Characterization of Surface Acidity of Carbonated Materials by IR

ARTICLE pubs.acs.org/JPCC

Characterization of Surface Acidity of Carbonated Materials by IR-Sensitive Molecular Probes: Advantages of Using tert-Butyl Cyanide Jun Ni,† Frederic C. Meunier,*,† Saul Robles-Manuel,‡ Joel Barrault,‡ and Sabine Valange‡ † ‡

Laboratoire Catalyse et Spectrochimie, ENSICAEN, Universit
e de Caen, CNRS, 6 Bd Mar
echal Juin, F-14050 Caen, France Laboratoire de Catalyse en Chimie Organique, Universit
e de Poitiers, CNRS UMR 6503, ENSIP, 1 rue Marcel Dor
e, F-86022 Poitiers Cedex, France ABSTRACT: Bulk carbonates or carbonated surfaces are increasingly relevant materials applied to many base-catalyzed reactions. Various basic molecular probes were considered for the assessment of the surface acidity of a highly carbonated catalyst, namely a high surface area MgO prepared by sol gel and activated at 240 °C. Using such a low activation temperature results in the presence of large amounts of residual superficial carbonates that hinders analysis with common IR acidity probes. Compared with pyridine, acetonitrile, and its deuterated counterpart CD3CN, tert-butyl cyanide (noted TBC, also known as pivalonitrile) appeared as the most appropriate probe to assess surface acidity at room temperature on this material. TBC did not lead to any measurable dissociative adsorption and easily enabled the differentiation between Lewis and Brønsted (i.e., surface hydroxyls) acid sites on carbonated solids on which the characteristic pyridine adsorption region (1700 1200 cm 1) is completely obscured by the signal of carbonates. The interpretation of the TBC-based spectra was also much more straightforward than those based on acetonitrile and deuterated acetonitrile, which both led to significant probe dissociation on the surface of the sample. TBC therefore appears as a suitable acidity probe for carbonated materials, opening the way to facile characterization of carbonate-rich base catalysts activated at low temperatures.

1. INTRODUCTION The interest in reaction catalyzed by heterogeneous bases is on the increase.1 4 Carbonated surfaces have been proposed as being the active phase, rather than oxide surface ions, in a few cases.5 7 In actual fact, many more phases based on carbonates can be expected to be the true active phase since basic oxides are often calcined ex situ and readily get carbonated during storage or handling in ambient air. Valange and co-workers5 investigated the synthesis of phytosterol esters from transesterification of a fatty methyl ester (dodecanoate) with natural sterols carried out in the presence of basic solid catalysts (lanthanum oxides) and revealed the presence of residual unidentate, bidentate, polydentate, and mineral carbonate species inside all of the solids even after activation. The phytosterol ester yield was related to the basic strength of these carbonate species: the lower the carbonate basicity (unidentate species), the higher the phytosterol ester yield. Thus, it was concluded that the synthesis of phytosterol esters from fatty methyl esters and sterols required ionic carbonate species of medium basic strength. Carbonate phases have been shown to demonstrate catalytic activity for many important reactions. A study of carbon dioxide re-forming of methane conducted by Zhang and Verykios7 indicated that the presence of La2O2CO3 on Ni/La2O3 catalyst, formed when the support La2O3 contacted with the reactant gases, was of great importance in the reforming reaction and responsible for high activity and coke resistance of catalyst in spite of the severe reaction conditions. Kimura et al.8 showed that economically viable alkali-carbonate-supported aluminosilicate r 2011 American Chemical Society

efficiently catalyzed the combustion of diesel soots. These authors were able to stabilized the alkaline component of the materials by using a carrier of the nepheline type that prevented alkali leaching.8 Moeinpour et al. have reported a new simple catalytic method for the synthesis of 2-aminothiophenes via Gewald reaction using Cs2CO3 as an efficient, reusable, and green heterogeneous catalyst, thus paving the way for improved routes toward these important molecules used as the scaffold motif of a variety of agrochemicals, dyes, and biologically active products.9 The measure of the acidity of such basic samples can be important because the acid sites also present on the surface can be responsible for undesired side reactions or catalyst deactivation. The present contribution aims at investigating the acidity of the surface of a MgO-based catalyst activated at 240 °C. This temperature was chosen because it is similar to that of the activation and reaction temperatures used for glycerol condensation.10 Infrared spectroscopy and IR-sensitive probe molecules are routinely used to unravel the number, location, and strength of acid sites.11 CO was shown to be too weakly bound at room temperature on the MgO sample activated at 240 °C. Pyridine (Py) is widely used as a probe molecule to determine the surface acidity of metal oxides. Pyridine can form coordinated species, pyL, on Lewis acid sites and pyridinium ions, pyH+, on protonic Received: September 5, 2011 Revised: November 6, 2011 Published: November 08, 2011 24931

