Pipecolinic acid (PCA) is one of the mostimportant intermediate compounds for the syntheses of a wide range of medicinesand biologically active chemical compounds [1].  The fact that makesthe deaminocyclization of L-lysine (L-Lys) a preferable chemistry process toobtain L-PCA the starting material is optically pure, cheap and readilyavailable [2].  The optical purity of the product PCA (OPPCA)depends on the type of photocatalyst used and the use of a TiO2 basedphotocatalyst is common.However Pal et al. [2] stated that they were not able to obtainoptically pure PCA by TiO2 due to its lack of selectivity.  This has been addressed through the studies ofIkeda et al. [3]. Their strategy is thefabrication of a novel core-shell composite photocatalyst, consisting of commercially available TiO2 particles incorporated into a hollow silica shell (SiO2/void/TiO2).  Besides showing the abilityto decompose small substrates, the SiO2/void/TiO2 also exhibited the capacity to retain the intrinsic activity of original TiO2 due tothe presence of a void space between the TiO2 core and thehollow silica shell.  In this study, SiO2/void/TiO wassynthesized by firstly preparing carbon-coated TiO2 hydrothermally. Subsequently, tetraethyl orthosilicate(TEOS) was used to yield SiO2/C/TiO2, followed by heat treatment to remove the carbon layerto obtain SiO2/void/TiO2. SEM images in transmission mode (Fig 1) showed the presence of void space of 3-10 nm in width between shell ofaround 30 nm in thickness and core TiO2 particles.  The resulting material andcommercially available TiO2 were tested out in the photocatalytic redox-combinedsynthesis of L-PCA from L-lys. The results show that platinized SiO2/void/TiO2 displayeda higher OPPCA of L-PCAas compared to normal platinized TiO2, although with lower conversion percentage.  This indicatesthe potential of the core-shell structure in enhancing the photocatalyticability of TiO2.[1]Bailey, P. D.; et al., Chem.lCommun.1998, (6), 633-640.[2]Pal, B.; etal.., J. Catal.2003, 217, (1),152-159.[3]Ikeda, S.; etal.., Chem.Commun.2007,3753-3755.

Photocatalytic redox-combined synthesis of L-pipecolinic acid from L-lysine using titania particles encapsulated in silica shell

243rd National Meeting (2012)

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