II International Symposium on Carbon for Catalysis ABSTRACTS

PP-<strong>II</strong>-16
EVALUATION OF DIFFERENT ACTIVATED CARBONS AS SUPPORTS FOR THE
PALLADIUM CATALYZED HYDROGENOLYSIS OF Z-GROUPS
Möbus K., Tacke T., Dunn T. 1 , Chen B. 1
Degussa AG, Rodenbacher Chaussee 4, 63457 Hanau Wolfgang, Germany
1 Degussa Corporation, 5150 Gilbertsville Hwy, Calvert City, KY 42029 USA
e-mail: : konrad.moebus@degussa.com
The chemical pathways to the complex molecules produced by the fine chemical,
pharmaceutical and agrochemical industries often involve multi-step synthesis. Protective
groups are commonly used to block reactive sites that would otherwise react in an undesired
way. A common protective group for the protection of amines is the Z group, also called Cbz
or carbobenzyloxy group. This group can be easily removed by catalytic hydrogenolysis in
the presence of a heterogeneous catalyst, preferably palladium on activated carbon [1]. We
have developed a useful method to determine the activity of a catalyst by measuring the CO 2
generation rate by means of NDIR detection [2].
One of the factors that affects the activity of palladium on carbon catalysts is the porous
structure of the activated carbon used as the catalyst support. For nitrobenzene
hydrogenations it was shown that the catalytic activity correlates with the pore size
distribution of the activated carbon, concluding that a significant amount of active metal is
located in small pores and therefore is unavailable for the catalytic reaction [3]. In the present
work, we focused on the effect of pore size on the activity of activated carbon supported
palladium catalysts for Z-cleavage reactions, and investigated how the size of the Z-protected
compound determines the catalytic activity. Two activated carbons with different pore size
distribution as shown by their nitrogen isotherms were used as support (Figure 1). Palladium
catalysts were prepared by a Degussa proprietary method in order to achieve a similar
palladium particle distribution. Palladium dispersion was measured by CO chemisorption and
was determined to be 20% for both catalysts. To check for steric effects coming from the
substrate, four different sized Z-group protected compounds were used as test
molecules: Z-Glycine 1, Z-phenylalanine 2, Z-citrullyl-L-leucine-methylester 3 and
Z-O-tert-butyl-L-tyrosyl-D-homocitrullyl-L-leucine-methylester 4 (Figure 2).
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