Catalytic Versatility of Novel Sulfonamide Functionalized Magnetic

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On the catalytic versatility of novel sulfonamide functionalized magnetic composites Somayeh Ostovar, Pepijn Prinsen, Alfonso Yepez, Hamid Reza Shaterian, and Rafael Luque ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03251 • Publication Date (Web): 07 Feb 2018 Downloaded from http://pubs.acs.org on February 9, 2018

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ACS Sustainable Chemistry & Engineering

On the catalytic versatility of novel sulfonamide functionalized magnetic composites Somayeh Ostovar,† Pepijn Prinsen,‡ Alfonso Yepez,‡ Hamid Reza Shaterian,*† and Rafael Luque,*‡ †

Department of Chemistry, University of Sistan and Baluchestan, Faculty of Sciences, PO Box

98135-674, Zahedan, Iran. ‡

Departamento de Química Orgánica, Campus de Rabanales, Edificio Marie Curie, Ctra. Nnal.

IV, Km. 396, E-14014, Cordoba, Spain Correspondence to: Fax: +34957212066. E-mail: [email protected] KEYWORDS Magnetic sulfonamide catalyst, Propargylamines synthesis, Dioxooctahydroxanthenes synthesis, Toluene alkylation

ABSTRACT: The present work describes two novel magnetic composite catalysts, synthesized by functionalizing the silica/iron oxide composite surface with sulfaguanidine and sulfadiazine. The sulfaguanidine functionalized catalyst was found to be very efficient for multicomponent coupling reactions of phenylacetylene with various aldehydes and amines. The sulfadiazine functionalized catalyst was successfully applied in the synthesis of various 1,8-dioxo-

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octahydroxanthenes in water. Both the sulfaguanidine and sulfadiazine functionalized catalysts were very active and selective in the alkylation of toluene with benzyl chloride.

INTRODUCTION In recent years, numerous works have been reported on the design of reusable nanocatalysts. Metal oxides have been widely studied, both as heterogeneous catalysts and as supports for several important organic transformations,1-3 but also in drug delivery4 and other research fields. One particular group of metal oxide nanocatalysts are magnetic iron oxide nanoparticles.5 They represent an attractive group of multifunctional catalysts, as they can be separated efficiently from reaction mixtures.6-10 Besides this magnetic feature, it can also serve as a support for metals,11 biomolecules12,13 and organic ligands.14,15 Surface functionalization of nanocatalysts has proven to be a useful tool in catalyst design.16-19 MNPs have abundant hydroxyl groups which can react with tetraethyl orthosilicates (TEOS) to form Si–O bonds in core- and yolk-shell structures.20,21 One way to prepare core-shell structures is to coat the mangnetic core with a dense layer of silica to improve the chemical stability of the nanoparticles and to provide surface silanol groups, providing reactive centers for further functionalization with alkoxy organosilanes.22,23 Sulfaguanidine (1-(p-aminophenyl)sulfonyl guanidine, SGD) is an important sulfonamide with anti-microbial activity, commonly used in human and veterinary medicine.24 SGD exists in tautomeric forms, which have the imide group in different orientations through electron and proton delocalization (Scheme 1a). Sulfadiazine (SDA) is another sulfonamide, often used as anti-microbial agent.25 Important also is the fact that different salts of SDA have been isolated and characterized,26 which are formed upon protonization and deprotonization of SDA (Scheme 1b). Whereas abundant bibliography exists on the synthesis of sulfonamides, few reports have


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been published on the synthesis of sulfonamide containing catalysts,27-29 as sulfonamide groups are relatively unreactive. Guanidine base catalysts in contrast have been reported for many assymetric organocatalysis reactions,30 including the Pictet-Spengler reaction31 and the threecomponent inverse electron-demand aza-Diels–Alder reaction (using benzaldehyde, aminophenyls and cyclopentadiene as the dienophile).32

((Scheme 1))

The present work reports two novel magnetic composite catalysts, functionalized with SGD and SDA. A silica coating was introduced to link the biomolecules´ amino groups with the paramagnetic metal oxide surface. The catalysts showed good results in line with the literature for the synthesis of propargylamines through three-component coupling of phenylacetylene with various aldehydes and amines, for the synthesis of 1,8-dioxo-octahydroxanthenes through Knoevenagel-Michael addition and in the alkylation of toluene with benzyl chloride.