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The Journal of Physical Chemistry C sites. The infrared spectra of pyL and pyH+ species are clearly distinct in region (1700 1200 cm 1), so that the corresponding surface sites can easily be distinguished.12,13 However, in the case of carbonated metal oxides as described in this study, pyridine is not ideal because the useful pyridine absorption region may be partly or totally obscured by the signal of carbonates (1650 1200 cm 1). Acetonitrile (CH3CN) can alternatively be used to determine the acidic properties of a sample. When interacting with acid sites, the wavenumbers of the stretching vibration of both surface hydroxyl groups and acetonitrile ν(CN) shift. This makes acetonitrile an interesting probe for Lewis as well as Brønsted acid sites. However, the CN spectral region is complicated by Fermi resonance between the ν(CN) and the combination of δs(CH3) + ν(CC) frequencies. The utilization of the deuterated form (CD3CN) is known to facilitate the interpretation of the spectra. The use of tert-butyl cyanide, (CH3)3C CN, noted TBC, as a probe for acid sites is less common.14 23 TBC has yet been mostly used to study the accessibility of acid sites of zeolitic materials.14 22 To the best of our knowledge, there is no report in the literature regarding the use of tert-butyl cyanide for the characterization of strongly carbonated metal oxides such as those based on magnesia activated at low temperature. The adsorption of TBC was reported on MgO activated overnight at 600 °C, for which a carbonate-free sample is expected.23 The main purpose of the present work was to compare the utilization of acetonitrile (CH3CN), deuterated acetonitrile (CD3CN), tert-butyl cyanide ((CH3)3C CN), and pyridine (C5H5N) in the characterization of surface acidity of unsupported MgO prepared by the sol gel route. Our results will show that the interpretation of the TBC-based spectra was much more straightforward than those based on acetonitrile and deuterated acetonitrile, which both led to significant probe dissociation on the surface of the sample. TBC therefore appears as a suitable acidity probe for carbonated materials that are relevant to many base-catalyzed reactions. This opens the way to facile characterization of carbonate-rich base catalysts activated at relevantly low temperatures, which otherwise were overlooked or done by activating samples at too high temperature leading to the formation of oxide surface that were irrelevant.

2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. The high surface area MgO sample was synthesized by a sol gel process using magnesium ethoxide as precursor. Mg(OEt)2 powder (2.74 g) was predissolved in an ethanol/toluene mixed solution (1:0.94 v/v) under stirring (solution A). The addition of a second solution containing 0.8 mol L 1 of water in a mixture of ethanol/toluene (1:2.9 v/v) was made dropwise to solution A so as to start the gelation process. The gel solution was refluxed at 75 °C for 30 h and then cooled down to room temperature. The solvent was then removed with a rotary evaporator at 80 °C, and the resulting solid powder was dried at 90 °C for 12 h, before being calcined at 500 °C in air flow for 5 h (heating rate of 1 °C min 1). The calcined MgO sample displays typical features of mesoporous solids exhibiting high pore diameters. The pore size, determined by applying the BJH model to the isotherm adsorption branch (Micromeritics ASAP 2010 instrument), is centered at 13 nm and is coupled to a pore volume of 0.81 cm3 g 1. The resulting specific surface area is 230 m2 g 1.

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Figure 1. In situ spectra of MgO activated at 240 °C (a) and 500 °C (b).

2.2. IR Spectroscopy. IR spectra were recorded on a Nicolet Nexus spectrometer with a spectral resolution of 4 cm 1. Samples were pressed as self-supported wafers. Disks of about 10 mg cm 2 were prepared and activated in the cell as described elsewhere.11 The samples were evacuated up to 240 or 500 °C (10 °C min 1) for 30 min and then brought back to room temperature prior to contact of probe molecules. Calibrated doses of CH3CN, CD3CN, tert-butyl cyanide (TBC), and pyridine were introduced on the activated samples at room temperature. Exposure to the probe molecules under a fixed pressure was also used to determine the adsorption equilibrium state over the surface hydroxyl groups. The spectrum collected over the empty cell was used as background for calculating the absorbance, unless otherwise stated.

