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Applied Catalysis A: General 479 (2014) 121–133

Contents lists available at ScienceDirect

Applied Catalysis A: General

jou rn al hom ep age: www.elsev ier .com/ locate /apcata

riacylglycerol self-metathesis over highly chemoselectiveethyltrioxorhenium supported on ZnCl2-promotedesoporous alumina

ubha Kumaraswamy Pillai a,b,d, Abdelnasser Abidli a,c,d, Khaled Belkacemia,d,∗

Department of Soil Sciences and Food Engineering, Laval University, Quebec, Canada G1V0A6Department of Chemical Engineering, Laval University, Quebec, Canada G1V0A6Department of Food Sciences and Nutrition, Laval University, Quebec, Canada G1V0A6Centre de Recherche en Catalyse et Chimie Verte (C3V ex: CERPIC), Laval University, Quebec, Canada G1V0A6

r t i c l e i n f o

rticle history:eceived 18 November 2013eceived in revised form 28 March 2014ccepted 5 April 2014vailable online 14 April 2014

eywords:elf-metathesisriolein

a b s t r a c t

Since triolein is the main constituent of most oils such as olive and high oleic sunflower oils, self-metathesis of this triacylglycerol at mild reaction conditions was investigated via a heterogeneousapproach, in the presence of ZnCl2-modified mesoporous alumina supported methyltrioxorhenium(MTO) as a catalyst. Both intra and intermolecular metathesis reactions were observed. While, 9-octadecene, dimers and trimers of the triacylglycerol were isolated, intermolecular cyclization metathesisproducts were also obtained. The MTO-based catalyst was found to be highly chemoselective afford-ing only desired metathesis product formation. In contrast, more than 50% of triolein was converted toundesired solid product in the presence of the homogeneous Grubbs 2nd generation catalyst. Triolein

ethyltrioxorhenium (MTO)nCl2-promoted mesoporous aluminaetathesis polymerization

metathesis products were effectively separated by chromatographic techniques and identified using massspectrometric and NMR analyses. The reported results show that 3%MTO/ZnCl2–Al2O3-meso is an efficientand selective heterogeneous catalyst for bulky functionalized olefins metathesis such as triacylglyce-rols and edible oils, avoiding the use of costly homogeneous catalysts, or the use other rhenium-basedcatalysts with toxic promoters such as R4Sn.

. Introduction

In an era of ever increasing global awareness for the needs ofnvironmental liability, sustainability and natural-resource man-gement, there is a strong push toward the adoption of a bio-basedconomy. Lowering the cost and improving the properties of bio-ased materials are the challenging key steps to achieve this goal.

Replacement of petroleum-based raw materials by renewablend sustainable resources is of great interest, because of economicnd environmental aspects [1]. Plant-based resources can be usedor the synthesis of a wide range of value-added products compris-ng pharmaceuticals [2], cosmetics, polymers [3], fine chemicals [4]nd bio-fuels [5]. This has subsequently gathered a higher attention

n non-food applications of seed oils during the limited supply andhe escalating price of petroleum and petroleum-based products6].

∗ Corresponding author at: Université Laval, Soil Sciences & Agri-Food Engineer-ng, Rue de l’agriculture, Pavillon, Quebec, QC, Canada G1V0A6.el.: +1 418 656 2131x6511; fax: +1 418 656 3723.

E-mail address: khaled.belkacemi@fsaa.ulaval.ca (K. Belkacemi).

ttp://dx.doi.org/10.1016/j.apcata.2014.04.016926-860X/© 2014 Elsevier B.V. All rights reserved.

© 2014 Elsevier B.V. All rights reserved.

Oilseed-processing, food manufacturing, animal-product ren-dering and meat packing generate large quantities of oils/fatsstreams. As a result, the production systems for these fatty mate-rials have been underused and often have been operated belowfull capacities, leading to disposal problems or causing a marketsurplus to many product sectors [7]. However, these low-costfatty materials are suitable, readily available starting materialsfor many gainful oleochemical processes. About 14% of the annualworld production of fats and oils (103 million tons) are used in theoleochemical industry as starting material producing a wide rangeof interesting products [8]. More than 90% of all oleochemicalreactions of fatty acid esters are carried out at the carboxy function[9]. Moreover, carbon–carbon double bond transformations byhydrogenation, epoxidation, ozonolysis, metathesis and hydro-formylation are becoming industrially more important [7]. Amongthese transformations, catalytic olefin metathesis is a powerfultool in organic synthesis for the alkenes carbon–carbon double

bond formation [10].

Catalytic metathesis of natural oils and fats and their deriva-tives is considered as a clean synthetic route from the greenchemistry aspects [11]. Fats and oils containing carbon–carbon

1 ysis A:

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22 S.K. Pillai et al. / Applied Catal

ouble bonds can undergo transformation by metathesis pro-iding access to highly desired products [12–16], while variouslefin metathesis pathways are possible, including self-metathesisSM), cross-metathesis (CM), ring closing metathesis (RCM), ring-pening metathesis (ROM) and ROM-polymerization (ROMP) asell as acyclic diene metathesis polymerization (ADMET) [17,18].etathesis of triacylglycerols containing unsaturated long-chain

atty acids occurs intramolecularly via SM [13–16], as well as inter-olecularly via CM predominantly [19–24].A number of catalytic systems have been developed to carry

ut the metathesis of triacylglycerols and vegetable oils. Homo-eneous catalysts consisting of the transition metals 6–7 groupere found to be highly active metathesis catalysts. Catalytic sys-

ems such as WCl6/Sn(CH3)4 [25–28] or the commercially availablerubbs or Hoveyda–Grubbs catalysts [29] have been reported to befficient and selective catalysts for vegetable oils and triacylglyce-ols metathesis. However, their low stability and decompositionindered the recycling process [25]. In addition, their high costs

imited their implementation at commercial scale. This situationromoted intensive studies toward the development of more cost-ffective and recyclable catalysts, where heterogeneous catalystsould be a plausible alternative.

Early discoveries in the field of homogeneous catalysis inves-igating functionalized alkenes widely reported a high tolerancef tungsten-tin and molybdenum alkylidenes, then this approachas emerged with other transition metals complexes as good ini-

iators for functionalized olefin metathesis [30]. Most of reportedapers describing methyloleate, triacylglycerol and/or vegetableil metathesis have been achieved using homogeneous catalysts,hereas, only few studies were reported using heterogeneous cat-

lysts, such as Al2O3 or SiO2–Al2O3 supported Re2O7-based solidatalysts promoted with SnR4 (R = Me, Et, Bu, Alkyl) [31,32]. How-ver, all these catalyst systems suffered from disposal of toxicolvents and toxic spent catalysts due to the presence of tin-ased promoter, as well as sensitivity to oxygen which hamperedheir regeneration and prevent the metathesis reaction pathway33].

