Jy. Yoon et al., A PALLADIUM COMPLEX CATALYST FOR THE REGIOSELECTIVE HYDROCARBOXYLATION OF 4-METHYLSTYRENE, Journal of molecular catalysis. A, Chemical, 118(2), 1997, pp. 181-187
With a homogeneous catalyst system of PdCl2-CuCl2-PPh3 dissolved in a
polar solvent, highly regioselective hydrocarboxylation of 4-methylsty
rene to the branched alpha-(4-methylphenyl) propionic acid has been ac
hieved. Effects of additives (mineral acids and O-2) and reaction cond
itions (amounts of catalyst components, reaction temperature, pressure
and solvents) have been studied. Compared with the previous results o
f hydrocarboalkoxylation of 4-methyl-styrene to the ester by the same
catalyst, the hydrocarboxylation required severer reaction conditions
and the presence of a polar solvent that could solubilize water. Effic
ient hydrocarboxylation was achieved only after fine adjustments of th
e reaction conditions and addition of a halogen compound. And the addi
tion of HCl improved the reaction rate significantly. This improvement
was due to the effect of chlorine, not the effect of the proton. The
addition of oxygen reduced reaction rates by oxidizing carbon monoxide
and PPh3.