3. RESULTS AND DISCUSSION 3.1. Effect of the Activation Temperature. The MgO activated at 240 °C displayed a high proportion of hydroxyl groups (located in the 3700 3000 cm 1 region) and carbonates (1700 1200 cm 1 region), which corresponded probably to both surface and bulk species (Figure 1a). The carbonate signal was so intense that total signal absorption was observed in the corresponding region despite the small amount of sample analyzed (17.4 mg). For the sake of comparison, the signal collected over the MgO material activated at 500 °C is also shown in Figure 1b. The treatment at 500 °C enabled removing most of the hydroxyl and carbonate species. 3.2. Pyridine as an Acidity Probe. The infrared spectrum in the 1400 1700 cm 1 region is typically used to follow pyridine adsorption on acidic solids, as the spectrum of pyridine coordinately bonded to the surface is markedly different from that of the pyridinium ion. From the frequency shift of one of the bands of coordinately bonded pyridine as compared to that observed in the liquid phase and from the relative retention of the band upon evacuation and heating, a very rough estimate of the strength of surface Lewis sites can be inferred.11,12 The position and the multiplicity of the ring vibration of ν8b chemisorbed pyridine (1579 cm 1 in the liquid phase) are usually related to the strength and the number of the different kinds of Lewis acid sites, while their quantification is measured from the area of the band ν19b. Unfortunately, no meaningful signal could be obtained in this region because of the very strong adsorption due to the presence of carbonate species (spectrum not shown). The utilization 24932

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Scheme 2. Formation of Acetamide-Type Species

Figure 2. Acetonitrile adsorption (0.8 Torr) on MgO activated at 240 °C (a) and at 500 °C (b). The spectrum of the activated sample was used as background to calculate the absorbance.

Scheme 1. Formation of the Carbanion CH2CN on a Cationic Site of MgO

Figure 3. Acetonitrile adsorption on MgO activated at 240 °C.

of the CH (or CD) stretching region has been shown to be possible to determine the strength of Lewis acid sites, but band deconvolution and quantification appear quite complex.11 3.3. Acetonitrile as an Acidity Probe. Acetonitrile (CH3CN) molecules interact with Lewis and Brønsted acid sites through the electron lone pair located on the nitrogen atom. When acetonitrile forms a coordination complex (adduct) with an electron acceptor molecule, the fundamental CN stretching frequency always increases (with respect to the liquid phase, i.e., 2267 cm 1; note that a doublet due to Fermi resonance is actually observed, vide infra). The increase of the CN stretching frequency can be used to predict the strength of Lewis acidity for the acceptors. The changes on coordination in the nitrogen 2s lone-pair orbital are responsible for the strengthening of the CN bond. The upward frequency shift of the ν(CN) mode enabled discriminating between Lewis coordinated nitrile species (ΔνCN generally occurs in the 40 60 cm 1 range) and nitrile species interacting with medium-weak Brønsted acid sites (ΔνCN normally occurs in the 20 30 cm 1 range). For both types of acid centers, the larger the ΔνCN, the stronger the acidity of the centers involved.24,25 Figure 2 shows the IR spectra following adsorption of acetonitrile on MgO that was activated at 240 and 500 °C. The absorption peaks between 3000 and 2900 cm 1 are assigned to CH3 stretching vibrations. The band at 1332 cm 1 can be ascribed to the delta mode of the CH3 deformation. We assign the bands at 2151 (for MgO activated at 240 °C) and 2160 cm 1 (for MgO activated at 500 °C) to the ν(CN) wavenumber of the carbanion (CH2CN ) adsorbed on a cationic site of MgO,26,27 as shown in Scheme 1. The intensity of the carbanion band was clearly much more intense in the case of the sample activated at higher temperature, ∼10-fold higher as compared to that activated at 240 °C. This shows that the concentration of sites able to

