Aerobic Oxidative Esterification of Benzyl Alcohol and Acetaldehyde over Gold Supported on Nanostructured Ceria-Alumina Mixed Oxides

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols

The direct oxidative esterification of benzaldehydes and benzyl alcohols to high value-added aromatic esters under mild and green reaction conditions is significant in the fine chemical industry. The accurate design of catalysts with high catalytic performance is crucial for this process. Herein, 2,4,6-trimethylpyridine, benzoic anhydride, and terephthalaldehyde were used to prepare a covalent organic framework (COF) material, which was then used as a template to construct a mesoporous CeO2-supported Au nanoparticles catalyst. The obtained Au@CeO2 catalyst was thoroughly characterized, and it possessed a mesoporous structure with a high surface area. Meanwhile, the as-prepared Au@CeO2 exhibited excellent catalytic performance in the oxidative esterification of benzaldehydes and benzyl alcohols with methanol, affording the corresponding aromatic esters under mild and green reaction conditions. Furthermore, the Au@CeO2 catalyst could also be recycled. Therefore, this study provides a green and sustainable pathway for the synthesis of high-value-added esters through a direct oxidative esterification strategy.

Insight into the Effective Aerobic Oxidative Cross-Esterification of Alcohols over Au/Porous Boron Nitride Catalyst

Boron nitride (BN) has attracted great attention with an unexpected ability in aerobic catalysis. Still, its related probe reactions are relatively rare, and the effect of the BN-supported metal catalyst on O₂ activation is still ambiguous, and opinions are varied. In this work, the porous BN (pBN)-supported Au catalyst with a porous structure and exposed edges exhibits high activity in the oxidative cross-esterification reactions between the aromatic and C₁-C₃ aliphatic alcohols at ambient temperature. The turnover frequency value for methyl benzoate is 118 h^-1 at 30 °C, and the calculated apparent activation energy (Ea, 58 kJ/mol) is comparable to that of AuPd/TiO₂, Ru/Al₂O₃, and PdBiTe catalysts. Combined with temperature-programmed  desorption (TPD) results, the loading of Au enhances the desorption of O₂ and the interaction with alcohols; thus, a synergistic effect between the O-rich pBN and Au is considered. The free-radical scavenger can dramatically suppress the conversion (∼6%), suggesting that the reaction proceeds via the O₂* radicals. According to the vibration of ν_O-O, δ_OO-H, and ν_B-O-O-B detected by attenuated total reflectance-infrared spectroscopy (ATR-IR), we are prone to consider the oxygen activation route by the edge B atoms. Then, a possible L-H reaction mechanism was proposed: benzyl alcohol and O₂ adsorb on the Au/pBN initially, then O₂ is converted to O₂*, and the α-H elimination proceeds; as the semi-acetal formed, another α-H elimination proceeds and methyl benzoate is finally formed.

Pd-Colloids-Catalyzed/Ag2 O-Oxidized General and Selective Esterification of Benzylic Alcohols

Palladium colloids obtained from the degradation of Hermann-Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative-esterification successfully.

Development of N-Doped Carbon-Supported Cobalt/Copper Bimetallic Nanoparticle Catalysts for Aerobic Oxidative Esterifications Based on Polymer Incarceration Methods

Heterogeneous nitrogen-doped carbon-incarcerated cobalt/copper bimetallic nanoparticle (NP) catalysts, prepared from nitrogen-containing polymers, were developed, and an efficient catalytic process for aerobic oxidative esterification was achieved in the presence of a low loading (1 mol %) of catalyst that could be reused and easily reactivated. This protocol enabled diverse conditions for the bimetallic NP formation step to be screened, and significant rate acceleration by inclusion of a copper dopant was discovered. The catalytic activity of the bimetallic Co/Cu catalysts is much higher than that for cobalt catalysts reported to date and is even comparable with noble-metal NP catalysts.

Promoting effects of MgO, (NH4)2SO4or MoO3modification in oxidative esterification of methacrolein over Au/Ce0.6Zr0.4O2-based catalysts

The MgO, (NH₄)₂SO₄or MoO₃-modified Au/Ce_0.6Zr_0.4O₂catalysts presented better catalytic performance in the oxidative esterification of MAL to MMA and the active oxygen species assigned to low-temperature reduction played a significant role.