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Hydrogenation of pyrrole derivatives. II. Hydrogenations over supported noble metal catalysts
/
A PP LE ILY DSS CA TA I A: GENERAL
ELSEVIER
Applied Catalysis A: General 147 (1996) 407-414
Hydrogenation of pyrrole derivatives. II. Hydrogenations over supported noble metal catalysts L4szl6 Hegedtis a,*, Tibor M4th6 b, Antal Tungler a a Department of Organic Chemical Technology, Technical University of Budapest, H-1521 Budapest, Mi~egyetem, P.O. Box 91, Hungary b Research Group for Organic Chemical Technology, Hungarian Academy of Sciences, Technical Universio" of Budapest, H-1521 Budapest, Mi~egyetem, P.O. Box 91, Hungary Received 17 April 1996; revised 3 June 1996; accepted 3 June 1996
Abstract The heterogeneous catalytic hydrogenation of 1-methyl-2-pyrroleethanol resulted in 1-methyl2-pyrrolidineethanol, an important and valuable pharmaceutical intermediate. Various noble metal catalysts on different supports have been screened. The best results were achieved with a carbon supported rhodium catalyst, in non-acidic medium, under mild reaction conditions (6 bar, room temperature). Ruthenium on carbon also showed high activity in this hydrogenation. Keywords: Heterogeneous catalytic hydrogenation; 1-Methyl-2-pyrrolidineethanol; Rhodium; Ruthenium
1. Introduction In our previous study [1] we reported the heterogeneous catalytic hydrogenation of 1-methyl-2-pyrroleethanol 1 to 1-methyl-2-pyrrolidineethanol 2 in nonacidic medium over palladium (Scheme 1). Earlier we described the hydrogenation methods of pyrroles in presence of different catalysts in detail [1]. Since remarkable results were achieved with supported rhodium and ruthenium catalysts only [2]; now the hydrogenations over these catalysts are shown on several examples.
* Corresponding author. Tel.: (+ 36-1) 4631261 ; fax: ( + 36-1) 4633648; e-mail: [email protected]. 0926-860X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PH S 0 9 2 6 - 8 6 0 X ( 9 6 ) 0 0 2 17-7
408
L. Hegedi~s et al. / Applied Catalysis A: General 147 (1996) 407-414
~ " 'I~ / " ~ O H CH3 1
H2 Catalyst, Solvents
~ ' ~ O H [
CH3 2
Scheme 1. The heterogeneouscatalytichydrogenationof 1-methyl-2-pyrroleethanolto l-methyl-2-pyrrolidineethanol. Using rhodium on alumina in the hydrogenation of pyrrole derivatives good results were obtained under mild reaction conditions, but only in acidic medium. For example, 2,5-dimethyl-pyrrole was hydrogenated to 2,5-dimethyl-pyrrolidine in acetic acid, over 5% Rh/A1203 (7% with respect to substrate), at 20°C and 3 bar with 70% yield [3]. The hydrogenation of 2-(ethoxycarbonyl-methyl)pyrrole gave the corresponding pyrrolidine derivative in the presence of 5% Rh/AI203 with 62% yield [4]. Supported ruthenium catalysts (e.g. Ru/AI203) can saturate the pyrrole ring with over 90% conversion, but at comparatively high temperatures (130-150°C) and pressures (25-30 bar). 2,5-Dimethylpyrrole was converted over Ru/AI203 catalyst (3% by weight of substrate) at 130°C and 35 bar, in water to 2,5-dimethyl-pyrrolidine with 85-98% conversion [5,6]. In the present study the hydrogenation of 1 over different noble metal catalysts is described. The influence of these catalysts on the conversion and the rate of the hydrogenation is discussed.