EXPERIMENTAL SECTION Solvents and reagents. See Supporting Information. Catalyst synthesis. γ-Fe2O3/SiO2 composite particles were prepared in analogy with previously reported work from our group.33 The co-precipitation method was used to prepare γFe2O3,34,35 dissolving 0.401 g FeCl2.4H2O and 1.092 g FeCl3.6H2O in 2 and 4 mL of a 2 M HCl


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solution, respectively. Both iron precursor solutions were stirred (800 rpm). After 15 min. 50 mL of a 0.7 M NH4OH solution was slowly added to the mixture, causing the color of the solution to change from orange to dark brown. After 1 h further stirring, the particles were magnetically decanted and washed with deionized water for several times. The solid product was separated from the solution by magnetic induction using a hand magnet and subsequently added to 1-2 mL of tetramethylammonium hydroxide surfactant. The sample was dried at room temperature overnight and then calcined at 300 ºC for 3 h. γ-Fe2O3 particles were coated through silanization with tetraethyl orthosilicate (TEOS): ca. 1.0 g of particles was dispersed in 40 mL ethanol using ultrasound for 1 h at 40 ºC to produce a homogeneous suspension, after which 5 mL of TEOS was added and left stirring for 24 h; the obtained γ-Fe2O3/SiO2 nanoparticles were washed with ethanol and diethylether and dried under vacuum at 100 ˚C for 12 h. For the functionalization of the composite nanoparticles, first, 2.0 g γ-Fe2O3/SiO2 was dispersed in 40 mL dry toluene, sonicated at 40 ºC for 45 min., followed by the addition of 3-chloropropyl trimethoxysilane (0.5 mL) under continuous stirring at 105 ºC during 24 h. Then, the particles were collected using an external magnet and washed three times with diethyl ether and dichloromethane. The solids were dried overnight at 30 °C under vacuum, to obtain the chloro-functionalized γ-Fe2O3/SiO2 particles. Subsequently, sulfonamide (1.0 g SGD or SDA) was dissolved in 40-50 mL ethanol. This dissolution was added to a suspension of 1.0 g of chloro-functionalized γ-Fe2O3/SiO2 in 20 mL ethanol. The mixture was stirred during 24 h. The obtained solids were separated magnetically and washed with a mixture of water and ethanol (1:1). The obtained γ-Fe2O3/SiO2SGD and γ-Fe2O3/SiO2-SDA powders presented a dark brown color and were further dried during 2 h under vacuum at 60 ºC.


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Catalyst characterization. Fourier Transform Infrared (FTIR) spectra of the samples were recorded using a Spectrum TwoTM instrument (PerkinElmer, Waltham, MA, USA) by the Attenuated Total Reflectance (ATR) technique. The spectra were recorded from 4000 cm−1 to 450 cm−1 with a resolution of 4 cm−1. Thermogravimetric (TGA) analysis was performed on a Perkin-Elmer thermal analyzer, by heating the sample up to 800 ºC at 10 ºC min.-1 under dynamic air atmosphere (10 mL min.-1). Thin-layer chromatography (TLC) was performed on silica gel plates (Poly Gram SIL G/UV 254). Elemental compositions were analyzed with energy dispersive X-ray spectrometry (EDX-SEM) using a Leo 1450 VP scanning electron microscope equipped with an SC7620 energy dispersive spectrometer with 133 eV resolution at 20 kV. Powder X-ray diffraction patterns (XRD) were recorded on a Bruker D8-advance X-ray diffractometer with Cu Kα radiation (0.154 nm) over the 2Ө range of 10−80 º. Transmission electron microscopy (TEM) images of the samples were obtained using a JEM 1400 microscope (JEOL, Peabody, MA, USA) with tungsten filament and 100 kV acceleration voltage. Samples were dispersed in ethanol using ultrasound irradiation and directly deposited on a copper grid prior to analysis. Elemental mapping was performed using transmission electron microscopyenergy dispersive X-ray spectroscopy (TEM-EDX) on an Oxford x-max 80-t system with SiLi detector at 136 eV resolution. Quantitative processing was performed with EInca energy 250 v5.04 software. Brønsted and Lewis acid sites on the catalysts were quantified by 2,6dimethylpyridine (DMPY) titration experiments, conducted via gas phase adsorption of the basic probe molecules utilizing a pulse chromatographic titration methodology at 70 °C and 90 °C, respectively. Briefly, small amounts of probe molecules (typically 1–2 µL) were injected (to approach conditions of gas-chromatography linearity) into a gas chromatograph through a microreactor in which the solid acid catalyst was previously placed. The temperature of the


