52 research outputs found
Switching the stereochemical outcome of 6-endo-trig cyclizations; Synthesis of 2,6-Cis-6-substituted 4-oxopipecolic acids
A base-mediated 6-endo-trig cyclization of
readily accessible enone-derived α-amino acids has been
developed for the direct synthesis of novel 2,6-cis-6-
substituted-4-oxo-L-pipecolic acids. A range of aliphatic and
aryl side chains were tolerated by this mild procedure to give
the target compounds in good overall yields. Molecular
modeling of the 6-endo-trig cyclization allowed some insight as
to how these compounds were formed, with the enolate
intermediate generated via an equilibrium process, followed by irreversible tautomerization/neutralization providing the driving force for product formation. Stereoselective reduction and deprotection of the resulting 2,6-cis-6-substituted 4-oxo-L-pipecolic acids to the corresponding 4-hydroxy-L-pipecolic acids was also performed
Oxidation of diols in aqueous solution over supported- Pt, Pt-Au and Pd-Au catalysts: influence of chain length of diol and of catalyst composition
SSCI-VIDE+CDFA+MMG:NPR:CPI:MBEInternational audienceSelective oxidation with air of -diols to hydroxyl-carboxylic acids and diacids over heterogeneous catalysts is a green attractive route for the production of polymers [1]. Noble metals are commonly used for this reaction [2] and the composition of the catalyst may affect the reaction rate, the reaction pathway and thus the final yields. Moreover, the carbon number of diol could also have an influence. The objectives of this study were to compare monometallic Pt/ZrO2 and bimetallic Pt-Au/ZrO2 and Pd-Au/ZrO2 catalysts for oxidation of C4-C6 aliphatic diols.The series of catalysts were prepared by wet-impregnation of ZrO2 (109 m2 g-1) with aqueous solution of metallic salts and NaBH4 reduction [3]. XRD patterns (Fig. 1) show Pt particles sizes of ca ~ 7 nm over monoclinic ZrO2; AuPt and AuPd alloys were formed over Pt-Au/ZrO2 and Pd-Au/ZrO2 materials with particles of ca ~ 5 nm, as confirmed by TEM analysis. The composition of the alloys by XRD were close to the nominal Au/Pt and Au/Pd ratios of 1 of the solids.Oxidation reactions of diols (1,4-butanediol BDO, 1,5-pentanediol PDO and 1,6-hexanediol HDO) were performed in a 300 mL batch reactor (0.1 M diol in water) under 40 bar air at 70°C or 90°C. Liquid samples of the reaction medium were regularly collected and analysed by HPLC and for Total Organic Carbon TOC.Conversion of the diol was very rapid and the reaction was sequential via the corresponding hydroxy-aldehyde (ALD), hydroxy-acid (HA), aldehyde-acid (AA) and diacid (DA) (Scheme 1). During oxidation of BDO, cyclization reactions took place and formed -butyrolactone (GBL), which was poorly reactive.Regardless of the nature of the catalyst, the rate of oxidation of the diol decreased withdecreasing chain length; the order of rate was Pt > Pt-Au > Pd-Au. Moreover, the productsdistribution at similar conversion (50-60%) was different according to the catalyst (Table 1).Theinitial selectivity to ALD was high over Pt and the oxidation of the aldehyde group took placesmoothly; in contrast, over Pd-Au ALD was very rapidly converted to HA, which wasconsequently formed with high initial selectivity.Under the same reaction conditions after 48 h of reaction, the yield of DA increased with thechain length. The Au-Pt catalyst yielded 66% succinic acid, 81% glutaric acid, and 96% adipicacid (Table 1). Reactions performed at 90°C improved the yield of DA over Pd-Au catalyst to97% after 48 h and greatly accelerated oxidation of BDO over Pt-Au.In conclusion, Pt/ZrO2 catalyst is active for oxidation of diols to the diacids. The use of bimetalliccatalysts allowed to improve the final yield of DA. By adjusting the operating conditions, onecan obtain very selectively the desired acid