2. Experimental 2.1. Materials
The 1-methyl-2-pyrroleethanol (purity 97% by GC) was prepared from 1-methylpyrrole in a five-step synthesis developed in our laboratory. The solvents, methanol and n-hexane, were supplied by Reanal (Fine Chemical Comp.), in p.a. grade. The catalysts were partly commercial products: 5% P d / C Selcat [7] (Finomvegyszer Fine Chemical Comp.), 5% Rh/A1203 (Degussa) and 5% P t / C (Heraeus). 5% R h / C , 5% R u / C and 5% I r / C catalysts were prepared as follows. The calculated amount of the catalyst precursors (RhC13.3H20, (NH4)2RuC16, (NH4)zIrC16) was added to the aqueous suspension of the support. The pH value of the solution was adjusted to 10-11 by addition of KOH. The suspension was boiled for 1 h then HCOONa was added to the boiling mixture. After half an hour the suspension was cooled, the catalyst was filtered and washed with distilled water.
L. Hegediis et aL /Applied Catalysis A: General 147 (1996) 407-414
409
2.2. Hydrogenations The catalytic hydrogenations were carried out in a 0.5 dm 3 autoclave (Autoclave Engineers) equipped with a magnetically driven turbine stirrer and an automatic gas-controlling unit, at 80°C or room temperature. The reaction mixtures were worked up and purified in the same way as described in Ref. [1]. The reaction mixtures and the products were analyzed by GC. The product was identified by 1H-NMR measurements.
2.3. Analysis Gas-chromatographic analyses were carried out using 1 m column, filled with Carbowax ® 20 M 5% on Chromosorb W 100-120 mesh, at 190°C with FID.
3. Results and discussion
3.1. Effect of catalytic metals The effect of catalytic metals on the conversion and the initial rate of the hydrogenation of 1 ( % ) in n-hexane/methanol mixture is depicted in Fig. 1.
100
100 / 80 V~
!
i //
60• //
40 -~ • //
2O -~ ~.onversion [%1 102 [nl 1-12/gcat. h]
/ Pd
Pt
Ru
Ir
Rh
* w i t h o u t 102 Fig. 1. Effect of catalytic metals on the conversion and the initial rate of the hydrogenation of 1-methyl-2-pyrroleethanol. Conditions: carbon support, 10.0 g substrate, 2.0 g catalyst, 250 ml n-hexane and 60 ml methanol, 6 bar, 80°C, reaction time 6 h.
L. Hegediis et al. / Applied Catalysis A: General 147 (1996) 407-414
410
Using platinum and iridium on carbon the saturation of the pyrrole ring was very slow and stopped at low conversions. Contrary to the low activity of these catalysts the carbon supported ruthenium and palladium had an almost similar good activity. The highest rate and conversion values were observed using rhodium on carbon. This result is in agreement with the literature data [2] that supported rhodium is the most active catalyst in the hydrogenation of nitrogen containing heterocycles. On the basis of our hydrogenation results it can be stated that the closely related noble metals such as rhodium, ruthenium and palladium are the most active catalytic metals in saturation of the pyrrole ring of 1, while platinum and iridium are not suitable for this hydrogenation.
3.2. Investigation of rhodium catalysts The activity of rhodium on carbon was outstandingly high at 80°C, therefore the influence of temperature on the activity of R h / C was investigated. As is shown in Fig. 2. the hydrogenation was also completed in n-hexane/methanol at 30°C, but it required longer reaction time (ca. 6 h). Nevertheless, this hydrogenation was faster at 30°C than the reaction with palladium on carbon at 80°C. There are further differences between rhodium and palladium: the reaction rate
c o n v e r s i o n [%] 100
80
60
40
20
0 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
time [h] Fig. 2. Conversion of 1-methyl-2-pyrroleethanol vs. time over rhodium on carbon. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar.
L. Hegediis et al. / Applied Catalysis A: General 147 (1996) 407-414
411
Table 1 Comparison of the activities of rhodium on carbon, palladium on carbon and rhodium on alumina in the hydrogenation of 1-methyl-2-pyrroleethanol No.
