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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 5
BKCSDE 32(5)
May 20, 2011 

Dependence of an Interfacial Diels-Alder Reaction Kinetics on the Density of the Immobilized Dienophile: An Example of Phase-Separation
Kyoungmi Min, Deokho Jung, Suin Chae, Youngeun Kwon *
SAMs, Diels-Alder reaction, Phase separation, Interfacial reaction kinetics, Electrochemistry
Interfacial reactions kinetics often differ from kinetics of bulk reactions. Here, we describe how the density change of an immobilized reactant influences the kinetics of interfacial reactions. Self-assembled monolayers (SAMs) of alkanethiolates on gold were used as a model interface and the Diels-Alder reaction between immobilized quinones and soluble cyclopentadiene was used as a model reaction. The kinetic behavior was studied using varying concentrations of quinones. An unusual threshold density of quinones (Γc = 5.2-7.2%), at which the pseudo-first order rate constant started to vary as the reaction progressed, was observed. This unexpected kinetic behavior was attributed to the phase-separation phenomena of multi-component SAMs. Additional experiments using more phase-separated two-component SAMs supported this explanation by revealing a significant decrease in Γc values. When the background hydroxyl group was replaced with carboxylic or phosphoric acid groups, Γc was observed at below 1%. Also, more phase-separated thermodynamically controlled SAMs produced a lower critical density (3% < Γc < 4.9%) than that of the less phaseseparated kinetically controlled SAMs (6.5% < Γc < 8.9%).
1679 - 1684
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