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1. OH chemistry of non-methane organic gases (NMOGs) emitted from laboratory and ambient biomass burning smoke: evaluating the influence of furans and oxygenated aromatics on ozone and secondary NMOG formation

   https://doi.org/10.5194/acp-19-14875-2019  

   Coggon, Matthew M.; Lim, Christopher Y.; Koss, Abigail R.; Sekimoto, Kanako; Yuan, Bin; Gilman, Jessica B.; Hagan, David H.; Selimovic, Vanessa; Zarzana, Kyle J.; Brown, Steven S.; et al (January 2019, Atmospheric Chemistry and Physics)

   Abstract. Chamber oxidation experiments conducted at the Fire Sciences Laboratory in 2016 are evaluated to identify important chemical processes contributing to the hydroxy radical (OH) chemistry of biomass burning non-methane organic gases (NMOGs). Based on the decay of primary carbon measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), it is confirmed that furans and oxygenated aromatics are among the NMOGs emitted from western United States fuel types with the highest reactivities towards OH. The oxidation processes and formation of secondary NMOG masses measured by PTR-ToF-MS and iodide-clustering time-of-flight chemical ionization mass spectrometry (I-CIMS) is interpreted using a box model employing a modified version of the Master Chemical Mechanism (v. 3.3.1) that includes the OH oxidation of furan, 2-methylfuran, 2,5-dimethylfuran, furfural, 5-methylfurfural, and guaiacol. The model supports the assignment of major PTR-ToF-MS and I-CIMS signals to a series of anhydrides and hydroxy furanones formed primarily through furan chemistry. This mechanism is applied to a Lagrangian box model used previously to model a real biomass burning plume. The customized mechanism reproduces the decay of furans and oxygenated aromatics and the formation of secondary NMOGs, such as maleic anhydride. Based on model simulations conducted with and without furans, it is estimated that furans contributed up to 10 % of ozone and over 90 % of maleic anhydride formed within the first 4 h of oxidation. It is shown that maleic anhydride is present in a biomass burning plume transported over several days, which demonstrates the utility of anhydrides as markers for aged biomass burning plumes. 

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2. Impact of Bentonite Clay on In Situ Pyrolysis vs. Hydrothermal Carbonization of Avocado Pit Biomass

   https://doi.org/10.3390/catal12060655  

   Karod, Madeline; Pollard, Zoe A.; Ahmad, Maisha T.; Dou, Guolan; Gao, Lihui; Goldfarb, Jillian L. (June 2022, Catalysts)

   Biofuels produced via thermochemical conversions of waste biomass could be sustainable alternatives to fossil fuels but currently require costly downstream upgrading to be used in existing infrastructure. In this work, we explore how a low-cost, abundant clay mineral, bentonite, could serve as an in situ heterogeneous catalyst for two different thermochemical conversion processes: pyrolysis and hydrothermal carbonization (HTC). Avocado pits were combined with 20 wt% bentonite clay and were pyrolyzed at 600 °C and hydrothermally carbonized at 250 °C, commonly used conditions across the literature. During pyrolysis, bentonite clay promoted Diels–Alder reactions that transformed furans to aromatic compounds, which decreased the bio-oil oxygen content and produced a fuel closer to being suitable for existing infrastructure. The HTC bio-oil without the clay catalyst contained 100% furans, mainly 5-methylfurfural, but in the presence of the clay, approximately 25% of the bio-oil was transformed to 2-methyl-2-cyclopentenone, thereby adding two hydrogen atoms and removing one oxygen. The use of clay in both processes decreased the relative oxygen content of the bio-oils. Proximate analysis of the resulting chars showed an increase in fixed carbon (FC) and a decrease in volatile matter (VM) with clay inclusion. By containing more FC, the HTC-derived char may be more stable than pyrolysis-derived char for environmental applications. The addition of bentonite clay to both processes did not produce significantly different bio-oil yields, such that by adding a clay catalyst, a more valuable bio-oil was produced without reducing the amount of bio-oil recovered. 

