Performing organic transformations using magnetic catalysts based on Fe3O4 core is a practical and attractive field in catalysis researches [1-12]. This class of catalysts has several unique features, including durability at high temperatures and in different chemical conditions, facile recycling, reusability, capability to graft with diverse functional groups and simple preparation of their magnetic core [1-12].
A wide range of applications have been reported for the compounds bearing bisamide functional group [13-24]; they have been used as antiviral , selective anion-receptors , antitumor , insecticide , kinase inhibitor  and anti-metastasis  agents, and for recovery of fuels . Furthermore, complexes of bisamides-metal ions have been applied for absorption and selective isolation of cationic dyes , fluorescent sensing  and photocatalysis processes , and as reagents in organic transformations [22,23] and MRI contrast agent . A class of bisamide derivatives is N,N′-alkylidene bisamides that are constructed via the reaction of arylaldehydes (1 eq.) and primary amides (2 eq.), promoted by a catalyst [25-34].
Here, we have reported the production of a novel magnetic catalyst namely [Fe3O4@SiO2@RNMe2-SO3H][Cl/MeSO3] (FSRNSCM), and its characterization using EDS, FE-SEM, FT-IR, XRD, VSM, TG and DTG analyses. Thereafter, we have examined its catalytic performance for the solvent-free reaction of arylaldehydes (1 eq.) and primary amides (2 eq.) leading to N,N′-alkylidene bisamides.
Chemicals and instruments
Information on chemicals and instruments have been given in supplementary material.
Production of [Fe3O4@SiO2@RNMe2-SO3H][Cl/MeSO3] (FSRNSCM)
Nano-Fe3O4 was prepared by the reported protocol . Then, a mixture of nano-Fe3O4 (1.16 g), Si(OEt)4 (3.5 mL), NH3 solution (3.5 mL), H2O (23 mL) and EtOH (93 mL) was stirred in reflux conditions for 12 h to construct I . Compound I and (3-chloropropyl) trimethoxysilane (5 mmol, 0.92 g) in dry toluene (40 mL) was stirred and refluxed under a flow of nitrogen gas for 12 h to produce II . Then, N1, N1, N2, N2-tetramethylethane-1,2-diamine (5 mmol, 0.75 mL) and II in dry toluene (30 mL) were stirred (accompanied by refluxing) for 12 h, and compound III was prepared [6,7]. III was added gradually to a stirring solution of ClSO3H (5 mmol, 0.34 mL) in dry methylene chloride (20 mL) at 10 °C, and the mixture was stirred for 5 h at ambient temperature to afford IV. Finally, a solution of MeSO3H (5 mmol, 0.48 g) in dry methylene chloride (15 mL) was gradually added to IV at ambient temperature, and stirred for 10 h at this temperature and 2 h under reflux conditions to furnish FSRNSCM (Scheme 1). Before each step, the reaction mixture was dispersed by ultrasound irradiation; furthermore, the produced compound in each step was magnetically isolated, washed by the used solvent in that step, and dried.
SCHEME 1 The production of FSRNSCM
General method for the construction of N,N′-alkylidene bisamides
A mixture of aldehyde (1 mmol), amide (2 mmol) and FSRNSCM (0.04 g) was stirred by a rod at 90 °C. After consuming the reactants (as seen by TLC) and cooling the mixture to ambient temperature, ethyl acetate (15 mL) was added, and stirred for 2 min in reflux conditions. The unsolvable catalyst was magnetically separated, and the solvent of the remained solution was distilled; the formed precipitate was recrystallized from ethanol (95%) to produce the pure bisamide. Selected NMR data of the products have been reported in supplementary material.
Results and discussion
The catalyst characterization
Elements including Fe, O, Si, C, N, S and Cl are existing in the structure of FSRNSCM; in the EDS spectrum, the peaks related to the elements were seen (Figure 1). Additionally, no impurity was observed in the spectrum.
As for the FE-SEM image (Figure 2), nanoparticles and bulk particles are present in the catalyst powder; nevertheless, most of the particles have nano sizes. In addition, the particles have different crystalline forms.
FIGURE 1 The EDS spectrum of FSRNSCM
FIGURE 2 The FE-SEM micrograph of the magnetic catalyst
The FT-IR spectrum (Figure 3) confirms that the Fe3O4 core has been coated by SiO2, and the organic moieties have been anchored to the SiO2 surface; i.e. the magnetic catalyst has been successfully prepared. The FT-IR results are illustrated in Table 1 that are in agreement with those mentioned in the chemistry sources [7,35,36].
