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Abstract Propylene oxide plays a pivotal role as an organic synthesis intermediate, boasting extensive downstream applications and promising market prospects. Propene epoxidation via molecular oxygen has garnered considerable attention due to its cost‐effectiveness, environmental friendliness, ease of operation, and straightforward product separation. This paper provides an in‐depth exploration of recent advancements, ranging from nanoparticle to Single‐atom catalysts (SACs), in the context of propene epoxidation using molecular oxygen. Conventional nanoparticle catalysts, including those based on Ag, Cu, and other metals, are examined with regard to their contributions to support effects, electron effects, or crystal‐plane effects within the mechanistic investigation. Furthermore, emerging SACs (specifically Mo, Cu, and Co) are discussed in terms of synthesis strategies, characterization methods, and mechanism studies. This comprehensive review sheds new light on design strategies, relevant characterizations, and thorough mechanism investigations aimed at fostering the development of efficient catalysts, thereby expediting progress in the industrial implementation of propene epoxidation.

The cis‐MoO2(acac)2 catalyzed epoxidation of ethylene by H2O2 or tert‐butyl hydroperoxide (TBHP) was studied by density functional theory at ωB97x–D using the 6‐31G(d,p) and 6‐311G(2d,p) basis sets and the PCM model to include the effect of acetonitril solvation. Three initial MoO2(acac)2⋅H2O2 adducts were identified. An associative pathway with a barrier of 26.7 kcal/mol is favored for H2O2 which inserts first into an acac ligand coordination site of the catalyst. TBHP favors instead a step‐wise mechanism in which a catalyst's Mo=O bond inserts into the oxidant upon which ethylene gets epoxidized by the hepta‐coordinate MoO(OH)(acac)2 (TBHP‐κ2O,O') intermediate with an activation energy of 33.8 kcal/mol. The reaction barriers for H2O2 and TBHP are both within the typical temperature range (70 °C) used for Mo catalyzed epoxidations. The results indicate that the mechanism depends largely on the nature of the oxidant and the dioxo molybdenum catalysts used. [ABSTRACT FROM AUTHOR]

Aim. To compare the mechanism of the epoxidation reaction of terpenes Geraniol and Limonene with peracetic acid and perbenzoic acid based on the quantum chemical study. Materials and methods. For the calculation the density functional theory (approximation UBH & HLYP/6-31G (d) Gaussian 09) method was applied. The specified density functional allows to correctly describing biradical structures; it is rather economic in terms of the computer time cost, which allows its use in the study of sufficiently complex organic compounds and reactions. Results and discussion. The quantum chemical study of mechanisms of the epoxidation reaction of such terpenes as Geraniol and Limonene with peracetic and perbenzonic acids using the density functional theory (approximation UBH & HLYP/6-31G (d) Gaussian 09 program) has been conducted. It has been shown that epoxidation of geraniol with both peroxyacids occurs preferably by the double bond C6=C7 due to stabilization of the corresponding transition state as a result of formation of hydrogen bond between the allyl hydroxyl group and the oxygen atom of the peroxy acid. Epoxidation of Limonene with perbenzoic and peracetic acids occurs via the cyclic double bond characterized by the lowest activation barrier, and it is consistent with the regioselectivity of the process generally known and experimentally proven. Conclusions. The results obtained are consistent with the experimental data, confirming the correctness of the use of this UBH & HLYP/6-31G (d) approach to study the regiochemical pecularities of the epoxidation process of alkenes containing several isolated double bonds.

A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO 2 (HL 5 )]·MeOH·H 2 O (H 2 L 5 = pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO 2 moiety. A DFT study of this molecule and of the related [VO 2 (H 2 L 5 )] complex of V IV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert -butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs . olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert -butoxido ( t BuOO – ) ligand, without the need to generate a peroxido (O 2 2– ) ligand. [ABSTRACT FROM AUTHOR]