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Hydrogenation of double bonds in olefin-modified starch
Catalysis Communications 4 (2003) 465–468 www.elsevier.com/locate/catcom
Hydrogenation of double bonds in olefin-modified starch Catherine Pinel *, Cecile Donze, Pierre Gallezot Institut de Recherches sur la Catalyse, 2 avenue Albert Einstein, 69626 Villeurbanne Cedex, France Received 13 June 2003; accepted 10 July 2003 Published online: 31 July 2003
Abstract Catalytic hydrogenation of octadienyl-modified starch was performed with Rh complexes. The nature of solvent played a significant role as it has two distinct actions: swelling of the substrate and solubilization of the catalyst. Complete hydrogenation was performed with Rh/TPPTS-based catalyst at 40 °C and under 30 atm Hydrogen in H2 O/ EtOH(50/10) mixture. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Substituted starch; Catalytic hydrogenation; Water-soluble catalyst; TPPTS
1. Introduction Modified starches found applications in many fields. Introduction of long alkyl chains allowed the preparation of hydrophobic starches that were introduced in paper coating, biodegradable plastics, food stuffs or paint [1]. It was shown that modification in the degree of substitution or the nature of the lateral chain could affect dramatically the properties of the modified starch [2]. In previous works, we developed palladium-catalyzed telomerization of butadiene with starch [3]. Low to moderate degrees of substitution were obtained depending upon experimental conditions. Modified starch with low degrees of substitution (DS < 0.1) were successfully introduced in latex
*
Corresponding author. Fax: +33-4-7244-5399. E-mail address: [email protected] (C. Pinel).
but the corresponding paints did not fulfil the required commercial specifications particularly in term of sheen and colour. Because of the presence of double bonds in the lateral chain of the starch, further chemical modifications are conceivable (see Scheme 1). We considered at this stage, that hydrogenation of the double bonds to linear alkyl chains should influence the physical properties of the modified starch. The main difficulty was due to the insolubility of the substrate in classical solvents e.g., the octadienyl starch was isolated after precipitation in acetone. To our knowledge there are few data in literature on the hydrogenation of C@C bondscontaining insoluble polymers. Iridium catalyst described by Crabtree, [Ir(COD)(PR3 )2 ]PF6 , was efficient for hydrogenation of polybutadiene in the absence of solvent [4]. Most of the time, the wellknown WilkinsonÕs catalyst, Rh(PPh3 )3 Cl, was used to perform hydrogenation of polymers [5,6].
1566-7367/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1566-7367(03)00116-X
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C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
Scheme 1. Catalytic synthesis of substituted starch with saturated alkyl chain.
Depending on the structure of the polymer, 1–50 atm H2 and room temperature to 100 °C were necessary to get full hydrogenation. Based on these data, we focussed on the use of Wilkinson-based catalysts to perform hydrogenation of octadienyl starch.
appeared at 0.85 ppm (corresponding to the terminal CH3 group). The advancement of the reaction was calculated from the ratio of the integration of these two signals.
