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Hydroxylation of vegetable oils using acidic resins as catalysts
Industrial Crops and Products 43 (2013) 183–187
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Hydroxylation of vegetable oils using acidic resins as catalysts ˜ Luis Rios ∗ , David Echeverri, Fernando Cardeno Grupo Procesos Fisicoquímicos Aplicados, Universidad de Antioquia, Sede de Investigación Universitaria, Cra. 53 # 61-30 Medellín, Colombia
a r t i c l e
i n f o
Article history: Received 16 April 2012 Received in revised form 17 July 2012 Accepted 18 July 2012 Keywords: Hydroxylation Vegetable oils Jatropha oil Glycols Polyols Acid resins
a b s t r a c t A new modification of the Prileschajew method to produce hydroxylated vegetable oils using in situ generated peracetic acid and acidic resins, of the sulfonated polystyrene type, as heterogeneous catalysts is reported. Jatropha oil methylesters were chosen as model substrate. Reaction mixtures were characterized by 1 H NMR and gas chromatography. The effect of cross-linking degree of the resins on the conversion and the selectivity to glycols was analyzed. Best results were obtained with Amberlyst 15 catalyst, ca. 100% conversion and 80% selectivity at 57 ◦ C over 24 h, stable through five re-uses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Hydroxy fatty acids/esters are of considerable interest in commercial applications such as lubricants and cosmetics (Maurer and Schmid, 2005). Another important application of hydroxylated oils is the production of dicarboxylic acids such as azelaic acid, via epoxidation/ring opening using H2 O2 and tungsten-containing iso- or heteropoly-compounds followed by subsequent oxidative cleavage of the intermediate diol with, for instance, peracetic acid (Köckritz and Martin, 2011). Besides, they could be used for the production of biodegradable and renewable-feedstocked polymers (Tomoda et al., 1998; Wang et al., 2008; Mazo et al., 2010). Hydroxylated oils occur naturally only in few vegetable oils, most notably castor oil, and some other alternative crops such as lesquerella (Roetheli et al., 1991). Chemically, hydroxy fatty acids have been synthesized by peracid oxidation of unsaturated fatty acids or direct oxidation of the double bond with reagents such as potassium permanganate or hydrogen peroxide/tungstic acid to give vicinal diols (Sonntag, 1979). Wiberg and Saegebarth (1957) studied the hydroxylation of olefins such as oleic acid with potassium permanganate with excellent yield (98%) but the reaction required alkaline pH (pH 12) an a large excess of KMnO4 (1.45–2 mol%). Luong et al. (1967) reported the direct preparation with high yield (70–90%) of threo-1,2-glycols without isolation of
∗ Corresponding author. Tel.: +57 4 2196589, fax: +57 4 2196543. E-mail addresses: [email protected], [email protected], [email protected] (L. Rios). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.07.035
intermediates from oleic acid, methyl oleate and oleyl alcohol by oxidation with a hydrogen peroxide (70%)–tungstic acid system at pH 0–1 and 45–55 ◦ C without solvent. The threo-isomers were formed from intermediate epoxides by in situ hydration with accompanying inversion. Preincorporation of about 2% of the glycol reaction product into oleic acid or methyl oleate speeds up the oxidation reactions markedly and adds to their control and reproducibility. With oleyl alcohol, addition of reaction product is not necessary. Maerker et al. (1964) reported the acid-catalyzed conversion of epoxyesters to hydroxyesters. Esters of 9,10-epoxystearic acid (epoxidized oleic acid), dissolved in 1,4-dioxane, were treated at 15 ◦ C, first with aqueous acid and then with water to convert them to 9,10-dihydroxystearates in high yields. Treatment of methyl 9,10-epoxystearate with diluted (24%) fluoboric acid gave methyl 9,10-dihydroxystearate in 89% yield. Hydration of methyl 9,10-epoxystearate with concentrated H2 SO4 led to the formation of considerable amount of byproducts, principally methyl 9(10)-ketostearate. Side reactions were inhibited by diluting the acid-catalyst. Allylic hydroxylation of double bonds with selenium dioxide has been also reported in the synthesis of hydroxy fatty acids (Knothe et al., 1993). That work shows the potential usefulness of the SeO2 /TBHP system not only in monohydroxylation, but also in allylic dihydroxylation of monounsaturated fatty materials. The allylic dihydroxy products are obtained as erythrolthreo diastereomers. Recently, Daniel et al. (2011) explored two well-known methods for the synthesis of hydroxylated jatropha oil, i.e., a Prilezhaev dihydroxylation using performic acid and an Upjohn dihydroxylation
184
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using osmium tetroxide as catalyst and 4-methylmorpholine Noxide as the oxidant. The Prilezhaev method using in situ generated performic acid from hydrogen peroxide and formic acid gave the trans-vicinal diol, as a colorless oil in 87% yield, essentially quantitative carbon–carbon double bond conversion (96%) and selectivity to diols of about 80% (20% for formyl branches). The cis-vicinal diol was obtained with the Upjohn dihydroxylation, at 60 ◦ C for 18 h; the solid product was isolated in 48% yield and full conversion of the carbon–carbon double bonds to diols was achieved. In a recent study published by our group, sulphonated polystyrene resins, Nafion–silica and immobilized lipase were used as heterogeneous catalysts for the epoxidation of Jatropha oil (Rios et al., 2011). Immobilized lipase showed ca. 100% conversion and 100% epoxide selectivity at 24 h. Amberlite IR-120 was the best heterogeneous catalysts, yielding ca. 90% conversion and 70% epoxide selectivity, both stable through five re-uses. Jatropha oil was chosen as model substrate; this oil is a very interesting raw material for the production of oleochemicals (biodiesel, fatty acids, soap, fatty nitrogenous derivatives, surfactants and detergents, etc.) because it has ca. 80% of unsaturated compounds and it is a non-edible oil. Jatropha curcas has a very high oil content (oil content of jatropha kernel was determined at 63.2%) compared to other plants and can produce 2000 l/ha oil per annum (Akbar et al., 2009). Therefore, this oil could lead to a lower consumption of edible oils for chemical purposes, which is currently a very hot discussion topic. Besides, jatropha plants grow under not very stringent conditions. Owing all these attributes, production of jatropha is currently being undertaken by some developing countries. Herein, we present a new modification of the Prilezhaev method to produce hydroxylated vegetable oils using in situ generated peracetic acid and acidic resins, of the sulfonated polystyrene type, as heterogeneous catalysts. The use of these heterogeneous catalysts makes the purification of products easier and avoids the disposal of salts formed during the final neutralization of soluble acids and technical problems associated with their use, such as corrosion and separation operations; besides, the catalyst could be re-utilized.
