Catalysis of Organic..

Wang et al. 25The rate expressions for formation of product C and alcohol D are:Rate (product C formation) = k2 KB [B] [H2] Θtotal / ( 1 + KA [A] + KB [B] ) (3)Rate (alcohol D formation) = k3 KA [A] [H2] Θtotal / ( 1 + KA [A] + KB [B] ) (4)Wherek2 is the rate constant for product C formation.KB is equal to kb1/kb-1, the adsorption equilibrium constant for Schiff’s base B.k3 is the rate constant for product D formation.KA is equal to ka1/ka-1, the adsorption equilibrium constant for aldehyde.Θtotal is the total surface fractional coverage (equals one).By dividing equation (4) by equation (3), the ratio of alcohol to productformation is:Ratio=k3KA[A]/k2 KB [B] (5)Separate hydrogenation kinetic studies were performed using the sameEngelhard Escat 142 catalyst (edge coated, reduced) (4) to compare the adsorptionstrength and hydrogenation rate between the Schiff’s base and aldehyde. The kineticsare modeled using a conventional Langmuir-Hinshelwood expression to correlate theinitial rate with the substrate concentration (5).Experimental Section(a) Catalytic hydrogenationIn our development studies, Endeavor (5 mL) and Buchi (1L) reactor systems wereused to screen catalysts and to evaluate the impurity profile under various processconditions. Hydrogenation kinetic studies were carried out using a 100 mL EZ-sealautoclave with an automatic data acquisition system to monitor the hydrogen uptakeand to collect samples for HPLC analysis. Standard conditions of 5 g of aldehyde in25 mL ethyl acetate and 25 mL methanol with 0.5 g of 5%Pd/C Engelhard Escat 142were used in this investigation. For the Schiff’s base formation and subsequenthydrogenation, inline FT-IR was used to follow the kinetics of the Schiff’s baseformation under different conditions. Tables 1 and 2 show the changes in thesubstrate concentration under different conditions. Both experiments were carriedwithout any limitations of gas-liquid mass transfer.Table 1. Hydrogenation of aldehyde A to form the alcohol D40°C, 30psig, 2500 rpm in autoclave reactorTime H2 uptake A dA/dt(min) (mL) (mmole) (mmole/min)