 1–4, 6–8 and 10–11) and reused at least eight times without

any signiﬁcant loss of its catalytic activity as well (Table 3 , entries 6, 7–8 and 11). Notice-

ably, using environmentally friendly solvent is another merit of this catalytic methodology

(Table 3, entries 1, 4–8 and 10–11).

Table 3. Comparison of the catalytic activity of 3D hierarchical core-shell Fe₃O₄@NiO/Co₃O₄micro-

spheres with some literature precedents S-arylation reaction.

Temperature

(°C)

Time

(h)

Yield

(%)

Entry

Catalyst

Solvent

Base

Reusability

Ref.

1

2

3

4

5

6

7

8

CuO nanoparticles

SBA-16/GPTMS-TSC-CuI

CuI

DMSO

–

PEG-200 Na₂CO₃

DMF/H₂O

DMF

DMSO

H₂O

Cs₂CO₃

KOH

110

120

130

120

110

120

Reﬂux

130

120

15

1

4

7

4

6

–

5

4

–

98

95

93

85

94

98

95

65

88

95

96

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

15

12

4

24

2

Cu(II)-2-MPE^a@MCM-41

Magnetic nano CuFe₂O₄

CuO@GO

KOH

K₂CO₃

Cs₂CO₃

NaOEt

Cs₂CO₃

KOH

GO-N-isatin-Ni (II)

MCM-41-2N-CuI

b

9

10

11

mPANI/pFe₃O₄

PdNP-PNF^c

DMSO

KOH

[27]

[28]

Ni(II)-modiﬁed-SBA-15

4

Present

study

12

3D hierarchical core-shell

Fe₃O₄@NiO/Co₃O₄

microspheres

PEG-400

KOH

100

20 (min)

8

95

^a2-methoxy-1-phenylethanone.

^bmesoporous polyaniline/porous magnetic Fe₃O₄.

^cPd nanoparticles on the peptide nanoﬁber.

JOURNAL OF SULFUR CHEMISTRY

11

3. Conclusion

In summary, 3D hierarchical core–shell Fe₃O₄@NiO/Co₃O₄microspheres was introduced

as a magnetically separable nanostructured heterogeneous catalyst for the one-pot odorless

preparation of diary thioethers from the reaction of aryl halides with thiourea. Experimen-

tal results illustrate that this hierarchical nanostructured catalyst could promote the C–S

cross coupling reaction of a large library of functional substrates including electron-rich

and electron-poor aryl iodides /or aryl bromides /or aryl chlorides with thiourea with a

remarkable yield in a green solvent (PEG-400). The uniqueness and long-term durability

of this catalyst can be related to its small nano crystalline size (10–47 nm, according to

the XRD and TEM data), bimetallic core–shell nanostructure and using cobalt and nickel

species as a low-cost, non-toxic and readily available metal ions in its structure. The notable

features of the present study are as follows: (a) use of readily accessible and non-toxic sulfur

transfer reagent, (b) short reaction times, (c) magnetic separation of the nanocatalyst by

using an external, (d) low environmental impact and high recovery of the nanocatalyst at

least for eight times without a signiﬁcant decrease in its catalytic activity in the S-arylation

reaction.

4. Experimental

4.1. Material and methods

Iron (III) chloride hexahydrate (FeCl₃.6H₂O), sodium acetate (NaOAc), nickel (II) nitrate

hexahydrate (Ni(NO₃)₂.6H₂O), cobalt(II) nitrate hexahydrate (Co(NO₃)₂.6H₂O), mer-

capto acetic acid (MMA), benzene-1,3,5-tricarboxylic acid (trimesic acid) (H₃BTC), ethy-

lene glycol (99%) and absolute ethanol were purchased from Merck chemical company

and were used as received without further puriﬁcation. The purity determinations of the

products and the progress of the reactions were accomplished by thin layer chromatog-

raphy on silica gel polygram STL G/UV 254 plates. The melting points of the products

were determined with an Electrothermal Type 9100 melting point apparatus. The FT-IR