To the best of our knowledge, this is the first report describinghe self-metathesis of triacylglyceols in the presence of hetero-eneous mesostructured catalyst. Recently, we have reported forhe first time that methyltrioxorhenium (MTO) impregnated onnCl2-modified mesoporous alumina (MTO/ZnCl2–Al2O3-meso) isn efficient catalyst for self-metathesis of methyloleate, a modelolecule of triacylglycerols present in vegetable oils, with high

ctivity and good selectivity toward desired metathesis products34,35].

The aim of this work is to study for the first time theelf-metathesis of more bulky functionalized molecules; tri-cylglycerols, like triolein over MTO/ZnCl2–Al2O3-meso as aeterogeneous catalyst in comparison to the most used homoge-eous commercial Grubbs’ second generation catalyst. Since all theetails about MTO//ZnCl2–Al2O3-meso catalyst synthesis and itsharacterization were already reported in our previously reportedork [34,35], efforts will be focused at presenting comparatively

he product time course profiles and elucidating the chemical struc-ure of the products obtained from the triolein self-metathesis overoth catalysts.

. Experimental

.1. Materials

All reagents were of the highest purity and were used withouturther purification. Aluminum-tri-sec-butoxide (C12H27AlO3,7%), zinc chloride (ZnCl2, 99.9%), methyltrioxorhenium

General 479 (2014) 121–133

(MTO, CH3O3Re 71–76%), glyceryl trioleate (triolein), 2,7-dichlorofluorescein, benzylidene [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene] dichloro (tricyclohexylphosphine) ruthe-nium (2nd generation Grubbs catalyst) were obtained fromSigma-Aldrich Canada Ltd. (Oakville, ON, Canada). Trielaidinwas purchased from Nu-Chek Prep Inc. (Elysian, USA). Silica gel60 F254 precoated glass-backed TLC plates were used for thinlayer chromatography (EMD Millipore Corp.). Triblock copolymerof poly(ethylene glycol)–poly(propylene glycol)–poly(ethyleneglycol), (Pluronic P123, EO20PO70EO20, Mav = 5900 g/mol) wasgraciously offered by BASF. All the solvents used were anhydrous.

2.2. Materials synthesis and characterization

2.2.1. Synthesis of Al2O3-mesoMesoporous alumina (Al2O3-meso) was synthesized according

to the procedure described by Ray et al. [36] using pluronic acidas the templating agent with further modifications reported in ourprevious work [34,35].

2.2.2. Synthesis of ZnCl2–Al2O3-mesoModification of Al2O3-meso by incorporation of zinc chloride

was performed according to Oikawa et al. [37] with further mod-ifications as reported in our previous work [34,35]. In a typicalexperiment, the addition of ZnCl2 (0.668 g, 4.9 mmol) in ethanol(5 mL) was done drop wise to Al2O3-meso (2 g) under stirring andthe ethanol was allowed to dry (after 24 h). The dried sampleobtained was heated under an air flow to 400◦ C at ramping rateof 2 ◦C/min and calcined at 400◦ C for 4 h to give ZnCl2-modifiedAl2O3-meso with optimized Al/Zn ratio of 8.

2.2.3. Synthesis of the MTO/ZnCl2–Al2O3-meso catalystThe MTO/ZnCl2–Al2O3-meso catalyst was synthesized as previ-

ously described in our work [34,35], where we reported that 3 wt%is the optimum loading of MTO [34,35]; ZnCl2–Al2O3-meso supportwas heated under nitrogen at 540 ◦C for 2 h before impregnation ofMTO.

2.2.4. Catalyst characterizationThe MTO catalyst was characterized using nitrogen physisorp-

tion, X-ray diffraction (XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy (TEM) techniques. Fur-ther elemental CNS composition analysis was performed for bothfresh and spent MTO/ZnCl2–Al2O3-meso.

Nitrogen adsorption/desorption isotherms of calcined sampleswere obtained using a volumetric adsorption analyzer (ModelAutosorb-1, Quantachrome Instruments, Boyton Beach, FL) at−196 ◦C (77 K). Before the adsorption analysis, the samples weredegassed for 3 h at 200 ◦C. Total pore volume was estimated fromthe amount adsorbed at 0.99 relative pressures. Pore size distri-butions were calculated using the desorption branch of the N2adsorption/desorption isotherms and the Barrett–Joyner–Halenda(BJH) [38].

Powder X-ray diffraction (XRD) patterns were obtained usingan Ultima III Rigaku Monochromatic Diffractometer using Cu K�radiation (� = 1.5406 A) at 40 kV and 44 mA. Small angle powderdiffraction patterns were acquired at a scanning rate of 0.5◦/min inthe 2� range of 0.6–3◦.

Transmission electron microscopy (TEM) images were taken ona JEM-3010 electron microscope (JEOL, Japan) with an accelerationvoltage up to 200 kV.

Elemental carbon/nitrogen/sulfur (CNS) composition was car-

ried out using TruMac series instrument (LECO Corp.). CNS analysiswas performed for both fresh and spent MTO/ZnCl2–Al2O3-meso.The combustion was carried out at 1350 ◦C under atmospheric gasflow, followed by a complete oxidation under ultra pure oxygen

ysis A:

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S.K. Pillai et al. / Applied Catal

ithin 5 min. The instrument system measurement accuracy was1.0%.

.3. Metathesis reaction and analysis of the products

.3.1. Metathesis reactionSelf-metathesis reactions were carried out in a small batch

nd controlled-inert atmosphere quartz reactor. Typically, glyc-ryl trioleate or triolein (100 mg) in hexane (1 mL) was addedo the catalyst (100 mg with 3 wt% MTO loading) in dry condi-ions at the investigated temperature of 45 ◦C. The stirring rate of00 rpm was taken constant throughout the reaction time. Theseonditions were found to be suitable for optimum activity of the

wt% MTO/ZnCl2–Al2O3-meso catalyst, as previously reported inur work [34,35]. Metathesis reaction over the homogeneous 2ndeneration Grubbs catalyst was performed under the same condi-ions described above using 2.67 mg of catalyst.

.3.2. Product analysisBulkier molecules were obtained from the triolein metathesis,

heir separation and analysis by gas chromatography was difficult.o the obtained products were subjected to column chromatog-aphy in order to separate them and the fractions obtained weredentified by thin layer chromatographic (TLC) analysis. Amonghe isolated fractions, alkene and triolein were quantified usingas chromatographic analysis and the remaining products weredentified through 1H- and 13C-NMR analysis, in addition to ESI-MSnalysis.

