Elsevier

Applied Catalysis A: General

Volume 509, 5 January 2016, Pages 52-65
Applied Catalysis A: General

Magnesium and/or calcium-containing natural minerals as ecologically friendly catalysts for the Baeyer–Villiger oxidation of cyclohexanone with hydrogen peroxide

https://doi.org/10.1016/j.apcata.2015.10.021Get rights and content

Highlights

  • First report on catalytic synthesis of ϵ-caprolactone over natural Mg(Ca) minerals.

  • Catalysts performance–physicochemical properties correlation has been established.

  • Ground magnesite and sepiolite perform better than the reference hydrotalcite.

Abstract

Magnesium and/or calcium-containing natural minerals of basic character were tested as catalysts for the Baeyer–Villiger oxidation of cyclohexanone to ϵ-caprolactone. Two types of widely available, nontoxic and inexpensive minerals were investigated: carbonates, i.e. magnesite, dolomite and calcite (limestone), and silicates, i.e. talc, sepiolite and hectorite. The minerals were characterized with XRD, SEM, XRF, ICP OES, XPS, N2 adsorption at −196 °C, laser diffraction particle sizing, and contact angle measurement. Surface basicity was determined by adsorption of organic acids with different pKa values. Mechanochemical treatment of the samples was performed in a planetary mill. The yields of ϵ-caprolactone over the as received carbonate minerals were comparable with the yield obtained for the reference Mg–Al hydrotalcite catalyst. Of the layered magnesium silicate group, the untreated hectorite gave the best performance, yielding ϵ-caprolactone in the amount similar to that obtained for the reference catalyst. The study of the effect of grinding on the catalytic performance of minerals revealed that the treatment may affect not only the mineral grain size and morphology, but also other factors relevant for the catalytic reaction, such as hydrophilic/hydrophobic properties of the mineral surface and the ease of alkaline earth leaching. The final effect of grinding depended on the interplay between all these factors. Thus, grinding-induced enhancement of catalytic performance was most pronounced for magnesite, less significant for dolomite, and practically negligible for limestone. In the series of magnesium silicates grinding increased the ϵ-caprolactone yield over sepiolite, while little effect was observed for talc and hectorite. The maximum yields of ϵ-caprolactone over ground magnesite and ground sepiolite were by factor 1.4 higher than the yield over the reference hydrotalcite catalyst. Thus, magnesite and sepiolite prove as particularly promising, eco-friendly catalysts for the Baeyer–Villiger oxidation of cyclohexanone to ϵ-caprolactone.

Introduction

The Baeyer–Villiger oxidation of ketones and aldehydes to esters and lactones [1] is a process of great importance in industrial organic synthesis, widely exploited in pharmacy, medicine, cosmetic industry, agrochemistry and polymer manufacturing [2]. Initially, Baeyer–Villiger reactions were carried out as stoichiometric oxidations with peroxysulfuric acid, known as Caro's acid, then with various organic peroxy acids [3]. The reaction mechanism, postulated originally by Criegee [4], involves a nucleophilic attack of the peroxyacid at the carbonyl bond with formation of an intermediate, so called Criegee adduct, followed by a concerted rearrangement, entailing reconstitution of carbonyl group and departure of the acid moiety (Fig. 1).

However, the use of peroxyacids is connected with an adverse environmental impact, because the reagents are explosive and generate hazardous acid waste. For this reason there is a growing interest in developing greener procedures and more benign oxidants for this process [5]. A very promising approach is associated with the replacement of a stoichiometric reaction with a catalytic one and the use of hydrogen peroxide as an oxidizing agent [5], [6], [7], [8], [9]. Beside molecular oxygen, hydrogen peroxide is the most environmentally friendly and atom-efficient oxidant, generating water as the only byproduct. Both homogeneous and heterogeneous catalytic systems have been used, the interest in the latter being chiefly due to the ease of catalyst separation from the reaction mixture [7].

Baeyer–Villiger oxidation of cyclohexanone to ϵ-caprolactone, a monomer extensively used in the synthesis of biodegradable polymers, is a processes of particular importance, and a rich literature exists on the heterogeneous catalytic synthesis of this compound with the use of H2O2 as an oxidant [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38]. Catalytic systems include acids, bases, transition metal complexes and enzymes. In particular, a number of reports point to laboratory synthesized magnesium-containing basic inorganics, e.g., hydrotalcite-like solids, or mesoporous magnesia, as catalysts active and selective in this process [18], [20], [21], [22], [23], [24], [28], [30], [31], [33]. Results presented in this report demonstrate for the first time that also naturally occurring magnesium-containing minerals of basic character possess significant catalytic potential for the Baeyer–Villiger oxidation of cyclohexanone, comparable with that of a synthetic hydrotalcite-like material. In addition, it is shown that also calcium-containing basic rocks display catalytic activity in this reaction. Noteworthy, literature search shows that the only Mg-containing mineral, palygorskite, tested previously as catalyst support in the Baeyer–Villiger oxidation of ketones, on its own appeared inactive [39].

Two types of widely availabile, nontoxic and inexpensive minerals were investigated: carbonates (magnesite, dolomite and limestone) and silicates (talc, sepiolite and hectorite). Magnesite, with the chemical formula MgCO3, is a widespread ore of magnesium which finds applications in many industries, its main use being the production of refractory materials [40]. Dolomite is a calcium magnesium carbonate, with ideal formula CaMg(CO3)2. It is a major rock-forming mineral, occurring plentifully worldwide, with numerous uses, primarily in construction industry, for refractory applications, as well as agricultural and pharmaceutical purposes [40]. Limestone constitutes ca. 10% of all sedimentary rocks and is composed primarily of the mineral calcite, i.e., calcium carbonate, CaCO3 [40]. Its widespread uses encompass construction, glass, ceramics, cosmetics, food, and pharmaceuticals industries. Calcium carbonate is also extensively used in agriculture as a soil conditioner. Calcite and magnesite exhibit the same trigonal-rhombohedral crystal structure, in which alkaline earth sites are surrounded with six octahedrally coordinated carbonate anions (Fig. 2). The structure of dolomite is similar, except that layers of magnesium and calcium atoms alternate, as depicted in schematic structure model in Fig. 2. Talc, known as the softest mineral on earth, can be found worldwide. It is a layered magnesium silicate with the layer composed of magnesium-based octahedral sheet sandwiched between two tetrahedral silica sheets, as schematically illustrated in Fig. 3. This type of layered structure is referred to as 2:1 [41]. The chemical formula of talc is Mg3[Si4O10](OH)2. Talc is widely used as an additive in the production of paper, plastics, food, cosmetics, pharmaceuticals, and ceramics. Sepiolite is an abundant and cheap, naturally occurring fibrous magnesium silicate with the idealized chemical formula Mg4[Si6O15](OH)2·6H2O and structure made up of talc-like ribbons arranged in staggered rows separated by tunnels with cross-section of 10.8 × 4.0 Å, running parallel to the fiber axis [41]. In reality, a little Al for Si substitution may occur in the tetrahedral sheet, balanced by a comparable amount of Al for Mg substitution in the octahedral sheet, leaving the sepiolite framework charge-balanced and with almost no ion exchange capacity. Sepiolite is widely used as adsorbent, filler in plastics manufacturing and an additive to construction materials. Hectorite is a layered silicate, with theoretical chemical formula Na0.33(Mg2.67Li0.33)[Si4O10](OH)2. Its structure is related to that of talc, in so far as part of magnesium in the octahedral sheet is substituted with lithium, and the deficit of layer charge is compensated by the presence of exchangeable cations (e.g. Na+, Ca2+) in the interlayer [41]. A certain degree of Al for Si substitution may also contribute to the evolution of layer charge. Hectorite deposits are less common, but mining is economically viable due to a number of industrial uses, primarily as an additive in cosmetics manufacturing.

Our work shows that some of these common materials represent an attractive alternative as ecologically friendly catalysts for manufacturing of ϵ-caprolactone. Moreover, we demonstrate that catalytic performance of natural minerals may be in some cases enhanced by means of a simple mechanochemical treatment.

