synthesis of glycerol 1-monooleate by condensation of oleic acid with glycidol catalyzed by...

Synthesis of Glycerol 1-Monooleate by Condensation of Oleic Acid with GlycidolCatalyzed by Anion-Exchange Resin in Aqueous Organic Polymorphic System

Zephirin Mouloungui,* Vony Rakotondrazafy, Romain Valentin, and Bachar Zebib

UniVersite de Toulouse-UMR1010 Chimie Agro-Industrielle, ENSIACET, INPT, INRA, 118 Route de Narbonne,F- 31077 Toulouse Cedex 4, France

The condensation of technical-grade oleic acid (OA) (65%, 85%, and 90% oleic acid) with glycidol (Gly)was carried out in an aqueous medium in the presence of a macroporous anion-exchange resin containingammonium groups. The reaction was optimized by a unifactorial method and by a 2n-1 fractional factorialplan. The effects of the following main parameters were quantified from experiments based on a 2(5-1) ) 24

factorial design: OA/Gly molar ratio, concentration (mmol of OA/mL of H2O), catalytic efficiency (mequivof X/mmol of OA), and temperature. The conditions were optimized for a discontinuous process in a stirredreactor for selective synthesis of glycerol 1-monooleate (1-GMO) in a polymorphic system (solid resin/emulsion or microemulsion) consisting of OA/Gly/H2O/1-GMO. The catalytic role of the Ambersep 900-Xresin was demonstrated by conducting the reaction using the resin in the different functional forms Ambersep900-OH- and Ambersep 900-HCO3

- and in the nonfunctionalized form Ambersep 900-Cl-. The highestyield of 1-GMO (97%) was obtained with the nonfunctionalized form Ambersep 900-Cl- at 70 °C.

Introduction

In view of their polyfunctional nature and their emulsify-ing, complexing, and lubricating properties, fatty acidmonoglycerides find application in the food,1,2 cosmetics,pharmaceutical,3-5 and textile and fiber industries.6,7 Incertain applications, their efficacy hinges on the incorporationof pure monoglycerides (>90%) as additives.8 However, toour knowledge, few industrial processes give rise to puremonoglycerides. All of the conventional methods for thepreparation of monoglycerides, either by direct esterificationof glycerol by fatty acids or by hydrolysis or transesterifi-cation of oils, lead to mixture of glycerides. Pure monoglyc-erides are generally obtained by molecular distillation, whichraises their cost. An alternative chemical method is to preparethe monoglycerides from glycidol according to Scheme 1.

In general, this reaction is conducted in the presence of abasic catalyst in a homogeneous medium: amines and/orquaternary ammonium salts,9 metal alcoholates,10,11 or bases.12

Although the yields of the glycerol monoesters are relativelysatisfactory, the operating conditions in the homogeneous phaserequire phase-transfer agents and solvents that are able towithstand high temperatures. Furthermore, 1-monoglycerides arenot readily extractable from these media, and the catalysts cannotbe immediately recycled.13,14 In heterogeneous catalysis, aminessupported on mesoporous materials present good results,especially with hydrophobic surfaces.13 Similar catalysts canbe recycled 11 times without loss of activity.15

The process described herein for the synthesis of puremonoglycerides, glycerol 1-monooleate in the present case,involves the direct condensation of oleic acid with glycidol inaqueous medium in the presence of an anion-exchange resin asa recyclable catalyst.8,16,17

The new objective in organic chemistry is the developmentof reactions using water as the solvent instead of organic liquids.Of course, glycidol is a solvent of oleic acid, and glycidol andwater are also miscible. 1-GMO and water produce emulsions.

The condensation reaction presented herein is an unusualoutcome in water or in aqueous medium.

Experimental Section

Materials. Technical-grade oleic acid (68-85% GC) wasobtained from Fluka (L’Isle d’Abeau Chesnes, France). Theimpurities detected were essentially linoleic stearic and palmiticacids. Glycidol (2,3-epoxypropan-1-ol, 96%) was supplied byAldrich Fluka (L’Isle d’Abeau Chesnes, France). The anionicresin, Ambersep 900, was purchased from Rohm & Haas(Lauterbourg, France). The solvents used in processing thereaction medium were obtained from SDS (Peypin, France) andwere of synthetic grade, and HPLC-grade solvents wereemployed for the quantitative analyses by thin layer chroma-tography with flame ionization detection (TLC/FID).

Pretreatment of Resin. Anionic resins are usually suppliedin chloride form and contain water. They need to be suitablyfunctionalized before use. To this end, a volume V (in milliliters)of resin, previously swollen in deionized water, was placed ona column equipped with a sintered filter of porosity 0. Theresidual impurities were removed by washing with a volume2V of deionized water. The column was percolated with 5V ofaqueous 2 N sodium hydroxide or potassium bicarbonatethrough the resin bed to replace the Cl- ions with OH- orHCO3

- ions. The resin was then washed with deionized wateruntil neutral pH and subsequently washed with technical ethanol(2V) and ethyl ether (2V) to remove the water. The resin wasdried under a vacuum for 10 min.