Aerobic oxidation of C-4-C-6 alpha,omega-diols to the diacids in base-free medium over zirconia-supported (bi)metallic catalysts
SSCI-VIDE+CDFA+CPI:NPR:MBEInternational audience--
Oxydation catalytique de diols et triols biosourcés en diacides surcatalyseurs mono et bimétalliques Pt/ZrO2, Pt-Au/ZrO2 et Pd-Au/ZrO2
SSCI-VIDE+CDFA+MMG:NPR:CPI:MBEInternational audienceLa substitution partielle des dĂ©rivĂ©s de la pĂ©trochimie par ceux issus de la biomasselignocellulosique abondante est un des grands enjeux actuels. Dans cette dĂ©marche dedĂ©veloppement durable, la production de synthons polyols partiellement hydroxylĂ©s, en particulierles -diols, pour la synthĂšse de polymĂšres biosourcĂ©s devient rĂ©aliste [1]. Dans ce travail, nousavons Ă©tudiĂ© lâoxydation catalytique par lâair en phase aqueuse des diols C4-C6 (butane-1,4-diol« BDO», pentane-1,5-diol «PDO» et hexane-1,6-diol «HDO») et dâun triol (lâhexane-1,2,6-triol«HTO») en diacides (DA) correspondants sur des catalyseurs Pt, Pt-Au et Pd-Au supportĂ©s surzircone. Ces catalyseurs aux mĂ©taux nobles supportĂ©s sont particuliĂšrement intĂ©ressants pourcette rĂ©action et lâutilisation de systĂšmes bimĂ©talliques permet de sâaffranchir de lâutilisation debase soluble [2].La caractĂ©risation des catalyseurs prĂ©parĂ©s par imprĂ©gnation voie humide et rĂ©duction par NaBH4(DRX, MET, EDX, XPS) a mis en Ă©vidence la formation dâalliage AuPt et AuPd [3]. La rĂ©action estrĂ©alisĂ©e dans un rĂ©acteur batch avec 0.1 M de substrat dans lâeau sous 40 bar dâair Ă 70°C ou90°C. Les prĂ©lĂšvements liquides au cours de la rĂ©action sont analysĂ©s par HPLC.La conversion du diol est trĂšs rapide et larĂ©action jusquâau diacide a lieu de façonsĂ©quentielle ; lâune des fonctions alcool estoxydĂ©e en acide (HA), via lâaldĂ©hyde (ALD), puisla deuxiĂšme fonction alcool est oxydĂ©e vialâaldĂ©hyde acide (AA) (Figure 1). Dans le cas duBDO, la -butyrolactone (GBL) est Ă©galementobservĂ©e comme intermĂ©diaire.Dans les mĂȘmes conditions, aprĂšs 48 h Ă 70°C,le rendement en DA augmente avec la longueurde chaine du diol (Figure 2). Le catalyseur Pt-Au/ZrO2 (Au/Pt at. ~1) est le plus efficace(rendements en acides adipique, glutarique, etsuccinique de 96%, 81%, et 66% aprĂšs 48 h).Une tempĂ©rature de 90°C, dâune part accĂ©lĂšre laconversion des intermĂ©diaires sur Au-Pd(rendement de 97% aprĂšs 48 h), et dâautre partaccĂ©lĂšre la vitesse dâoxydation de la GBL peurĂ©active jusquâĂ un rendement en acidesuccinique de 80%.La prĂ©sence dâune fonction hydroxyle dans HTOrĂ©duit fortement lâactivitĂ© des catalyseurs danscette rĂ©action.En conclusion, les catalyseurs Pt-Au et Pd-AusupportĂ©s convertissent les diols dĂ©rivĂ©s de labiomasse en diacides pour la synthĂšse debiopolymĂšres avec de trĂšs bons rendements
Oxidation of diols in aqueous solution over supported- Pt, Pt-Au and Pd-Au catalysts: influence of chain length of diol and of catalyst composition
SSCI-VIDE+CDFA+MMG:NPR:CPI:MBEInternational audienceSelective oxidation with air of ïĄïŹï·-diols to hydroxyl-carboxylic acids and diacids over heterogeneous catalysts is a green attractive route for the production of polymers [1]. Noble metals are commonly used for this reaction [2] and the composition of the catalyst may affect the reaction rate, the reaction pathway and thus the final yields. Moreover, the carbon number of diol could also have an influence. The objectives of this study were to compare monometallic Pt/ZrO2 and bimetallic Pt-Au/ZrO2 and Pd-Au/ZrO2 catalysts for oxidation of C4-C6 aliphatic diols.The series of catalysts