.3.2.1. Column chromatography. For the separation and purifica-ion of the reaction mixture obtained with either Grubbs’ catalystr MTO-based heterogeneous catalyst, a glass column (60 cmong × 1.5 cm diameter) was clamped vertically and a small piece ofotton was used as plug to support the silica gel as adsorbent. Carehould be taken when placing the cotton compressed to supporthe packing but loose enough to allow the solvent flow. The solventsed comprised hexane and diethylether mixed with a determinedexane:diethylether volume ratio (80:20). Sand was added to form

cm layer on top of the plug and the column was gently tapped toxpel any trapped air. The silica gel was taken in a flask and enougholvent was added to form slurry. The slurry was poured onto theolumn with opening of the stopcock to allow draining of excessolvent.

The column packing must be uniform with no air bubblesrapped in it. A final layer of sand was added to the column to pro-ect the packed silica gel. After the column packing, the sampleas introduced in the column by adding carefully along the sides

n order to avoid disturbing of the column packing.Elution of the sample was done by adding the solvent and the

ractions were collected. About 40 fractions were collected and eachf them was tested by TLC.

.3.2.2. TLC analysis. The isolated fractions from column chro-atography were identified by TLC. In a typical experiment, the

ommercially prepared 60-mesh Silica gel 60 F254 precoated glass-acked TLC plates (Whatman K6F, Maidstone, UK) were used forhe component identification in the different fractions. Fractionsere spotted in the plates and they were placed in the glass

hamber saturated with the solvent system for developing it. Theolvent system used is the same as the eluting solvent in the col-mn chromatography, i.e. hexane:diethylether (80:20). The plates

ere visualized under UV light (254 nm). For fractions that were

n smaller concentration, the spots were visualized under UV bypraying the fluorescent dye 2,7-dichloro fluorescein ethanol solu-ion (0.2 wt%).

General 479 (2014) 121–133 123

2.3.2.3. Gas chromatographic analysis. The fractions containing tri-olein were pooled and analyzed by gas chromatography in HP6890gas chromatograph with capillary inlet (split–split) mode with aconstant split ratio (1:50). The capillary column used was RTX-65(30 m long × 0.25 mm i.d. × 0.10 �m film thickness) with H2 as car-rier gas. The injector and detector were set at 400 ◦C. The oventemperature profile was: initial temperature of 250 ◦C, ramp at10 ◦C/min to 335 ◦C and then to 360 ◦C at ramp of 1.5 ◦C/min andhold at this temperature for 3 min. The results obtained from the FIDdetector were analyzed using Chemstation software. The fractionscontaining triolein and trielaidin were identified using commer-cially available pure triolein and trielaidin triacylglycerol (TAG)standards. The quantification of triolein and trielaidin levels in thesamples was carried out using tripalmitin as an internal standard.The quantification of 9-octadecene was carried out by HP6890series gas chromatograph system equipped with a flame ioniza-tion detector using dodecane as internal standard. The column usedwas BPX-70 (60 m × 0.25 mm × i.d × 0.25 �m film thickness) withhydrogen as carrier gas. The oven temperature profile was: initialtemperature 60 ◦C, ramp at 10 ◦C/min to 190 ◦C, hold for 15 min;ramp at 5 ◦C/min to 240 ◦C, hold for 10 min [14]. The collected datawere analyzed using Chemstation software. All the solvents andstandards used were GC grade.

2.3.2.4. Mass spectroscopy (MS) analysis. Electrospray ionizationmass spectrometry (ESI-MS) analyses were performed using Agi-lent technologies 1100 series LC/MS Trap by direct infusion ofsample (10 �L/min) using KD Scientific infusion pump using theprocedure reported by Byrdwell and Neff [39] with little modi-fications. The analysis was performed at positive mode with thefollowing operating parameters: dry temperature 325 ◦C, nebulizer15 psi, dry gas (4 L/min), average of 7 spectra with a scan range m/z(600–2200). The sample was diluted in ethylacetate:acetonitrile(1:1) and the sensitivity of the analysis was enhanced using ammo-nium acetate solution (20 mmol in 1:4 H2O:acetonitrile). Dataacquisition and analysis were carried out using LC–MSD Trap soft-ware 5.2 (Bruker Daltonik GmBH).

2.3.2.5. Nuclear magnetic resonance spectroscopy (1H- and 13C-NMR)analysis. One dimensional (1D) 1H- and 13C-NMR investigationswere performed on a Varian 500DD2-VNMRS 500 system (Agi-lent technologies) at 25 ◦C; 1H-NMR spectra were acquired over8 ppm spectral window with a 1-s recycle delay with a pulse of 45◦

and acquiring time of 4.089 s. 13C-NMR spectra were recorded over230 ppm spectral window with a 1-s recycle delay with a pulse of45◦ on a power of 43 db continuously on WALTZ-16 modulated sys-tem. CDCl3 was used as solvent for analysis and the processing ofthe acquired data was done using GRAMS software (Thermo FisherScientific).

3. Results and discussion

3.1. Characterization of textural and surface properties of thematerials

Even though characterization of the MTO/Al2O3-meso wasalready reported in our previous works [34,35], it’s worth todemonstrate that the re-synthesized catalyst for the special needsof the present work shows identical characterizations, confirmingthereby, the repetitiveness of its formulation.

Indeed, nitrogen physisorption of the mesoporous Al2O3support and MTO/ZnCl2-modified mesoporous alumina catalyst

reveals a mesoporous structure with high BET surface area up to492 m2/g with narrow pore size distribution centered at 8 ± 0.1 nmof average pore size and a total pore volume of 1.2 cm3/g, as pre-sented in Table 1. By incorporation of MTO and after modification

124 S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133

Table 1Textural properties of Al2O3-meso and 3%MTO/ZnCl2-modified Al2O3-meso.

Materials Al2O3-meso 3%MTO/ZnCl2-modifiedAl2O3-meso

BET surface area (m2/g) 490 ± 1 418 ± 1Pore size (nm) 8.0 ± 0.1 7.6 ± 0.1Total pore volume (cm3/g) 1.2 ± 0.1 1.0 ± 0.1

Fm

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siiao

are subjected to metathesis conditions, there is plausible intra-molecular pathway for metathesis reaction. Hence both intra- andintermolecular reactions are possible as depicted in Scheme 2.