* To whom correspondence should be addressed. Tel.: +33 5 62 8857 24. Fax: +33 5 62 88 57 30. E-mail: [email protected].

Scheme 1. Mechanism of Glycidol Epoxide Ring-Opening byFatty Acid to Obtain 1-GMO, Catalyzed by Anion-ExchangeResin

Ind. Eng. Chem. Res. 2009, 48, 6949–6956 6949

10.1021/ie900101k CCC: $40.75 2009 American Chemical SocietyPublished on Web 07/02/2009

The Ambersep 900-OH- resin now marketed under the nameAmbersep 900 OH is a macroporous anion-exchange resin basedon polystyrene containing type I quaternary ammonium groups.The Ambersep 900-X resins have the following characteristics:mean pore size, 40-70 nm; contact surface area, 25-30 m2/g;porosity, 0.5 mL pore/mL of beads; moisture retention, e73%(HO- form) or 2.44 mequiv/g (HCO3

- form); coefficient ofuniformity, e1.35; reversible swelling, 25% from Cl- to HO-

form. In view of their uniform particle size and the existenceof large channels in the particles, the Ambersep 900 macroporousresins readily adsorb fatty acids.

Experimental Setup. For each experiment, 2 g of anionicresin was placed in a 100-mL three-neck flask fitted with acooling system and mechanical stirrer. Oleic acid (16 mmol)was added, and the mixture heated at 70 °C for 15 min to allowcomplete adsorption. At time t ) 0, an aqueous solution ofglycidol (4.3 mmol/mL) was then added, and the reactionmixture was kept at 70 °C on a thermostatted bath. The mixturewas stirred (500 rpm) for the whole 4 h of the reaction. Becausethe rate of the process was controlled by the chemical reaction,stirring was not an important factor. At the end of the reaction,the reaction medium was filtered, and the resin was washed ona column by eluting first with 100 mL of technical ethanol andthen with 100 mL of a mixture of hexane/ethanol (50:50 byvolume) containing 0.1 N acetic acid. The solvent was thenremoved in a rotary evaporator. The crude reaction mixture wasanalyzed by TLC/FID.

Iatroscan TLC/FID Analysis. The sample for analysis wasdissolved in chloroform at a concentration of 20 mg/mL, and 1µL of this solution was deposited on the SII chromarods in anIatroscan MK5 apparatus. The rods were run in a hexane/ethylether/formic acid mixture (75:25:0.04 by volume) for a migrationtime of 20 min. The hydrogen and air flow rates at the detectorwere adjusted to 140 mL/min and 1.8 L/min, respectively. Therods were swept with the flame at a rate of 35 s/chromarod.The spectra were recorded and quantitation was carried out usingBoreal software (Bionis, France). The yield of the reaction(% 1-GMO) was calculated as the ratio of the number of molesof 1-GMO formed to the initial number of moles of either oneof the reactants (OA or Gly).30

Microscopy. The mixtures were examined using a polariza-tion light microscope (Olympus CH2) equipped with a rotatingpolarizer and analyzer and a thermostatted plate to monitor theeffect of temperature on the phase behavior. The samples wereplaced between the slide and the coverslip and examined at amagnification of ×40.

Preparation of Pseudoternary Phase Diagrams for theOA/Gly/1-GMO/H2O System. A series of samples wereprepared with different water contents, and after being weighed,the tubes were incubated in a thermostatted water bath at 35°C (1-GMO is a fluid at this temperature). The tubes werevortexed (speed 5) for 2 min, and their contents were thenexamined under a microscope. The tubes were then returned tothe water bath at 35 °C, and their contents were re-examined 2and 24 h later. The other mixtures of OA and 1-GMO (B andH) were treated in the same way. The compositions of themixtures are listed in Table 1, and the phase diagrams arepresented in Figures 1 and 2.

Results

Effect of the Reactant Addition Mode. We investigated theeffect of the order of addition of the reactants on the synthesisof glycerol 1-monooleate. Prior adsorption of oleic acid ontothe resin enhanced progress of the reaction, whereas the yield

of 1-GMO fell somewhat if OA and Gly were both added tothe resin at the same time. No reaction occurred if the glycidolwas added before the oleic acid. These differences in behaviorcan be explained in terms of differences in the polarities of thespecies present. Glycidol is thought to have a higher solvatingcapacity for the resin than either OA or an OA/Gly mixture.As a result, if glycidol is added first, the active sites on theresin are made inaccessible to oleic acid, and no reaction takesplace. On the other hand, upon contact with the first moleculesof oleic acid, the matrix of the resin becomes hydrophobic. Ahydrophobic film is formed on the surface of the hydrophobicmatrix, and the anion-exchange resin acquires both chemicaland mechanical stability. The lipochemical reaction takes placesvia mass-transfer-facilitated affinity and the structural similaritiesbetween the “hydrophobic” resin and the fatty acid.18,8 Theadsorbed fatty acid is thus activated, generating new reactioncenters and thereby propagating the reaction.

