THE KINETICS AND MECHANISM OF STYRENE HYDROCARBOXYLATION CATALYZED BYA PDCL2(PH3P)2 COMPLEX .2. THE INFLUENCE OF THE STYRENE, PD COMPLEX, AND TRIPHENYLPHOSPHINE CONCENTRATIONS ON THE RATE AND REGIOSELECTIVITYOF THE PROCESS

The influence of the concentrations of a catalyst (PdCl2(Ph3P)2), Ph3P , and styrene on the initial rates of the formation of styrene hydroca rboxylation products, 3- and 2-phenylpropionic acids (r(I) and r(II), respectively), was studied. Both rates depend linearly on catalyst con centration. Triphenylphosphine decreases r(II) to a greater extent tha n r(I); the inhibiting effect of Ph3P is enhanced with an increase in [H2O]. As the styrene content increases, r(I) virtually remains consta nt, whereas r(II) increases markedly. The relationships obtained are c onsistent with the hydride mechanism, comprising four routes for the f ormation of phenylpropionic acids and involving three types of catalyt ically active intermediates HPdCl(CO)n(Ph3P)2-n (n = 0-2). The regiose lectivity of the intermediates with respect to 3-phenylpropionic acid decreases from 100 to 0% as n increases from 0 to 2.