R2 R3

R1[M]

R1

R2

[M]

R3

[M]R1

R3R2R2 R3

R1[M]

R2 R3R2 R3

R1[M]

R1[M][M]

R1

R2

R1

R2

[M]

R3

[M]

R3

[M]R1

R3R2

[M]R1

R3R2

ig. 1. The small angle XRD patterns of the mesoporous alumina support, ZnCl2-odified mesoporous alumina as well as 3 wt% MTO/ZnCl2–Al2O3-meso catalyst.

ith ZnCl2, the BET surface area slightly decreased to 418 m2/g.owever the total pore volume and the average pore size remainedearby 1 cm3/g and 8 nm, respectively.

Small-angle X-ray diffraction patterns of mesoporous alu-ina, ZnCl2-modified mesoporous alumina as well as 3 wt%TO/ZnCl2–Al2O3-meso catalyst are shown in Fig. 1 which exhibit

strong broad peak centered at 2 ≈ 0.65◦. Similar low angle XRDatterns were previously reported by Bagshaw and Pinnavaia [39]or mesoporous silica using amines as templates and also by Rayt al. [36] using aluminum tri-sec-butoxide and TEOS in the pres-nce of Pluronic 123 as a templating agent. These authors associatedhese patterns to the presence of disordered worm-hole like struc-ure. These results are consistent with the TEM analysis depictedn Fig. 2a. The TEM micrographs covering various agglomeratesnd closer regions confirm the presence of such a wormhole poretructure throughout the material.

The porosities and surface areas of alumina samples were inves-igated by N2 adsorption–desorption at −196 ◦C. The prepared

aterials presented an IV-type isotherm which was illustrated inur previously reported work [34,35], approving the mesoporoustructure with interconnected cylinder pore. In good accordanceith the N2 adsorption–desorption analysis results, the TEM micro-

raph showed that they presented an interconnected worm-likeore network. Furthermore, some slight changes were observed onhis structure when the mesoporous alumina was modified withnCl2 where less-identified interconnected pores regions wereetected (Fig. 2b). This may be attributed to the presence of Zn–Cl,nd/or Cl–Zn–Cl attached to the OH groups of alumina.

A promoting effect of ZnCl2 in functionalized olefins metathesisuch as methyloleate was reported in our previous work [34,35]. Its worth mentioning that these modifications were not investigated

n the present work. Surface study and characterization of aluminand ZnCl2-modified alumina supports are currently underway inur laboratory, to establish the structure–activity relationship of

Fig. 2. TEM image of the mesoporous alumina materials: (a) mesoporous Al2O3

material; (b) ZnCl2-modified mesoporous alumina.

the ZnCl2-modified alumina throughout metathesis pathway, andresults will be reported shortly.

3.2. Self-metathesis of triolein

Metathesis is a clean catalytic reaction, where olefins are con-verted into new products through scission and regeneration ofC C double bonds. It is a powerful tool in organic synthesis pro-viding access to many interesting products in an efficient andselective manner. Metathesis reaction mechanism was first estab-lished by Herrison and Chauvin [40,41] where a metal alkylideneforms a metallocyclobutane with the alkene, then a rearrangementis occurred affording new alkene and metal alkylidene with a dif-ferent redistribution of alkene fragments [42]. The mechanism isdepicted in Scheme 1.

Volatile alkenes are expected from triacylglycerols metathesis;diacylglycerols by intermolecular reaction and monoacylglycerolsby intramolecular reaction [42–44]. Since the triacylglycerolspossess three fatty acid fragments containing double bonds, which

Scheme 1. The general mechanism of olefin metathesis reaction by Herrison andChauvin [40].

S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133 125

+

+Intra

Inter

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cheme 2. Intra- and intermolecular pathways for triolein metathesis [24].

In the intramolecular cyclization, a ring-closing metathesis canccur between two fatty acid fragments of triolein, while thentermolecular pathway can occur via a metathesis between twodentical triolein molecules (self-metathesis) [42]. The formationf inter and intramolecular products is similar to the mechanismnitially proposed by Van Dam et al. [24].

The self-metathesis of triolein over MTO/ZnCl2–Al2O3-mesoatalyst afforded oligomers (n = 2 or higher) and 9-octadecene, therimary metathesis products.

After stopping the reaction by addition of acetone, with either% MTO/ZnCl2–Al2O3-meso or 2nd generation Grubbs catalysts,wo distinct phases (liquid and solid) were observed in the reac-ion mixture. After centrifugation the liquid phase was separated,nd then subjected to column chromatography (CC). In the case ofTO/ZnCl2–Al2O3-meso catalyst, the solid phase contains mainly

he recycled catalyst which was stocked for other use. From the liq-id phase, exactly 40 fractions were obtained by CC; each fractionas analyzed by thin layer chromatography (TLC).

TLC analysis showed that the first six fractions correspondedo the solvent used, the fractions no. 7 to no. 14 contained 9-ctadecene which was compared with the prepared standards fromelf-metathesis reaction of methyloleate. The fraction nos. 15 to 19ere identified as triolein and its isomer trielaidin confirmed by

ommercial standards. The remaining fractions (i.e. nos. 20 to 40)ere pooled together and identified as soluble metathesis prod-cts and subjected to another set of CC and TLC analyses. Again, 40ub-fractions were collected. Similarly the sub-fraction nos. 1–16ontained solvent. The sub-fractions no. 17–19 contained traces ofriolein and trielaidin mixture (denoted Mixture 1 in the text). Theub-fraction nos. 20–25 (Mixture 2 in the text), nos. 26–29 (Mixture, in the text), no. 30–33 (Mixture 4, in the text), nos. 34–37 (Mix-ure 5, in the text) were attributed to the metathesis products whileub-fraction nos. 37–40 contained only the solvent. Quantificationf 9-octadecene, triolein and trielaidin in the reaction mixture wasone using GC with appropriate internal standards.

Afterwards, the centrifuged solid phase was filtered and washedith hexane to remove any traces of the liquid product. The white

olid observed with Grubbs 2nd generation catalyst, has a sheet-ike form when dry (Fig. 3) which is insoluble in all organic solvents.n the other hand with the MTO-based catalyst, the solid phase

as a yellowish-brown color, in an identical form of the pre-ared catalyst, while no other solid products were observed. Afterentrifugation and washing, both fresh (before triolein metathe-is reaction) and spent (used) MTO/ZnCl2–Al2O3-meso catalysts

able 2omparison of catalytic activity of MTO/ZnCl2–Al2O3 and Grubbs 2nd generation catalyst

Catalyst Triolein conversion(%)

Trielaidin yield (%)

MTO/ ZnCl2–Al2O3 65.01 40.19

2nd generation Grubbs catalyst 95.24 2.80

a Reaction conditions: 45 ◦C, 60 min, 400 rpm.b Metathesis products are products detected in Mixtures 2 to 5 excluding the remainetathesis product.