Determination of Optimal Operating Conditions by Fac-tor Study. The results presented here reflect the yields afterrecovery of product. The reaction parameters employed foroptimization of operating conditions thus consisted of thecatalytic efficiency, expressed in milliequivalents of OH- permillimole of OA; the OA/Gly molar ratio, the initial amount ofwater present, reflected by the condensation of OA (mmol ofOA/mL of water); the temperature T; and the reaction time t.

We first employed a factor-by-factor method to evaluate in aqualitative way the influence of each of these reaction parameterson the yield of 1-GMO with respect to a reference experimentcarried out under the following experimental conditions: OA,16 mmol; OA/Gly molar ratio, 1:1; Ambersep resin 900-OH,

Table 1. Compositions of Reaction Mixtures

mixture OA/Gly (mg) 1-GMO (mg) OA (%) Gly (%) 1-GMO (%)

A 39.7 651.2 16.6 0.4 83.0B 63.7 492.0 21.3 0.8 77.9C 84.0 496.9 23.7 1.0 75.3D 122.3 474.7 28.6 1.4 70.0E 142.5 436.7 31.9 1.8 66.3F 196.1 414.4 38.0 2.3 59.7G 232.2 386.0 42.4 2.7 54.9H 256.1 353.6 46.0 3.0 51.0

Figure 1. Pseudoternary phase diagram of the oleic acid/glycidol/1-GMO/water system at 35 °C after 24 h. Visual observations: 1, oil; 2, inhomo-genous translucent solid (gel appearance); 3, white fatty solid; 4, translucentsolid and white fat/white solution; 5, white fatty solid/milky solution (cloudysolution); 6, oil/water; 7, oil/milky solution.

6950 Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009

0.75 mequiv of OH-/mmol of OA; OA concentration, 0.64mmol of OA/mL of H2O; temperature, 50 °C; reaction time,6 h.

Effect of Resin Amount. In the absence of resin, the reactionhardly progressed. Excess resin was also detrimental to thesynthesis of 1-GMO. The amount of Ambersep 900-OH- resincatalyst must thus be chosen carefully. Over a range of catalystconcentrations from 0.25 to 1.25 mequiv of OH-/mmol of OA,the yield of 1-GMO ranged from 0% to 8%. The maximumyield was attained at a catalyst concentration of 0.5 mequiv ofOH-/mmol of OA.

Effect of Counterion. The catalytic performance of theanionic resin was also investigated with respect to the natureof the counterion: the strong anionic form OH-, the weakanionic form HCO3

-, or the original chloride anionic form Cl-.Effect of Molar Ratio. Zlatanos et al.19 showed that the

monoglyceride yield of the condensation reaction of fatty acidwith glycidol catalyzed by tetraethylammonium iodide can beimproved by adjusting of the molar ratio of the reactants. Weobserved that an excess of either of the reactants (OA/Gly molarratios of 4:1 and 1:2) led to a significant improvement in theyield of 1-GMO (14% and 12%, respectively).

Effect of Water. With respect to the initial amount of water,over a range of OA concentrations from 0.21 to 2.29 mmol ofOA/mL of water, it was apparent that the more dilute mediadid not favor the formation of 1-GMO. This finding is in linewith that observed with excess reactants. A maximum yield of15% was obtained.

Effect of Temperature. Temperature was also found to bean important parameter. Heat was found to be favorable for theformation of 1-GMO. From room temperature (25 °C) to 70°C (maximum operating temperature of Ambersep 900 resin inits OH- form), the yield rose from 2% to 12%.

Effect of Time. Furthermore, a study of the reaction progresswith time showed that prolonged reaction times (under thereference conditions) led to a drop in yield of 1-GMO at theexpense of byproducts, the corresponding glycerol di- andtrioleates, indicating that the duration of the reaction needs tobe controlled.

The factor-by-factor study produced a maximum 1-GMOyield of 15%, indicating the feasibility of synthesizing 1-GMO

in an aqueous medium. In addition, this study showed that thecondensation of oleic acid with glycidol is a catalytic reaction.The anion-exchange resin acts as a “triphase catalyst”, that is,a catalyst that is basically supported and used in a reaction ina two-phase system (aqueous-organic). Thus, there is a greatscope to highlight the appropriate reaction mechanism andassociated reaction parameters.

Optimization by Factorial Design of Experiments. Wechose an empirical model for predicting the effects of theparameters on the response in the form of a second-degreepolynomial

where Y is the 1-GMO yield, Xi corresponds to the main effects,XiXj corresponds to the interaction effects, and Xi

2 correspondsto the squared terms.

We employed the same reaction parameters as describedabove and limited the experimental domain by upper and lowercutoffs (Table 2). Table 3 summarizes the experimental resultsobtained.