2. Material and methods 2.1. Materials Amberlyst 15, Amberlite IR-120 and Dowex 50X2 were purchased from Aldrich. Jatropha oil was provided by a local farmer and converted to the methylesters following a reported procedure (Echeverri et al., 2011). All the other reagents used were of analytical grade purchased from Sigma–Aldrich.
1 H NMR (300 MHz, CDCl ): ␦ (ppm) = 0.81–0.92 (CH CH H 3 3 2 ), 1.15–1.70 ( CH2 ), 2.21–2.38 ( CH2 COO ), 3.36–3.53 ( CHOH), 3.67 ( OCH3 ). 13 C NMR (75 MHz, CDCl ): ␦ (ppm) = 13.58 ( CH 3 C 2 CH3 ), 22.09 ( CH2 CH3 ), 24.46–34.11 ( CH2 ), 50.90 ( OCH3 ), 76.04–76.88 ( CH OH), 173.75 ( COO ). Reaction mixtures were analyzed by gas chromatography with an Agilent 7890A GC equipped with a flame ionization detector and a 60-m FS-SE54 column. Reaction products were identified by GC–MS (Agilent 5975C MSD). Hydroxylated samples were silylated before GC analyses according to a published procedure (Jover et al., 2005). Iodine value (g iodine/100 g simple, ASTM D5554-95), epoxide value (g oxygen/100 g sample, ASTM D1652-04) and hydroxyl value (mg KOH/g sample, ASTM D4274-05) were also measured.
2.4. Catalytic experiments Hydroxylations were carried out in round-bottom glass reactors immersed in a heated oil bath at 57 ◦ C. The agitation was performed using a turbine impeller (2 cm radious, 500 rpm) to prevent attrition of the catalyst. A mixture of jatropha oil methylesters was employed as substrate. Resin-based catalysts were evacuated overnight at 120 ◦ C under high vacuum and kept under argon atmosphere. Jatropha oil methylesters, acetic acid and the solvent (toluene) were mixed for 15 min at the reaction temperature (3.8 g oil/g toluene, 11.9 g oil/g acetic acid)), then the catalyst was added (10 g oil/g catalyst) and the mixture was stirred for another 15 min at the end of which a 10% molar excess of hydrogen peroxide (35% in water) was added at once. As a comparison basis, the epoxidation of the substrate, catalyzed by sulfuric acid, was performed following a procedure already known (Wallace, 1978). Reaction conditions were chosen from previous works (Rios et al., 2005; D’Addieco, 1956; Mungroo et al., 2008; Goud et al., 2007). Effect of resin crosslinking (2, 8 and 20% of divinylbenzene) and catalyst type (resins and H2 SO4 ) were evaluated through a replicate factorial design. Data plotted in the accompanying figures correspond to the means of triplicate experiments with a relative standard deviation <5% in all cases. To investigate the effect of stirring speed on the three-phase reaction system, reactions were carried out over a range of stirring speeds (100–1000 rpm). It was observed that the ethylenic unsaturation conversion increased with the stirring speed, but beyond 500 rpm there was no appreciable change in the rate of reaction. Therefore, all the subsequent experiments were carried out under a stirring speed of 500 rpm to ensure that there was no mass-transfer limitation in the liquid phases. 3. Results and discussion
2.2. Catalyst characterization The total amount of Bronsted acid sites in Amberlyst 15, Amberlite IR-120 and Dowex 50X2 was determined by ion exchange with NaCl solution 1.0 M (10 mL/g of catalyst) and titrating the residual solution with NaOH 0.01 M. 2.3. Reaction mixtures characterization The 1 H NMR and 13 C NMR were recorded in CDCl3 as the solvent using a Mercury-300 BB spectrometer. For 1 H NMR spectra, a total of 16 scans were performed with a relaxation delay of 0.100 s and width of 8103.7 Hz. 320 scans were recorded for 13 C NMR spectra with a relaxation delay of 0.100 s and width of 19607.8 Hz. 1 H NMR and 13 C NMR spectra of hydroxylated jatropha oil methylesters gave the following signals:
Results on the characterization of acidic resins are shown in Table 1. Brönsted acidity is introduced by sulfonyl groups ( SO3 H) anchored to the skeleton of the resin, as shown in Table 1. Because of their chemical composition, the acid strength of all the polystyrene resins is the same. Hammet acidity and NMR of mesityl oxide indicate that these resins are moderately strong acids, similar to the acid strength of a 45% sulfuric acid solution. The amount of acid sites is quite similar in all the resins, in the range 4.3–4.72 meq H+ /g, in accordance with the data supplied by de manufacturer. One important difference among these resins is that Amberlyst 15 is the only one in a macroreticular form while the others are gels. Therefore, Amberlyst 15 keeps its granular form in solution while the other resins swell as a function of their DVD content and the solvent polarity. The composition of the methylesters of jatropha oil, determined by gas chromatography, is shown in Table 2. According to this
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Table 1 Physicochemical properties of the acid resins. Amberlyst 15
C H2
Amberlite IR-120
H C
x
H C C H2
y
HSO3 C C H2 H
Structure Composition
Styrene + 20% divinylbenzene
Styrene + 8% divinylbenzene Ho = −2.2 (Hammet acidity) NMR of mesityl oxide: ı = 32.4 ppm, equivalent to 45% H2 SO4 4.7 4.5 51 Non measurable 40–80 Non measurable 0.600–0.850 0.252
Acid strength Acidity (meq H+ /g) Surface area (m2 /g) Pore size (nm) Particle size (mm)