3. Results and discussion 2. Experimental The potato starch was a gift from Raisio Chemicals (Finland). It contained 80% amylose and 20% amylopectine on a dry basis and had a moisture content of 16% by weight. Octadienyl starch was prepared as described previously [3]. TPPTS was a gift from Rhodia (France). NMR analysis was done on a Bruker 250 MHz machine with d 6 -DMSO as solvent. In a typical experiment, reaction was performed in a 150 ml stainless steel autoclave, equipped with mechanical stirring and heating mantle. Modified starch (4 g) and adequate amount of catalyst were introduced in the autoclave with solvent (60 ml). The mixture was stirred for a few minutes. The autoclave was purged with argon then hydrogen was introduced to the desired pressure. The mixture was heated to the desired temperature for 15 h. After reaction, the autoclave was cooled, degassed and purged with argon. The mixture was poured in 200 ml acetone and stirred for 15 min. The precipitate was filtered, washed with 200 ml acetone, 200 ml dichloromethane and dried under vacuum. The advancement of the reaction was followed by 1 H NMR in d 6 -DMSO. The signal at 2.0 ppm (corresponding to CH2 next to the double bond in the lateral chain) decreased while a new signal
Several parameters were shown to influence the hydrogenation reaction, the first one being the temperature of the preparation of the octadienyl starch. This parameter affects significantly the texture of the solid. When telomerization was performed at 90 °C, gelatinization occurred and the material was difficult to handle compared to that prepared at 50 °C [3]. These modifications can be easily observed on SEM pictures (Fig. 1). Native potatoes starch (Fig. 1(a)) is constituted of oblong smooth granules smaller than 50 lm. After telomerization reaction at 50 °C (Fig. 1(b)), the distribution of the particle size was larger (20–100 lm) but the granules have kept their smooth surface. When telomerization reaction was performed at 90 °C (Fig. 1(c)), large granules were observed (100 lm) showing very rough surface. Both samples, prepared at 50 and 90 °C, were subjected to catalytic hydrogenation in the presence of WilkinsonÕs catalyst (1% weight). The modified starch was suspended in ethanol at room temperature under 30 atm H2 for 15 h. The octadienyl starch prepared at 90 °C (DS ¼ 0.65) was fully converted to octyl starch. Both terminal and substituted double bonds were successively hydrogenated. Under the same reaction conditions, no transformation occurred with the sample prepared at 50 °C (DS ¼ 0.10–0.15). Considering the texture of the granules, we proposed that the
C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
467
Fig. 1. Starch samples: (a) native starch, (b) modified starch prepared at 50 °C, and (c) modified starch prepared at 90 °C.
catalyst and/or hydrogen, diffused much more easily in the sample prepared at 90 °C allowing hydrogenation. In order to perform hydrogenation of sample prepared at 50 °C, the influence of solvent, particularly, different mixtures EtOH/H2 O, was studied. Results are reported in Fig. 2. While no hydrogenation occurred in EtOH, some transformation was observed in the presence of water. A volcano-shaped curve was observed with a maximum conversion at 50–70% of ethanol. We supposed that this optimum was reached when the solid swelled significantly and the catalyst was still soluble in the solvent.
To circumvent the solubility limitation of catalyst in aqueous medium, we turned to the use of water-soluble catalysts. Rhodium-based catalysts such as [RhCl(TPPTS)3 ] were described in literature using TPPTS (tris(m-sulphonatophenyl)phosphine) as ligand [7]. We prepared also the corresponding ruthenium catalyst, [RuCl2 (TPPTS)2 ]2 , for comparison [8] (see Table 1). The hydrogenation of substituted octadienyl starch prepared at 50 °C (DS < 0.1) was performed in H2 O/EtOH (50/10) mixture under 30 atm H2 overnight. Rhodium catalyst was much more efficient than the corresponding ruthenium complex for this transformation. Whatever the reaction conditions, grey solids were obtained after reaction due to the probable degradation of catalysts. Considering the low degree of substitution of starch, we lowered the amount of catalyst. To observe complete hydrogenation of the two double bonds after 15 h
Table 1 Hydrogenation of octadienyl starch with water-soluble catalysts Catalyst
Fig. 2. Influence of EtOH/H2 O ratio on hydrogenation. Reaction conditions: 30 atm H2 ; RT, 12 h; catalyst/starch ¼ 4% (w/w).