The significance of the effects calculated with respect to theexperimental error was obtained from analysis of the repeat-ability of the experimental results (Table 4). The values of thecoefficients R (Table 5) were computed using the NEMRODstatistics program. The parameters favorable to the reactionemerging from this analysis did not differ significantly fromthose identified in the previous factor-by-factor study. Specif-ically, use of catalytic amounts of the anion-exchange resin,marked effect of an excess of glycidol and high concentrationof oleic acid in water, and favorable effect of heat on theformation of 1-GMO.

The main effects and the effects of interactions between thevarious parameters were obtained from this experimentalanalysis. The isoresponse curves reflecting the effect of eachof the variables as a function of time (Figure 3) showed thepredominant effects of reactant concentration and temperature.Optimization of these parameters raised the yield to 25%. Anincrease in yield to 45% was obtained by analysis of theisoresponse curves reflecting the interaction of these two terms(Figure 4). The predicted yield was thus comparable to thesynthetic yield.

To validate this predictive model, an experiment wasconducted under the operating conditions defined by the plan:OA, 16 mmol; OA/Gly molar ratio, 1:4; Ambersep resin900-OH-, 0.25 mequiv of OH-/mmol of OA; OA concentra-tion, 1.07 mmol of OA/mL of H2O; temperature, 70 °C; andreaction time, 4 h.

Under these conditions, the maximum yield of the 1-GMOwas increased from 45% to 71%, which confirms the validityof the model.

Analysis of Parameters Acting on the Progress of theReaction. In view of the complexity of the triphasic system,the study of the reaction progress was conducted in a discon-tinuous manner. Each point on the plots of the kinetics

Figure 2. Pseudoternary phase diagram of the oleic acid/glycidol/1-GMO/water system at 35 °C after 2 h. Visual observation: 1, oil; 2, inhomogeneoustranslucent solid gel (gel appearance); 3, with fatty solid; 4, translucentsolid and with fat/milky solution (cloudy solution); 5, white fatty solid/milky solution; 6, with solution/water; 7, oil/milky solution; 8, white foam;9, white gel.

Table 2. Experimental Domain for Studying the Effects of DifferentFactors (Xi)

levels

i factor -1 0 1

1 catalytic efficiency (mequiv of OH-/mmol of OA) 0.25 0.63 1.002 OA/Gly (molar ratio) 4 0.47 0.253 concentration (mmol of OA/mL of H2O) 0.32 0.70 1.074 duration (h) 3 13.5 245 temperature (°C) 30 50 70

Y ) R0 + ∑RiXi + ∑RijXiXj + ∑RiiXi2

Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009 6951

corresponds to an experiment carried out for a defined reactiontime. Three parameters were analyzed: the OA/Gly molar ratio,the initial amount of water, and the temperature.

Molar Ratio. The results for the effect of the OA/Gly molarratio (Figure 5) exhibited two distinct types of reaction progress.Similar kinetics were obtained for reactions carried out witholeic acid in excess or in stoichiometric proportions. Theinduction period was prolonged, and the yield did not exceed30%. On other hand, reactions conducted with excess glycidolgave rise to quite different kinetics, with a maximum 1-GMOyield of 71%.

Molar Composition. We conducted further studies usingthese proportions of reactants, but at different initial concentra-tions (Figure 6) and different temperatures (Figure 7). Theprogress of the reaction was found to depend of these conditions,and the zone of greatest influence (80% 1-GMO) correspondedto a concentration of 2.13 mmol of OA/mL of H2O for atemperature of 70 °C and a reaction duration between 2 and3 h. The reaction was found to be slower and to have a longerinduction period at other values of these parameters.

Temperature. In light of these results, we carried out similarexperiments using different counterions. Preliminary studiesshowed that the chloride and hydrogen carbonate forms of theAmbersep 900 had comparable catalytic efficiencies. Temper-ature was found to have markedly different effects on thekinetics of the reactions in the presence of these different formsof the catalyst (Figures 8 and 9). Although there was littlerelationship between reaction progress and temperature, thekinetics were accelerated at higher temperatures.

In this qualitative study, the optimal conditions for a 97%yield of 1-GMO were found to be as follows: OA, 16 mmol;

OA/Gly molar ratio, 1:4; Ambersep resin 900-OH-, 0.25mequiv of OH-/mmol of OA; OA concentration, 2.13 mmol ofOA/mL of H2O; temperature, 70 °C; and reaction time, 3 h.

Structured Phases and Phase Diagram. Phase diagrams ofthe OA/Gly (7% by weight of Gly)/1-GMO/H2O system areshown in Figures 1 and 2. These diagrams were establishedfrom mixtures with reconstituted compositions (Table 1) closeto those of the crude reaction mixtures. The samples wereexamined microscopically at different times at 35 °C and highertemperatures. Samples were heated to 70 °C and then cooledto 35 °C, after which they were reheated to 100 °C and cooledto 35 °C. Depending of the water content, the solid mixtureswere homogeneous or inhomogeneous. Upon heating from 35°C, the mixture formed a hexagonal crystalline structure ataround 45 °C, and with additional gradual heating, droplets wereobserved at 79 °C. Upon cooling from 100 °C, the hexagonalcrystalline structure was again observed at 65 °C. We observedhexagonal crystalline, isotropic liquid, and reverse crystallinehexagonal phases. The microemulsion phases appeared as oilsand were characterized by a perfectly homogeneous structure.They were stable and transparent, with water as the continuousphase. All other mixtures were emulsions.