1 2 3
Catalyst type
5% R h / C 5% P d / C 5% R h / A I 2 0 3
Conversion (%)
u 0 . 102 (nl H 2 / g cat. h)
Hexane/MeOH
MeOH
Hexane/MeOH
MeOH
100 a,b 80.0 b 78.9 a, 100 b
100 a 44.0 b 90.8 a
134 a, 1793 b 42.9 b 32.3 ~, 537.7 b
269 " 35.8 t, 43.0 ~
Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar, a 30oc, b 80oc, reaction time: 6 h.
over rhodium was higher in methanol than in the mixture of n-hexane and methanol (Table 1). The effect of the temperature on the conversion and the rate of the hydrogenation of 1 is summarized in Table 2. Decreasing the reaction temperature from 80°C to 30°C (catalyst/substrate ratio = 0.05) the conversion of 1 decreased significantly and the hydrogen uptake became much slower. At 50°C the rate of the hydrogenation was higher than at 30°C, but the reaction did not take place completely. At 80°C the conversion has already reached 100%. The influence of lower catalyst/substrate ratios (0.03 and 0.01) on the conversion is shown in Fig. 3. The saturation of 1 was not completed even at 80°C; the hydrogen uptakes stopped at lower conversions (90% and 35.5%), presumably because of the poisoning of the catalyst. According to these results, this substrate can be hydrogenated with 100% conversion and appropriate rate over R h / C , when the reaction temperature is 80°C and the catalyst/substrate ratio is 0.05, at least. Conversions of 1 over rhodium on alumina are depicted in Fig. 4. Comparing the carbon supported rhodium with the supported alumina under similar reaction conditions, there is no significant difference between the activity of these catalysts at 80°C. However, this difference became more significant when the reaction temperature was decreased to 30°C, namely rhodium on alumina showed much lower activity than rhodium on carbon at this temperature. On the other hand, the hydrogen uptake of 1 over Rh/A1203 was faster in methanol than in n-hexane/methanol mixture, similarly to R h / C (Table 1).
Table 2 Influence of the temperature on the conversion and the initial rate of the hydrogenation of 1-methyl-2-pyrroleethanol No.
Reaction temperature (°C)
c o • 102 (nl H 2 / g cat. h)
Conversion (%)
1 2 3
30 50 80
165 394 2001
32.6 75.8 100
Conditions: 10.0 g substrate, 0.5 g R h / C catalyst, 300 ml methanol, 6 bar, reaction time: 6 h.
412
L. Heged~s et al. /Applied Catalysis A: General 147 (1996) 407-414 conversion [%]
1O0
t
,f~
80
~1~
~1(
~K
)1(
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
40
2O
0
0
1
2
3
4
5
6
7
8
time [h] Fig. 3. Conversion of 1-methyl-2-pyrroleethanol vs. time over R h / C , at lower catalyst/substrate ratios. Conditions: 10.0 g substrate, 300 ml methanol, 6 bar, 80°C.
conversion [%] 1O0
80
•
60
40
20
0 0
I
2
3
4
5
6
7
8
9
time [h] Fig. 4. Conversion of 1-methyl-2-pyrroleethanol vs. time over rhodium on alumina. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar.
L. Hegediis et al. / Applied Catalysis A." General 147 (1996) 407-414
413
conversion [%] 1O0
80
60
40
20
0 0
1
2
3
4
5
6
7
8
9
time [h] Fig. 5. Conversion of 1-methyl-2-pyrroleethanol vs. time over ruthenium on carbon. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, ph.: prehydrogenated catalyst, 80°C, 6 bar.
The activity of these rhodium catalysts was not strongly dependent on their supports, contrary to palladium described previously [1], i.e. the main factor determining reaction rate is the rhodium metal itself in this hydrogenation. 3.3. Hydrogenations o v e r ruthenium on carbon
Hydrogen uptakes in the carbon supported ruthenium mediated hydrogenations of 1 are shown in Fig. 5. It can be observed that the conversion curve has an induction period, which can be eliminated by 1 h prehydrogenation of the catalyst at room temperature. Similarly to the supported rhodium catalysts, the hydrogenation of 1 over R u / C was also faster in methanol than in the mixture of n-hexane and methanol. Ruthenium on carbon is highly active in methanol, so applying the two-phase n-hexane/methanol mixture is not necessary in order to increase its activity, as was done when using palladium on carbon.