Fig. 3. Solid product formed in the reaction with 2nd generation Grubbs catalyst.

as well as the catalyst support (ZnCl2 modified Al2O3-meso) hadundergone a CNS composition analysis, to see if any carbonaceousproduct deposition on the catalyst was present after the metathesisreaction was completed.

The results showed that ZnCl2-modified mesoporous aluminaexhibited traces of carbon (∼2.3 ± 1.0%) attributed to the remainedpluronic acid template after the calcination step. The impregna-tion of MTO on the support with 3% loading increased very slightlythe carbon content to approximately 3.7 ± 1.0%. The spent catalystseemed to have a tiny little more carbon (∼4.3 ± 1.0%), about 0.6%more than the fresh catalyst (< to the measurement accuracy of theelemental CNS analyzer, 1.0%) which is considered as an insignifi-cant shift in carbon composition, even without taking into accountthe instrument system measurement accuracy (±1.0%). This allowssaying that no carbonaceous products were deposited on the spentcatalyst.

Table 2 depicts the results obtained; triolein conversion,metathesis solid products, 9-octadecene, and soluble metathesisproduct yields of both catalysts for triolein self-metathesis, within60 min at the investigated conditions.

A conversion of 65% was reached for the self-metathesis oftriolein over 3% MTO/ZnCl2–Al2O3-meso, achieving ∼22% yieldof soluble metathesis products, and ∼4% of 9-octadecene, while∼40% of trielaidin, the triolein trans-isomer, was obtained as thenon-productive metathesis product. Noteworthy that, the cis-transisomerization route during metathesis reaction has been widelystudied, and reported to be occurring competitively with metathe-sis reaction mechanistic pathway, while the isomerization productsresulted from different active carbene bond scissions [43–50]. Thisis in a good agreement with previous papers reporting the trielaidinas a non-productive triolein metathesis [43–50]. Moreover; all theformed products were also detected in their trans conformation inhigher proportion than cis conformation [51,52].

In the presence of the 2nd generation Grubbs catalyst, ∼95%triolein conversion was observed, achieving ∼20% yield of solublemetathesis products, 20% of 9-octadecene and ∼3% of trielaidin.Remarkably, despite the lower conversion with the heterogeneousMTO catalyst, no solid product was formed; meanwhile, the desired

soluble metathesis products yield is slightly higher than obtainedwith homogeneous catalyst. The white solid formation with the 2ndgeneration Grubbs catalyst was observed within only 5 min con-suming about 50% of the starting material. It may account to the

s for triolein self-metathesisa.

9-Octadecene yield(%)

Soluble metathesisproductb yield (%)

Solid product (%)

3.98 22.20 0.0020.25 20.09 50.38

ed triolein presents in the fractions and trielaidin obtained as a non-productive

126 S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133

to 5 i

ntu8fgptt

a(

Fig. 4. Structures of Component 1

on-desired highly cross-linked polymers. Similar polymer forma-ion was reported by Tian and Larock [51] on triolein metathesissing 1st generation Grubbs catalyst as solid material produced in7% yield, which was insoluble in all organic solvents. Similarly, theormation of this product was also observed for self-metathesis oflycerol trilinoleate using the same catalyst [51]. The cross-linkingolymerization may be associated with the additional polymeriza-ion due to the three double bonds of the triolein which behave as

rifunctional monomer to produce dendrimers [51].

It is worth noting that the results of carbon content by CNSnalysis are in agreement with the reaction mixture analysisTable 2) indicating no traces (0.00%) of metathesis solid products

dentified as metathesis products.

formed and/or deposited on the catalyst surface when usingMTO/ZnCl2–Al2O3-meso as a catalyst.

3.3. Quantification and identification of soluble metathesisproducts

3.3.1. Product quantification

After column chromatography (CC) separation and thin

layer chromatographic (TLC) analysis, the sub-fractions denotedMixtures 1–5 were obtained. The fraction containing triolein self-metathesis products at the investigated reaction conditions over

S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133 127

athesi

bT

pobpsoscI

Fig. 5. Mass spectrometric analysis of the met

oth catalysts were quantified by GC analysis and summarized inable 2.

GC analysis of these sub-fractions containing soluble metathesisroducts showed almost similar patterns with the appearancef four to five spots in TLC plates, when visualized under UVy spraying the dye for both catalysts. The soluble metathesisroducts overall yield reached 20 to 26 wt%, while all productstructures (Components 1 to 5) are illustrated in Fig. 4. The yield

f each detailed sub-fraction did not exceed 9%, when the trioleinelf-metathesis was carried out over MTO/ZnCl2–Al2O3-mesoatalyst, where Components 1 and 2 were the major products.n contrast, with the 2nd generation Grubbs catalyst, the dimer

s products obtained with MTO-based catalyst.

of triacylglycerols (TAG) molecules obtained via intramolecularmetathesis and Component 3 is the major product.

Further analyses of these sub-fractions were accomplished bymass spectroscopy (ESI-MS) and 1H- and 13C-NMR for their struc-tural identification.

3.3.2. Mass spectrometric analysisESI-MS analysis results of the metathesis products are presented

in Table 3. Hence, the peak corresponding to 902.8 [M + NH4]+ valuein Mixture 1 collected with both catalysts (MTO/ZnCl2–Al2O3-mesoand 2nd generation Grubbs catalysts), represents a mass of 884.8,which is the triolein or trielaidin molecular weight (Component 1).

128 S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133

etathe

Tsac

cttotwwr

Fig. 6. Mass spectrometric analysis of the m

his is also is confirmed by the mass spectrometric analysis of thetandards. This is attributed to the triolein remained after reactionnd the trielaidin formed by non-productive metathesis over bothatalysts as indicated in Table 2.

The MS spectra of Mixture 2 for both catalysts (see Figs. 5 and 6)onsisted primarily of 1536.3 [M + NH4]+ peak which correspondso the dimer (Component 2) with actual mass of 1518.3 formedhrough the two triolein molecules metathesis and eliminationf one octadecene molecule. The ESI-MS molecular mass calcula-

ion ((884.8 × 2) − 252 = 1517.6) fits well with the actual moleculareight of the Component 2 (1518.3) as indicated in Table 3here 252 is the mass of octadecene eliminated during the

eaction.

sis products obtained with Grubbs catalyst.

