KINETICS OF CARBOXYLATION OF STYRENE USING A HOMOGENEOUS PALLADIUM COMPLEX CATALYST

Kinetics of carboxylation of styrene to methyl 2-phenylpropionate and methyl 3-phenylpropionate has been investigated using a homogeneous Pd (OAc)(2)/PPh3/p-toluenesulfonic acid catalyst system. The effect of co ncentration of styrene, catalyst, water, and partial pressure of CO on the activity, selectivity, and rate of reaction has been studied in a temperature range of 338-358 K. The activity of the catalyst as well as the selectivity of the products was sensitive to all the reaction p arameters studied. The selectivity of 2-phenylpropionate was found to decrease substantially with an increase in temperature and was enhance d by an increase in the partial pressure of CO and beyond a styrene co ncentration of 3.84 kmol/m(3). The rate of carboxylation varied linear ly with the catalyst and was zero order with respect to styrene concen tration in the range of 0.567-3.84 kmol/m(3). An unusual trend of an i ncrease in activity was observed beyond a styrene concentration of 3.8 4 kmol/m(3). The rate also increased with an increase in the partial p ressure of CO initially and was independent beyond 3.4 MPa. Water show ed a promoting effect up to a concentration of 9.244 x 10(-2) kmol/m(3 ). 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.