materials Article
Solvent-Free Esterification of Carboxylic Acids Using Supported Iron Oxide Nanoparticles as an Efficient and Recoverable Catalyst Fatemeh Rajabi 1, *, Mohammad Abdollahi 1 and Rafael Luque 2 1 2
*
Department of Science, Payame Noor University, P.O. Box 19395-4697, Tehran 19569, Iran;
[email protected] Departamento de Química Orgánica, Universidad de Córdoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, km 396, Cordoba 14014, Spain;
[email protected] Correspondence:
[email protected]; Tel.: +98-281-333-6366; Fax: +98-281-334-4081
Academic Editor: Eduardo J. García-Suárez Received: 9 May 2016; Accepted: 23 June 2016; Published: 12 July 2016
Abstract: Supported iron oxide nanoparticles on mesoporous materials (FeNP@SBA-15) have been successfully utilized in the esterification of a variety carboxylic acids including aromatic, aliphatic, and long-chain carboxylic acids under convenient reaction conditions. The supported catalyst could be easily recovered after reaction completion and reused several times without any loss in activity after up to 10 runs. Keywords: supported iron oxide nanoparticles; esterification; carboxylic acid
1. Introduction Esters play a significant role in daily living and the chemical industry. The reaction of carboxylic acids with alcohols to form esters is among the mildest and most efficient of organic transformations, largely a consequence of the high accessibility and stability of reactants. High ester usage in the synthesis of drugs, fine chemicals, pharmaceuticals, solvents and plasticizers as intermediates makes these substrates one of the most important types of compounds in organic chemistry [1]. In this context, some protocols for the synthesis of esters are well-known, including Fisher esterifications [2] and methylation reactions [3] of carboxylic acids. Due to the wide synthetic and biological applications of esters, a number of reagents such as ortho esters [4], N,N-dimethylformamide dialkyl acetals [5], triazene derivatives [6] and O-dialkyl isoureas [7] have been reported for the esterification of various aromatic/aliphatic carboxylic acids. The reaction of carboxylic acids and alcohols in the absence of catalysts is very slow and requires a long time for the reaction to reach equilibrium. To accelerate reaction rates, a number of catalysts have been reported inthe literature. These include classical solid acids such as ion exchange resins [8–10], zeolites [11,12], super acids [13,14], heteropolyacids [15–18] and supported chlorides [19]. Metal oxides such as CaO and MgO [20], metal-layered hydroxides [21,22], and efficient enzymatic catalysts [23,24] have also been employed in esterification reactions. However, many of these methods suffer from inherent drawbacks such as the need for expensive or harmful materials as reagents and catalysts, the formation of undesired side products, highly acidic conditions, the use of hazardous and toxic solvents, high reaction temperatures, low yield of products and prolonged reaction times. A need to develop an improved catalytic system for the synthesis of esters in terms of operational simplicity and economic viability is of utmost importance. Herein, a nanomaterial based on supported iron oxide nanoparticles on SBA-15 (FeNP@SBA-15) has been utilized as an efficient catalyst for a mild esterification of various carboxylic acids to their corresponding esters (Scheme 1). The combination of iron nanoparticles and the mesoporous structure of the material showed excellent synergistic effects on the enhancement of Materials 2016, 9, 557; doi:10.3390/ma9070557
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Materials 2016, 9, 557
Materials 2016, 9, 557
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synergistic effects on the enhancement of activity and stability of the catalyst. Apart from a high
Materials 9, 557 of the catalyst. Apart from a high activity, the successful recycling of this2catalytic of 9 activity and 2016, stability activity, the successful recycling of this catalytic system allows a more economic and environmentally Materials 2016, 9,more 557 economic and environmentally friendly process which is of special advantage 2 of 9 system allows a friendly process which is of special advantage forstability large-scale andfrom industrial synergistic effects on the enhancement activity and of thepreparations catalyst. Apart a high for large-scale preparations and industrialofapplications. applications.
synergistic on the enhancement of activity andallows stability of the catalyst. Apart from a high activity, the effects successful recycling of this catalytic system a more economic and environmentally activity, the successful recycling this catalytic systemfor allows a more economic and environmentally friendly process which is of ofspecial advantage large-scale preparations and industrial COOH COOMe friendly process which is of specialFeNP@SBA-15 advantage for large-scale preparations and industrial applications. applications. MeOH, Reflux COOH COOMe FeNP@SBA-15 COOH COOMe FeNP@SBA-15 Scheme 1. Esterificationofof benzoic acid acid with onon SBA-15. Scheme 1. Esterification benzoic withFeNP FeNPsupported supported SBA-15. MeOH, Reflux
2.