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injector and detector was set at 300 °C and 250 °C, respectively. Basic compounds are adsorbed until saturation is completed giving rise to the detection of the probe molecules in the GC gas phase. The quantity of probe molecules adsorbed by the solid acid catalyst is then quantified. In order to distinguish between Brønsted and Lewis acidity, it is assumed that DMPY (2,6dimethylpyridine) selectively titrates Brønsted sites (methyl groups hinder coordination of nitrogen atoms with Lewis acid sites) while PY (pyridine) adsorbs both on Brønsted and Lewis acidity. Thus, the difference between the amounts of PY (total acidity) and DMPY (Brønsted acidity) adsorbed should correspond to Lewis acidity in the materials. Synthesis of propargylamines. The synthesis of propargylamines was accomplished by coupling of amine (1.2 mmol) and phenylacetylene (1.5 mmol) being added to a solution of aldehyde (1 mmol) in solvent (5 mL) under stirring, followed by the addition of the γFe2O3/SiO2-SGD catalyst (25 mg). The suspension was stirred at 25 ºC and the reaction progress was monitored by TLC using silica-gel Poly Gram SIL G/UV 254 plates with hexane/ethyl acetate as the mobile phase. After completion of the reaction as seen from TLC, a yellow precipitate was observed in the reaction mixture, the catalyst was separated by an external magnet. The remaining reaction suspension contained a precipitated yellow solid which was collected by filtration. The obtained crude product was dried and recrystallized from an ethanol/ethyl acetate (2:1) mixture to yield the pure product. The melting points (mp) of the products were determined in open capillaries using a BUCHI510 melting point apparatus. The melting points of the products in Table 1 were in accordance with data from the literature: 66 ºC (entry 1),36 126-128 ºC (entry 2),36 94-95 ºC (entry 3),37 52-55 ºC (entry 4),38,39 52-53 ºC (entry 5a),39 80 ºC (entry 5b),39 90-91 ºC (entry 5c),40,41 96-98 ºC (entry 6)36 and 73-74 ºC (entry 7).39


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In the catalytic recycle experiments, the recovered catalyst was thoroughly washed with DMF and dried at 40 ºC. Synthesis of 1,8-dioxo-octahydroxanthenes. The catalytic experiments were carried out in glass round bottom flask submerged in an oil bath at 90 ºC, using 0.7 mmol aldehyde, 1.4 mmol dimedone (5,5-dimethyl-1,3-cyclohexanedione) and 50 mg of γ-Fe2O3/SiO2-SDA catalyst in 4 mL water. When reaching the desired reaction temperature, the mixture was stirred magnetically during 2 h. The melting points of the products in Table 3 were in accordance with data from the literature: 195-197 ºC (entry 1),37 231-233 ºC (entry 2a),42 210-214 ºC (entry 2b),42 243-246 ºC (entry 2c),43 229-231 ºC (entry 2d),43 238-240 ºC (entry 2e),42 241-243 ºC (entry 2f),42 218-221 ºC (entry 2g),42 165-168 ºC (entry 3a)43 and 186-187 ºC (entry 3b).43 Alkylation of toluene. The catalytic alkylation of toluene (18.6 mmol) with benzyl chloride (1.7 mmol) was carried out in open glass vessels heated by microwave irradiation (300 W, CEMDISCOVER with PC control), using 25 mg of catalyst. When the reaction temperature was reached (90-100 ºC), the mixture was further stirred for 3 min. Then, the vessels were cooled to room temperature and samples were taken, filtered over a 0.22 µm syringe filter and analyzed by GC-FID, using a HP5890 Series II gas chromatograph with a HP-101 capillary column (Hewlett Packard, 25 m × 0.2 mm × 0.2 µm), operating at 60 mL min-1 N2 carrier flow and 20 psi column top head pressure. The oven temperature was initially set at 150 ºC (10 min. hold), raised at 10 ºC min.-1 to 170 ºC (18 min. hold) and further raised at 10 ºC min.-1 to 200 ºC (20 min. hold). The injector and detector temperature were set at 300 ºC. RESULTS AND DISCUSSION


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The different synthesis steps of the magnetic composite material functionalized with sulfaguanidine and sulfadiazine (γ-Fe2O3/SiO2-SGD and γ-Fe2O3/SiO2-SDA) are illustrated in Scheme 2. In essence, it stands on the anchoring of organosilane groups on the silica coating with organocatalysts containing an amine linker group. In the present study, 3-chloropropyl trimethoxysilane was used to provide anchor points for the functionalization with SGD through nucleophilic substitution of the chloride terminal groups in the propyl chains.