The MS spectra of Mixture 3 for both catalysts revealedthe presence of primarily 3 peaks with 2168.8, 1536.3 and1283.1 [M + NH4]+ for which the actual masses are 2150.8,1518.3, and 1265.1, respectively. The first peak correspondsto the trimer (Component 3) formed through three trioleinmolecules cross-metathesis and elimination of 2 ocatadecenemolecules, while the ESI-MS molecular mass calculation confirms((884.8 × 3) − (2 × 252) = 2150.4) the actual mass of 2150.8. Thetwo remaining peaks revealed the presence of dimer (Compo-

nent 2), already discussed. The spectra revealed also a modifiedtriolein dimer in which an intramolecular ring-closing metathe-sis reaction occurred in one of the two attached monomers((884.8 × 2) − (2 × 252) = 1265.6), corresponding to the synthesis of

S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133 129

Table 3Yields and mass spectrometric detection by ESI-MS of molecular weight of ions for different products contained in the fractions obtained after TLC analysis for trioleinself-metathesis over both catalysts.

Catalysts MTO/ZnCl2–Al2O3 catalysta 2nd generation Grubbs catalystb

Fractions Components Yields (%)c [Mw + NH4]+d Components Yields (%)c [Mw + NH4]+d

Mixture 1 Component 1 4.03 902.8 Component 1 0.40 902.8Mixture 2 Component 2 9.50 1536.3 Component 2 4.42 1535.4Mixture 3 Component 2 5.57 1536.3 Component 4 2.34 1536.3

Component 3 0.99 2168.8 Component 5 0.26 2168.8Component 4 0.14 1283.1 Component 2 0.12 1283.1

Mixture 4 Component 2 3.51 1536.3 Component 4 3.73 1664.3Component 3 1.35 2168.8 Component 5 0.21 2183.1Component 4 0.18 1283.1

Mixture 5 Component 2 0.76 1536.3 Component 4 8.18 1663.3Component 3 0.03 2168.8 Component 5 1.02 1283.1Component 4 0.25 1283.1Total 26.33 Total 20.49

a After 5 h of reaction.b

ed mass of the mixtures obtained by TLC and absolute abundances of ESI-MS analysis.

Ccaia

m[io1ewtcm

shi

whptuFrG

p[awoaarrt

pddi

After 1 h of reaction.c Yield % = product amount (mg)/triolein amount (mg) × 100.d m/z of [Mw + NH4]+; the product amounts (mg) were determined by the collect

omponent 4. The possible triolein metathesis products with theirorresponding masses were elucidated by Li et al. [52] which serveds a reference to identify the products formed in the present workn the presence of either 3% MTO/ZnCl2–Al2O3-meso or 2nd gener-tion Grubbs catalyst.

The MS-spectrum of Mixture 4, in the case of MTO/ZnCl2–Al2O3-eso, revealed mainly three peaks at 2168.8, 1536.3 and 1263.1

M + NH4]+ corresponding to the presence of same molecules foundn Mixture 3. On the other hand, the MS-spectrum of Mixture 4btained with Grubbs catalyst, exhibited essentially two peaks at283.1 and 1664.3 [M + NH4]+. The first one indicates the pres-nce of Component 4, while the second one is in agreementith the actual mass of Component 5 (1646.3) corresponding

o the modified triolein trimer in which an intramolecular ring-losing metathesis reaction occurred in two of the three attachedonomers.No discernible differences were detected between the MS-

pectra of Mixture 5 and those of Mixture 4 for both catalysts, thatave been already discussed as presented in Figs. 5 and 6 as well as

n Table 3.The products formed with the MTO catalyst are in agreement

ith the results reported by Refvik and Larock [26] through hisomogeneous approach for metathesis of soybean oil. Also similarroducts were obtained by Tian and Larock [51] for metathesis ofriolein where formation of dimer, trimer, tetramer and cyclic prod-ct was observed in the presence of Grubbs’ ruthenium catalyst.urthermore, similar results with structural identification wereeported recently for metathesis of triolein using 2nd generationrubbs catalyst [52].

It is worth to mention that when the mass spectrometriceaks were magnified, expected signal were observed, i.e. 1535.4M + NH4]+, but multiple signals additionally appeared (before andfter) at 1521.3, 1550.3, 1564.3, 1578.3 [M + NH4]+ which differith 14 to 15 Da as shown in Fig. 7. Similar results have been

btained for metathesis of vegetable oils over Grubbs 2nd gener-tion catalyst where the difference of 14 Da methylene units wasssigned to be resulted from C C double bonds isomerization sideeactions during self-metathesis. Such isomerization reactions giveise to shorter as well as longer chain metathesis products due tohe formation of metal-hydride intermediate species [53,54].

If double bonds isomerize, the resulting new olefin can partici-

ate in self- and cross-metathesis reactions, leading to observedistribution with mass difference of 14 Da [26]. Several studiesescribing these products formation with methylene group dur-

ng vegetable oils metathesis have been reported, especially for

Fig. 7. Magnified view of the peaks obtained in the mass spectrometric analysis.

ADMET polymerization. In case of internal alkenes several isom-erization steps could be occurred, leading to different terminalalkenes through the carbene formation, which will be involvedin several metallocyclobutane intermediates, providing access tomany metathesis products [55,56].

3.3.3. NMR analysisPrevious analysis demonstrated that same metathesis products

were obtained using either MTO-based catalyst or 2nd gener-ation Grubbs catalyst. For this reason only 1H- and 13C-NMRspectra of Mixtures 1 to 5 that have been issued from trioleinself-metathesis over MTO-based catalyst will be displayed and dis-cussed (Figs. 8 and 9, respectively).

The products of all mixtures analyzed contain the same back-bone as they are made up from repeating units of triolein.Therefore, in all 1H-NMR spectra, the olefinic protons CH CHand methine proton in glyceryl group CH2 CH(O) CH2 dis-played signals at ı = 5.50–5.26 ppm, while the methylene protonsin the glyceryl group CH2 CH(O) CH2 displayed the sig-nal at ı = 4.29–4.14 ppm, the signal at ı = 2.42–2.19 ppm wereassigned to the �-methylene protons adjacent to carbonylcarbon C( O) CH2 , where the signal at ı = 2.09–1.79 ppmwere assigned to allyl methylene protons CH CH2 . In addi-tion, the signals at ı = 1.79–1.47 ppm, ı = 1.47–1.12 ppm andı = 1.04–0.51 ppm were assigned to the �-methylene protons from

carbonyl carbon C( O) CH2CH2 , methylene protons on satu-rated carbon atoms CH2 , and to the terminal methyl protons

CH3, respectively. Meanwhile, the peak at 7.35–7.18 ppm isassigned to the proton exchange with CDCl3 analysis solvent

130 S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133

Fc

[w

aomitpo

tt

tl

ig. 8. 1H-NMR spectra of mixtures issued from triolein metathesis over MTO-basedatalyst.

