Para-substituted phenylethanol

For the deracemization of phenylethanol derivatives using G. candidum under aerobic conditions (Figure 8.41b), the (S)-specific enzyme was reversible and (R) enzyme was irreversible, so (R)-alcohol accumulated when the cell and racemic alcohols were mixed [31b,c]. Para-substituted phenylethanol derivatives gave better results than meta-substituted derivatives. Sphingomonas was used for... 

The oxidation of a series of meta- and para-substituted a-phenylethanols shows that electron-donating substituents facilitate reaction (p = —1.01) . A similar study of primary aliphatic alcohols confirmed this trend p = —1.06 + 0.06). 

In a time course study on the conversion of ( )-l-phenylethanol 13 (X=H), formation of acetophenone was observed to a maximum of around 20% during the conversion of (S)- to (R)- alcohol which occurred over 24 h to give (R)-13 in 96 % yield, 99% e.e. The effect of ring substitution on the efficiency of the dera-cemization was notable. While para substituents (Cl, OMe, Me) gave good results, ortho derivatives could not be deracemized and the biocatalyst showed little activity towards meta substituted compounds. On addition of allyl alcohol, improvements in e.e. were obtained, particularly for the conversion of l-(m-methylphenyl)ethanol (from 21 to 94% e.e.). However these improvements did appear to be at the expense of yield (89% diminished to 55%). The authors sug-... 

---