Table 2 Fatty acid profile of methylesters from jatropha oil. Fatty acid (mehyl ester)
Concentration (wt%)
Myristic Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Eicosanoic
0.15 17.01 0.99 11.03 34.32 36.11 0.39 0.37
composition, the jatropha oil is a good substrate for the hydroxylation reaction since it is composed of about 80% of unsaturated compounds. The iodine value of jatropha oil methylesters was determined as 95.00 ± 0.07 g iodine/100 g sample. NMR spectrum of the final product is shown in the Fig. 1. Presence of protons connected to the carbons of oxirane ring (around 2.52 ppm) was not detected, which indicates a complete conversion of epoxides. On the other hand, the peaks corresponding to the protons connected to the carbons bearing hydroxyl functionality (carbons 9, 10, 12 and 13) were observed at 3.36–3.53 ppm.
Fig. 1.
Dowex 50X2
1
H NMR spectrum of hydroxylated methylesters.
Styrene + 2% divinylbenzene 4.6 Non measurable Non measurable 0.150
To investigate the effect of resin type, resins with different crosslinking degree, determined by the content of divinylbenzene (DVB) were selected: Dowex 50WX2, Amberlite IR-120 and Amberlyst 15, with 2%, 8% and 20 wt% of DVB content, respectively. In the presence of a polar medium these resins swell and the accessibility to the acidic sites increases. This swelling is reduced by increasing the cross-linking of the resin, i.e. the content of DVB. The effects of the cross-linking degree of the resins on the epoxidation of jatropha oil methylesters are shown in Figs. 2 and 3. From the point of view of conversion, the three catalysts have similar behavior at higher reaction times, but at lower reaction times (less than 10 h) the following order of activity can be observed: Dowex 50X2 > Amberlite IR-120 > Amberlyst15. It is observed that the decrease in the crosslinking of the resins leads to higher conversions. This is explained by the greater accessibility of the acetic acid to the acid sites to form the respective peracid which then, in the homogeneous phase (without the need of acid sites), epoxidizes the unsaturations of the oil. Results on selectivity, shown in Fig. 3, reveal two interesting aspects: (a) with resins that are in gel form, i.e. 2% and 8% DVB, the selectivity to the glycols increases by lowering the cross-linking. Thus, glycols are produced by adding water to the epoxides that
Fig. 2. Effect of resin type on the conversion.
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Fig. 4. Effect of catalyst type, inorganic-soluble vs. organic-solid, on the conversion.
Fig. 3. Effect of resin type on the selectivity to glycols.
are activated (protonate) on the acid sites, and the formation of these glycols is enhanced with low cross-linking. (b) The resin with 20% DVB, which has the highest cross-linking, also shows a high selectivity to glycols. This result can be attributed to the fact that this resin has a macro-reticular structure and therefore it has a high extra-particular surface area on which epoxides can be protonated and opened by water to form glycols. These results indicate that for the hydroxylation of vegetable oils with percarboxylic acids the most important issue to obtain high selectivity is to improve the contact of the formed epoxides with the acid sites of the catalyst. This can be achieved by using resins with low cross-linking degree and/or high external surface area. It is also worth to mention the very high selectivity toward glycols obtained with the resin with the lowest cross-linking, i.e. Dowex 50WX2. According to Figs. 2 and 3, these glycols could be produced with more than 90% selectivity at conversions of ca. 90%. The other identified byproducts were the epoxides; therefore, conversion and selectivity could be further improved by increasing the reaction time and/or catalyst loading, because the epoxides are intermediate products in the synthesis of glycols. Fig. 4 shows that the conversion obtained with H2 SO4 was higher than the obtained with Dowex 50X2, which can be explained by the lowest acid strength of this resin, as shown in Table 2, which is equivalent to 45% H2 SO4 . However, the selectivity toward glycols obtained with H2 SO4 is very poor (less than 5%) (Fig. 5). This low selectivity achieved with sulfuric acid is due to the high insolubility of the epoxidized oil phase in the aqueous phase, where the sulfuric acid is dissolved, which avoids the formation of glycols.Results of re-using (Fig. 6) indicate that Amberlyst 15 can be reused up to five times without significant loss in conversion and selectivity. Amberlyst 15 was chosen for these tests because it has better mechanic stability and better morphology (granular form and higher particle size) for industrial use than Dowex 50X2; besides it has good activity and selectivity for the hydroxylation. Table 3 shows the characteristics of the final product obtained in this investigation. Complete conversion of carbon–carbon double bonds was achieved. Selectivity to glycols of ca. 80% was
Fig. 5. Effect of catalyst type, inorganic-soluble vs. organic-solid, on the selectivity to glycols.