Section snippets

Materials

Carbonate minerals/raw materials were provided by the Department of Mineralogy, Petrography and Geochemistry, AGH University of Science and Technology (Poland), and included magnesite from the Sobótka deposit (Lower Silesia, Poland), dolomite from the Rędziny deposit (Lower Silesia, Poland), and limestone from the Wojcieszów deposit (Lower Silesia, Poland). Magnesium-containing silicates were obtained from commercial suppliers, and included talc, particle size 10 μm, supplied by Sigma–Aldrich,

Catalysts characterization

Fig. 4, Fig. 5 show, respectively, the XRD patterns of the carbonate and silicate minerals, as received (top diagrams), and after the mechanochemical treatment. XRD results confirm that the investigated solids possess crystal structures expected for the relevant minerals. In most samples the presence of minority impurity phases, typical of naturally occurring materials, can be inferred both from the X-ray diffraction and from the chemical analysis data presented in Table 1. Thus, trace amounts

Conclusions

The present work demonstrates that widely available, nontoxic and inexpensive magnesium and/or calcium contatining minerals, represent an attractive alternative as ecologically friendly catalysts for manufacturing of ϵ-caprolactone. The yields of ϵ-caprolactone over the as received carbonate minerals are comparable with the yield obtained for the reference Mg–Al hydrotalcite catalyst. Of the layered magnesium silicate group, the untreated hectorite gives the best performance, yielding

Acknowledgement

This work received funding from the Marian Smoluchowski Krakow Research Consortium—a Leading National Research Centre KNOW supported by the Ministry of Science and Higher Education.

References (68)

  • C. Jimenez-Sanchidrián et al.

    Tetrahedron

    (2008)
  • R.A. Michelin et al.

    Coord. Chem. Rev.

    (2010)
  • G.A. Olah et al.

    Mater. Chem. Phys.

    (1987)
  • J. Fischer et al.

    Appl. Catal. A

    (1999)
  • A. Corma et al.

    J. Catal.

    (2003)
  • U.R. Pillai et al.

    J. Mol. Catal. A: Chem.

    (2003)
  • Z. Lei et al.

    Tetrahedron Lett.

    (2005)
  • J.R. Ruiz et al.

    Tetrahedron

    (2006)
  • C. Jimenez-Sanchidrian et al.

    Appl. Catal. A

    (2006)
  • R. Llamas et al.

    Tetrahedron

    (2007)
  • R. Llamas et al.

    Appl. Catal. B

    (2007)
  • Q. Zhang et al.

    React. Funct. Polym.

    (2006)
  • C. Li et al.

    Catal. Commun.

    (2007)
  • R.A. Steffen et al.

    J. Mol. Catal. A: Chem.

    (2008)
  • Z. Lei et al.

    Catal. Commun.

    (2007)
  • J. Li et al.

    Catal. Commun.

    (2008)
  • L. Balbinot et al.

    Catal. Commun.

    (2008)
  • M. Paul et al.

    Chem. Eng. Sci.

    (2012)
  • Q. Ma et al.

    Catal. Commun.

    (2014)
  • A. Ibrahim et al.

    J. Supercrit. Fluids

    (2014)
  • Z. Lei et al.

    J. Organomet. Chem.

    (2006)
  • M.F. Brigatti et al.

    Structure and mineralogy of clay minerals

  • K. Kaneda et al.

    J. Mol. Catal. A

    (1995)
  • A. Michalik et al.

    Appl. Clay Sci.

    (2008)
  • K. Parida et al.

    J. Mol. Catal. A: Chem.

    (2000)
  • F. Cavani et al.

    Catal. Today

    (1991)
  • J.O. Titiloye et al.

    Geochim. Cosmochim. Acta

    (1998)
  • S.L.S. Stipp

    Geochim. Cosmochim. Acta

    (1999)
  • R.A. Schoonheydt et al.

    Surface and interface chemistry of clay minerals

  • B. Benli et al.

    Colloid Surf. A

    (2012)
  • T. Chen et al.

    Chem. Eng. J.

    (2011)
  • E.F. Aglietti

    Appl. Clay Sci.

    (1994)
  • A. Baeyer et al.

    Ber. Dtsch. Chem. Ges.

    (1899)
  • G.R. Krow

    Org. React.

    (1993)
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