Achieving pH and Qr oscillations in a palladium-catalysed phenylacetylene oxidative carbonylation reaction using an automated reactor system

2014

The palladium-catalyzed oxidative carbonylation of phenylacetylene (PCPOC reaction) is known to exhibit autonomous oscillations in a variety of parameters including pH, redox potential and heat of reaction. Previous studies report that external addition of both an oxidizing agent and water is required to allow production/ consumption of H ? in an oscillatory fashion. In this work we show that solutions of PdI 2 / KI dried over 3 Å molecular sieves can catalyze phenylacetylene carbonylation in the absence of an external oxidizing agent. Oscillations are readily achieved in this considerably simplified PCPOC system. Palladium-catalyzed carbonylation of methanol generates HI as a by-product, which can react with excess KI and methanol producing methyl iodide and water in situ. Methyl iodide can also undergo decomposition, generating iodine as an internally formed oxidizing agent, which accounts for recorded catalyst regeneration. Oscillations are observed in the pH range 1.5-3.5 commencing, at the earliest, 70 min after introduction of phenylacetylene. Oscillations vary in period between 1 and 3.5 h and last for several days. The onset of oscillations may be delayed via portion-wise addition of the phenylacetylene substrate.

Section: Introductionmentioning

confidence: 60%

Section: Resultsmentioning

confidence: 90%

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Oscillatory carbonylation of phenylacetylene in the absence of externally supplied oxidant

Donlon

2014

“…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.…”

Section: Resultsmentioning

confidence: 99%

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

2017

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 9 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.

“…When phenylacetylene (PhAc) was used as the substrate in methanol (palladium-catalyzed phenylacetylene oxidative carbonylation, PCPOC), oscillations in pH, redox potential and gas uptake (CO and O 2 ) were discovered [3][4][5][6][7]. Further study of this reaction using power compensation calorimetry found the oscillations in pH were accompanied by oscillations in heat of reaction, Q r [8]. The products of the reaction have been identified in both oscillatory and non-oscillatory modes and consist of mono-and di-esters, anhydrides, acids and heterocyclic compounds depending on the reaction conditions [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Autonomous reorganization of the oscillatory phase in the PdI2 catalyzed phenylacetylene carbonylation reaction

2016

The PdI 2 catalyzed oxidative carbonylation of phenylacetylene has been shown to produce pH oscillations over the temperature range 0-40°C under semibatch conditions. The decrease in reaction temperature resulted in an increase in the period and amplitude of the pH oscillations. In addition, reducing the reaction temperature enabled the observation of different phases in the oscillatory pH behavior confirming the ability of the reaction system to autonomously produce multiple clusters of oscillatory phases. Sets of pH oscillations were recorded at 0 and 10°C. At temperatures of 0-20°C, oscillations commenced as pH was falling during the initial stages of the reaction while, at 30 and 40°C, the oscillations commenced once the pH started to increase after the initial drop. Oscillations in turbidity were observed at 20 and 30°C. Experiments were conducted in an HEL Simular reaction calorimeter enabling precise temperature control. Operating at 0°C reduced the reaction rate prolonging the duration of pH oscillations. The oscillatory pH behavior was recorded for 11 days without additional substrate at which point the run was terminated although the oscillations would likely have continued.