Catalyst Initiation in the Oscillatory Carbonylation Reaction

Palladium(II) iodide is used as a catalyst in the phenylacetylene oxidative carbonylation reaction that has demonstrated oscillatory behaviour in both pH and heat of reaction. In an attempt to extract the reaction network responsible for the oscillatory nature of this reaction, the system was divided into smaller parts and they were studied. This paper focuses on understanding the reaction network responsible for the initial reactions of palladium(II) iodide within this oscillatory reaction. The species researched include methanol, palladium(II) iodide, potassium iodide, and carbon monoxide. Several chemical reactions were considered and applied in a modelling study. The study revealed the significant role played by traces of water contained in the standard HPLC grade methanol used. 1. Introduction The palladium-catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction stands out in a number of respects. It provides a novel pH oscillator operating in a stirred batch reactor [1–8]. Furthermore, when operating the PCPOC system in an oscillatory regime high levels of product selectivity are reported compared to operating in a nonoscillatory mode [6]. The ability to achieve selective product formation in this way is a new and notable result in terms of reaction engineering that, once understood, may be imposed on and exploited in industrially significant reactions. Moreover, the PCPOC reaction represents the first example of complex molecules synthesised from relatively simple reagents proceeding in a catalytic system in an oscillatory mode. Scientifically this is significant as all other oscillating processes, including those driven by heterogeneous catalysis, involve the oxidation, hydrogenation, or destruction of complex molecules [3]. In addition to oscillations in pH, the PCPOC reaction has the capacity to produce significant oscillatory pulses of heat (i.e., 600？J/oscillation) over long periods of time (i.e., days) that may be regulated by the reaction conditions [5, 6, 8]. For that reason, the importance of the PCPOC reaction for pH and temperature-responsive “smart materials” and their future applications may be foreseen, for example, in drug delivery [9]. The aforementioned results imply the need for a fundamental understanding of the PCPOC reaction in order to make use of the observed phenomena and apply the knowledge gained to other systems. The key to achieving this is in obtaining a reaction network (i.e., rate determining reactions in a chemical mechanism) responsible for the oscillatory nature of the PCPOC reaction. The PCPOC