((Scheme 2))

The magnetic composite particles were characterized using X-ray powder diffraction spectrometry (XRD), Fourier transform infrared spectroscopy (FRIR) using the Attenuated Total Reflection (ATR) technique, thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometry (VSM). The XRD spectra of γ-Fe2O3/SiO2-SGD/SDA are shown in Figure 1. Both magnetite and maghemite display a spinel structure. The signals at 30.3, 35.7, 43.3, 53.8, 57.2 and 62.9 ° pertain to the crystal planes 220, 311, 400, 422, 511 and 440 of the cubic structure of maghemite (γ-Fe2O3, JCPDS 04-0755).44,45 At first sight it looks rather difficult to distinguish the crystal phases of maghemite and magnetite (as most of their diffraction peaks are located within 1° difference), however both crystal phases can be identified by considering the peaks at 57.2 and 62.9 º, which differ more than 1 º between both crystal phases. Preliminary studies indicated that, using the co-precipitation method (Fe2+ and Fe3+ precursors), magnetite crystals were obtained. After coating the iron oxide particles with silica, it appeared that the obtained iron oxide-silica


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composite was much less efficient in anchoring the organocatalyst (SGD). When calcining the sample at 300 ºC during 3 h, the magnetite crystal phase was efficiently transformed in the maghemite phase. The maghemite-silica composite was effective in anchoring SGD groups. The crystal phase of the iron oxide did not change during the different synthesis steps, as seen from the maghemite diffraction signals present in the XRD patterns recorded from γ-Fe2O3, γFe2O3/SiO2 and γ-Fe2O3/SiO2-SGD/SDA samples. Applying the Debye-Scherrer equation using the full width at half height of the 311 reflection peak at 35.7 ° (2θ) and a shape factor of 0.9, the mean crystal size of the maghemite phase was ca. 9.8 nm. The surface morphology of the composite particles was analyzed with SEM (Figure 2). On average, the diameter of the particles obtained from their size distribution histogram varied in the 9-20 nm range in diameter with 1213 nm as the most frequent size. No clear evidence was observed for the formation of core-shell structures in TEM analysis (Figure 3) of the (γ-Fe2O3/SiO2) sample, instead the penetration of the electron beam was distributed homogeneously over the whole surface of a single particle (Figure 3b), which indicates that a silica-iron oxide composite material was synthesized. EDX images (Figures 3e-g) also suggested this. The composite particle size observed was in the range of the sizes observed in the SEM analysis. BET surface areas of γ-Fe2O3, γ-Fe2O3/SiO2-SGD and γ-Fe2O3/SiO2-SDA nanoparticles were 75, 50 and 25 m2 g-1, respectively (see Table S1 and Figure S1 in the Supporting Information). Comparing the Barret-Joyner-Halenda pore volume (0.1-0.2 cm3 g-1) of the functionalized composite particles to the neat iron oxide particles (0.3 cm3 g-1), it becomes clear that the silica coating and the functionalized surface (with SGD and SDA groups) occupies a considerable part of the space in the catalyst pores. The EDX profiles (see Figure S2 in the Supporting Information) and the corresponding elemental distribution (Table S2) clearly indicates the presence of Fe, O, Si, C, N, S and residual Cl species in the


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catalysts. The atomic percentage of N and S were 2.6 and 0.6 % in the γ-Fe2O3/SiO2-SGD catalyst and 5.1 and 1.6 % in the γ-Fe2O3/SiO2-SGZ catalyst, respectively. This indicates that the molar SDZ content in the latter is 2-3 times higher than the molar SGD content in the former (organic fraction).