Discussion

The condensation of oleic acid with glycidol to form glycerol1-monooleate is heterogeneously catalyzed by anion-exchangeresins. The following processes are involved in the overallreaction:20(a) diffusion of reagents to the catalytic sites of resins,(b) adsorption of reagents in the catalytic sites of the resin, (c)reaction at the surface between adsorbed reagents, (d) diffusionof the reaction products from the pores to the external layer ofthe resin, and (e) desorption of the reaction products into theliquid phase.

After the reaction has been initiated, stages a and b no longergovern the overall kinetics. We found that the product andunreacted starting reactants were strongly bound in the poly-

Table 3. Optimization by 2 × 2 Factorial Plan [2(5-1)]

expt X1 X2 X3 X4 X5 1-GMOa (%) GDOb,c GTOc,d

1 -1 -1 -1 -1 +1 trace 0 02 +1 -1 -1 -1 -1 0 0 03 -1 +1 -1 -1 -1 trace 0 04 +1 +1 -1 -1 +1 1.4 0 05 -1 -1 +1 -1 -1 0 0 06 +1 -1 +1 -1 +1 1.7 0 07 -1 +1 +1 -1 +1 45.5 0 08 +1 +1 +1 -1 -1 1.7 0 s9 -1 -1 -1 +1 -1 trace 0 010 +1 -1 -1 +1 +1 trace 0 s11 -1 +1 -1 +1 +1 30.6 0 012 +1 +1 -1 +1 -1 4.4 0 -13 -1 -1 +1 +1 +1 24.3 0 014 +1 -1 +1 +1 -1 trace 0 -15 -1 +1 +1 +1 -1 13.4 0 -16 +1 +1 +1 +1 +1 0 0 s17 -1 0 0 0 0 10.1 0 s18 +1 0 0 0 0 7.6 ++ s19 0 -1 0 0 0 5.3 0 -20 0 +1 0 0 0 4.3 ++ +21 0 0 -1 0 0 16.8 0 s22 0 0 +1 0 0 32.0 - -23 0 0 0 -1 0 5.6 0 024 0 0 0 +1 0 6.3 ++ s25 0 0 0 0 -1 10.8 0 026 0 0 0 0 +1 22.4 ++ s27 0 0 0 0 0 21.9 ++ -

a 1-GMO, glycerol 1-monooleate. b GDO, glycerol dioleate. c s, trace; -, low content; +, medium content; ++, high content. d GTO, glyceroltrioleate.

Table 4. Reproducibility of the Experimental Results

expt X1 X2 X3 X4 X5 1-GMO (%)

28 -0.35 -0.60 -0.16 -0.71 0 3.929 -0.35 -0.60 -0.16 -0.71 0 4.130 -0.35 -0.60 -0.16 -0.71 0 4.2


meric matrix of the resin. Because desorption did not occurautomatically, stage e was not considered as limiting to theoverall kinetics of the reaction.

Therefore, the reaction on the surface (process c) is assumedto be the sole stage determining the kinetics.

Hydrophobic-hydrophilic interactions of the molecules ofthe organic reactants were involved in the pseudoternaryaquiorganic system.21

Based on observations of the evolution of the resin and themonooleate glycerol during the reaction, two types of adsorptionphenomenon can explain the interactions between glycerolmonooleate and resin on one hand and oleic acid and resin onthe other hand: physisorption of glycerol monooleate in the outerlayer of resin and chemisorption of oleic acid. The former

phenomenon is demonstrated by the easy retrieval of the productby a simple solvent extraction. In the latter case, desorption ofthe resin was achieved through the ion-exchange reaction ofoleate ions with acetate ions. The extractant used was an ethanol/hexane mixture containing acetic acid. The latter was chemicallyactive because acetate ion presented a greater structural affinityfor the anionic resin matrix than did oleate ion. We confirmedthe classification determined by the affinities of the anions withrespect to the active center of heavy anionic resins22 chloride >bicarbonate > acetate > oleate > hydroxyl.

This explanation is validated by the fact that oleic acid ledto more swelling of the OH- form of the resin than did contactwith water (increase in volume of 50-55% with respect to thatof the dry resin at 25 and 70 °C versus 28-30%). The marked

Table 5. Coefficients of the Polynomial Model

i Ri standard error ii Rii standard error ij Rij standard error ij Rij standard error

0 14.6 5.71 -6.0 0 11 -4.7 2.7 12 -3.7 0 24 -2.8 02 +3.8 0 22 -8.5 2.7 13 -3.4 0 25 +2.8 03 +3.6 0 33 +10.8 2.7 14 -1.4 0 34 -2.8 04 +1.2 0 44 -7.3 2.7 15 -5.6 0 35 +1.8 05 +5.3 0 55 +2.9 2.7 23 -0.1 0 45 -0.6 0

Figure 3. Effects of interactions of the predominant parameters as functionsof reaction time.