Fig. 6. Conversion and selectivity as a function of the number of reuses for Amberlyst 15.
Table 3 Properties of the final product. Material
Iodine value
Epoxide value
Hydroxyl value
Conversion (titration)b
Selectivity (titration)
Conversion (1 H NMR)
Selectivity (1 H NMR)
JO methylesters Hydroxylated methylestersa
95.00 0
0 0.37
0 325.59
100
77.54
99.03
81.45
a b
Product obtained at 24 h with Dowex 50X2. Theoretical hydroxyl value = 4.42 × iodine value = 419.9.
L. Rios et al. / Industrial Crops and Products 43 (2013) 183–187
also obtained. Results on conversion and selectivity obtained by titration and 1 H NMR agree quite well. It is important to remark that the selectivity could be further improved by increasing the reaction time and/or catalyst loading because the epoxides are intermediate products in the synthesis of glycols. 4. Conclusions Acidic resins of the sulfonated polystyrene type are suitable catalysts for the hydroxylation of vegetable oils, such as jatropha oil methylesters, if their acid sites are easily accessed by the intermediates epoxides formed in the process. Therefore, glycols selectivity strongly depends on the resin cross-linking and morphology. The most crucial feature to favor the formation of glycols is to improve the exposure of the epoxides to the acidic sites of the catalyst, which can be achieved using resins with a low cross-linking and/or with high external surface area. Amberlyst 15 gave ca. 100% conversion and 80% selectivity, stable through five re-uses. Acknowledgements Financial support of “Departamento Administrativo de Ciencia, Tecnología e Innovación-Colciencias” and “Universidad de Antioquia” is acknowledged. References Akbar, E., Yaakob, Z., Kamarudin, S.K., Ismail, M., Salimon, J., 2009. Characteristic and composition of Jatropha curcas oil seed from malaysia and its potential as biodiesel feedstock. Eur. J. Sci. Res. 29, 396–403. D’Addieco, A.A., 1956. E.I. Du Pont de Nemours & Co., Can Patent 531112. Daniel, L., Ardiyanti, A.R., Schuur, B., Manurung, R., Broekhuis, A.A., Heeres, H.J., 2011. Synthesis and properties of highly branched Jatropha curcas L. oil derivatives. Eur. J. Lipid Sci. Technol. 113, 18–30. ˜ F., Rios, L.A., 2011. Glycerolysis of soybean oil with crude Echeverri, D.A., Cardeno, glycerol containing residual alkaline catalysts from biodiesel production. J. Am. Oil. Chem. Soc. 88, 551–557.
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Goud, V.V., Patwardhan, A.V., Dinda, S., Pradhan, N.C., 2007. Kinetics of epoxidation of Jatropha oil with peroxyacetic and peroxyformic acid catalysed by acidic ion exchange resin. Chem. Eng. Sci. 62, 4065–4076. Jover, E., Adahchour, M., Bayona, J.M., Vreuls, R.J., Brinkman, U.A., 2005. Characterization of lipids in complex samples using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry. J. Chromatogr. A 1086, 2–11. Knothe, G., Weisleder, D., Bagby, M.O., Peterson, R.E., 1993. Hydroxy fatty acids through hydroxylation of oleic acid with selenium dioxide/tert.butylhydroperoxide. J. Am. Oil. Chem. Soc. 70, 401–404. Köckritz, A., Martin, A., 2011. Synthesis of azelaic acid from vegetable oil-based feedstocks. Eur. J. Lipid Sci. Technol. 113, 83–91. Luong, T.M., Schriftman, H., Swern, D., 1967. Direct hydroxylation of fats and derivatives with a hydrogen peroxide tungstic acid system. J. Am. Oil. Chem. Soc. 44, 316–320. Maerker, G., Haeberer, E.T., Ault, W.C., 1964. Acid-catalyzed conversion of epoxyesters to hydroxyesters. J. Am. Oil. Chem. Soc. 41, 585–588. Maurer, S.C., Schmid, R.D., 2005. Biocatalysts for the epoxidation and hydroxylation of fatty acids and fatty alcohols. In: Hou, C.T. (Ed.), Handbook of Industrial Biocatalysis. CRC Press, NY, pp. 4-1–4-25. Mazo, P., López, L., Restrepo, D., Rios, L., 2010. Síntesis y caracterización de adhesivos reposicionables de poliuretano dispersos en agua, obtenidos a partir de aceite de castor maleinizado. Polim. Cienc. Tecnol. 20, 134–140. Mungroo, R., Pradhan, N.C., Goud, V.V., Dalai, A.K., 2008. Epoxidation of canola oil with hydrogen peroxide catalyzed by acidic ion exchange resin. J. Am. Oil Chem. Soc. 85, 887–896. Rios, L.A., Hoelderich, W.F., Schuster, H., Weckes, P., 2005. Mesoporous and amorphous Ti–silicas on the epoxidation of vegetable oils. J. Catal. 