57–59]. Little difference in the relative area of the displayed signalsas detected, depending on the number of repeating units.

The differences detected in 1H-NMR between linear oligomersnd cyclic compounds of the mixtures are mainly at the protonsf the glyceryl group and the double bonds. The ratios of the �-ethylene protons adjacent to carbonyl on the methylene protons

n the glyceryl group ( O C( O) CH2 :CH2 CH(O) CH2 ) andhe ratio of the terminal methyl protons CH3 on the methylenerotons in the glyceryl group were used to identify the structuresf the pure compounds as listed in Table 4.

Similarly, in all 13C-NMR spectra of all mixtures analyzed,he carbonyl carbon COO showed peak at ı ≈ 173 ppm,he olefin CH CH at ı ≈ 131–129 ppm, the glyceryl group

CH2 CH(O) CH2 at ı ≈ 70–61 ppm, the �-methylene adjacent

o carbonyl carbon C( O) CH2 at ı ≈ 47–34 ppm, allyl methy-ene CH CH2 at ı ≈ 32 ppm, the �-methylene from carbonyl

Fig. 9. 13C-NMR spectra of mixtures issued from triolein metathesis over MTO-based catalyst.

carbon C( O) CH2CH2 at � ≈ 30 ppm, the saturated carbonatoms CH2 at ı ≈ 23–27 ppm, and the terminal methyl CH3 atı ≈ 14 ppm, while the peak at circa 77 ppm is assigned to CDCl3analysis solvent [59,60]. All these peaks are present in all mixtureswith small differences observed in their intensities. The main struc-

tural differences between the different compounds as exhibited inthe 13C-NMR spectra are chemical shifts of double bonds and theglyceryl group.

S.K. Pillai et al. / Applied Catalysis A: General 479 (2014) 121–133 131

Table 4Ratio of selected protons identified from the 1H-NMR spectra.

( CH2 CH(O) CH2 ) ( CH2 CH(O) CH2 ) ( CH3)

3% MTO/ZnCl2–Al2O3

Mixture 1 1.00 1.43 2.61Mixture 2 1.00 1.48 1.44Mixture 3a NDa ND NDMixture 4a ND ND ND

2nd generation Grubbs catalystMixture 2 1.00 1.50 1.72Mixture 3a ND ND NDMixture 4a ND ND NDMixture 5a ND ND ND

Expected valuesb

Component 1 1.00 1.50 2.25Component 2 1.00 1.50 1.50Component 3 1.00 1.50 1.12Component 4 1.00 1.50 0.75Component 5 1.00 1.50 0.25

t was

ined b

cmitivo1

gcıTamb

r9idw(11igml

oe2tfoedpbpwpof

a ND signifies not determined. Owing to the impure nature of the Mixtures 3–5, ib Expected values based on the theoretical prediction for the products as determ

The 1H-NMR signals of Mixture 1 fit with those of triolein (100%is) and/or trielaidin (100% trans) [61] (Fig. 8). The ratios of the �-ethylene protons adjacent to carbonyl on the methylene protons

n the glyceryl group ( O C( O) CH2 : CH2 CH(O) CH2 ) andhat of terminal methyl protons CH3 on the methylene protonsn the glyceryl group are of 1:1.43 and 1:2.61, respectively. Thesealues are fairly comparable to the expected ratios based on the-retical predictions for triolein and trielaidin structure 1:1.5 and:2.25 (Table 4).

In 13C-NMR spectra of Mixture 1 described in Fig. 9, the olefinroup -CH CH displayed a signal at � ≈ 131–129 ppm, and thehemical shift at ı < 130 ppm is assigned to cis-configuration while

> 130 ppm is assigned to trans-configuration which is a major one.he obtained results are consistent with those obtained by ESI-MSnalysis, and we can conclude that Component 1 in Mixture 1 hasainly a trielaidin structure. However, traces of triolein could also

e present.The 1H and 13C NMR spectra of Mixture 2 are similar to those

eported and discussed by Li et al. [52] where bis(1,3-bis(octadec--enoyloxy)propan-2-yl)octadec-9-enedioate and its isomers were

dentified as metathesis products (Fig. 8). This product is a linearimer resulted from two triolein molecules metathesis reactionith elimination of octadecene as confirmed by ESI-MS analysis

denoted Component 2). Moreover, the proton ratios are 1:1.48 and:1.44 which could reasonably correspond to the theoretical ratios:1.50 and 1:1.50 characterizing a triolein dimer (Table 3). Indeed,

n 13C-NMR spectra of Mixture 2 described in Fig. 9, the glycerylroup with methine carbon CH2 CH(O) CH2 at ı ≈ 69 ppm andethylene carbon CH2 CHOR CH2 at ı ≈ 62 ppm defines the

inear triolein dimer [26].The mass spectrometric results revealed the presence of two

thers molecules with Component 2 in the Mixture 3. Differ-nce in peaks intensities between 1H-NMR spectra of Mixtures

and 3 confirm the presence of others compounds containinghe same functional groups (Fig. 8). There is a linear trimerormed by the reaction of three triolein molecules and eliminationf two octadecene molecules; the 18-bis(1,3-bis (octadec-9-noyloxy) propan-2-yl)1,1-3-(octadec-9-enoyloxy)propane-1,2-iyldioctadec-9-enedioate and its isomers representing the Com-onent 3. This compound structure was elucidated and discussedy Li et al. [26], which was obtained via triolein metathesis in theresence of 2nd generation Grubbs catalyst, further confirmation

as reported recently by Tian and Larock [52] during ADMETolymerization of Soybean oil. The third molecule could be a dimerf triolein in which two of the three oleate chains of one trioleinragment has undergone an intramolecular metathesis cyclization.

not possible to determine the ratios of selected protons.y Li et al. [52].

Li et al. [26] also isolated and identified this dimer by NMR analysisas 1-(2,3-bis(octadec-9-enoyloxy)propyl)18-(5,22-dioxo-1,4-dioxacyclodocos-13-en-2-yl)methyloctadec-9-enedioate and/or1-(1,3-bis(octadec-9-enoyloxy)propan-2-yl)18-(6,23-dioxo-1,5-dioxacyclotricos-14-en-3-yl)octadec-9-enedioate and its isomers(denoted Component 4).