Figure 4. Main effect of each of the parameters as a function of reactiontime.

Figure 5. Effect of the OA/Gly molar ratio on the progress of the reactioncatalyzed by Ambersep 900-OH- resin. OA, 16 mmol; Ambersep900-OH- resin, 2 g; water, 15 mL; temperature, 70 °C.

Figure 6. Effect of the initial concentration of OA on the progress of thereaction in the presence of Ambersep 900-OH- resin.


swelling of the anionic resin with oleic acid indicates that thefatty acid penetrated the resin and that oleic acid was in contactwith the active sites, where it was adsorbed and activated.

We also noted a marked elimination of water during the phaseof preadsorption of oleic acid onto the Ambersep 900-X (X )OH-, Cl-, HCO3

-) anion-exchange resins. Oleic acid thusappears to effectively desiccate the polymeric lattice, therebyenhancing the organohydrophobic nature of the solid polymericcatalyst.

Then, adsorption of the fatty acid is governed by van derWaals-type forces between the fatty hydrophobic hydrocarbonchains of the acid and the cross-linked polystyrene matrix, givingrise to a strong adsorbing capacity.

The long-term stability of the resins is thus increased, withan enhanced catalytic system. We believe with a good degreeof confidence that the same phenomenon occurs with the otherstudied resins.

The bulky nature of oleic acid and its rigid structure suggestthat adsorption takes place in the macroporous sites as well inthe microporous sites (gel) both on the surface and within theresin.23 The reaction takes place in the zone where there areboth macroporous active sites and micropores, which favor

condensation between the adsorbed oleic acid and the solubleglycidol. By preadsorbing oleic acid onto the resin, the stageof transport and diffusion (stage a) of the fatty acid is no longera limiting step in the overall reaction. The ensuing condensationbetween oleic acid and glycidol in an OA/Gly molar ratio of1:1 or 4:1 is a surface reaction. It takes place between reactantswithin the droplets dispersed in the continuous organic hydro-phobic pseudophase within and on the surface of the macroporousparticles and gels.

The kinetics appeared to obey those described by theLangmuir-Rideal model24,25 for the surface reaction betweenoleic acid and glycidol in an aquiorgano hydrophobic resinsystem providing the transport of reacting droplets in thehydrophobic organic pseudophase for an OA/Gly molar ratioof 1:1 or 1:4.

The catalytic efficiency of the active sites of the hydrophobicresin is probably favored by the level of hydration around thehydroxide, chloride, or bicarbonate ions of the resins.

On the other hand, under conditions in which glycidol ispresent in excess (OA/Gly ) 1:4), the organic pseudophasebecomes strongly organophilic. Water and glycidol are quitemiscible, and at the start of the reaction, mixtures consisting ofhydrophobic anionic resin/oleic acid/glycidol/water are triphasic.

Figure 7. Effect of temperature on the progress of the reaction in thepresence of the Ambersep 900-OH- resin. OA, 16 mmol; OA/Gly, 1:4;Ambersep 900-OH- resin, 2 g; water, 15 mL.

Figure 8. Effect of temperature on the progress of the reaction in thepresence of Ambersep 900-Cl- resin. OA, 16 mmol; OA/Gly, 1:4;Ambersep 900-Cl- resin, 2 g; water, 7.5 mL.

Figure 9. Effect of temperature on the progress of the reaction in thepresence of Ambersep 900-HCO3

- resin. OA, 16 mmol; OA/Gly, 1:4;Ambersep 900-HCO3

- resin, 2 g; water, 7.5 mL.

Figure 10. Reaction progress in the presence of the three types of Ambersep900 resins.


This system can be considered as an emulsion or a microemul-sion supported on a solid catalytic phase and presents a largesurface exchange in the system, which is favorable to an increasein the catalytic efficiency by contacting largely all of thecomponents. As the reaction progresses (Figure 10), 1-GMO,itself a surface-active agent, is formed, and we found that itsconcentration outside the particles of Ambersep 900-OH- resinincreased, whereas the particles themselves contained undisso-ciated and unreacted oleic acid. The presence of molecules ofwater and glycidol in the pores of the resin effectively expelled1-GMO from the resin particles. The internal layer of the resinis thus not completely hydrophobic, but is a living layer thatcan be a water-in-oil emulsion, an oil-in-water emulsion, or amicroemulsion depending on the reaction progress. Indeed,examination of the crude reaction mixture containing oleic acid/glycidol/water/glycerol monooleate by polarizing microspcopyindicated the existence of organized media consisting of directand reverse hexagonal liquid crystal phases in stable micro-emulsions and emulsions. The formation of direct and reversehexagonal liquid crystal phases with increasing temperaturestems from the requirement of a larger cross-sectional area ofthe hydrocarbon chain compared to the area of the polarheadgroup with increasing thermal mobility of the chain tail.26