were prepared by wet-impregnation of ZrO2 (109 m2 g-1) with aqueous solution of metallic salts and NaBH4 reduction [3]. XRD patterns (Fig. 1) show Pt particles sizes of ca ~ 7 nm over monoclinic ZrO2; AuPt and AuPd alloys were formed over Pt-Au/ZrO2 and Pd-Au/ZrO2 materials with particles of ca ~ 5 nm, as confirmed by TEM analysis. The composition of the alloys by XRD were close to the nominal Au/Pt and Au/Pd ratios of 1 of the solids.Oxidation reactions of diols (1,4-butanediol BDO, 1,5-pentanediol PDO and 1,6-hexanediol HDO) were performed in a 300 mL batch reactor (0.1 M diol in water) under 40 bar air at 70°C or 90°C. Liquid samples of the reaction medium were regularly collected and analysed by HPLC and for Total Organic Carbon TOC.Conversion of the diol was very rapid and the reaction was sequential via the corresponding hydroxy-aldehyde (ALD), hydroxy-acid (HA), aldehyde-acid (AA) and diacid (DA) (Scheme 1). During oxidation of BDO, cyclization reactions took place and formed ï§-butyrolactone (GBL), which was poorly reactive.Regardless of the nature of the catalyst, the rate of oxidation of the diol decreased withdecreasing chain length; the order of rate was Pt > Pt-Au > Pd-Au. Moreover, the productsdistribution at similar conversion (50-60%) was different according to the catalyst (Table 1).Theinitial selectivity to ALD was high over Pt and the oxidation of the aldehyde group took placesmoothly; in contrast, over Pd-Au ALD was very rapidly converted to HA, which wasconsequently formed with high initial selectivity.Under the same reaction conditions after 48 h of reaction, the yield of DA increased with thechain length. The Au-Pt catalyst yielded 66% succinic acid, 81% glutaric acid, and 96% adipicacid (Table 1). Reactions performed at 90°C improved the yield of DA over Pd-Au catalyst to97% after 48 h and greatly accelerated oxidation of BDO over Pt-Au.In conclusion, Pt/ZrO2 catalyst is active for oxidation of diols to the diacids. The use of bimetalliccatalysts allowed to improve the final yield of DA. By adjusting the operating conditions, onecan obtain very selectively the desired acid
Oxydation catalytique de diols et triols biosourcés en diacides surcatalyseurs mono et bimétalliques Pt/ZrO2, Pt-Au/ZrO2 et Pd-Au/ZrO2
SSCI-VIDE+CDFA+MMG:NPR:CPI:MBEInternational audienceLa substitution partielle des dĂ©rivĂ©s de la pĂ©trochimie par ceux issus de la biomasselignocellulosique abondante est un des grands enjeux actuels. Dans cette dĂ©marche dedĂ©veloppement durable, la production de synthons polyols partiellement hydroxylĂ©s, en particulierles ïĄïŹï·-diols, pour la synthĂšse de polymĂšres biosourcĂ©s devient rĂ©aliste [1]. Dans ce travail, nousavons Ă©tudiĂ© lâoxydation catalytique par lâair en phase aqueuse des diols C4-C6 (butane-1,4-diol« BDO», pentane-1,5-diol «PDO» et hexane-1,6-diol «HDO») et dâun triol (lâhexane-1,2,6-triol«HTO») en diacides (DA) correspondants sur des catalyseurs Pt, Pt-Au et Pd-Au supportĂ©s surzircone. Ces catalyseurs aux mĂ©taux nobles supportĂ©s sont particuliĂšrement intĂ©ressants pourcette rĂ©action et lâutilisation de systĂšmes bimĂ©talliques permet de sâaffranchir de lâutilisation debase soluble [2].La caractĂ©risation des catalyseurs prĂ©parĂ©s par imprĂ©gnation voie humide et rĂ©duction par NaBH4(DRX, MET, EDX, XPS) a mis en Ă©vidence la formation dâalliage AuPt et AuPd [3]. La rĂ©action estrĂ©alisĂ©e dans un rĂ©acteur batch avec 0.1 M de substrat dans lâeau sous 40 bar dâair Ă 70°C ou90°C. Les prĂ©lĂšvements liquides au cours de la rĂ©action sont analysĂ©s par HPLC.La conversion du diol est trĂšs rapide et larĂ©action jusquâau diacide a lieu de façonsĂ©quentielle ; lâune des fonctions