Kinetics of Carboxylation of Styrene Using a Homogeneous Palladium Complex Catalyst

Kinetics of carboxylation of styrene to Me 2-phenylpropionate and Me 3-phenylpropionate has been investigated using a homogeneous Pd(OAc)2/PPh3/p-toluenesulfonic acid catalyst system. The effect of concn. of styrene, catalyst, water, and partial pressure of CO on the activity, selectivity, and rate of reaction has been studied in a temp. range of 338-358 K. The activity of the catalyst as well as the selectivity of the products was sensitive to all the reaction parameters studied. The selectivity of 2-phenylpropionate was found to decrease substantially with an increase in temp. and was enhanced by an increase in the partial pressure of CO and beyond a styrene concn. of 3.84 kmol/m3. The rate of carboxylation varied linearly with the catalyst and was zero order with respect to styrene concn. in the range of 0.567- 3.84 kmol/m3. An unusual trend of an increase in activity was obsd. beyond a styrene concn. of 3.84 kmol/m3. The rate also increased with an increase in the partial pressure of CO initially and was independent beyond 3.4 MPa. Water showed a promoting effect up to a concn. of 9.244 × 10-2 kmol/m3. On the basis of the initial rate data obtained, a rate equation was proposed and the kinetic parameters evaluated. The activation energy was found to be 65.49 kJ/mol. Also, a plausible reaction mechanism for the carboxylation of styrene has been proposed.