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

Abstract

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.

Highly Efficient Synthesis of p-Benzoquinones Catalyzed by Robust Two-Dimensional POM-Based Coordination Polymers

“…Second, radical trapping experiments were used to determine whether the radical pathway exists, which is frequently proposed in Cu-catalyzed TMP oxidation. , As shown in Figure b, the conversion of TMP pronounced decreases to 54, 62, 42, and 65% for 1 , 2 , 3 , and 4 , respectively, when the reactions were carried out in the presence of Ph 2 NH (an efficient scavenger of oxygen radicals). Similarly, adding 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO, carbon-radical trap) will cause the conversion of TMP to be suppressed to 50–65%, which indicates that the intramolecular electron rearrangement may be along with this pathway.…”

“…Then, an alternative industrial synthesis of TMBQ was achieved by catalytic oxidation of TMP with CuCl 2 and O 2 . For this catalytic system, the co-catalysts, such as LiCl, MgCl 2 , NH 2 OH·HCl, and ionic liquids, or changing phase media, including mixed-phase systems, are required to achieve a high yield of the target BQs (>95%). − The main drawbacks of this process are the production of Cl-containing byproducts and the need for a special corrosion-resistant apparatus. Some recent attempts to reduce or avoid the use of CuCl 2 focused on the employment of di­(poly)­nuclear copper complexes (oxygenase analogs) coupled with oxygen as an oxidant .…”

A tiny charge‐scaling in the OPLS‐AA + L‐OPLS force field delivers the realistic dynamics and structure of liquid primary alcohols

“…Despite its widespread practical use, there remain intriguing questions regarding the microscopic characteristics of alcohols; for example, the self-organization in water, [1][2][3] the influence on conformational stability of macromolecules, [4][5][6] and the inhomogeneous mixing for catalytic reactions. 7,8 Molecular dynamics (MD) simulations fascinatingly deliver sub-nanometer scale insights. However, the single model that simultaneously reproduces dynamics and structure of liquid alcohols is lacked.…”

Distribution of Spin Density on Phenoxyl Radicals Affects the Selectivity of Aerobic Oxygenation of Phenols

“…Recently, we reported a solvent effect study on the copper-catalyzed oxidation of 2,3,6-TMP, in which the active state of catalyst was simulated by the reaction between CuCl–LiCl and dioxygen in alcohols. This species showed highly efficient dehydrogenating activity on 2,3,6-TMP, giving the phenoxyl radical.…”

“…11 Furthermore, with electron paramagnetic resonance (EPR), Brigati et al have investigated many para-substituted 2,6-di-tert-butyllphenoxyl radicals and revealed the relationship between the hyperfine coupling constant of meta protons and the O−H bond dissociation enthalpy. 12 Recently, we reported a solvent effect study on the coppercatalyzed oxidation of 2,3,6-TMP, 13 in which the active state of catalyst was simulated by the reaction between CuCl−LiCl and dioxygen in alcohols. This species showed highly efficient dehydrogenating activity on 2,3,6-TMP, giving the phenoxyl radical.…”