These phase structures are formed by self-aggregation as a resultof hydrophobic interactions between the hydrocarbon tails andwater and the favorable interactions between polar head groupsand water or water/glycidol.27 The alkyl chains in the aggregatesare highly mobile and liquid-like.26,28

The pure 1-GMO formed in situ gives rise to thermodynami-cally stable structured phases, such as microemulsions, that favorsolubilization of the fatty acid and accelerate condensation ofthe oleic acid with glycidol, so that the reactants are welldispersed to the catalytic sites in the ion-exchange resin. The

Ambersep 900-Cl- resins produced the highest yield of 1-GMO(97%), and the high catalytic activity of this nonfunctionalizedform of the resin indicates that the reaction is essentiallycatalyzed by quaternary ammonium cations within the polysty-rene lattice. We propose the scheme in Figure 11 to describethe overall reaction. These solid catalysts thus behave as cationicsurfactants whose properties depend on the nature of theassociated anion. Cl- is an excellent counterion for generatingaqueous micelles in which the carboxylic groups of oleic acidare strongly bound to the ammonium cations of the surfactant.29

The latter co-micellizes with glycidol whose hydroxyl group isin contact with the aqueous pseudophase, whereas the acylhydrocarbon chain of the fatty acid remains in the hydrophobicenvironment of the polystyrene polymer.

Conclusions

To understand the mechanism of this type of condensationreaction and to optimize the yield of 1-GMO, it is of majorimportance to characterize the different phases of the system.Because of the existence of hexagonal and microemulsion,isotropic liquid, inverse liquid crystal hexagonal, and micro-emulsion phases, the hydrophobic effect appears to be dominant.The interaction between all surface-active agents, which are alsothe chemical reactants, appears of major importance. Theinteractions of oleic acid (reagent) and/or glycerol 1-monooleate(product) molecules at the solid/liquid interface determine thestability and catalytic activity of the polystyrene-polymer-supported ammonium ions. In the surrounding liquid, theglycidol is an alcohol that acts as a reactant, a solvent, and apseudocomponent of the reaction medium. An increase of theglycidol concentration leads to a decrease of the interactionenergy of the interface with water. Consequently, the glycidol

Figure 11. Physicochemical evolution of the condensation reaction of glycidol with oleic acid in the presence of Ambersep 900-Cl- resin, (w/o, water/oil;o/w, oil/water; µe, microemulsion). Resin before reaction (hydrophilic resin). Adsorption of oleic acid on resin (hydrophobic resin). Contact of glycidol/water solution with resin (hydrophilic/hydrophobic resin). Resin surrounded by polymorphic system (w/o system, o/w system, or microemulsion system).


is a cosurfactant, and the interactions of glycidol at the liquid/liquid and liquid/solid interfaces are balanced at a highertemperature and a higher mass fraction.

Then, the use of new water-containing systems made up ofincompatible components reveals the ability to produce newreaction media in the field of green chemistry. Hydrophobicand hydrophilic reagents are compatibilized at the liquid/liquidand solid/liquid interfaces by emulsification phenomena en-hanced by synthesis products such as monoglycerides. Conse-quently, organic and toxic solvents can be substituted bymicroemulsion or emulsion catalytic media acting as solventsfor organic molecules, increasing mass transfer in continuousseparation systems.

Acknowledgment

The authors acknowledge the financial support from ONIDOLthrough J.P. Jamet, the Region Midi-Pyrénées LanguedocRoussillon, and the European Community.

Literature Cited

(1) Hartunian-Sowa, S. M.; White, P. J.; Batres, L. V. Influence ofMonoglycerides of Different Chain Lengths on Texture and Flavor of BreadsMade with Waxy Cornstarch. Starch-Starke 1990, 42 (2), 53–56. 1990, 42,2, 53.

(2) Fujimura, M.; Yamauchi, H.; Matsushita, T.; Oshima, M.; Oya, K.Shortenings Containing Glycerides and Amylase and/or Protease and TheirManufacture. Japanese Patent JP 03 292 848, 1991.

(3) Rieger, M. Glyceryl stearate, chemistry and use. Cosmet. Toiletries1990, 105, 51.

(4) Kabara, J. J.; Lie, M. S. F. Antimicrobial Lipids: Natural andSynthetic Fatty Acids and Monoglycerides. Lipids 1977, 12 (9), 753.

(5) Kato, N. Antimicrobial Activity of Fatty Acids and Their Estersagainst a Film-Forming Yeast in Soy Sauce. J. Food Safety 1981, 3 (2),121.

(6) Kamei, T.; Teraoka, T.; Hirano, H. Antistatic Acrylic Polymer orPolycarbonate Laminate Sheets. Japanese Patent JP 02 276 636, 1990.

(7) Mc Intire, R. T. Fatty Acids in Industry; Marcel Dekker: New York,1989.