spectra were recorded on an AVATAR 370 FT-IR spectrometer (Therma Nicolet spectrom-

eter, USA) using KBr plates at room temperature in the range between 4000 and 400 cm⁻¹

with a resolution of 4 cm⁻¹. Mass spectra were recorded with a CH7A Varianmat Bremen

instrument at 70 eV electron impact ionization, in m/z (rel.%). The NMR spectra were

recorded on a Bruker Avance 400 MHz instrument in CDCl₃and DMSO-d₆as the sol-

vents. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was carried

out on a 76004555 SPECTRO ARCOS ICP-OES analyzer. All yields refer to the isolated

products after puriﬁcation by thin layer chromatography.

4.2. Synthesis of Fe₃O₄-MAA NPs (I)

Fe₃O₄-MAA NPs (I) was synthesized through a simple solvothermal procedure [37].

Accordingly, FeCl₃·6H₂O (4 mmol, 1.08 g), mercapto acetic acid (MAA) (0.6 mmol,

0.052 g) and sodium acetate (0.1 mol, 8.2 g) were orderly mixed together in 40 mL ethy-

lene glycol at 60°C. The obtained yellow mixture was transferred to a 50 mL Teﬂon-lined

stainless-steel autoclave and kept at 200°C for 12 h to achieve Fe₃O₄-MAA NPs (I).

12

A. VATANDOUST NAMANLOO ET AL.

The precipitate was separated by magnetic decantation, washed with deionized water

(3 × 20 mL), ethanol (3 × 20 mL) and dried at 70°C overnight.

4.3. Synthesis of Fe₃O₄@Ni-Co-BTC NPs (II)

To a suspension of 0.06 g Fe₃O₄-MAA NPs (I) in ethanol (20 mL) (dispersed in an ultra-

sonic bath for 30 min), a solution of 1.7 mmol of Ni(NO₃)₂·6H₂O (0.494 g) and 3.5 mmol

of Co(NO₃)₂·6H₂O (1.017 g) in 20 mL ethanol was added. The obtained mixture was son-

icated for 30 min. Then, 2.8 mmol of trimesic acid (0.588 g in 20 mL ethanol) was added

to the resulting suspension and the obtained mixture was dispersed again for 30 min. The

mixture was then transferred into a 100 mL Teﬂon-lined stainless-steel autoclave and main-

tained at 150°C for 12 h. As a ﬁnal step, the obtained black product (Fe₃O₄@Ni-Co-BTC

NPs (II)) was separated by magnetic decantation, washed with ethanol for three times and

dried at 60˚C [38].

4.4. Synthesis of 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres (III)

To achieve black powder 3D hierarchical Fe₃O₄@NiO/Co₃O₄microspheres (III), the

obtained Fe₃O₄@Ni-Co-BTC NPs (II) powder was put into an electrical furnace and

annealed in air at 450°C for 2 h with a heating rate of 2°C min⁻¹[39].

4.5. Typical procedure for the preparation of diphenyl sulﬁde in the presence of 3D

hierarchical core-shell Fe₃O₄@NiO/Co₃O₄microspheres

To a stirred solution of iodobenzene (1.0 mmol, 0.204 g) and thiourea (0.5 mmol, 0.038 g)

in PEG-400 (3.0 mL) at room temperature, 3D hierarchical core–shell Fe₃O₄@NiO/Co₃O₄

microspheres (3.2: 2.8 mol% ratio of Ni: Co, 0.01 g) and KOH (4 mmol, 0.224 g) was added.

The resultant mixture was heated at 100˚C for 20 min. The progress of the reaction was

monitored by TLC. After the reaction was completed, the reaction mixture was allowed

to cool, and diluted by a 1:1 mixture of ethyl acetate/water (6 mL). The catalyst was sep-

arated from the reaction mixture using an external magnetic ﬁeld, followed by washing

with EtOH (3 × 10 mL), and then dried at 70°C overnight for the next run. The combined

organic extract was separated and dried with anhydrous Na₂SO₄. Afterwards, the solvent

was completely removed under vacuum to give the crude product, which was puriﬁed by

thin layer chromatography (ethyl acetate/ n-hexane, 1:5) to aﬀord diphenyl sulﬁde in 95%

yield (0.176 g).

