Molecule-Induced Peroxide Homolysis

The autoxidation of polyether-polyurethane open cell soft foam: An analytical aging method to reproducibly determine VOC emissions caused by thermo-oxidative degradation

We present a new method for investigating the oxidation and emission behavior of air-permeable materials. Employing this method, a differentiated statement can be made about the extent to which critical volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, and acrolein are contained in the material as impurities or formed by thermo-oxidative degradation of the polymer matrix in the use phase. The parameters affecting methods of VOC analysis are reviewed and considered for the developed method. The molecular mechanisms of VOC formation are discussed. Toxicological implications of the reaction kinetics are put into context with international guidelines and threshold levels. This new method enables manufacturers of cellular materials not only to determine the oxidative stability of their products but also to optimize them specifically for higher durability. ENVIRONMENTAL IMPLICATION: Cellular materials are ubiquitous in the technosphere. They play a crucial role in various microenvironments such as automotive interiors, building insulation, and cushioning. These materials are susceptible to oxidative breakdown, leading to the release of formaldehyde, acetaldehyde, and acrolein. The ecotoxicological profiles of these compounds necessitate monitoring and regulation. The absence of reproducible and reliable analytical methods restricts research and development aimed at risk assessment and mitigation. This work significantly enhances the toolbox for optimizing the oxidative stability of any open-cell cellular material and evaluating these materials in terms of their temperature-dependent oxidation and emission behavior.

Acetic Acid: An Underestimated Metabolite in Ethanol-Induced Changes in Regulating Cardiovascular Function

Acetic acid is a bioactive short-chain fatty acid produced in large quantities from ethanol metabolism. In this review, we describe how acetic acid/acetate generates oxidative stress, alters the function of pre-sympathetic neurons, and can potentially influence cardiovascular function in both humans and rodents after ethanol consumption. Our recent findings from in vivo and in vitro studies support the notion that administration of acetic acid/acetate generates oxidative stress and increases sympathetic outflow, leading to alterations in arterial blood pressure. Real-time investigation of how ethanol and acetic acid/acetate modulate neural control of cardiovascular function can be conducted by microinjecting compounds into autonomic control centers of the brain and measuring changes in peripheral sympathetic nerve activity and blood pressure in response to these compounds.

Using the Water Absorption Ability of Dried Hydrogels to Form Hydrogel-Supported Lipid Bilayers

The formation of supported lipid bilayers (SLBs) on hydrogels can act as a biocompatible anti-fouling interface. However, generating continuous and mobile SLBs on materials other than conventional glass or mica remains a significant challenge. The interaction between lipid membrane vesicles and a typical hydrogel is usually insufficient to induce membrane vesicle rupture and form a planar lipid membrane. In this study, we demonstrate that the water absorption ability of a dried polyacrylamide (PAAm) hydrogel could serve as a driving force to facilitate the formation of the hydrogel-SLBs. The absorption driving force vanishes after the hydrogels are fully hydrated, leaving no extra interaction hindering lipid lateral mobility in the formed SLBs. Our fluorescence recovery after photobleaching (FRAP) results show that SLBs only form on hydrogels with adequate absorption abilities. Moreover, we discovered that exposure to oxygen during drying could lead to the formation of an oxidized crust on the PAAm hydrogel surface, impeding SLB formation. Therefore, minimizing oxygen exposure during drying is crucial to achieving high-quality hydrogel surfaces for SLB formation. This water absorption method enables the straightforward fabrication of hydrogel-SLBs without the need for additional substrates or charges, thereby expanding their potential applications.

Strain-Promoted Oxidation of Methylenecyclopropane Derivatives using N-Hydroxyphthalimide and Molecular Oxygen in the Dark

The hydroperoxidation of alkylidenecyclopropanes and other strained alkenes using an N-hydroxylamine and molecular oxygen occurred in the absence of catalyst, initiator, or light. The oxidation reaction proceeds through a radical pathway that is initiated by autoxidation of the alkene substrate. The hydroperoxides were converted to their corresponding alcohols and ketones under mild conditions.

