Catalysis of Organic..

24Hydrogenation of a Schiff’s BaseONACH 3 CHOk 1O CH 3HClO + . H 2 N CO 2 CH 3 N Ok -1BN+ H 2 OCOOMek 2ONCH 3 NH COOMeOCk 3O CH 3N ODCH 2 OHWhere:A: AldehydeB: Schiff's baseC: ProductD: Side Product, AlcoholE: Over reduction Impurity (MW = 293)ONCH 3 CH 3EOThe objective of the present study is to provide a kinetic evaluation for the rate offormation of byproduct D, impurity E and possibly other impurities related tothe intermediate Schiff’s base B.Kinetic AnalysisLiquid phase hydrogenation catalyzed by Pd/C is a heterogeneous reaction occurringat the interface between the solid catalyst and the liquid. In our one-pot process, thehydrogenation was initiated after aldehyde A and the Schiff’s base reachedequilibrium conditions (A⇔B). There are three catalytic reactions A ⇒ D, B ⇒ C,and C ⇒ E, that occur simultaneously on the catalyst surface. Selectivity andcatalytic activity are influenced by the ability to transfer reactants to the active sitesand the optimum hydrogen-to-reactant surface coverage. The Langmuir-Hinshelwood kinetic approach is coupled with the quasi-equilibrium and the twostepcycle concepts to model the reaction scheme (1,2,3). Both A and B areadsorbed initially on the surface of the catalyst. Expressions for the elementarysurface reactions may be written as follows:A ⇔ A*A* + H2 ⇒ D + *B ⇔ B*B* + H2 ⇒ C + *The equilibrium constants for the adsorption of the aldehyde and Schiff’s baseare KA = ka1/ka–1 and KB = kb1/kb-1 respectively. Product C may adsorb but is lesscompetitive than the surface adsorption of the Schiff’s base B and aldehyde A. Thetotal surface coverages are expressed as the sum of the adsorbed species and emptysites ΘA + ΘB + Θ° = 1.The expressions for ΘA and ΘB are:ΘB = KB [B] / ( 1 + KA [A] + KB [B] ) (1)ΘA = KA [A] / ( 1 + KA [A] + KB [B] ) (2)