4.5.1. Diphenyl sulfide [19] (1a)

Diphenyl sulﬁde (0.176 g, 95%); Colorless oil; ¹H NMR (400 MHz, CDCl₃): δ

[ppm] = 7.34-7.31 (m, 5H), 7.29-7.25 (m, 3H), 7.23-7.19 (m, 2H); ¹³C NMR (100 MHz,

CDCl₃): δ [ppm] = 135.9, 131.2, 129.4, 127.2; MS (70 eV, EI); m/z (%): 186 (M⁺, 12%),

184 (M-2, 100%), 108 (C₆H₄S, 90%), 76 (C₆H₄, 42%), 65 (C₅H₅, 40%), 51 (C₄H₃, 28%).

JOURNAL OF SULFUR CHEMISTRY

13

4.5.2. 4,4^ꢀ-Thiodibenzonitrile [19] (2b)

4,4^ꢀ-Thiodibenzonitrile (0.198 g, 84%); Yellow solid; mp 134–135 °C (Lit. 134–135 °C); ¹H

NMR (400 MHz, CDCl₃): δ [ppm] = 7.43 (d, J = 8.8 Hz, 4 H, Ar-H), 7.19 (d, J = 8.4 Hz,

4 H, Ar-H); ¹³C NMR (100 MHz, CDCl₃): δ [ppm] = 140.6, 133.0, 131.2, 118.2, 111.4.

4.5.3. Bis (4-nitrophenyl) sulfane [19] (3c)

Bis (4-nitrophenyl) sulfane (0.231 g, 84%); Yellow solid; mp 149–150 °C (Lit. 149–150 °C);

¹H NMR (400 MHz, DMSO-d₆): δ [ppm] = 7 δ 8.25 (dd, J = 8.4, 1.6 Hz, 4H), 7.64 (dd,

J = 8.4, 2.0 Hz, 4H); ¹³C NMR (100 MHz, DMSO-d₆): δ [ppm] = 146.7, 142.2, 131.3,

124.8; MS (70 eV, EI), m/z (%): 276 (M⁺, 20%), 275 (M-1, 40%), 123 (C₆H₅NO₂, 90%).

4.5.4. Bis (4-chlorophenyl) sulfane [40] (4d)

Bis (4-cholorophenyl) sulfane (0.123 g, 45%); white solid; mp 89–90 °C (Lit. 91–92 °C); MS

(70 eV, EI), m/z (%): 254 (M⁺,100%), 256 (M + 2,66%), 218 (C₁₂H₈ClS,20%), 184 (C₁₂H₈S,

82%), 143 (C₆H₄ClS,18%), 108 (C₆H₄S,28%).

4.5.5. Di-(p-tolyl) sulfane [19] (5e)

Di-(p-tolyl) sulfane (0.158 g, 74%); Colorless oil; (Lit. 43–46 °C); H NMR (400 MHz,

1

CDCl₃): δ [ppm] = 7.23 (d, J = 8.4 Hz, 4 H, Ar-H), 7.10 (d, J = 7.6 Hz, 4H, ArH), 2.32

(s, 6H, CH₃); ¹³C NMR (100 MHz, CDCl₃): δ [ppm] = 137.1, 132.8, 131.2, 130.1, 21.3;

MS (70 eV, EI), m/z (%): 212 (M-2, 50%), 91 (C₇H₇, 67%).

4.5.6. Bis (4-methoxyphenyl) sulfane [19] (6f)

Bis (4-methoxyphenyl) sulfane (0.172 g, 70%); Yellow liquid; ¹H NMR (400 MHz, CDCl₃):

δ [ppm] = 7.27 (d, J = 8.8 Hz, 4 H, Ar-H), 6.83 (d, J = 8.8 Hz, 4 H, Ar-H), 3.78 (s, 6 H,

OCH₃); ¹³C NMR (100 MHz, CDCl₃): δ [ppm] = 159.1, 132.9, 127.6, 114.9, 55.5; MS (70

eV, EI), m/z (%): 246 (M⁺, 5%), 243 (M-2, 65%), 77 (C₆H₅, 80).