(8) Mouloungui, Z.; Gauvrit, C. Synthesis and influence of fatty acidesters on the foliar penetration of herbicides. Ind. Crops Prod. 1998, 8, 01.

(9) Lok, C. M. Glyceride Esters. U.S. Patent 4,234,498, 1980.(10) Burgos, C. E.; Ayer, D. E.; Johnson, R. A. A new, asymmetric

synthesis of lipids and phospholipids. J. Org. Chem. 1987, 52 (22), 4973.(11) Caron, M.; Sharpless, K. B. Titanium isopropoxide-mediated

nucleophilic openings of 2,3-epoxy alcohols. A mild procedure forregioselective ring-opening. J. Org. Chem. 1985, 50 (9), 1557.

(12) Tamura, T. Preparation of Higher Fatty Acid Monoglycerides fromFatty Acids and Glycidol. Japanese Patent JP 04182451, 1992.

(13) Cauvel, A.; Renard, G.; Brunel, D. Monoglyceride Synthesis byHeterogeneous Catalysis Using MCM-41 Type Silicas Functionalized withAmino Groups. J. Org. Chem. 1997, 62 (3), 749.

(14) Janis, J.; Krejc, J.; Klasek, K. Preparation of 1-monoacylglyceroIsfrom glycidoI and fatty acids catalyzed by the chromium(III)-fatty acidsystem. Eur. J. Lipid Sci. Technol. 2000, 102 (5), 351.

(15) Jaenicke, S.; Chuah, G. K.; Lin, X. H.; Hu, X. C. Organic-inorganichybrid catalysts for acid- and base-catalyzed reactions. MicroporousMesoporous Mater. 2000, 35-36, 143.

(16) Mouloungui, Z.; Rakotondrazafy, V.; Peyrou, G.; Gachen, C.;Eychenne, V. Pure R-monoglycerides for industrial applications. Agro FoodInd. Hi-Tech. 1998, 9 (4), 10–14.

(17) Jamet, J.-P.; Mouloungui, Z.; Peyrou, G.; Gachen, C.; Rakoton-drazafy, V.; Gaset, A. Process and equipment for the synthesis ofmonoglycérides. French Patent FR 2723088, 1995.

(18) Chapelle, S.; Baudrand, V.; Rakotondrazafi, V.; Mouloungui, Z.;Gaset, A. Deacidification of lipophilic media by binding free fatty acids toanion exchange resins. RiV. Ital. Sost. Grasse 1995, 72, 153.

(19) Zlatanos, S.; Sagredos, A.; Papageorgiou, V. High yield monoglyc-erides preparation from glycidol and carboxylic acids, Society. J. Am. OilChem. Soc. 1985, 62 (11), 1575.

(20) Dooley, K. M.; Williams, J. A.; Gates, B. C.; Albright, L. Sulfonatedpoly(styrene-divinylbenzene) catalysts: II. Diffusion and the influence ofmacroporous polymer physical properties on the rate of reesterification. J.Catal. 1982, 74, 361.

(21) Jiang, X.-K. Hydrophobic-Lipophilic Interactions. Aggregation andSelf-Coiling of Organic Molecules. Acc. Chem. Res. 1988, 21, 362.

(22) Harris, D. C. QuantitatiVe Chemical Analysis, 3rd ed.; W. H.Freeman & Company: New York, 1991; p 734.

(23) Ihm, S.-K.; Oh, I.-H. Correlation of a two-phase model formacroreticular resin catalyst. J. Chem. Eng. Jpn. 1984, 17, 58.

(24) Satterfield, C. N. Heterogeneous Catalysts in Industrial Practice,2nd ed.; McGraw-Hill: New York, 1991.

(25) Ljusberg-Wahren, H.; Herslof, M.; Larsson, K. A comparison ofthe phase behaviour of the monoolein isomers in excess water. Chem. Phys.Lipids 1983, 33 (2), 211.

(26) Krog, N.; Larsson, K. Phase behaviour and rheological propertiesof aqueous systems of industrial distilled monoglycerides. Chem. Phys.Lipids 1968, 2 (1), 129.

(27) Garti, N. Microemulsions as microreactors for food applications.Curr. Opin. Colloid Interface Sci. 2003, 8 (2), 197.

(28) Larsson K. Lipids: Molecular Organization, Physical Functionsand Technical Applications, The Oily Press: Dundee, Scotland, 1994.

(29) Hinze, W. L. Utilization of surfactant systems in chemical separa-tion. Ann. Chim. (Roma) 1987, 77, 167.

(30) Peyrou, G.; Rakotondrazafy, V.; Mouloungui, Z.; Gaset, A.Separation and quantitation of mono-, di-, and triglycerides and free oleicacid using thin-layer chromatography with flame-ionization detection. Lipids1996, 31 (1), 27.

ReceiVed for reView January 20, 2009ReVised manuscript receiVed April 16, 2009

Accepted June 17, 2009

IE900101K


synthesis of glycerol 1-monooleate by condensation of oleic acid with glycidol catalyzed by...

Documents