232, 19–26. Rios, L.A., Echeverri, D.A., Franco, A., 2011. Epoxidation of jatropha oil using heterogeneous catalysts suitable for the Prileschajew reaction: acidic resins and immobilized lipase. Appl. Catal. A 394, 132–137. Roetheli, J.C., Carlson, K.D., Kleiman, R., Thompson, A.E., Dierig, D.A., Glaser, L.K., Blase, M.G., Goddell, J., 1991. Lesquerella as a source of hydroxy fatty acids for industrial products. In: USDA-CSRS Office of Agricultural Materials, Growing Industrial Materials Series (unnumbered), Washington, DC. Sonntag, N.O.V., 1979. Reactions of fats and fatty acids. In: Swern, D. (Ed.), Bailey’s Industrial Oil and Fat Products. John Wiley & Sons, NY, pp. 99–175. Tomoda, H., Sugimoto, H., Tani, Y., Watanabe, S., 1998. Characteristic properties of cutting fluid additives derived from the reaction products of hydroxyl fatty acids with some acid anhydrides. J. Surfact Deterg. 1, 533–537. Wallace, J.G., 1978. Encyclopedia of Chemical Technology. Wiley, NY. Wang, H.J., Rong, M.Z., Zhang, M.Q., Hu, J., Chen, H.W., Czigány, T., 2008. Biodegradable foam plastics based on castor oil. Biomacromolecules 9, 615–623. Wiberg, K.B., Saegebarth, K.A., 1957. The mechanisms of permanganate oxidation. IV. Hydroxylation of olefins and related reactions. J. Am. Oil. Chem. Soc. 79, 2822–2824.
Contents lists available at SciVerse ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Hydroxylation of vegetable oils using acidic resins as catalysts ˜ Luis Rios ∗ , David Echeverri, Fernando Cardeno Grupo Procesos Fisicoquímicos Aplicados, Universidad de Antioquia, Sede de Investigación Universitaria, Cra. 53 # 61-30 Medellín, Colombia
a r t i c l e
i n f o
Article history: Received 16 April 2012 Received in revised form 17 July 2012 Accepted 18 July 2012 Keywords: Hydroxylation Vegetable oils Jatropha oil Glycols Polyols Acid resins
a b s t r a c t A new modification of the Prileschajew method to produce hydroxylated vegetable oils using in situ generated peracetic acid and acidic resins, of the sulfonated polystyrene type, as heterogeneous catalysts is reported. Jatropha oil methylesters were chosen as model substrate. Reaction mixtures were characterized by 1 H NMR and gas chromatography. The effect of cross-linking degree of the resins on the conversion and the selectivity to glycols was analyzed. Best results were obtained with Amberlyst 15 catalyst, ca. 100% conversion and 80% selectivity at 57 ◦ C over 24 h, stable through five re-uses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Hydroxy fatty acids/esters are of considerable interest in commercial applications such as lubricants and cosmetics (Maurer and Schmid, 2005). Another important application of hydroxylated oils is the production of dicarboxylic acids such as azelaic acid, via epoxidation/ring opening using H2 O2 and tungsten-containing iso- or heteropoly-compounds followed by subsequent oxidative cleavage of the intermediate diol with, for instance, peracetic acid (Köckritz and Martin, 2011). Besides, they could be used for the production of biodegradable and renewable-feedstocked polymers (Tomoda et al., 1998; Wang et al., 2008; Mazo et al., 2010). Hydroxylated oils occur naturally only in few vegetable oils, most notably castor oil, and some other alternative crops such as lesquerella (Roetheli et al., 1991). Chemically, hydroxy fatty acids have been synthesized by peracid oxidation of unsaturated fatty acids or direct oxidation of the double bond with reagents such as potassium permanganate or hydrogen peroxide/tungstic acid to give vicinal diols (Sonntag, 1979). Wiberg and Saegebarth (1957) studied the hydroxylation of olefins such as oleic acid with potassium permanganate with excellent yield (98%) but the reaction required alkaline pH (pH 12) an a large excess of KMnO4 (1.45–2 mol%). Luong et al. (1967) reported the direct preparation with high yield (70–90%) of threo-1,2-glycols without isolation of
∗ Corresponding author. Tel.: +57 4 2196589, fax: +57 4 2196543. E-mail addresses: [email protected], [email protected], [email protected] (L. Rios). 0926-6690/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2012.07.035
intermediates from oleic acid, methyl oleate and oleyl alcohol by oxidation with a hydrogen peroxide (70%)–tungstic acid system at pH 0–1 and 45–55 ◦ C without solvent. The threo-isomers were formed from intermediate epoxides by in situ hydration with accompanying inversion. Preincorporation of about 2% of the glycol reaction product into oleic acid or methyl oleate speeds up the oxidation reactions markedly and adds to their control and reproducibility. With oleyl alcohol, addition of reaction product is not necessary. Maerker et al. (1964) reported the acid-catalyzed conversion of epoxyesters to hydroxyesters. Esters of 9,10-epoxystearic acid (epoxidized oleic acid), dissolved in 1,4-dioxane, were treated at 15 ◦ C, first with aqueous acid and then with water to convert them to 9,10-dihydroxystearates in high yields. Treatment of methyl 9,10-epoxystearate with diluted (24%) fluoboric acid gave methyl 9,10-dihydroxystearate in 89% yield. Hydration of methyl 9,10-epoxystearate with concentrated H2 SO4 led to the formation of considerable amount of byproducts, principally methyl 9(10)-ketostearate. Side reactions were inhibited by diluting the acid-catalyst. Allylic hydroxylation of double bonds with selenium dioxide has been also reported in the synthesis of hydroxy fatty acids (Knothe et al., 1993). That work shows the potential usefulness of the SeO2 /TBHP system not only in monohydroxylation, but also in allylic dihydroxylation of monounsaturated fatty materials. The allylic dihydroxy products are obtained as erythrolthreo diastereomers. Recently, Daniel et al. (2011) explored two well-known methods for the synthesis of hydroxylated jatropha oil, i.e., a Prilezhaev dihydroxylation using performic acid and an Upjohn dihydroxylation
184
L. Rios et al. / Industrial Crops and Products 43 (2013) 183–187
using osmium tetroxide as catalyst and 4-methylmorpholine Noxide as the oxidant. The Prilezhaev method using in situ generated performic acid from hydrogen peroxide and formic acid gave the trans-vicinal diol, as a colorless oil in 87% yield, essentially quantitative carbon–carbon double bond conversion (96%) and selectivity to diols of about 80% (20% for formyl branches). The cis-vicinal diol was obtained with the Upjohn dihydroxylation, at 60 ◦ C for 18 h; the solid product was isolated in 48% yield and full conversion of the carbon–carbon double bonds to diols was achieved. In a recent study published by our group, sulphonated polystyrene resins, Nafion–silica and immobilized lipase were used as heterogeneous catalysts for the epoxidation of Jatropha oil (Rios et al., 2011). Immobilized lipase showed ca. 100% conversion and 100% epoxide selectivity at 24 h. Amberlite IR-120 was the best heterogeneous catalysts, yielding ca. 90% conversion and 70% epoxide selectivity, both stable through five re-uses. Jatropha oil was chosen as model substrate; this oil is a very interesting raw material for the production of oleochemicals (biodiesel, fatty acids, soap, fatty nitrogenous derivatives, surfactants and detergents, etc.) because it has ca. 80% of unsaturated compounds and it is a non-edible oil. Jatropha curcas has a very high oil content (oil content of jatropha kernel was determined at 63.2%) compared to other plants and can produce 2000 l/ha oil per annum (Akbar et al., 2009). Therefore, this oil could lead to a lower consumption of edible oils for chemical purposes, which is currently a very hot discussion topic. Besides, jatropha plants grow under not very stringent conditions. Owing all these attributes, production of jatropha is currently being undertaken by some developing countries. Herein, we present a new modification of the Prilezhaev method to produce hydroxylated vegetable oils using in situ generated peracetic acid and acidic resins, of the sulfonated polystyrene type, as heterogeneous catalysts. The use of these heterogeneous catalysts makes the purification of products easier and avoids the disposal of salts formed during the final neutralization of soluble acids and technical problems associated with their use, such as corrosion and separation operations; besides, the catalyst could be re-utilized.
2. Material and methods 2.1. Materials Amberlyst 15, Amberlite IR-120 and Dowex 50X2 were purchased from Aldrich. Jatropha oil was provided by a local farmer and converted to the methylesters following a reported procedure (Echeverri et al., 2011). All the other reagents used were of analytical grade purchased from Sigma–Aldrich.
1 H NMR (300 MHz, CDCl ): ␦ (ppm) = 0.81–0.92 (CH CH H 3 3 2 ), 1.15–1.70 ( CH2 ), 2.21–2.38 ( CH2 COO ), 3.36–3.53 ( CHOH), 3.67 ( OCH3 ). 13 C NMR (75 MHz, CDCl ): ␦ (ppm) = 13.58 ( CH 3 C 2 CH3 ), 22.09 ( CH2 CH3 ), 24.46–34.11 ( CH2 ), 50.90 ( OCH3 ), 76.04–76.88 ( CH OH), 173.75 ( COO ). Reaction mixtures were analyzed by gas chromatography with an Agilent 7890A GC equipped with a flame ionization detector and a 60-m FS-SE54 column. Reaction products were identified by GC–MS (Agilent 5975C MSD). Hydroxylated samples were silylated before GC analyses according to a published procedure (Jover et al., 2005). Iodine value (g iodine/100 g simple, ASTM D5554-95), epoxide value (g oxygen/100 g sample, ASTM D1652-04) and hydroxyl value (mg KOH/g sample, ASTM D4274-05) were also measured.