Radical-Pair Formation in Hydrocarbon (Aut)Oxidation

The reaction profiles for the uni- and bimolecular decomposition of benzyl hydroperoxide have been studied in the context of initiation reactions for the (aut)oxidation of hydrocarbons. The unimolecular dissociation of benzyl hydroperoxide was found to proceed through the formation of a hydrogen-bonded radical-pair minimum located +181 kJ mol^-1 above the hydroperoxide substrate and around 15 kJ mol^-1 below the separated radical products. The reaction of toluene with benzyl hydroperoxide proceeds such that O-O bond homolysis is coupled with a C-H bond abstraction event in a single kinetic step. The enthalpic barrier of this molecule-induced radical formation (MIRF) process is significantly lower than that of the unimolecular O-O bond cleavage. The same type of reaction is also possible in the self-reaction between two benzyl hydroperoxide molecules forming benzyloxyl and hydroxyl radical pairs along with benzaldehyde and water as co-products. In the product complexes formed in these MIRF reactions, both radicals connect to a centrally placed water molecule through hydrogen-bonding interactions.

Oxidative functionalization of C–H compounds induced by the extremely efficient osmium catalysts (a review)

In recent years, osmium complexes have found applications not only in thecis-hydroxylation of olefins but also very efficient in the oxygenation of C–H compounds (saturated and aromatic hydrocarbons and alcohols) by hydrogen peroxide as well as organic peroxides.

Unravelling the radical transition during the carbon-catalyzed oxidation of cyclohexane by in situ electron paramagnetic resonance in the liquid phase

The selective oxidation of hydrocarbons is of great importance in the chemical industry.

Selective oxidative dehydrogenation of propane to propene using boron nitride catalysts

The exothermic oxidative dehydrogenation of propane reaction to generate propene has the potential to be a game-changing technology in the chemical industry. However, even after decades of research, selectivity to propene remains too low to be commercially attractive because of overoxidation of propene to thermodynamically favored CO₂ Here, we report that hexagonal boron nitride and boron nitride nanotubes exhibit unique and hitherto unanticipated catalytic properties, resulting in great selectivity to olefins. As an example, at 14% propane conversion, we obtain selectivity of 79% propene and 12% ethene, another desired alkene. Based on catalytic experiments, spectroscopic insights, and ab initio modeling, we put forward a mechanistic hypothesis in which oxygen-terminated armchair boron nitride edges are proposed to be the catalytic active sites.

Initiation Chemistries in Hydrocarbon (Aut)Oxidation

For the (aut)oxidation of toluene to benzyl hydroperoxide, benzyl alcohol, benzaldehyde, and benzoic acid, the thermochemical profiles for various radical-generating reactions have been compared. A key intermediate in all of these reactions is benzyl hydroperoxide, the heat of formation of which has been estimated by using results from CBS-QB3, G4, and G3B3 calculations. Homolytic O-O bond cleavage in this hydroperoxide is strongly endothermic and thus unlikely to contribute significantly to initiation processes. In terms of reaction enthalpies the most favorable initiation process involves bimolecular reaction of benzyl hydroperoxide to yield hydroxy and benzyloxy radicals along with water and benzaldehyde. The reaction enthalpy and free energy of this process is significantly more favorable than those for the unimolecular dissociation of known radical initiators, such as dibenzoylperoxide or dibenzylhyponitrite.

Mechanism evolution for the oxidative dehydrogenation of ethyl benzene to styrene over V2O5/TiO2 catalyst: computational and kinetic approach

A kinetic study of the oxidative dehydrogenation of ethylbenzene has been performed in a differential flow reactor over a V₂O₅/TiO₂ catalyst.

Aerobic oxidation of alkylaromatics using a lipophilic N-hydroxyphthalimide: overcoming the industrial limit of catalyst solubility

4,4'-(4,4'-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO-H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated.

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

Since the beginning of the century, N-hydroxyphthalimide and related compounds have been revealed to be efficient organocatalysts for free-radical processes and have found ample application in promoting the aerobic oxidation of a wide range of organic substrates. When combined with different co-catalysts, they are activated to the corresponding N-oxyl radical species and become able to promote radical chains, involving molecular oxygen, directly or indirectly. Most of the examples reported in the literature describe the use of these N-hydroxy derivatives in the presence of transition-metal complexes. However, eco-friendly standards, including the demand for highly selective transformations, impose the development of metal-free processes, especially for large-scale productions, as in the case of the oxygenation of hydrocarbons. For this reason, many efforts have been devoted in the past decade to the design of new protocols for the activation of N-hydroxy imides in the presence of nonmetal initiators. Herein we provide a concise overview of the most significant and successful examples in this field, with the final aim to furnish a useful instrument for all scientists actively involved in the O₂-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis.