P. Mäki-Arvela et al. / Journal of Catalysis 225 (2004) 155–169
169
The total selectivity to pulegols was very high over all
the catalysts being close to 100%, independent of the con-
version of citronellal. The stereoselectivity to isopulegols
varyed between 55 and 72%, but no correlation between the
stereoselectivity and the concentration of acid sites was seen.
From a mechanistic point of view, it can be concluded that
the formation of different isopulegols was parallel; i.e., no
interconversion between different pulegols occurs. Addition-
ally the stability of the reaction intermediates obtained by
quantum mechanical calculations correlated reasonable well
with the obtained stereoselectivities in the cyclization of cit-
ronellal.
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In the cyclization of racemic citronellal very high cycliza-
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whereas the catalyst exhibiting the highest specific surface
area and high concentration of acid sites, namely H-Y cat-
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from pore-diffusion limitations of isopulegol or due to de-
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Acknowledgments
This work is part of the activities at the Åbo Akademi
Process Chemistry Centre within the Finnish Centre of Ex-
cellence Programme (2000–2005) by the Academy of Fin-
land. The authors are grateful to Mr. Markku Reunanen, who
performed the MS analysis.
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