1158867-65-2Relevant academic research and scientific papers
Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation
Firkala, Tams,Tlas, Emlia,Kristyn, Sndor,Sz?ll'si, Gy?rgy,Drotr, Eszter,Mink, Jnos,Mihly, Judith
, p. 1102 - 1109 (2015)
The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)-2,3-diphenylpropenoic acid, (E)-2-(2-methoxyphenyl)-3-phenylpropenoic acid, (E)-2,3-di-(4-methoxyphenyl)phenylpropenoic acid and (E)-2-(2-methoxyphenyl)-3-(4-fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO- around 1394 cm-1 and νC-C of the -C-COO- moiety at 951 cm-1. In these series the plane of the α-phenyl group (γCH out-of-plane vibrations at 850-700 cm-1) is almost parallel to the silver surface, while the β-phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in-plane mode) at 1075 cm-1, νCC (ring breathing mode, in-plane) at 1000 cm-1 and γCCC (out-of-plane mode) around 401 cm-1. The other class of propenoic acids (cinnamic acid, (E)-2-phenyl-3-(4-methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm-1 in the FT-Raman spectra of methanolic solutions.
C{single bond}H...F hydrogen bonds as the organising force in F-substituted α-phenyl cinnamic acid aggregates studied by the combination of FTIR spectroscopy and computations
Tolnai,Kiss,Felf?ldi,Pálinkó
experimental part, p. 27 - 31 (2009/10/01)
Various F-substituted E-2,3-diphenyl propenoic acid molecules were synthesised and their aggregation behaviour was studied by experimental (FT-IR spectroscopy) and computational (semiempirical and DFT) methods. Experimental approach embraced the identific
Up to 96% enantioselectivities in the hydrogenation of fluorine substituted (E)-2,3-diphenylpropenoic acids over cinchonidine-modified palladium catalyst
Szollosi, Gyoergy,Herman, Beata,Felfoeldi, Karoly,Fueloep, Ferenc,Bartok, Mihaly
supporting information; experimental part, p. 2804 - 2814 (2009/10/20)
The enantioselective hydrogenation of methoxy-and fluorine-substituted (E)-2,3-diphenylpropenoic acid derivatives was studied over cinchonidine- modified, supported palladium catalysts in the absence and presence of benzylamine as additive. The fluorine substituent in the appropriate position was even more efficient than the methoxy group in increasing the optical purity of the saturated product. High enantioselectivities, up to 96%, were obtained in the hydrogenation of some disubstituted derivatives, unprecedented in the hydrogenation of prochiral unsaturated carboxylic acids over modified heterogeneous catalyst. The best optical purities were reached in the hydrogenation of derivates bearing a para-substituent on the β phenyl and an ortho-substituent on the a phenyl ring, respectively. The influence of the substituent on the β phenyl ring was attributed to the increase in the efficiency of the modifier-substrate interaction by electronic effects or to a decrease in the adsorption strength of the substituted acid over modified surface sites. The beneficial effect of the ortho-substituent on the a phenyl ring was assumed to be due to the additional interaction of this substituent with the modifier on the surface, its steric hindrance contributing only in a small part to the observed effect. These suggestions were supported by results obtained in the hydrogenations of some methyl-substituted derivatives.