deprotonate acetonitrile was much larger once the MgO surface had been cleared from most hydroxyl and carbonate groups. The bands observed at ca. 3300, 1536, 1464, and 1181 cm 1 in the case of the MgO activated at 500 °C were probably due to the formation of acetamide-type species,28 which were formed from the reaction of surface hydroxyl groups, as shown in Scheme 2. The acetamide bands (at least the NH-stretching vibration at 3300 cm 1) were absent in the case of the MgO activated at 240 °C, indicating that the corresponding adsorption/reaction site was not accessible at this temperature. According to the literature,24 Lewis coordinated nitrile species can be activated for a nucleophilic attack by a neighboring OH group, giving rise to surface-bound acetamide species. This reaction is observed only when “basic” OH groups free from any H-bonding (before the Lewis coordination to the nitrile) are available at the surface. When no such OH species are available, because (i) the sample is still hydrated or because (ii) the basic centers have been consumed by acidic dopants (e.g., sulfates), the hydrolysis reaction cannot proceed. These observations indicate that acetonitrile is not an inert probe because it can lead to the formation of new hydroxyl groups by dissociative adsorption and even more complex surface species such as amides. As seen above, the most sensitive spectral region in the case of nitriles was the region between 2350 and 2000 cm 1, where the CN stretching mode fell. It is suggested that not only the π and lone pair electrons of the CN group were involved in the bonding between the acetonitrile and the solid but also the methyl group as well as the C atom of the CN group, which both should exhibit acceptor functions and interact with surface oxygen.29 The CN stretching region of the sample activated at 240 °C is discussed in more details hereafter (Figure 3). The bands at 2305 and 2275 cm 1 detected at room temperature are assigned to the ν(CN) fundamental mode of acetonitrile N-bonded to Lewis acid sites, split by coupling with 24933

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Scheme 3. Structure Configuration of Nitriles

Figure 4. Acetonitrile-d3 adsorption on MgO activated at 240 °C. Under vapor pressure of 0.8 and 2.0 Torr: the perturbed OH group located at 3699 cm 1 (inset A); the difference of adsorption band intensity (inset B). The spectrum of the activated sample was used as background and the gas phase of acetonitrile-d3 was removed.

the δs(CH3) (ν3 at 1385 cm 1) + ν(CC) (ν4 at 920 cm 1) combination. The 2294 and 2250 cm 1 doublet was similar to that observed for liquid acetonitrile and can be assigned here to the ν(CN) Fermi resonance doublet of hydrogen-bonded acetonitrile on the sample Brønsted OH groups.30 32 It is clear from these data that the IR spectra obtained upon acetonitrile adsorption were highly complex and difficult to deconvolute/ quantify. The adsorption using the corresponding deuterated compound was then looked at, since the shift of the D-containing bond vibration is expected to cancel the Fermi resonance effects. 3.4. Deurerated Acetonitrile as an Acidity Probe. CD3CN may be more convenient to use than CH3CN, as the CN spectral region of the latter is strongly complicated by Fermi resonance between the ν(CN) and the combination δs(CH3) + ν(CC) frequencies,24 as discussed above. The adsorption of acetonitrile-d3 on MgO is shown in Figure 4. The band at 2288 cm 1 was due to the stretching of the CtN bond of a CD3CN species on Mg2+ sites, while the peak at 2258 cm 1 was at the same position as that of liquid CD3CN.33 It is reasonable to assign the latter peak to the molecule in weak interaction with hydroxyl groups. The band at 2111 cm 1 is assigned to the νs(CD3) modes of a liquid-like CD3CN. The 2187 2122 cm 1 spectral region was characteristic of the ν(CN) modes of anionic species (CD2CN and/or polymeric anions) formed from deprotonation of the acetonitrile-d3 on strongly basic O2 sites and adsorbed thereafter onto adjacent cationic sites.34 This dissociative adsorption resulted in the formation of new hydroxyl groups, leading to overestimation of the amount of Brønsted acid sites. With the increase of the vapor pressure of CD3CN, all the peak areas increased (inset B in Figure 4), whereas the intensity of surface OH groups at 3699 cm 1 decreased from vapor pressure of 0.8 Torr to 2.0 Torr (inset A of Figure 4). In the meantime, the intensity of the peaks of modes of a liquid-like CD3CN at 2258 and 2111 cm 1 increased in the extent higher than that of peaks for adsorption of the CtN bond on Lewis acid sites at 2288 cm 1 and of modes of anionic species at 2144 cm 1 (inset B in Figure 4). This confirms the involvement of the OH