4. Conclusions The 1-methyl-2-pyrroleethanol was converted to the corresponding pyrrolidine derivative in non-acidic medium, over supported noble metal catalysts,
414
L. Hegedfis et aL / Applied Catalysis A: General 147 (1996) 407-414
under mild reaction conditions with high conversion. The best results were obtained with rhodium on carbon in methanol, under low hydrogen pressure (6 bar) and at room temperature. The activity of the different supported rhodium catalysts did not strongly depend on their supports (active C, A1203), contrary to palladium. Ruthenium on carbon had also high activity at 80°C, similarly to P d / C , but its activity was higher in methanol than that of palladium on carbon in n-hexane/methanol. On the basis of these results, the fact [2] that pyrrole and its derivatives are considered to be the most poisonous heterocycles in catalytic hydrogenation reactions, is not acceptable any more. The saturation of the pyrrol ring takes place relatively easily, besides in these hydrogenations it is unnecessary to use acids to eliminate the strong poisoning of the catalyst. This poisoning caused by secondary or tertiary N can be decreased significantly applying the appropriate solvents or solvent mixtures. In addition, taking into consideration the price of different noble metals, it can be stated that the application of R u / C and P d / C catalysts, under these reaction conditions in the catalytic hydrogenation of 1-methyl-2-pyrroleethanol, is also economical on an industrial scale.
References [1] [2] [3] [4] [5] [6] [7]
L. Heged~is, T. Mfith~ and A. Tungler, Appl. Catal. A, 143 (1996) 309. M. Freifelder, Practical Catalytic Hydrogenation, Wiley, New York, 1971, p. 577. C.G. Overberger, L.C. Palmer, B.S. Marks and N.R. Byrd, J. Am. Chem. Soc., 77 (1955) 4100. R. Adams, S. Miyano and M.D. Nair, J. Am. Chem. Soc., 83 (1961) 3323. H.N. Benedict and R.S. De Pablo, U.S. Patent 3 766 089 (1972). L.L. Benezra, R.S. De Pablo and E.R. Osgood, Ger. Often. 2 344 509 (1973). T. Mfith~, A. Tungler and J. Petr6, U.S. Patent 4 361 500 (1982).
A PP LE ILY DSS CA TA I A: GENERAL
ELSEVIER
Applied Catalysis A: General 147 (1996) 407-414
Hydrogenation of pyrrole derivatives. II. Hydrogenations over supported noble metal catalysts L4szl6 Hegedtis a,*, Tibor M4th6 b, Antal Tungler a a Department of Organic Chemical Technology, Technical University of Budapest, H-1521 Budapest, Mi~egyetem, P.O. Box 91, Hungary b Research Group for Organic Chemical Technology, Hungarian Academy of Sciences, Technical Universio" of Budapest, H-1521 Budapest, Mi~egyetem, P.O. Box 91, Hungary Received 17 April 1996; revised 3 June 1996; accepted 3 June 1996
Abstract The heterogeneous catalytic hydrogenation of 1-methyl-2-pyrroleethanol resulted in 1-methyl2-pyrrolidineethanol, an important and valuable pharmaceutical intermediate. Various noble metal catalysts on different supports have been screened. The best results were achieved with a carbon supported rhodium catalyst, in non-acidic medium, under mild reaction conditions (6 bar, room temperature). Ruthenium on carbon also showed high activity in this hydrogenation. Keywords: Heterogeneous catalytic hydrogenation; 1-Methyl-2-pyrrolidineethanol; Rhodium; Ruthenium
1. Introduction In our previous study [1] we reported the heterogeneous catalytic hydrogenation of 1-methyl-2-pyrroleethanol 1 to 1-methyl-2-pyrrolidineethanol 2 in nonacidic medium over palladium (Scheme 1). Earlier we described the hydrogenation methods of pyrroles in presence of different catalysts in detail [1]. Since remarkable results were achieved with supported rhodium and ruthenium catalysts only [2]; now the hydrogenations over these catalysts are shown on several examples.