2.4. Catalytic experiments Hydroxylations were carried out in round-bottom glass reactors immersed in a heated oil bath at 57 ◦ C. The agitation was performed using a turbine impeller (2 cm radious, 500 rpm) to prevent attrition of the catalyst. A mixture of jatropha oil methylesters was employed as substrate. Resin-based catalysts were evacuated overnight at 120 ◦ C under high vacuum and kept under argon atmosphere. Jatropha oil methylesters, acetic acid and the solvent (toluene) were mixed for 15 min at the reaction temperature (3.8 g oil/g toluene, 11.9 g oil/g acetic acid)), then the catalyst was added (10 g oil/g catalyst) and the mixture was stirred for another 15 min at the end of which a 10% molar excess of hydrogen peroxide (35% in water) was added at once. As a comparison basis, the epoxidation of the substrate, catalyzed by sulfuric acid, was performed following a procedure already known (Wallace, 1978). Reaction conditions were chosen from previous works (Rios et al., 2005; D’Addieco, 1956; Mungroo et al., 2008; Goud et al., 2007). Effect of resin crosslinking (2, 8 and 20% of divinylbenzene) and catalyst type (resins and H2 SO4 ) were evaluated through a replicate factorial design. Data plotted in the accompanying figures correspond to the means of triplicate experiments with a relative standard deviation <5% in all cases. To investigate the effect of stirring speed on the three-phase reaction system, reactions were carried out over a range of stirring speeds (100–1000 rpm). It was observed that the ethylenic unsaturation conversion increased with the stirring speed, but beyond 500 rpm there was no appreciable change in the rate of reaction. Therefore, all the subsequent experiments were carried out under a stirring speed of 500 rpm to ensure that there was no mass-transfer limitation in the liquid phases. 3. Results and discussion
2.2. Catalyst characterization The total amount of Bronsted acid sites in Amberlyst 15, Amberlite IR-120 and Dowex 50X2 was determined by ion exchange with NaCl solution 1.0 M (10 mL/g of catalyst) and titrating the residual solution with NaOH 0.01 M. 2.3. Reaction mixtures characterization The 1 H NMR and 13 C NMR were recorded in CDCl3 as the solvent using a Mercury-300 BB spectrometer. For 1 H NMR spectra, a total of 16 scans were performed with a relaxation delay of 0.100 s and width of 8103.7 Hz. 320 scans were recorded for 13 C NMR spectra with a relaxation delay of 0.100 s and width of 19607.8 Hz. 1 H NMR and 13 C NMR spectra of hydroxylated jatropha oil methylesters gave the following signals:
Results on the characterization of acidic resins are shown in Table 1. Brönsted acidity is introduced by sulfonyl groups ( SO3 H) anchored to the skeleton of the resin, as shown in Table 1. Because of their chemical composition, the acid strength of all the polystyrene resins is the same. Hammet acidity and NMR of mesityl oxide indicate that these resins are moderately strong acids, similar to the acid strength of a 45% sulfuric acid solution. The amount of acid sites is quite similar in all the resins, in the range 4.3–4.72 meq H+ /g, in accordance with the data supplied by de manufacturer. One important difference among these resins is that Amberlyst 15 is the only one in a macroreticular form while the others are gels. Therefore, Amberlyst 15 keeps its granular form in solution while the other resins swell as a function of their DVD content and the solvent polarity. The composition of the methylesters of jatropha oil, determined by gas chromatography, is shown in Table 2. According to this
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Table 1 Physicochemical properties of the acid resins. Amberlyst 15
C H2
Amberlite IR-120
H C
x
H C C H2
y
HSO3 C C H2 H
Structure Composition
Styrene + 20% divinylbenzene
Styrene + 8% divinylbenzene Ho = −2.2 (Hammet acidity) NMR of mesityl oxide: ı = 32.4 ppm, equivalent to 45% H2 SO4 4.7 4.5 51 Non measurable 40–80 Non measurable 0.600–0.850 0.252
Acid strength Acidity (meq H+ /g) Surface area (m2 /g) Pore size (nm) Particle size (mm)
Table 2 Fatty acid profile of methylesters from jatropha oil. Fatty acid (mehyl ester)
Concentration (wt%)
Myristic Palmitic Palmitoleic Stearic Oleic Linoleic Linolenic Eicosanoic
0.15 17.01 0.99 11.03 34.32 36.11 0.39 0.37
composition, the jatropha oil is a good substrate for the hydroxylation reaction since it is composed of about 80% of unsaturated compounds. The iodine value of jatropha oil methylesters was determined as 95.00 ± 0.07 g iodine/100 g sample. NMR spectrum of the final product is shown in the Fig. 1. Presence of protons connected to the carbons of oxirane ring (around 2.52 ppm) was not detected, which indicates a complete conversion of epoxides. On the other hand, the peaks corresponding to the protons connected to the carbons bearing hydroxyl functionality (carbons 9, 10, 12 and 13) were observed at 3.36–3.53 ppm.
Fig. 1.
Dowex 50X2
1
H NMR spectrum of hydroxylated methylesters.
Styrene + 2% divinylbenzene 4.6 Non measurable Non measurable 0.150
To investigate the effect of resin type, resins with different crosslinking degree, determined by the content of divinylbenzene (DVB) were selected: Dowex 50WX2, Amberlite IR-120 and Amberlyst 15, with 2%, 8% and 20 wt% of DVB content, respectively. In the presence of a polar medium these resins swell and the accessibility to the acidic sites increases. This swelling is reduced by increasing the cross-linking of the resin, i.e. the content of DVB. The effects of the cross-linking degree of the resins on the epoxidation of jatropha oil methylesters are shown in Figs. 2 and 3. From the point of view of conversion, the three catalysts have similar behavior at higher reaction times, but at lower reaction times (less than 10 h) the following order of activity can be observed: Dowex 50X2 > Amberlite IR-120 > Amberlyst15. It is observed that the decrease in the crosslinking of the resins leads to higher conversions. This is explained by the greater accessibility of the acetic acid to the acid sites to form the respective peracid which then, in the homogeneous phase (without the need of acid sites), epoxidizes the unsaturations of the oil. Results on selectivity, shown in Fig. 3, reveal two interesting aspects: (a) with resins that are in gel form, i.e. 2% and 8% DVB, the selectivity to the glycols increases by lowering the cross-linking. Thus, glycols are produced by adding water to the epoxides that
Fig. 2. Effect of resin type on the conversion.