Figure 5. Gas phase spectrum of tert-butyl cyanide.

group upon adsorption of CD3CN, which may be related to the increment of the peaks at 2258 and 2111 cm 1. The fact that deuterated acetonitrile is likely to lead to dissociative adsorption on basic oxides activated at low temperature demonstrates that it is not a suitable probe molecule for the characterization of carbonated solids. 3.5. tert-Butyl Cyanide (TBC) as an Acidity Probe. The ability of molecular acids to dissociate is in line with the acidity of these reagents in aqueous solution, rather than in the gas phase, thereby indicating that molecules of greater acid strength dissociate on MgO more easily.35 Considering the configuration of acetonitrile, acetonitrile-d3 and tert-butyl cyanide (CH3)3C CN, and due to the lack of protons on the α carbon atom in tertbutyl cyanide, it is thus reasonable to assume that the acidity of tert-butyl cyanide is much lower than that of the shorter cyanides (Scheme 3). As a consequence, tert-butyl cyanide is less likely to lead to a dissociative adsorption,27 making it an attractive acidity probe molecule to be investigated. The gas-phase signal of TBC (Figure 5) appears in three regions: (i) the methyl CH stretching components in the 3000 2800 cm 1 region; (ii) CN stretching region at 2300 2230 cm 1; (iii) CH deformation modes fall in 1500 1200 cm 1; (iv) skeletal bending modes in the region lower than 1000 cm 1. The detailed assignments36 of the characteristic bands of gas phase tert-butyl cyanide (Figure 5) are given in Table 1. The most informative bands potentially highlighting an interaction of the probe molecule with the catalyst surface are in the region of 2300 2230 cm 1. The adsorption bands for carbonate-rich MgO activated at 240 °C presented in Figure 6, not documented previously to the best of our knowledge, can be simply assigned based on the comparative analysis of the tert-butyl cyanide adsorption data on MgO with that previously reported on zeolite-type materials and MgO activated at 600 °C.14 23 The adsorption band for MgO around 2262 cm 1 was assigned to TBC species Lewis-bonded 24934

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Table 1. Vibration Modes of tert-Butyl Cyanide in Gas Phase wavenumber [cm 1]

band intensity

assignment

2987

very strong

perpendicular C H asymmetric stretching

2948

strong

parallel C H symmetric stretching

2922

strong

C H symmetric stretching

2887

strong

Fermi resonance of CH3 asymmetric deformation + CH3 symmetric deformation

2249

weak

CtN stretching

1483

strong

CH3 asymmetric deformation

1467

strong

perpendicular CH3 asymmetric deformation

1375 1251

strong strong

CH3 symmetric deformation C Ct symmetric stretching

1216

strong

C CH3 asymmetric stretching

medium

skeletal C C symmetric stretching

682

Figure 6. tert-Butyl cyanide adsorption on MgO activated at 240 °C. The zoom-in region of 2300 2150 cm 1 as well as deconvolution results are shown in the inset. The spectrum of the activated sample was used as background to calculate the absorbance.

to Mg cations (hexacoordinately Mg with net charge of +1/3).23 The single band existing implies that only one cationic site is responsible for the formation of Lewis-bonded species. The band around 2234 cm 1, also observed in the liquid phase, was due to the H-bonded or physisorbed species.15 17,36,37 The 2234 cm 1 feature decreased markedly upon degassing, confirming that it was associated with weakly adsorbed TBC.38 It should be noted that no components of the so-called “ABC spectrum” could be detected in the region near 2800, 2400, and 1700 cm 1, in agreement with earlier reports indicating that the ABC spectrum is much weaker in the case of TBC19 than in those involving methylpropionitrile (isobutyronitrile, IBN) or propionitrile (PrN).17,37 Furthermore, the absence of any TBC dissociative adsorption, as evidenced by the lack of any bands in the 2000 2200 cm 1 region, enables an accurate estimation of both the concentration of weakly Lewis acid sites (e.g., Mg2+) and nonacidic surface hydroxyls groups, contrary to the case of acetonitrile (vide supra). Additionally, the acidity strengths can be determined using the shift of the stretching vibration of the CtN for the adsorbed species with respect to that of the liquid phase value:36 the higher the position of that vibration, the greater the acidity of the corresponding site. A ranking of the acidic strength of the surface