[RuCl2 (TPPTS)2 ]2 RhCl(TPPTS)3 RhCl(TPPTS)3 RhCl(TPPTS)3
% Cat (w/w) 8 8 4 0.8
T (°C)
Advancement of the reaction (%)
20 20 20 50
45 100 40 100
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C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
TPPTS-based rhodium complex. Further works must be done to develop more stable water-soluble catalysts. Acknowledgements
Fig. 3. Influence of temperature and pressure on hydrogenation of octadienyl starch.
reaction it was necessary to heat at 50 °C in the presence of 0.8% weight of catalyst. The influence of pressure and temperature on the conversion was studied with the rhodiumbased catalysts; the results are reported on Fig. 3. As expected, the conversion increased with temperature and pressure. Complete hydrogenation was obtained at 40 °C after 12 h using 0.8% Rh catalyst and 30 atm H2 . The hydrogenation reaction was not optimized and alternative catalysts should be developed to improve activity. In conclusion, we have shown that hydrogenation of insoluble polymer was possible using homogeneous catalyst. Because of the specificity of starch granules that swell mainly in water, the hydrogenation was carried out successfully with
We are greatly indebted to the European Commission (The European Commission Fifth Framework Programme within ‘‘Competitive and Sustainable Growth’’ Project No: GRD1-199910200 – High Performance Industrial Polymers based on Modified Starch) for financial support. We are grateful to Paulette Buisson for SEM pictures, and Phil Taylor (ICI Paints, Slough, GB) for helpful discussions and permanent interest in this work. References [1] H. R€ oper, in: H. VanBekkum, H. Roepper, F. Voragen (Eds.), Carbohydrates as Organic Raw Materials III, WileyVCH, New York, 1996, p. 17. [2] J.M. Fang, P.A. Fowler, J. Tomkinson, C.A.S. Hill, Carbohydr. Polym. 47 (2002) 245. [3] C. Donze, C. Pinel, P. Gallezot, P.L. Taylor, Adv. Synth. Catal. 344 (2002) 906. [4] L.R. Gilliom, Macromolecules 22 (1989) 662. [5] N.A. Mohammadi, G.L. Rempel, Macromolecules 20 (1987) 2362. [6] Y. Doi, A. Yano, K. Soga, D.R. Burfield, Macromolecules 19 (1989) 2409. [7] C. Larpent, R. Dabard, H. Patin, Tetrahedron Lett. 28 (1987) 2507. [8] E. Fache, C. Santini, F. Senocq, J.M. Basset, J. Mol. Catal. 72 (1992) 331.
Hydrogenation of double bonds in olefin-modified starch Catherine Pinel *, Cecile Donze, Pierre Gallezot Institut de Recherches sur la Catalyse, 2 avenue Albert Einstein, 69626 Villeurbanne Cedex, France Received 13 June 2003; accepted 10 July 2003 Published online: 31 July 2003
Abstract Catalytic hydrogenation of octadienyl-modified starch was performed with Rh complexes. The nature of solvent played a significant role as it has two distinct actions: swelling of the substrate and solubilization of the catalyst. Complete hydrogenation was performed with Rh/TPPTS-based catalyst at 40 °C and under 30 atm Hydrogen in H2 O/ EtOH(50/10) mixture. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Substituted starch; Catalytic hydrogenation; Water-soluble catalyst; TPPTS
1. Introduction Modified starches found applications in many fields. Introduction of long alkyl chains allowed the preparation of hydrophobic starches that were introduced in paper coating, biodegradable plastics, food stuffs or paint [1]. It was shown that modification in the degree of substitution or the nature of the lateral chain could affect dramatically the properties of the modified starch [2]. In previous works, we developed palladium-catalyzed telomerization of butadiene with starch [3]. Low to moderate degrees of substitution were obtained depending upon experimental conditions. Modified starch with low degrees of substitution (DS < 0.1) were successfully introduced in latex
*
Corresponding author. Fax: +33-4-7244-5399. E-mail address: [email protected] (C. Pinel).
but the corresponding paints did not fulfil the required commercial specifications particularly in term of sheen and colour. Because of the presence of double bonds in the lateral chain of the starch, further chemical modifications are conceivable (see Scheme 1). We considered at this stage, that hydrogenation of the double bonds to linear alkyl chains should influence the physical properties of the modified starch. The main difficulty was due to the insolubility of the substrate in classical solvents e.g., the octadienyl starch was isolated after precipitation in acetone. To our knowledge there are few data in literature on the hydrogenation of C@C bondscontaining insoluble polymers. Iridium catalyst described by Crabtree, [Ir(COD)(PR3 )2 ]PF6 , was efficient for hydrogenation of polybutadiene in the absence of solvent [4]. Most of the time, the wellknown WilkinsonÕs catalyst, Rh(PPh3 )3 Cl, was used to perform hydrogenation of polymers [5,6].