* Corresponding author. Tel.: (+ 36-1) 4631261 ; fax: ( + 36-1) 4633648; e-mail: [email protected]. 0926-860X/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PH S 0 9 2 6 - 8 6 0 X ( 9 6 ) 0 0 2 17-7
408
L. Hegedi~s et al. / Applied Catalysis A: General 147 (1996) 407-414
~ " 'I~ / " ~ O H CH3 1
H2 Catalyst, Solvents
~ ' ~ O H [
CH3 2
Scheme 1. The heterogeneouscatalytichydrogenationof 1-methyl-2-pyrroleethanolto l-methyl-2-pyrrolidineethanol. Using rhodium on alumina in the hydrogenation of pyrrole derivatives good results were obtained under mild reaction conditions, but only in acidic medium. For example, 2,5-dimethyl-pyrrole was hydrogenated to 2,5-dimethyl-pyrrolidine in acetic acid, over 5% Rh/A1203 (7% with respect to substrate), at 20°C and 3 bar with 70% yield [3]. The hydrogenation of 2-(ethoxycarbonyl-methyl)pyrrole gave the corresponding pyrrolidine derivative in the presence of 5% Rh/AI203 with 62% yield [4]. Supported ruthenium catalysts (e.g. Ru/AI203) can saturate the pyrrole ring with over 90% conversion, but at comparatively high temperatures (130-150°C) and pressures (25-30 bar). 2,5-Dimethylpyrrole was converted over Ru/AI203 catalyst (3% by weight of substrate) at 130°C and 35 bar, in water to 2,5-dimethyl-pyrrolidine with 85-98% conversion [5,6]. In the present study the hydrogenation of 1 over different noble metal catalysts is described. The influence of these catalysts on the conversion and the rate of the hydrogenation is discussed.
2. Experimental 2.1. Materials
The 1-methyl-2-pyrroleethanol (purity 97% by GC) was prepared from 1-methylpyrrole in a five-step synthesis developed in our laboratory. The solvents, methanol and n-hexane, were supplied by Reanal (Fine Chemical Comp.), in p.a. grade. The catalysts were partly commercial products: 5% P d / C Selcat [7] (Finomvegyszer Fine Chemical Comp.), 5% Rh/A1203 (Degussa) and 5% P t / C (Heraeus). 5% R h / C , 5% R u / C and 5% I r / C catalysts were prepared as follows. The calculated amount of the catalyst precursors (RhC13.3H20, (NH4)2RuC16, (NH4)zIrC16) was added to the aqueous suspension of the support. The pH value of the solution was adjusted to 10-11 by addition of KOH. The suspension was boiled for 1 h then HCOONa was added to the boiling mixture. After half an hour the suspension was cooled, the catalyst was filtered and washed with distilled water.
L. Hegediis et aL /Applied Catalysis A: General 147 (1996) 407-414
409
2.2. Hydrogenations The catalytic hydrogenations were carried out in a 0.5 dm 3 autoclave (Autoclave Engineers) equipped with a magnetically driven turbine stirrer and an automatic gas-controlling unit, at 80°C or room temperature. The reaction mixtures were worked up and purified in the same way as described in Ref. [1]. The reaction mixtures and the products were analyzed by GC. The product was identified by 1H-NMR measurements.
2.3. Analysis Gas-chromatographic analyses were carried out using 1 m column, filled with Carbowax ® 20 M 5% on Chromosorb W 100-120 mesh, at 190°C with FID.
3. Results and discussion
3.1. Effect of catalytic metals The effect of catalytic metals on the conversion and the initial rate of the hydrogenation of 1 ( % ) in n-hexane/methanol mixture is depicted in Fig. 1.
100
100 / 80 V~
!
i //
60• //
40 -~ • //
2O -~ ~.onversion [%1 102 [nl 1-12/gcat. h]
/ Pd
Pt
Ru
Ir
Rh
* w i t h o u t 102 Fig. 1. Effect of catalytic metals on the conversion and the initial rate of the hydrogenation of 1-methyl-2-pyrroleethanol. Conditions: carbon support, 10.0 g substrate, 2.0 g catalyst, 250 ml n-hexane and 60 ml methanol, 6 bar, 80°C, reaction time 6 h.