4.5.7. 4,4^ꢀ-Thiodianiline [19] (7g)

4,4^ꢀ-Thiodianiline (0.177 g, 82%); Brown solid; mp 107–108 °C (Lit. 107–108 °C); ¹H NMR

(400 MHz, CDCl₃): δ [ppm] = 7.15 (d, J = 8.0 Hz, 4 H, Ar-H), 6.60 (d, J = 8.0 Hz, 4 H,

Ar-H), 3.67 (s, 4 H, NH₂); ¹³C NMR (100 MHz, CDCl₃): δ [ppm] = 145.8, 132.9, 125.2,

115.9.

4.5.8. Di (thiophen-2-yl) sulfane [19] (8h)

Di (thiophen-2-yl) sulfane (0.146 g, 74%); Yellow liquid; 1H NMR (400 MHz, CDCl3): δ

[ppm] = 7.63–7.53 (m, 2H), 7.45–7.34 (m, 2H), 7.27–7.11 (m, 2H); 13C NMR (100 MHz,

CDCl₃): δ [ppm] = 135.5, 132.7, 129.6, 137.47.

4.5.9. Di (naphthalen-1-yl) sulfane [27] (9i)

Di (naphthalen-1-yl) sulfane (0.214 g, 75%); White solid; mp 156–157 °C (Lit. 156–158

°C); ¹H NMR (400 MHz, CDCl₃): δ [ppm] = 8.43–8.40 (m, 2 H, Ar-H), 7.89–7.87 (m, 2

H, Ar-H), 7.78–7.76 (m, 2 H, Ar-H), 7.55–7.51 (m, 4 H, Ar-H), 7.32–7.30 (m, 4 H, Ar-H);

¹³C NMR (100 MHz, CDCl₃): δ [ppm] = 134.3, 132.8, 132.6, 130.1, 128.8, 128.2, 126.9,

126.6, 126.0, 125.3; MS (70 eV, EI), m/z (%): 286 (M⁺, 8%), 285 (M-1, 52%), 282 (M-4,

90%), 127 (C₁₀H₇, 60%).

14

A. VATANDOUST NAMANLOO ET AL.

4.5.10. 4,4^ꢀ-Thiodiphenol [19] (11k)

1

4,4^ꢀ-Thiodiphenol (0.137 g, 63%); White solid; mp 151–153 °C (Lit. 150–153 °C); H

NMR (400 MHz, DMSO-d₆): δ [ppm] = 9.62 (s, 2H), 7.14 (d, J = 8.4 Hz, 4H), 6.73 (d,

J = 8.4 Hz, 4H); ¹³C NMR (100 MHz, DMSO-d₆): δ [ppm] = 157.0, 132.7, 124.7, 116.3.

Acknowledgements

The authors gratefully acknowledge the partial support of this study by Ferdowsi University of

Mashhad Research Council (grant number p/3/51304). Furthermore, it should be noted that

this manuscript is derived from the thesis entitled ‘Ferromagnetic 3D hierarchical core-shell

Fe₃O₄@NiO/Co₃O₄microspheres as an eﬃcient and heterogeneous nanostructured ligand-free

catalyst for C–S bond formation in poly (ethylene glycol).’

Disclosure statement

No potential conﬂict of interest was reported by the author(s).

Funding

This study was supported by Ferdowsi University of Mashhad [grant number p/3/51304].

ORCID

Batool Akhlaghinia http://orcid.org/0000-0002-9940-5045

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Article Doi

Magnetically recoverable ferromagnetic 3D hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres as an efficient and ligand-free catalyst for C–S bond formation in poly (ethylene glycol)

DOI: 10.1080/17415993.2020.1753743

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Full text of DOI:10.1080/17415993.2020.1753743

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