1566-7367/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1566-7367(03)00116-X
466
C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
Scheme 1. Catalytic synthesis of substituted starch with saturated alkyl chain.
Depending on the structure of the polymer, 1–50 atm H2 and room temperature to 100 °C were necessary to get full hydrogenation. Based on these data, we focussed on the use of Wilkinson-based catalysts to perform hydrogenation of octadienyl starch.
appeared at 0.85 ppm (corresponding to the terminal CH3 group). The advancement of the reaction was calculated from the ratio of the integration of these two signals.
3. Results and discussion 2. Experimental The potato starch was a gift from Raisio Chemicals (Finland). It contained 80% amylose and 20% amylopectine on a dry basis and had a moisture content of 16% by weight. Octadienyl starch was prepared as described previously [3]. TPPTS was a gift from Rhodia (France). NMR analysis was done on a Bruker 250 MHz machine with d 6 -DMSO as solvent. In a typical experiment, reaction was performed in a 150 ml stainless steel autoclave, equipped with mechanical stirring and heating mantle. Modified starch (4 g) and adequate amount of catalyst were introduced in the autoclave with solvent (60 ml). The mixture was stirred for a few minutes. The autoclave was purged with argon then hydrogen was introduced to the desired pressure. The mixture was heated to the desired temperature for 15 h. After reaction, the autoclave was cooled, degassed and purged with argon. The mixture was poured in 200 ml acetone and stirred for 15 min. The precipitate was filtered, washed with 200 ml acetone, 200 ml dichloromethane and dried under vacuum. The advancement of the reaction was followed by 1 H NMR in d 6 -DMSO. The signal at 2.0 ppm (corresponding to CH2 next to the double bond in the lateral chain) decreased while a new signal
Several parameters were shown to influence the hydrogenation reaction, the first one being the temperature of the preparation of the octadienyl starch. This parameter affects significantly the texture of the solid. When telomerization was performed at 90 °C, gelatinization occurred and the material was difficult to handle compared to that prepared at 50 °C [3]. These modifications can be easily observed on SEM pictures (Fig. 1). Native potatoes starch (Fig. 1(a)) is constituted of oblong smooth granules smaller than 50 lm. After telomerization reaction at 50 °C (Fig. 1(b)), the distribution of the particle size was larger (20–100 lm) but the granules have kept their smooth surface. When telomerization reaction was performed at 90 °C (Fig. 1(c)), large granules were observed (100 lm) showing very rough surface. Both samples, prepared at 50 and 90 °C, were subjected to catalytic hydrogenation in the presence of WilkinsonÕs catalyst (1% weight). The modified starch was suspended in ethanol at room temperature under 30 atm H2 for 15 h. The octadienyl starch prepared at 90 °C (DS ¼ 0.65) was fully converted to octyl starch. Both terminal and substituted double bonds were successively hydrogenated. Under the same reaction conditions, no transformation occurred with the sample prepared at 50 °C (DS ¼ 0.10–0.15). Considering the texture of the granules, we proposed that the
C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
467
Fig. 1. Starch samples: (a) native starch, (b) modified starch prepared at 50 °C, and (c) modified starch prepared at 90 °C.
catalyst and/or hydrogen, diffused much more easily in the sample prepared at 90 °C allowing hydrogenation. In order to perform hydrogenation of sample prepared at 50 °C, the influence of solvent, particularly, different mixtures EtOH/H2 O, was studied. Results are reported in Fig. 2. While no hydrogenation occurred in EtOH, some transformation was observed in the presence of water. A volcano-shaped curve was observed with a maximum conversion at 50–70% of ethanol. We supposed that this optimum was reached when the solid swelled significantly and the catalyst was still soluble in the solvent.