((Figure 1))

((Figure 2))

((Figure 3))

The thermogravimetric behavior of the organocatalysts is shown in Figure 4a. A two-step weight loss was observed for the Fe2O3-SiO2-SDA sample while the combustion proceeded more gradually in the γ-Fe2O3-SiO2-SGD sample. The latter sample also showed significant moisture loss (0.6 %). The decomposition of the anchored organic molecules started at temperatures around 270 ˚C and prolonged until reaching ca. 515 and 540 ˚C for SDA and SGD, respectively, after which no significant weight loss occurred as only a stable γ-Fe2O3-SiO2 material remained at this stage. Taking into account the weight loss (3.6 %) in the γ-Fe2O3-SiO2-SGD sample and the moisture loss (0.6 %), together with the molecular weight ratios of SGD and propyl-SGD, it can be deduced that the neto weight which corresponds to SGD is 2.6 % and that 1 g of γ-Fe2O3-


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SiO2-SGD contained ca. 0.1 mmol SGD. Similarly, an SDA content of 0.3 mmol g-1 was estimated for the γ-Fe2O3-SiO2-SGD catalyst. In other words, the SDA content in γ-Fe2O3/SiO2SDA was 3.2 times higher than the SGD content in γ-Fe2O3/SiO2-SDA composite, slightly higher than the result found in the EDX analysis. The higher content of SDA in the final composite particles was also reflected in the ATR spectra (Figure 4b), where the absorption band signals of SDA in the γ-Fe2O3/SiO2-SDA sample were much more intense compared to the band signals of SGD in the γ-Fe2O3/SiO2-SGD sample. Moreover, a small shift to higher wavenumbers of the absorption bands of SGD and SDZ was observed in the spectra of γFe2O3/SiO2-SGD/SDZ, with the shift being larger for the SDZ functionalized composite, which also reflects the higher content of SDZ compared to SGD in the catalysts. The surface acidity of the SGD and SDA catalysts reached 160 and 280 µmol g-1 with 39 and 24 % Brϕnsted sites, respectively (see Table S3 in the Supporting Information). Finally, the magnetic susceptibility (χm) of the organocatalyts was tested (see Figure S3 in the Supporting Information). The saturation magnetization of γ-Fe2O3/SiO2-SGD was ca. 48×10-6 m3 kg-1, in the range of previously reported silica coated MNPs46 and high enough for efficient separation of reaction mixtures with a hand magnet. In comparison, pure magnetite nanoparticles generally show magnetic susceptibilities ca. 500×10-6 m3 kg-1.47

((Figure 4))

Sulfaguanidine (SGD) functionalized magnetic composite particles were tested in the coupling reaction of phenylacetylene with various aldehydes and amines (piperidine and morpholine) to


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synthesize the corresponding propargylamines (Table 1). After ca. 1 h reaction at room temperature, the products were isolated with 70-80 mol% yields, except for benzaldehyde (entry 1, 87 mol%) and naphthalene carboxaldehyde (entry 2, 65 mol%) as the reactant. The yield of 1(1,3-diphenylprop-2-ynyl)piperidine as the coupling of piperidine with benzaldehyde and phenylacetylene (entry 1) is 5-7 % lower compared with previously reported results (Table 2). Although the absolute product yields were slightly lower (0-15 %) compared to previous works, the present work demonstrates promising results, taking into account that the reactions were performed at room temperature with minimum amount of catalyst (0.25 mol%).

((Table 1))

((Table 2))

The mechanism (Scheme 3) proposed for the multicomponent reaction is based on the generation of electrophilic species through Mannich reaction and acetylenic hydrogen abstraction by guanidine, followed by nucleophilic addition of the acetylide to the iminium ion generated in situ from the aldehyde and the amine. After the recovery of the γ-Fe2O3/SiO2-SGD particles by means of a hand magnet, the re-usability was tested for the synthesis of 1-(1,3-diphenylprop-2ynyl)piperidine. The yield of the isolated product dropped gradually from 87 to 53 mol% over 4 consecutive catalytic experiments (Figure 5), showing lower catalytic re-usability compared to previously reported catalysts.50,51 Leaching of the organocatalyst (SGD) from the composite


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particles was the main cause of catalyst deactivation, as appreciated in the TGA analysis of fresh and spent γ-Fe2O3/SiO2-SGD (Figure S4 in the Supporting Information), which indicated that 57 % of the initial SGD content in the SGD functionalized composite was lost. At this level the SGD absorption bands were not appreciated anymore in the ATR spectrum of the spent catalyst recovered after 4 catalytic cycles (result not shown). An adapted preparation method or other functionalization strategies are required to deal with this leaching effect, at least in the present conditions used in the coupling reactions.

