Enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal platinum on SiO2

Abstract

A hidrogenação enantiosseletiva de piruvato de etila e de 1-fenil-1,2-propanodiona foi estudada a 298 K e sob 40 bar de H 2 sobre um catalisador de platina coloidal estabilizado com cinchonidina (CD) e suportado em sílica. O catalisador foi preparado por impregnação da platina coloidal em sílica, atingindo 1% em massa do metal no suporte. O colóide foi preparado a partir de uma solução aquosa de H 2 PtCl 6 estabilizada com diferentes quantidades de CD. O catalisador foi caracterizado por isotermas de adsorção-desorção de N 2 a 77 K e por XPS, XRD e TEM. As reações foram efetuadas em batelada em um reator de aço inoxidável, usando cicloexano como solvente e cinchonidina como modificador quiral. A adição de CD ao catalisador permite a estabilização e o controle do tamanho de partícula da platina, e também afeta o excesso enantiomérico (ee) do sistema, levando a um maior rendimento do produto com configuração R. A relação entre a concentração de CD adicionada in situ e a enantiosseletividade apresenta uma curva do tipo sino nas duas reações estudadas; este comportamento é um indicativo da importância da adsorção competitiva do modificador e do substrato na superfície do catalisador.The enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione was studied at 298 K and 40 bar of H 2 over colloidal Pt stabilized with cinchonidine (CD) and supported on silica. The catalysts were prepared by impregnation of colloidal Pt on SiO 2 , leading to a metal load close to 1 wt.%. The colloid was prepared from an aqueous solution of H 2 PtCl 6 and stabilized with different quantities of CD. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XPS, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The addition of CD to the catalysts allows the stabilization and control of the platinum particle size and also affects the enantiomeric excess (ee) of the system, affording a higher proportion of the (R)-product. The relationship between the enantioselectivity and the CD concentration (added in situ) exhibits a bell type curve for both reactions, this being indicative of the importance of a competitive adsorption of the modifier and substrate on the catalyst surface.Keywords: Pt colloids, enantioselectivity, ethyl pyruvate, 1-phenyl-1,2-propanedione, cinchonidine IntroductionEnantioselective hydrogenation reactions are important tools to obtain fine chemicals used in pharmaceutical and food products.1-4 Thus, the synthesis of chiral compounds is of growing interest; among them, the hydrogenation of a-ketoesters and ketones is the most widely studied. [5][6][7][8][9][10][11][12][13][14][15] Since Orito et al. reported the enantioselective hydrogenation of ethyl pyruvate to (R)-ethyl lactate over cinchonidine-modified Pt catalysts with ee's up to 95%, many other research teams have evaluated the performance of their catalytic systems in this reaction. [16][17][18] Indeed, this is n...

Silica Supported Rhodium Metal Nanoparticles Stabilized With (-)-Diop. Effect of Ligand Concentration and Metal Loading on the Enantioselective Hydrogenation of Ketones

“…Table 4 shows the conversion levels of different substrates studied at 420 min of reaction and ee obtained using 1.0Rh-3L catalyst. It should be mentioned that even though the enantioselectivity levels remains approximately constant with the conversion in the different studied reactions, conversion levels and pseudo constant rate are higher in lineal diketones, however, are lower in enantioselectivity, in line with results already reported [33][34] . On the other hand, aromatic ketones, PPD and AP, show higher %ee and lower activity, attributed to the structure of the aromatic compounds.…”

“…Catalysts with different ligand concentration and metal loading have been used as catalysts in enantioselective hydrogenation reactions of AP, PPD, HD, BD and EP as test reaction. These substrates are interesting due to the applications that have some of its (R)-product of hydrogenation [33][34][35] in synthesis of chiral drugs. Thus, (R)-1-hydroxy-1-phenylpropan-2-one, product of PPD hydrogenation, is a precursor for the production of ephedrine and analogues used as a nasal and bronchial decongestant among others 36 .…”

ENANTIOSELECTIVE HYDROGENATION OF 1-PHENYL-1,2-PROPANODIONE ON Pt/ ZrO2 CATALYSTS

“…First order reaction rate constants, in the hydrogenation of 1-phenyl-1, 2-propanodione at 298 K on Pt/ZrO 2 catalysts. k 1g , 10 3 min -1 k 1R , 10 3 min -1 k 1R , 10 3 min -1 k 2R , 10 3 min -1 k 2S , 10 3 min - Considering the previous results obtained in the ethyl pyruvate hydrogenation and also in the 1-phenyl-1, 2-propanodione hydrogenation [7][8][9][10][13][14][15][16][17][18] , it would be possible to enhance the yield to the desired products by adjusting CD coverage. For that reason the effect of the CD concentration added at the beginning of the reaction has been studied.…”

“…Heterogeneous enantioselective hydrogenation of diketones on cinchona alkaloid modified platinum represents a promising route for the synthesis of chiral molecules with high optical purity [1][2][3]. As catalysts Pt, Pd and Ir supported on SiO 2 , Al 2 O 3 among others are used [4][5][6][7][8]. Since Orito et al reported the enantioselective hydrogenation of ethyl pyruvate to (R)-ethyl lactate over cinchonidine-modified Pt catalysts with ee's up to 95%, many other research teams have evaluated their catalytic systems in the mentioned reaction [9][10][11].…”

CHIRAL Rh/SiO2 CATALYSTS FOR ENANTIOSELECTIVE HYDROGENATION REACTIONS: THE ROLE OF (S,S)-DIPAMP AS CHIRAL MODIFIER AND STABILIZER ON METALLIC NANOPARTICLES SYNTHESIS

“…A few research groups have focused their studies in using chiral nanoparticles as catalysts. NPs have been also used as catalysts in reactions such as hydroformylation, allylic alkylation, hydrosilylations, Suzuki and Heck-type, couplings, among others achieving good results [19][20][21][22][23][24][25][26] .…”