Restricting Effect of Solvent Aggregates on Distribution and Mobility of CuCl2 in Homogenous Catalysis

Extensive experimental and theoretical studies have proven the existence of solvent aggregates in alcohols, and some attempts have been made to explore the uneven distribution of solutes. Here, we studied the distribution and mobility of CuCl2 in 3-hexanol and ethanol and investigated the aerobic oxidation of 2,3,6-trimethylphenol under these systems. Small- and wide-angle X-ray scattering was applied to study the solvent aggregates and reveal the distribution of CuCl2 in alcohols. The electrical conductivity was used to study the mobility of CuCl2 in 3-hexanol and ethanol. As a result, while nearly homodisperse and free movement of CuCl2 was observed in ethanol, the CuCl2 was restricted within the polar regions of stable solvent aggregates in 3-hexanol. With the increase of CuCl2 concentration in 3-hexanol, the electron paramagnetic resonance suggested the switch of CuCl2 nuclearity from mononuclear to multinuclear, and meanwhile, the aerobic oxidation of 2,3,6-trimethylphenol was turned from aerobic oxidative coupling to oxygenation. Furthermore, when the same reaction was carried out in different alcohols, the effectivity of controlling the reaction pathway was found to decrease as the solvent possesses less stable solvent aggregates, and the main pathway in ethanol was always oxygenation whenever the reaction was catalyzed by 2 or 10 mM CuCl2.