L. Hegediis et al. / Applied Catalysis A: General 147 (1996) 407-414
410
Using platinum and iridium on carbon the saturation of the pyrrole ring was very slow and stopped at low conversions. Contrary to the low activity of these catalysts the carbon supported ruthenium and palladium had an almost similar good activity. The highest rate and conversion values were observed using rhodium on carbon. This result is in agreement with the literature data [2] that supported rhodium is the most active catalyst in the hydrogenation of nitrogen containing heterocycles. On the basis of our hydrogenation results it can be stated that the closely related noble metals such as rhodium, ruthenium and palladium are the most active catalytic metals in saturation of the pyrrole ring of 1, while platinum and iridium are not suitable for this hydrogenation.
3.2. Investigation of rhodium catalysts The activity of rhodium on carbon was outstandingly high at 80°C, therefore the influence of temperature on the activity of R h / C was investigated. As is shown in Fig. 2. the hydrogenation was also completed in n-hexane/methanol at 30°C, but it required longer reaction time (ca. 6 h). Nevertheless, this hydrogenation was faster at 30°C than the reaction with palladium on carbon at 80°C. There are further differences between rhodium and palladium: the reaction rate
c o n v e r s i o n [%] 100
80
60
40
20
0 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
time [h] Fig. 2. Conversion of 1-methyl-2-pyrroleethanol vs. time over rhodium on carbon. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar.
L. Hegediis et al. / Applied Catalysis A: General 147 (1996) 407-414
411
Table 1 Comparison of the activities of rhodium on carbon, palladium on carbon and rhodium on alumina in the hydrogenation of 1-methyl-2-pyrroleethanol No.
1 2 3
Catalyst type
5% R h / C 5% P d / C 5% R h / A I 2 0 3
Conversion (%)
u 0 . 102 (nl H 2 / g cat. h)
Hexane/MeOH
MeOH
Hexane/MeOH
MeOH
100 a,b 80.0 b 78.9 a, 100 b
100 a 44.0 b 90.8 a
134 a, 1793 b 42.9 b 32.3 ~, 537.7 b
269 " 35.8 t, 43.0 ~
Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar, a 30oc, b 80oc, reaction time: 6 h.
over rhodium was higher in methanol than in the mixture of n-hexane and methanol (Table 1). The effect of the temperature on the conversion and the rate of the hydrogenation of 1 is summarized in Table 2. Decreasing the reaction temperature from 80°C to 30°C (catalyst/substrate ratio = 0.05) the conversion of 1 decreased significantly and the hydrogen uptake became much slower. At 50°C the rate of the hydrogenation was higher than at 30°C, but the reaction did not take place completely. At 80°C the conversion has already reached 100%. The influence of lower catalyst/substrate ratios (0.03 and 0.01) on the conversion is shown in Fig. 3. The saturation of 1 was not completed even at 80°C; the hydrogen uptakes stopped at lower conversions (90% and 35.5%), presumably because of the poisoning of the catalyst. According to these results, this substrate can be hydrogenated with 100% conversion and appropriate rate over R h / C , when the reaction temperature is 80°C and the catalyst/substrate ratio is 0.05, at least. Conversions of 1 over rhodium on alumina are depicted in Fig. 4. Comparing the carbon supported rhodium with the supported alumina under similar reaction conditions, there is no significant difference between the activity of these catalysts at 80°C. However, this difference became more significant when the reaction temperature was decreased to 30°C, namely rhodium on alumina showed much lower activity than rhodium on carbon at this temperature. On the other hand, the hydrogen uptake of 1 over Rh/A1203 was faster in methanol than in n-hexane/methanol mixture, similarly to R h / C (Table 1).
Table 2 Influence of the temperature on the conversion and the initial rate of the hydrogenation of 1-methyl-2-pyrroleethanol No.
Reaction temperature (°C)
c o • 102 (nl H 2 / g cat. h)
Conversion (%)
1 2 3
30 50 80
165 394 2001
32.6 75.8 100
Conditions: 10.0 g substrate, 0.5 g R h / C catalyst, 300 ml methanol, 6 bar, reaction time: 6 h.
