The effect of using a methanol–water solvent mixture on pH oscillations in the palladium-catalyzed phenylacetylene oxidative carbonylation reaction

Abstract

The palladium-catalyzed phenylacetylene oxidative carbonylation reaction has been shown to produce regular oscillations in pH, reaction heat, and turbidity when conducted in batch with methanol as solvent. Previous studies of the catalytic system showed that water plays an important role in the behavior of the catalytic cycle. Investigating this role further, the reaction was performed in methanol–water mixtures. Experiments demonstrated that, under the conditions studied, oscillations in pH are feasible when the water concentration in the system is increased (0–30 V%). At the same time oscillations visually changed, being transformed from regular oscillations to more stepwise behavior as the proportion of water is increased. By establishing the relationship between the recorded pH and HI concentration it was found that increased water concentration suppresses HI formation and hence slows the autocatalysis in the reaction. It was also found that oscillations begin when the HI concentration is in the region of 1 × 10−3 mol L−1. Additionally, as the amount of water in the system increases a slight decrease in the concentration of HI when oscillations start was noted.