E. Toukoniitty et al., The effect of oxygen and the reduction temperature of the Pt/Al2O3 catalyst in enantioselective hydrogenation of 1-phenyl-1,2-propanedione, CATAL TODAY, 60(3-4), 2000, pp. 175-184
The effect of oxygen and catalyst reduction temperature in enantioselective
hydrogenation of 1-phenyl-1,2-propanedione over commercial Pt/Al2O3 cataly
st was investigated. Dichloromethane was used as solvent. The catalyst was
modified in situ with (-)-cinchonidine. Relatively high enantiomeric excess
es (65%) of (R)-1-hydroxy-1-phenyl-2-propanone were obtained with the solve
nt used as received, i.e. containing traces of dissolved oxygen and other i
mpurities. Dichloromethane dissociated partially on the Pt/Al2O3 surface ca
using desorption of methane, ethene and HCl from the catalyst during TPD ac
cording to mass spectrometric analysis. Under anaerobic conditions the reac
tion rate was low giving only about 40% enantiomeric excesses of (R)-1-hydr
oxy-1-phenyl-2-propanone. When injecting 5 mm(3) of oxygen into the reactor
a beneficial effect was observed (i.e. higher reaction rate and enantiomer
ic excess) in comparison with anaerobic conditions. Poisoning effect of oxy
gen was observed when injecting 500 mm(3) of oxygen into the reactor. Effec
t of catalyst reduction temperature was studied at three different temperat
ures (170, 400 and 455 degrees C). Highest reaction rates and enantiomeric
excesses were obtained with the catalyst reduced at 400 degrees C. Methane
was desorbed from the catalyst at temperatures between 263 and 383 degrees
C which could be the explanation for the lower activity of the catalyst red
uced at 170 degrees C. It was demonstrated that small amounts of oxygen can
have a beneficial effect in enantioselective hydrogenation of 1-phenyl-1,2
-propanedione and also that catalyst reduction temperature plays an importa
nt role in obtaining high enantiomeric excesses. (C) 2000 Elsevier Science
B.V. All rights reserved.