((Scheme 3))

((Figure 5))

The sulfadiazine (SDA) functionalized composite was tested for the synthesis of 1,8-dioxooctahydroxanthenes starting from dimedone and various aldehydes in water (Table 3). When the reaction was carried out without any catalyst, no product formation was observed, even after prolonged reaction time. Among the different benzaldehyde substituent groups and positions examined, the effects were not pronounced, with yields ranging between 80 and 91 mol% within 30-50 min. These yields are slightly lower as compared to a sulfated zirconia catalyst reported recently,52 although those results were obtained after 8 h in ethanol at 70 ˚C.


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((Table 3))

SGD and SDA functionalized composites were also employed in the alkylation of toluene with benzyl chloride (Figures 6b and 6c). Excess toluene was used both as reagent and solvent. In the absence of catalyst (blank), no significant product formation was observed in the GC-FID analysis. With catalyst, the mayor products (41-51 mol%) were 2- and 4-methyl diphenylmethane (ortho- and para-adduct, respectively), with only small amounts (4-9 mol%) of 3-diphenylmethane (meta-adduct). These selectivities are in accordance with previously published work on alkylation with halogen substituted benzyls.53,54 The catalysts were re-utilized successfully over 4 experiments, with the selectivity to the ortho/para-adduct dropping only slightly. When using benzyl alcohol instead, the conversion observed was negligible (results not shown). Additional experiments with the bare γ-Fe2O3/SiO2 composite material (Figure 6a) also showed high conversion, but with lower selectivity to the ortho and meta adducts. The combined selectivity to ortho and meta for the SGD and SDA functionalized catalyst dropped from 91 to 90 % over 4 catalytic cycles, while it dropped from 75 to 69 % for the Fe2O3/SiO2 catalyst.

((Figure 6))

The results herein reported illustrate the catalytic versatility of sulfaguanidin and sulfadiazine functionalized magnetic composites. We believe that their versatility is based on the multiple protonation sites and different tautomeric forms present in these organocatalysts (Scheme 1).


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CONCLUSIONS Two functionalized magnetic composite catalysts were synthesized successfully by anchoring sulfaguanidine (SGD) and sulfadiazine (SDA) on an iron oxide –silica composite. The functionalized magnetic particles showed good magnetic susceptibility, important for their efficient recovery from reaction mixtures. The as synthesized organocatalysts were tested for various organic transformations, including the synthesis of propargylamines by coupling of phenylacetylene with various amines and aldehydes, the synthesis of various 1,8-dioxooctahydroxanthenes in water and the alkylation of toluene with benzyl chloride. Product yields in the range of previous reported results were demonstrated, however with lower stability for the synthesis of propargylamines, due to leaching of SGD from the functionalized composite catalyst. ASSOCIATED CONTENT Supporting Information Detailed materials characterization results are available at. ACKNOWLEDGEMENTS The authors wish to thank the Microscopy Unit of the Central Service for Research Support of the University of Córdoba. R.L. gratefully acknowledges MINECO as well as FEDER funds for funding under project CTQ2016-78289-P and financial support from the University of Cordoba (Spain). H.S. gratefully acknowledges Sistan and Balouchestan University of Iran for the financial support of the research as well as Iran Nanotechnology Initiative Council for complementary financial supports.


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Table 1. Isolated yields of multicomponent coupling products of phenylacetylene with aldehydes and amines using γ-Fe2O3@SiO2-SGD catalyst.[a]

Entry

Aldehyde

Amine

CHO

1

N H

CHO

2

N H

Time (min.)

Yield[b] (mol%)

Product

40

N

87

90

N

65

N

3

CHO

O

4

CHO

N H

N H

45

65

80

O

70

N

CHO

R O

O

5a 5b 5c

6

7

Ra Rb = Me Rc = OMe

N H

CHO

O

Cl

N H

CHO

O

O

N H

45 55 55

N

80 (Ra) 72 (Rb) 78 (Rc)

R

O

50

N

45

N

Cl

O

70

76

O

[a]

1.5 mmol phenyl acetylene, 1 mmol aldehyde, 2 mmol amines, 25 mg catalyst (0.26 mol% SGD), 2 mL dimethylformamide (DMF), 20 ˚C. [b]

Isolated yield.


