The influence of reaction temperature on the oscillatory behaviour in the palladium-catalysed phenylacetylene oxidative carbonylation reaction

Abstract

This paper reports the influence of reaction temperature on the occurrence and characteristics of pH oscillations that are observed during the palladium-catalysed phenylacetylene oxidative carbonylation reaction in a catalytic system (PdI2, KI, air, NaOAc) in methanol. Isothermal experiments were performed over the temperature range 10-50 degrees C. The experiments demonstrate that oscillations occur in the range 10-40 degrees C and that a decrease in reaction temperature results in an increase in the period and amplitude of the pH oscillations. Furthermore, it is observed that during oscillations at any specific temperature, the time taken for pH to increase from a minimum to a maximum value varies with respect to reaction time. However, the time required for the pH to fall from maximum to new minimum is approximately constant with respect to the reaction time and is a function of the reaction temperature.

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

“…Previous studies of the PCPOC reaction at temperatures from 0 to 40°C found that changing the reaction temperature produced changes in the shape of the pH oscillations [7,12]. Increasing the water content of the reaction also affects the shape of the pH oscillations as shown in Table 3.…”

“…3d). As reactions where conducted in a reaction calorimeter, it was possible to apply power compensation calorimetry to record changes in reaction heat over time [7,12,13,16]. Oscillations in heater power were still evident with 5, 20 and 30% water, were in phase with the pH oscillations and reflected the changes in the pH oscillations as shown in Fig.…”

“…This temperature was selected as being within the interval that previously demonstrated oscillatory pH behavior for the PCPOC system. In previously reported results, this temperature gave pH oscillations with a maximum period of 45 min and a reaction time of 3600 min when compared to lower temperature runs that exhibited oscillatory behavior that lasted for several weeks [7,12,13]. All experiments were carried out in an HEL Simular reaction calorimeter so that changes in pH and reaction heat (Q r ) could be monitored continuously for extended periods of time.…”

Oscillatory carbonylation of phenylacetylene in the absence of externally supplied oxidant

“…In addition, it is revealed that this oscillatory system does not require an external oxidizing agent in order for catalyst recycling to occur. Furthermore, oscillatory behavior is recorded using considerably lower concentrations of both PdI 2 (approximately fivefold) and phenylacetylene (approximately 40-80-fold) compared to those reported previously [9][10][11]17]. As a result, the transparency of the reaction solution is significantly increased.…”

“…The pH then exhibits a steady rise over a period of 600 min after which stable oscillations in pH commence. The induction period observed prior to entering the oscillatory region is considerably shorter than the 2,000 min recorded previously at similar temperatures [17]. Temkin and co-workers [6,8] were able to achieve oscillations in pH within minutes of starting a PCPOC reaction, however they reported an experimental setup using mixed gases (CO/O 2 ) and higher reaction temperatures (40°C).…”