In the XRD pattern of FSRNSCM (Figure 4), some sharp diffraction lines (at 2θ = 35.4, 40.8, 48.5, 58.8, 62.4 and 68.1) and a broad one (at 2θ ≈ 21.0–34.0º) were observed. The sharp peaks appeared at 35.4, 48.5, 58.8, 62.4 and 68.1 can be related to Fe3O4 in the catalyst structure. The broad peak belongs to the amorphous structure of SiO2 layer [5,7,37].
FIGURE 3 The FT-IR spectrum of FSRNSCM
FIGURE 4 The XRD pattern of FSRNSCM
Saturation magnetization (Ms) of Fe3O4 which was utilized to prepare FSRNSCM was 52 emu.g−1 ; however, Ms of FSRNSCM was found to be ~15.2 emu.g−1. Figure 5 represents the VSM diagram of FSRNSCM. Decreasing Ms of the catalyst with respect to Fe3O4 can be ascribed to coating SiO2 layer on Fe3O4, and bonding the organic groups with the SiO2 surface.
FIGURE 5 The VSM diagram of the magnetic catalyst
During thermal gravimetric analysis, FSRNSCM lost its weight in three stages (Figure 6). Vaporizing the adsorbed solvents on the catalyst surface may be the reason for the weight loss less than ~170 °C. During the weight loss at ~170–405 °C (with Tmax at 388 °C in the DTG diagram), the organic groups bonded with the SiO2 surface have been decomposed. The weight loss at ~405–600 °C (with Tmax at 478 °C in the DTG diagram) seems to be due to condensing the silanol groups. The literature corroborates these interpretations .
FIGURE 6 The TG and DTG diagrams of FSRNSCM
Catalytic performance of FSRNSCM to promote construction of N,N′-alkylidene bisamides
To investigate catalytic performance of FSRNSCM for the constructionof N,N′-alkylidene bisamides, 4-chlorobanzaldehyde (1 mmol) was reacted with banzamide (2 mmol) in the presence of diverse quantities of FSRNSCM (e.g. 0.032 g, 0.040 and 0.048 g) at 80, 90 and 100 °C under solvent-free conditions (Scheme 2). The optimal reaction time and yield were acquired by application of 0.040 g of the catalyst at 90 °C (time: 15 min; yield: 97%).
SCHEME 2 The constructionof N,N′-alkylidene bisamides
Then, the influence of diverse arylaldehydes and primary amides (aromatic and aliphatic) on the constructionof N,N′-alkylidene bisamides using FSRNSCM were studied; the acquired results are represented in Table 2. All reactions were effectively performed, and the relevant bisamides were constructed in short times and high yields. Nevertheless, the arylaldehydes bearing electron-releasing substituents gave the related bisamides in longer reaction times in comparison to benzaldehyde and aldehydes possessing electron-withdrawing and halogen substituents (products 7 and 8). Moreover, aliphatic amide (acetamide) gave the corresponding products in slightly lower yields with respect to benzamide (products 9 and 10).
The reaction of banzamide with 4-chlorobanzaldehyde was chosen to study reusability of FSRNSCM; the procedure for recycling the catalyst has been mentioned in experimental section. When the fresh catalyst was applied, the reaction time and yield were 15 min and 97%, respectively. In first recycling of FSRNSCM, the reaction time and yield were 22 min and 93%, respectively. In second recycling, the reaction time increased up to 30 min, and the yield decreased to 78%. So, FSRNSCM was recyclable and reusable for one time with negligible diminution of catalytic activity; but, in second recycling and reusing, its catalytic activity decreased.
Briefly, a novel magnetic catalyst (FSRNSCM) was introduced for the construction of N,N'-alkylidene bisamides. This nanomaterial may also catalyze different organic reactions. High efficacy, wide scope, high yields of the products, short reaction times, usage of few amount of the FSRNSCM in the reaction, producing the bisamides without use of solvent, and good appliance with green chemistry principles are the advantages of this methodology.
The Research Council of our University has supported this work; we appreciate this Council.
Abdolkarim Zare: https://orcid.org/0000-0002-8210-3155
How to cite this article: Amir Hosain Karimi, Ali Hekmat-Ara, Abdolkarim Zare*, Marziyeh Barzegar, Roghayyeh Khanivar, Masoud Sadeghi-Takallo. Producing, characterizing and utilizing a novel magnetic catalyst to promote constructionof N,N′-alkylidene bisamides. Eurasian Chemical Communications, 2021, 3(6), 360-368. Link: http://www.echemcom.com/article_130191.html