To circumvent the solubility limitation of catalyst in aqueous medium, we turned to the use of water-soluble catalysts. Rhodium-based catalysts such as [RhCl(TPPTS)3 ] were described in literature using TPPTS (tris(m-sulphonatophenyl)phosphine) as ligand [7]. We prepared also the corresponding ruthenium catalyst, [RuCl2 (TPPTS)2 ]2 , for comparison [8] (see Table 1). The hydrogenation of substituted octadienyl starch prepared at 50 °C (DS < 0.1) was performed in H2 O/EtOH (50/10) mixture under 30 atm H2 overnight. Rhodium catalyst was much more efficient than the corresponding ruthenium complex for this transformation. Whatever the reaction conditions, grey solids were obtained after reaction due to the probable degradation of catalysts. Considering the low degree of substitution of starch, we lowered the amount of catalyst. To observe complete hydrogenation of the two double bonds after 15 h
Table 1 Hydrogenation of octadienyl starch with water-soluble catalysts Catalyst
Fig. 2. Influence of EtOH/H2 O ratio on hydrogenation. Reaction conditions: 30 atm H2 ; RT, 12 h; catalyst/starch ¼ 4% (w/w).
[RuCl2 (TPPTS)2 ]2 RhCl(TPPTS)3 RhCl(TPPTS)3 RhCl(TPPTS)3
% Cat (w/w) 8 8 4 0.8
T (°C)
Advancement of the reaction (%)
20 20 20 50
45 100 40 100
468
C. Pinel et al. / Catalysis Communications 4 (2003) 465–468
TPPTS-based rhodium complex. Further works must be done to develop more stable water-soluble catalysts. Acknowledgements
Fig. 3. Influence of temperature and pressure on hydrogenation of octadienyl starch.
reaction it was necessary to heat at 50 °C in the presence of 0.8% weight of catalyst. The influence of pressure and temperature on the conversion was studied with the rhodiumbased catalysts; the results are reported on Fig. 3. As expected, the conversion increased with temperature and pressure. Complete hydrogenation was obtained at 40 °C after 12 h using 0.8% Rh catalyst and 30 atm H2 . The hydrogenation reaction was not optimized and alternative catalysts should be developed to improve activity. In conclusion, we have shown that hydrogenation of insoluble polymer was possible using homogeneous catalyst. Because of the specificity of starch granules that swell mainly in water, the hydrogenation was carried out successfully with
We are greatly indebted to the European Commission (The European Commission Fifth Framework Programme within ‘‘Competitive and Sustainable Growth’’ Project No: GRD1-199910200 – High Performance Industrial Polymers based on Modified Starch) for financial support. We are grateful to Paulette Buisson for SEM pictures, and Phil Taylor (ICI Paints, Slough, GB) for helpful discussions and permanent interest in this work. References [1] H. R€ oper, in: H. VanBekkum, H. Roepper, F. Voragen (Eds.), Carbohydrates as Organic Raw Materials III, WileyVCH, New York, 1996, p. 17. [2] J.M. Fang, P.A. Fowler, J. Tomkinson, C.A.S. Hill, Carbohydr. Polym. 47 (2002) 245. [3] C. Donze, C. Pinel, P. Gallezot, P.L. Taylor, Adv. Synth. Catal. 344 (2002) 906. [4] L.R. Gilliom, Macromolecules 22 (1989) 662. [5] N.A. Mohammadi, G.L. Rempel, Macromolecules 20 (1987) 2362. [6] Y. Doi, A. Yano, K. Soga, D.R. Burfield, Macromolecules 19 (1989) 2409. [7] C. Larpent, R. Dabard, H. Patin, Tetrahedron Lett. 28 (1987) 2507. [8] E. Fache, C. Santini, F. Senocq, J.M. Basset, J. Mol. Catal. 72 (1992) 331.