It is important to notice that the cyclic Component 4 is a mixtureof two positional isomers, one with sn-1 and sn-3 ring structure(Component 4.a) so-called symmetric compound, and the otherwith a sn-1 and sn-2 rings (Component 4.b) so-called asymmetriccompound. The chemical environment of the cyclic compound ismore complex than linear oligomer environment, as illustrated bythe differences in 1H-NMR spectra of Mixtures 2 and 3 in Fig. 8. Par-ticularly, the methine proton in glyceryl group CH2 CH(O) CH2signal at ı ≈ 5.2 ppm shifts to ı ≈ 5.4 ppm, and it is partially over-lapped by the olefinic protons CH CH in the cyclic compoundfound in Mixture 3.

Mixtures 3, 4 and 5 exhibited identical signals for both 1H-NMRand 13C-NMR spectra, showing the same composition, confirmingthe ESI-MS. For these mixtures, the protons ratios are not deter-mined because the compounds need to be isolated separately foran accurate integration of the signals. In the case of the frac-tions separated from reaction mixture carried out with Grubbscatalyst, the Mixture 2 contains the Component 2 as underlinedby the protons ratio values for the �-methylene protons adja-cent to carbonyl on the methylene protons in the glyceryl group( O C( O) CH2 : CH2 CH(O) CH2 ), and the ratio of the ter-minal methyl protons CH3 on the methylene protons in theglyceryl group, of 1:1.50 and 1:1.72, respectively, which are close tothe theoretical expected values of 1:1.50 and 1:1.50 (Table 4). TheNMR spectra of Mixture 3 obtained with Grubbs catalyst are similarto the Mixture S 4 and 5 spectra obtained with MTO-based catalyst,where a little difference in peaks intensities were observed.

3.3.4. Kinetic aspects of triolein and metathesis productsMetathesis of esters of glycerol, i.e. unsaturated fatty oils, pro-

ceeds via intra- as well as intermolecular manners, while the latterstrongly predominates [19]. Thus, glyceryl trioleate, yields octadec-9-ene and polymeric glycerides (principally acyclic dimers andtrimers and their cyclic derivatives as demonstrated above).

In order to capture kinetically a representative picture of thetriolein self-metathesis pathway, it is worth to track down the evo-

lution of triolein consumption as well as the formation of both solidand liquid metathesis products during the investigated reactiontime. It is worth pointing out that, the study of the kinetic pro-file of triolein self-metathesis was hardly or not at all addressed

132 S.K. Pillai et al. / Applied Catalysis A:

Fm

iabc

aMtfifi

ibaa

npdtthn

Fm

ig. 10. Triolein depletion and products formation time course profiles during self-etathesis of triolein over MTO-based catalyst.

n literature. To the best of our knowledge, for the first time were describing the kinetic evolution of triolein self-metathesis overoth homogeneous Grubbs catalyst and heterogeneous MTO-basedatalyst.

Fig. 10 shows the time course profiles of triolein conversionnd self-metathesis products formation in the presence of 3%TO/ZnCl2–Al2O3-meso heterogeneous catalyst. It can be observed

hat the triolein consumption exhibits a fast kinetic period in therst 60 min, followed by a slower consumption of triolein, andnally stabilized within 6 h, reaching ≈ 75% of triolein conversion.

The trielaidin resulted from non-productive metathesisncreased rapidly achieving 40% yield after 1 h. Afterwards, itegins to undergo metathesis reaction. Indeed, it shows a moder-te decreases indicating its conversion into metathesis products,lready initiated by the triolein metathesis itself.

When the triolein metathesis was carried out over the homoge-eous 2nd generation Grubbs catalysts, the obtained time courserofiles for the products and triolein depletion were significantlyifferent as depicted in Fig. 11. In fact, the kinetics of triolein deple-

ion through metathesis was faster, as it is clearly observed thathe reaction goes to completion within 5 min, where the catalystas been found to be highly active for triolein metathesis. Unfortu-ately, the formation of the undesirable solid product reached more

ig. 11. Triolein depletion and products formation time course profiles during self-etathesis of triolein over 2nd generation Grubbs catalyst.

General 479 (2014) 121–133

than 40% yield within only 5 min, while 50% yield was achievedafter 60 min. The high production of undesirable solid product isan important drawback, since it represents more than the half ofthe isolated products, including desired metathesis products.

This phenomenon was also reported by Biermann et al.[62] when they carried out metathesis of triolein as model-triacylglycerol of high oleic sunflower oil over 2nd generationGrubbs catalyst without adding a chain polymerization stopper,methyl acrylate (MA). At least, the use of MA as additive wasrequired to control the formation of the polymeric solid product.Indeed, by using a high excess of MA, the polymerization of tria-cylglycerol was completely suppressed. This was also observed byTian and Larock [51] when they investigated the ADMET metathe-sis of soybean oil giving several polymeric materials such as stickyoils and rubbers-like products, while triolein metathesis affordedprimarily monocyclic oligomers as main products, which subse-quently cross-linked into polymeric product [51].

Advantageously, in the heterogeneous MTO-based catalystapproach, no traces of cross polymerization solid products weredetected, and no addition of polymerization chain stopper wasrequired.

Despite the fact that 2nd generation Grubbs catalyst is moreactive, it has been found that it is less selective toward the desiredmetathesis products, compared to the MTO-based heterogeneouscatalyst.

4. Conclusions

Methyltrioxorhenium incorporated on the ZnCl2-modifiedmesoporous alumina (3%MTO/ZnCl2–Al2O3-meso with Al/Zn = 8)was found to be a highly chemoselective heterogeneous catalyst forthe self-metathesis of triolein at optimized conditions, and foundvery efficient for metathesis of bulky functionalized olefins such astriolein.

The MTO-based heterogeneous catalyst afforded good conver-sion up to 75% within 5 h while the desired metathesis productswere isolated in ≈25–30% yield.

The undesired solid polymeric product formed by cross-linkingpolymerization during the triolein self-metathesis over homoge-neous Grubbs 2nd generation catalyst was advantageously avoidedin the presence of MTO-based catalyst.

Triolein self-metathesis gave rise selectively to the primarymetathesis products; dimer, trimer and their cyclic deriva-tives resulted from intramolecular metathesis pathway occurredsimultaneously over MTO/ZnCl2–Al2O3-meso, in addition to the9-octadecene formation, gathering a high industrial interest.

These promising results proved that the 3%MTO/ZnCl2–Al2O3-meso catalyst can be successfully applied for other vegetable oilsmetathesis reaction in a highly selective approach thus, simplify-ing access to many industrially important products and polymerbuilding blocks.

Acknowledgments

The authors gratefully acknowledge the Natural Sciences andEngineering Research Council of Canada (NSERC) who providedfunds for this research. M. Alain Gaudreau and Pierre Audet areacknowledged for Mass spectrometric and NMR analysis. N. Chorfais acknowledged for the helpful NMR analysis interpretations.

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