2. Results and Discussion
MeOH, Reflux
Scheme 1. Esterification of benzoic acid with FeNP supported on SBA-15. Results and Discussion 1. Esterification of benzoic withnanoparticles FeNP supported SBA-15. The catalyticScheme performance of supported ironacid oxide hasonbeen previously reported
The catalytic of supported iron oxide has been reported 2. andperformance Discussion byResults our research group [25–27]. In continuation of nanoparticles our previous study on previously the application of by 2. Results and Discussion our research groupas [25–27]. In continuation ofwe ourfound previous study on the application ofacids FeNP@SBA-15 FeNP@SBA-15 aperformance recoverable catalyst [26], that the esterification of carboxylic in the The catalytic of supported iron oxide nanoparticles has been previously reported as a recoverable catalyst [26], we found that the esterification of carboxylic acids in the presence of presence of FeNP@SBA-15 as an effective catalyst has not been investigated yet. Hence, we decided Theresearch catalytic group performance of supported iron oxide nanoparticles has been reported by our [25–27]. In continuation of our previous study on previously the application of to investigate the catalytic effect of FeNP@SBA-15 as a promoter system on the rate and efficiency of FeNP@SBA-15 as an effective catalyst has not been investigated yet. Hence, we decided to investigate by our research [25–27]. In continuation ofthat ourthe previous studyofon the application of FeNP@SBA-15 as agroup recoverable catalyst [26], we found esterification carboxylic acids in the esterification ofas acids. The FeNP@SBA-15 hasrate beenand previously described the catalytic effect ofcarboxylic as a material promoter system onesterification the efficiency of esterification FeNP@SBA-15 aFeNP@SBA-15 recoverable [26], we found thatbeen the of carboxylic acids inand the presence of FeNP@SBA-15 as ancatalyst effective catalyst has not investigated yet. Hence, we decided characterized byThe a series of including Inductively coupled plasma/Mass of carboxylic acids. material FeNP@SBA-15 has been previously and characterized presence of FeNP@SBA-15 astechniques an effective catalyst has been investigated yet. Hence, we decided to investigate the catalytic effect of FeNP@SBA-15 as a not promoter systemdescribed on the rate andspectrometry efficiency of by (ICP/MS), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron a series of techniques including Inductively coupled spectrometry (ICP/MS), to investigate thecarboxylic catalytic effect ofThe FeNP@SBA-15 as a plasma/Mass promoterhas system onpreviously the rate and efficiency ofX-ray esterification of acids. material FeNP@SBA-15 been described and microscopy (TEM) X-ray photoelectron spectroscopy (XPS) coupled [27]. esterification of carboxylic The material FeNP@SBA-15 has been previously described and and diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) characterized by a and series ofacids. techniques including Inductively plasma/Mass spectrometry TEM images the catalyst indicated that the iron oxide nanoparticle sizes were in theelectron 5–7 nm characterized byspectroscopy aofseries of (XRD), techniques including Inductively coupled plasma/Mass spectrometry X-ray diffraction Scanning electron microscopy (SEM), Transmission X-ray(ICP/MS), photoelectron (XPS) [27]. range, with an excellent homogeneous dispersion of the iron oxide nanoparticles on the support (ICP/MS), X-ray diffraction Scanning electron microscopy microscopy (TEM) and X-ray (XRD), photoelectron spectroscopy (XPS) nanoparticle [27]. (SEM), Transmission TEM images of the catalyst indicated that the iron oxide sizes were inelectron the 5–7 nm (Figure 1).images Fe species inX-ray the synthesized materials as measured by ICP/MS were foundintothe be 5–7 around microscopy (TEM) and photoelectron spectroscopy (XPS) [27]. TEM of the catalyst indicated that the iron oxide nanoparticle sizes were nm range, with an excellent homogeneous dispersion of the iron oxide nanoparticles on the support 0.5–0.6 wt. %, with average iron oxide nanoparticle sizes in the 5–8 nm range. XRD of the materials TEM images of the catalyst indicated that the iron oxide nanoparticle sizes were in the 5–7 range, with an excellent homogeneousmaterials dispersionasofmeasured the iron oxide nanoparticles on the to support (Figure 1). Fe species in theofsynthesized by ICP/MS were found benm around confirmed the presence the hematite phase (Fe 2O3, JCPDS card 39-0664) for FeNP@SBA-15 (Figure range, with an excellent homogeneous dispersion of the iron oxide nanoparticles on the support (Figure 1). Fe species in the synthesized materials as measured by ICP/MS were found to be around 0.5–0.6 wt. %,was with average ironby oxide nanoparticle sizes inFe the 5–8 nm range. XRD of3/2the materials 3+ bands 2), which also confirmed XPS measurements (typical BE 714 eV(Fe2p ) and 725 (Figure 1). %, Fe with species in the iron synthesized materials assizes measured by were found to be around 0.5–0.6 wt. average oxide nanoparticle in the 5–8ICP/MS nm at range. XRD of the materials confirmed the presence of the hematite phase (Fe O , JCPDS card 39-0664) for FeNP@SBA-15 (Figure 2), 2 3 eV (Fe2p 1/2), Figure 3), with only a very minor contribution (