species of carbonated solid samples is thus possible. The wavenumber of the CtN bond vibration of physisorbed TBC was found to be near 2240 cm 1 on carbonate free MgO (calcined and then outgassed overnight at 600 °C).23 This band was located at ca. 2260 cm 1 in the case of TBC coordinatively adsorbed on Lewis acid sites. This position of the Lewis acid-bonded TBC shifted markedly in the case of other oxides: 2280 cm 1 for MgOtreated alumina, 2292 cm 1 for alumina and silica aluminas, and 2301 cm 1 for F-treated alumina. The earlier work of Scokart and Rouxhet shows the relevance of TBC as an acidity probe for evaluating the strength of Lewis acid sites. In the case of our MgO sample, the Lewis and physisorbed bands were located at 2262 and 2234 cm 1. These values are therefore in agreement with those reported by Scokart and Rouxhet23 and shows that the strength of the Lewis acid sites is similar between the oxidic and carbonated forms of MgO. Since the critical radius of TBC is estimated to be near 6 Å as for any compound containing the tertbutyl group,39 for sample systems possessing channels, cavities, or supercages, the opening of these structures should be large enough to allow TBC entering the pores and interacting with both internal and external acid sites.36 In summary, the adsorption of TBC over carbonated MgO presents many advantages: (i) No decomposition/dissociation of TBC was noticed under our conditions, contrary to the case of acetonitrile and its deuterated counterpart. (ii) The IR spectral region of interest does not overlap with that of carbonates. (iii) Lewis sites can be easily discriminated from H-bonded and physisorbed species. 3.6. Conclusions. Various basic probes were considered for the assessment of the surface acidity of a MgO surface covered with carbonate species. The use of acetonitrile CH3CN as a probe was strongly complicated by Fermi resonance between the ν(CN) and the combination δs(CH3) + ν(CC) frequencies. While CD3CN led to simpler spectra than that of CH3CN, deuterated acetonitrile may still create surface hydroxyl groups by dissociating over surface basic O2 anions. The use of pyridine is complicated because most of the bands of interest (i.e., pyridinium ion or pyridine coordinated to a Lewis acid site) appear in the 1650 1300 cm 1 region, which cannot be monitored over magnesia evacuated at low temperature (total absorption due to carbonates). tert-Butyl cyanide (TBC) did not lead to dissociative adsorption on basic catalysts activated at low temperature and enabled easily differentiating between Lewis and Brønsted acid (i.e., surface hydroxyls) sites, thus appearing as an appropriate probe molecule. The acid strength measured by 24935

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’ AUTHOR INFORMATION Corresponding Author

*Phone: + 33 (0) 231452731; Fax: +33 (0) 231452822; e-mail: [email protected].

’ ACKNOWLEDGMENT The authors are grateful to the CNRS and the “Agence Nationale de la Recherche” under the NANOCAT project (MATETPRO-06174055) for their financial support and acknowledge the postdoctoral grant for J.N. at the University of Caen. S.R.M. also thanks CONACyT Mexico for his PhD research grant (no. 172373/ 217762) at the University of Poitiers. ’ REFERENCES (1) Hattori, H. Chem. Rev. 1995, 95, 537–558. (2) Busca, G. Chem. Rev. 2010, 110, 2217–2249. (3) Pouilloux, Y.; Courtois, G.; Boisseau, M.; Piccirilli, A.; Barrault, J. Green Chem. 2003, 5, 89–91. (4) Ni, J.; Rooney, D.; Meunier, F. C. Appl. Catal., B 2010, 97, 269–275. (5) Valange, S.; Beauchaud, A.; Barrault, J.; Gabelica, Z.; Daturi, M.; Can, F. J. Catal. 2007, 251, 113–122. (6) Lu, C.; Lin, J.-M. Catal. Today 2004, 90, 343–347. (7) Zhang, Z.; Verykios, X. E.; MacDonald, S. M.; Affrossman, S. J. Phys. Chem. 1996, 100, 744–754. (8) Kimura, R.; Elangovan, S. P.; Ogura, M.; Ushiyama, H.; Okubo, T. J. Phys. Chem. C 2011, 115, 14892–14898. (9) Moeinpour, F.; Omidinia, R.; Dorostkar-Ahmadi, N.; Khoshdeli, B. Bull. Korean Chem. Soc. 2011, 32, 2091–2092. (10) Barrault, J.; J
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