Acetic acid conversion to ketene on Cu2O(1 0 0): Reaction mechanism deduced from experimental observations and theoretical computations

Molecular Understanding of the Catalytic Consequence of Ketene Intermediates under Confinement

“…Ketenes, as one type of common active complexes in nucleophilic additions of organic synthesis, , can also act as a key intermediate with the simplest formula (CH 2 CO) during zeolite-catalyzed C1 chemistry, such as methanol to olefins (MTO), , dimethyl ether (DME) carbonylation to methyl acatate (MA), , carbon dioxide to hydrocarbons, syngas conversion, , and etc. , (Scheme ) For example, during the multicatalyst relay catalysis of oxide-zeolite for selective conversion of syngas to light olefins, ketene is produced from syngas over a metal oxide catalyst (e.g., ZnCrO x ), which then diffuses into silicoaluminophosphate (SAPO) or MOR and further reacts with Brønsted acidic sites (BAS) to ultimately attain the desirable light olefins (C 2 = –C 4 = ) selectivity under the shape selectivity of zeolites. , Similar chemistry has been exploited for direct hydrogenation of CO 2 to hydrocarbons by the bifunctional catalyst system comprising potassium superoxide doped iron oxide and acidic zeolites (e.g., ZSM-5 or MOR). Ketene generated from the deprotonation of surface acetyl over zeolitic catalyst has been shown to promote methylation and decarbonylation reactions during the MTO process. , However, ketene is also known to give rise to catalyst deactivation via coke deposition. , Evaluating the genuine role of ketene and its derivatives during catalytic reactions involving C1 feedstock is, therefore, a demanding but essential task.…”

Conditions Leading to Ketene Formation in Vaping Devices and Implications for Public Health

“…While the EVALI epidemic was due to acute respiratory damage from ketene derived from VEA, the general principle of acetates, including acetic acid itself, serving as starting materials for ketene formation holds and has been extensively documented in the chemistry literature. 13,17,20 In the gas phase, the reaction of ketene with water to form acetic acid has been shown to be relatively slow due to a high activation energy barrier, which is consistent with its potential to inflict lung tissue damage if inhaled. 32 Computational and experimental studies of chemical reaction energies indicate that a wide range of other acetates can also form ketene.…”

“…32 Computational and experimental studies of chemical reaction energies indicate that a wide range of other acetates can also form ketene. 8,13,17,20 Thermal degradation of various esters into acids, aldehydes, olefins, and ketene has been previously well documented. 33,34 Among them, the thermal decomposition of phenyl acetate brought much attention recently because it shares a similar aryl acetate group with VEA, a possible causative chemical compound that is responsible for the EVALI outbreak.…”

“…Various metals, including nickel, chromium, copper, iron, and aluminum, as well as silicon-rich rubbers, fluorinated polymers, and glass fiber, were found in the devices used by EVALI patients. 18 Tissot and colleagues 20 established that ketene is formed under conditions of some heat (approximately 350 °C) and that the energy required for this reaction is greatly reduced in the presence of a copper metal catalyst. The common factor in these reactions is the presence of heat and contact with metallic surfaces.…”

“…Vaping devices employ heating filaments that have metallic components that include nickel, chromium, iron, and aluminum . These metals, including copper, titanium, silver, and other metal oxides, are known to serve as catalysts in the production of ketene under industrial application conditions. − Indications are emerging that the metal components within vaping devices play a role in ketene formation, with reports showing that the thermal decomposition of VEA occurs at 356 °C in vaping, considerably lower than in a laboratory tube furnace (800–1200 °C), which does not contain metal components . Ketene is difficult to measure using conventional chromatography from collected air samples due to its highly reactive and transient nature.…”