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Table 2. Comparison of 1-(1,3-diphenylprop-2-ynyl)piperidine yields from the coupling of phenylacetylene with piperidine and benzaldehyde.

Entry

Catalyst

Conditions

Yield (mol%)

Ref.

1

Fe3O4

THF, 80°C, 24h

80

48

2

Graphene-Fe3O4

CH3CN, 80°C, 24h

92

49

3

Cu2O/CuFe2O4

Solvent-free, 90°C, 40min.

94

50

4

ZnS

CH3CN, 80°C, 4h

94

51

5

γ-Fe2O3@SiO2-SGD

DMF, 20°C, 40min.

87

This work

Table 3. Yields of 1,8-dioxo-octahydroxanthenes obtained from various aldehydes and dimedone catalyzed by γ-Fe2O3@SiO2-SDA.[a] Entry Aldehyde

Time (min.) 40

CHO

1

Product O

Yield (mol%) 90 O

O

2a 2b 2c 2d 2e 2f 2g

Ra = NO2 Rb = F Rc = Br Rd = Cl Re = OH Rf = OMe Rg = Me

3a 3b

Ra = NO2 Rb = Cl

CHO

R

30 35 40 35 45 35 50

R

O

O

O

91 (Ra) 89 (Rb) 90 (Rc) 87 (Rd) 86 (Re) 87 (Rf) 80 (Rg)

R

CHO

35 40

O

O

87 (Ra) 83 (Rb)

R O

[a]

0.7 mmol aldehyde, 1.4 mmol dimedone, 50 mg catalyst (2.3 mol% SDZ), 4 mL water, 100 ˚C.


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Scheme 1. (a) Neutral sulfaguanidine (SGD) tautomers and (b) sulfadiazine (SDA) and charged (de)protonated SDA salts.

Scheme 2. Synthesis of γ-Fe2O3, γ-Fe2O3/SiO2 composite and SGD/SDA functionalized composite (γ-Fe2O3/SiO2-SGD/SDA).

Scheme 3. Sulfonamide catalyzed multicomponent coupling mechanism of phenylacetylene.

Figure 1. Powder X-ray diffraction spectra of (a) γ-Fe2O3/SiO2-SGD, (b) γ-Fe2O3/SiO2-SDA, (c) pure magnetite and (d) pure maghemite.

Figure 2. (Up) SEM images and (Bottom) corresponding particle size distribution histograms of γ-Fe2O3/SiO2-SGD (left) and γ-Fe2O3/SiO2-SDA (right) catalysts.

Figure 3. (Left) TEM images and (Right) EDX images of γ-Fe2O3/SiO2 composite particles.

Figure 4. (a) TGA analysis of γ-Fe2O3/SiO2, γ-Fe2O3/SiO2-SGD and γ-Fe2O3/SiO2-SDA; (b) ATR spectra of γ-Fe2O3, γ-Fe2O3/SiO2, pure SGD and SDA and γ-Fe2O3/SiO2-SGD/SDA composites.


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Figure 5. 1-(1,3-diphenylprop-2-ynyl)piperidine yields in catalytic recycle experiments of phenylacetylene coupling with piperidine and benzaldehyde.

Figure 6. Catalytic performance in the alkylation of toluene with benzyl chloride with reutilization of (a) γ-Fe2O3/SiO2, (b) γ-Fe2O3/SiO2-SGD (0.15 mol%) and (c) γ-Fe2O3/SiO2-SDA (0.48 mol%) catalyst.


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For Table of Contents use only.

Two novel sulfonamide functionalized iron oxide-silica composites were successfully applied in (multicomponent) coupling reactions and in toluene alkylation with benzyl chloride.


29


Figure 1 59x146mm (150 x 150 DPI)


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Figure 2 159x163mm (150 x 150 DPI)



Figure 3 112x143mm (150 x 150 DPI)


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Figure 4 107x193mm (150 x 150 DPI)



Figure 5 116x75mm (150 x 150 DPI)


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Figure 6 182x78mm (150 x 150 DPI)



Scheme 1 177x60mm (150 x 150 DPI)


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Scheme 2 187x159mm (150 x 150 DPI)



Scheme 3 172x90mm (150 x 150 DPI)


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Catalytic Versatility of Novel Sulfonamide Functionalized Magnetic

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