NEW STRATEGIES IN ENANTIOSELECTIVE HYDROGENATION ON SUPPORTED TRANSITION METAL CATALYSTS. EFFECTS OF METAL SINTERING AND SUPPORT SWELLING

N. CARRARA; J. BADANO; G. MENDOWA; D. RUIZ; C.R. VERA; M. QUIROGA

JOURNAL OF THE BRAZILIAN CHEMICAL SOCIETY

SOC BRASILEIRA QUIMICA

Lugar: San Pablo; Año: 2019 vol. 30 p. 1678 - 1697

0103-5053

Theeffect of noble metal catalysts supported on an ionic exchange resin for theenantioselective hydrogenation of ethyl pyruvate to ethyl lactate was studied.  High activity and moderate enantioselectivitylevels were obtained. Pt was the best enantioselective metallicphase, followed by Pd and Au; Rh was the less enantioselective metallic phase.Theeffect of the active site was evaluated for the most enantioselective catalyst: 2Pt-WA30. Anovel method for sintering the Pt metal particles by nitriles reduction wasused, and a controlled migration of the metal particles to the surface layerswas observed.  There existed an optimalparticle size that maximized the enantiomeric excess, corresponding to 24 hsintering.  The hydrogenation of ethylpyruvate to ethyl lactate was found to be structure-sensitive and theimportance of the metal particle size for the adsorption of the chiral modifierwas proved.Besides,two different chirality induction methods were tried for the 2Pt-WA30 catalyst: i) theaddition of the Chiral Modifier to the reaction media, or ii) the modificationof the catalyst in a swelling medium prior to the reaction in order toencapsulate the Chiral Modifier. Lower activity but higher enantioselectivitylevels were obtained with method (ii).Finally,the reuse of the catalysts was also assessed by means of consecutive reactiontests.