The influence of mineral catalysts on racemization of secondary alcohols under pyrolytic temperatures

Pyrolysis of 1-phenylethanol (PE) enantiomers I(S) and (R)I with and without catalysts at different temperatures (200-700 degrees C) has been carried out. In the presence of catalysts the partial racemization (<= 25%) and formation of products like styrene, acetophenone, benzaldehyde and chiral benzylic ethers formation have been detected. Without a catalyst almost no racemization was observed and products formation was not appreciable. The kinetic of racemization has been calculated and a tentative mechanism has been proposed. Pyrolysis of (S)-1-phenylpropanol (PPEs) and (S)-1-phenyl-2,2,2-trifluoroethanol (FEs) have also carried out at 500 degrees C on ilmenite. The effect of the fluorine atoms in FEs has been evaluated by comparing the results with the pyrograms of nonfluorinated analogues. Using the trend of the enantiomeric excess in function of the temperature, a new approach to calculate the rate of racemization is proposed. (c) 2010 Elsevier B.V. All rights reserved.