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Fig. 4. Effect of catalyst type, inorganic-soluble vs. organic-solid, on the conversion.
Fig. 3. Effect of resin type on the selectivity to glycols.
are activated (protonate) on the acid sites, and the formation of these glycols is enhanced with low cross-linking. (b) The resin with 20% DVB, which has the highest cross-linking, also shows a high selectivity to glycols. This result can be attributed to the fact that this resin has a macro-reticular structure and therefore it has a high extra-particular surface area on which epoxides can be protonated and opened by water to form glycols. These results indicate that for the hydroxylation of vegetable oils with percarboxylic acids the most important issue to obtain high selectivity is to improve the contact of the formed epoxides with the acid sites of the catalyst. This can be achieved by using resins with low cross-linking degree and/or high external surface area. It is also worth to mention the very high selectivity toward glycols obtained with the resin with the lowest cross-linking, i.e. Dowex 50WX2. According to Figs. 2 and 3, these glycols could be produced with more than 90% selectivity at conversions of ca. 90%. The other identified byproducts were the epoxides; therefore, conversion and selectivity could be further improved by increasing the reaction time and/or catalyst loading, because the epoxides are intermediate products in the synthesis of glycols. Fig. 4 shows that the conversion obtained with H2 SO4 was higher than the obtained with Dowex 50X2, which can be explained by the lowest acid strength of this resin, as shown in Table 2, which is equivalent to 45% H2 SO4 . However, the selectivity toward glycols obtained with H2 SO4 is very poor (less than 5%) (Fig. 5). This low selectivity achieved with sulfuric acid is due to the high insolubility of the epoxidized oil phase in the aqueous phase, where the sulfuric acid is dissolved, which avoids the formation of glycols.Results of re-using (Fig. 6) indicate that Amberlyst 15 can be reused up to five times without significant loss in conversion and selectivity. Amberlyst 15 was chosen for these tests because it has better mechanic stability and better morphology (granular form and higher particle size) for industrial use than Dowex 50X2; besides it has good activity and selectivity for the hydroxylation. Table 3 shows the characteristics of the final product obtained in this investigation. Complete conversion of carbon–carbon double bonds was achieved. Selectivity to glycols of ca. 80% was
Fig. 5. Effect of catalyst type, inorganic-soluble vs. organic-solid, on the selectivity to glycols.
Fig. 6. Conversion and selectivity as a function of the number of reuses for Amberlyst 15.
Table 3 Properties of the final product. Material
Iodine value
Epoxide value
Hydroxyl value
Conversion (titration)b
Selectivity (titration)
Conversion (1 H NMR)
Selectivity (1 H NMR)
JO methylesters Hydroxylated methylestersa
95.00 0
0 0.37
0 325.59
100
77.54
99.03
81.45
a b
Product obtained at 24 h with Dowex 50X2. Theoretical hydroxyl value = 4.42 × iodine value = 419.9.
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also obtained. Results on conversion and selectivity obtained by titration and 1 H NMR agree quite well. It is important to remark that the selectivity could be further improved by increasing the reaction time and/or catalyst loading because the epoxides are intermediate products in the synthesis of glycols. 4. Conclusions Acidic resins of the sulfonated polystyrene type are suitable catalysts for the hydroxylation of vegetable oils, such as jatropha oil methylesters, if their acid sites are easily accessed by the intermediates epoxides formed in the process. Therefore, glycols selectivity strongly depends on the resin cross-linking and morphology. The most crucial feature to favor the formation of glycols is to improve the exposure of the epoxides to the acidic sites of the catalyst, which can be achieved using resins with a low cross-linking and/or with high external surface area. Amberlyst 15 gave ca. 100% conversion and 80% selectivity, stable through five re-uses. Acknowledgements Financial support of “Departamento Administrativo de Ciencia, Tecnología e Innovación-Colciencias” and “Universidad de Antioquia” is acknowledged. References Akbar, E., Yaakob, Z., Kamarudin, S.K., Ismail, M., Salimon, J., 2009. Characteristic and composition of Jatropha curcas oil seed from malaysia and its potential as biodiesel feedstock. Eur. J. Sci. Res. 29, 396–403. D’Addieco, A.A., 1956. E.I. Du Pont de Nemours & Co., Can Patent 531112. Daniel, L., Ardiyanti, A.R., Schuur, B., Manurung, R., Broekhuis, A.A., Heeres, H.J., 2011. Synthesis and properties of highly branched Jatropha curcas L. oil derivatives. Eur. J. Lipid Sci. Technol. 113, 18–30. ˜ F., Rios, L.A., 2011. Glycerolysis of soybean oil with crude Echeverri, D.A., Cardeno, glycerol containing residual alkaline catalysts from biodiesel production. J. Am. Oil. Chem. Soc. 88, 551–557.
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