412
L. Heged~s et al. /Applied Catalysis A: General 147 (1996) 407-414 conversion [%]
1O0
t
,f~
80
~1~
~1(
~K
)1(
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
40
2O
0
0
1
2
3
4
5
6
7
8
time [h] Fig. 3. Conversion of 1-methyl-2-pyrroleethanol vs. time over R h / C , at lower catalyst/substrate ratios. Conditions: 10.0 g substrate, 300 ml methanol, 6 bar, 80°C.
conversion [%] 1O0
80
•
60
40
20
0 0
I
2
3
4
5
6
7
8
9
time [h] Fig. 4. Conversion of 1-methyl-2-pyrroleethanol vs. time over rhodium on alumina. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, 6 bar.
L. Hegediis et al. / Applied Catalysis A." General 147 (1996) 407-414
413
conversion [%] 1O0
80
60
40
20
0 0
1
2
3
4
5
6
7
8
9
time [h] Fig. 5. Conversion of 1-methyl-2-pyrroleethanol vs. time over ruthenium on carbon. Conditions: 10.0 g substrate, 2.0 g catalyst, hexane/MeOH: 250 ml n-hexane and 60 ml methanol, MeOH: 300 ml methanol, ph.: prehydrogenated catalyst, 80°C, 6 bar.
The activity of these rhodium catalysts was not strongly dependent on their supports, contrary to palladium described previously [1], i.e. the main factor determining reaction rate is the rhodium metal itself in this hydrogenation. 3.3. Hydrogenations o v e r ruthenium on carbon
Hydrogen uptakes in the carbon supported ruthenium mediated hydrogenations of 1 are shown in Fig. 5. It can be observed that the conversion curve has an induction period, which can be eliminated by 1 h prehydrogenation of the catalyst at room temperature. Similarly to the supported rhodium catalysts, the hydrogenation of 1 over R u / C was also faster in methanol than in the mixture of n-hexane and methanol. Ruthenium on carbon is highly active in methanol, so applying the two-phase n-hexane/methanol mixture is not necessary in order to increase its activity, as was done when using palladium on carbon.
4. Conclusions The 1-methyl-2-pyrroleethanol was converted to the corresponding pyrrolidine derivative in non-acidic medium, over supported noble metal catalysts,
414
L. Hegedfis et aL / Applied Catalysis A: General 147 (1996) 407-414
under mild reaction conditions with high conversion. The best results were obtained with rhodium on carbon in methanol, under low hydrogen pressure (6 bar) and at room temperature. The activity of the different supported rhodium catalysts did not strongly depend on their supports (active C, A1203), contrary to palladium. Ruthenium on carbon had also high activity at 80°C, similarly to P d / C , but its activity was higher in methanol than that of palladium on carbon in n-hexane/methanol. On the basis of these results, the fact [2] that pyrrole and its derivatives are considered to be the most poisonous heterocycles in catalytic hydrogenation reactions, is not acceptable any more. The saturation of the pyrrol ring takes place relatively easily, besides in these hydrogenations it is unnecessary to use acids to eliminate the strong poisoning of the catalyst. This poisoning caused by secondary or tertiary N can be decreased significantly applying the appropriate solvents or solvent mixtures. In addition, taking into consideration the price of different noble metals, it can be stated that the application of R u / C and P d / C catalysts, under these reaction conditions in the catalytic hydrogenation of 1-methyl-2-pyrroleethanol, is also economical on an industrial scale.
References [1] [2] [3] [4] [5] [6] [7]
L. Heged~is, T. Mfith~ and A. Tungler, Appl. Catal. A, 143 (1996) 309. M. Freifelder, Practical Catalytic Hydrogenation, Wiley, New York, 1971, p. 577. C.G. Overberger, L.C. Palmer, B.S. Marks and N.R. Byrd, J. Am. Chem. Soc., 77 (1955) 4100. R. Adams, S. Miyano and M.D. Nair, J. Am. Chem. Soc., 83 (1961) 3323. H.N. Benedict and R.S. De Pablo, U.S. Patent 3 766 089 (1972). L.L. Benezra, R.S. De Pablo and E.R. Osgood, Ger. Often. 2 344 509 (1973). T. Mfith~, A. Tungler and J. Petr6, U.S. Patent 4 361 500 (1982).