alcool estoxydĂ©e en acide (HA), via lâaldĂ©hyde (ALD), puisla deuxiĂšme fonction alcool est oxydĂ©e vialâaldĂ©hyde acide (AA) (Figure 1). Dans le cas duBDO, la ï§-butyrolactone (GBL) est Ă©galementobservĂ©e comme intermĂ©diaire.Dans les mĂȘmes conditions, aprĂšs 48 h Ă 70°C,le rendement en DA augmente avec la longueurde chaine du diol (Figure 2). Le catalyseur Pt-Au/ZrO2 (Au/Pt at. ~1) est le plus efficace(rendements en acides adipique, glutarique, etsuccinique de 96%, 81%, et 66% aprĂšs 48 h).Une tempĂ©rature de 90°C, dâune part accĂ©lĂšre laconversion des intermĂ©diaires sur Au-Pd(rendement de 97% aprĂšs 48 h), et dâautre partaccĂ©lĂšre la vitesse dâoxydation de la GBL peurĂ©active jusquâĂ un rendement en acidesuccinique de 80%.La prĂ©sence dâune fonction hydroxyle dans HTOrĂ©duit fortement lâactivitĂ© des catalyseurs danscette rĂ©action.En conclusion, les catalyseurs Pt-Au et Pd-AusupportĂ©s convertissent les diols dĂ©rivĂ©s de labiomasse en diacides pour la synthĂšse debiopolymĂšres avec de trĂšs bons rendements
Oxydation catalytique de diols et triols biosourcés en diacides surcatalyseurs mono et bimétalliques Pt/ZrO2, Pt-Au/ZrO2 et Pd-Au/ZrO2
SSCI-VIDE+CDFA+MMG:NPR:CPI:MBENational audienceLa substitution partielle des dĂ©rivĂ©s de la pĂ©trochimie par ceux issus de la biomasse lignocellulosique abondante est un des grands enjeux actuels. Dans cette dĂ©marche de dĂ©veloppement durable, la production de synthons polyols partiellement hydroxylĂ©s, en particulier les -diols, pour la synthĂšse de polymĂšres biosourcĂ©s devient rĂ©aliste [1]. Dans ce travail, nous avons Ă©tudiĂ© lâoxydation catalytique par lâair en phase aqueuse des diols C4-C6 (butane-1,4-diol « BDO», pentane-1,5-diol «PDO» et hexane-1,6-diol «HDO») et dâun triol (lâhexane-1,2,6-triol «HTO») en diacides (DA) correspondants sur des catalyseurs Pt, Pt-Au et Pd-Au supportĂ©s sur zircone. Ces catalyseurs aux mĂ©taux nobles supportĂ©s sont particuliĂšrement intĂ©ressants pour cette rĂ©action et lâutilisation de systĂšmes bimĂ©talliques permet de sâaffranchir de lâutilisation de base soluble [2].La caractĂ©risation des catalyseurs prĂ©parĂ©s par imprĂ©gnation voie humide et rĂ©duction par NaBH4 (DRX, MET, EDX, XPS) a mis en Ă©vidence la formation dâalliage AuPt et AuPd [3]. La rĂ©action est rĂ©alisĂ©e dans un rĂ©acteur batch avec 0.1 M de substrat dans lâeau sous 40 bar dâair Ă 70°C ou 90°C. Les prĂ©lĂšvements liquides au cours de la rĂ©action sont analysĂ©s par HPLC.La conversion du diol est trĂšs rapide et la rĂ©action jusquâau diacide a lieu de façon sĂ©quentielle ; lâune des fonctions alcool est oxydĂ©e en acide (HA), via lâaldĂ©hyde (ALD), puis la deuxiĂšme fonction alcool est oxydĂ©e via lâaldĂ©hyde acide (AA) (Figure 1). Dans le cas du BDO, la -butyrolactone (GBL) est Ă©galement observĂ©e comme intermĂ©diaire. Dans les mĂȘmes conditions, aprĂšs 48 h Ă 70°C, le rendement en DA augmente avec la longueur de chaine du diol (Figure 2). Le catalyseur Pt-Au/ZrO2 (Au/Pt at. ~1) est le plus efficace (rendements en acides adipique, glutarique, et succinique de 96%, 81%, et 66% aprĂšs 48 h). Une tempĂ©rature de 90°C, dâune part accĂ©lĂšre la conversion des intermĂ©diaires sur Au-Pd (rendement de 97% aprĂšs 48 h), et dâautre part accĂ©lĂšre la vitesse dâoxydation de la GBL peu rĂ©active jusquâĂ un rendement en acide succinique de 80%. La prĂ©sence dâune fonction hydroxyle dans HTO rĂ©duit fortement lâactivitĂ© des catalyseurs dans cette rĂ©action. En conclusion, les catalyseurs Pt-Au et Pd-Au supportĂ©s convertissent les diols dĂ©rivĂ©s de la biomasse en diacides pour la synthĂšse de biopolymĂšres avec de trĂšs bons rendements
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