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3. Bifunctional Phosphine Ligand Enabled Gold‐Catalyzed Alkynamide Cycloisomerization: Access to Electron‐Rich 2‐Aminofurans and Their Diels–Alder Adducts

   https://doi.org/10.1002/ange.201908598  

   Li, Xingguang; Ma, Xu; Wang, Zhixun; Liu, Pei‐Nian; Zhang, Liming (October 2019, Angewandte Chemie)

   Abstract By using biphenyl‐2‐ylphosphines functionalized with a remote tertiary amino group as a ligand, readily available acetylenic amides are directly converted into 2‐aminofurans devoid of any electron‐withdrawing and hence deactivating/stabilizing substituents. These highly electron‐rich furans have rarely been prepared, let alone applied in synthesis, because of their high reactivities and low stabilities associated with the electron‐rich nature of the furan ring. In this work, these reactive furans smoothly undergo either in situ intermolecular Diels–Alder reactions to deliver highly functionalized/substituted aniline products or intramolecular ones to furnish carbazole‐4‐carboxylates in mostly good to excellent yields. This work offers general and expedient access to this class of little studies electron‐rich furans and should lead to exciting opportunities for their applications. 

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4. Heterolytic Cleavage of L _n Pd–SiR ₃ ⁺ Bonds Enable the Ring-Opening C–C Functionalization of Nonstrained Ethers

   https://doi.org/10.1021/jacs.5c12528  

   Owen, Bradley A; Basemann, Kevin; Hearne, William A; Gagné, Michel R (August 2025, Journal of the American Chemical Society)

   Silyl palladium cations (R3P)2Pd–SiR3+ catalyze the ring opening, C–C bond forming, and functionalization of 5- and 6-membered cyclic allyl ethers with O-silyl nucleophiles. Conditions for high regio-control are achieved by adjustments in the phosphine electronics, with the identity of the 2-substituent also influencing the functionalization location in unsymmetrical furans. Allyl alcohols are obtained with a regio-preference for terminal addition with unsubstituted ethers with E-products being obtained with XantPhos and Z- with (4-CF3–Ar)3 ligation. Styrenes dominate with phenyl-substituted dihydrofurans, and for 2-alkyl-substituted, secondary alcohols result from an allyl migration pathway. Mechanistic studies demonstrate the feasibility of Pd–Si+ bonds to facilitate C–O activation to yield π-allyl intermediates, and for one substrate class to also sequence π-allyl migration prior to nucleophilic addition. DFT calculations demonstrated the viability of silylium-activated ether as a competent ligand for Pd(0). 

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5. Revisiting the reaction of dicarbonyls in aerosol proxy solutions containing ammonia: the case of butenedial

   https://doi.org/10.5194/acp-21-8809-20  

   Jack C. Hensley, Adam W. (April 2021, Atmospheric chemistry and physics)

   null (Ed.)

   Reactions in aqueous solutions containing dicarbonyls (especially the α-dicarbonyls methylglyoxal, glyoxal, and biacetyl) and reduced nitrogen (NHx) have been studied extensively. It has been proposed that accretion reactions from dicarbonyls and NHx could be a source of particulate matter and brown carbon in the atmosphere and therefore have direct implications for human health and climate. Other dicarbonyls, such as the 1,4-unsaturated dialdehyde butenedial, are also produced from the atmospheric oxidation of volatile organic compounds, especially aromatics and furans, but their aqueous-phase reactions with NHx have not been characterized. In this work, we determine a pH-dependent mechanism of butenedial reactions in aqueous solutions with NHx that is compared to α-dicarbonyls, in particular the dialdehyde glyoxal. Similar to glyoxal, butenedial is strongly hydrated in aqueous solutions. Butenedial reaction with NHx also produces nitrogen-containing rings and leads to accretion reactions that form brown carbon. Despite glyoxal and butenedial both being dialdehydes, butenedial is observed to have three significant differences in its chemical behavior: (1) as previously shown, butenedial does not substantially form acetal oligomers, (2) the butenedial/OH− reaction leads to light-absorbing compounds, and (3) the butenedial/NHx reaction is fast and first order in the dialdehyde. Building off of a complementary study on butenedial gas-particle partitioning, we suggest that the behavior of other reactive dialdehydes and dicarbonyls may not always be adequately predicted by α-dicarbonyls, even though their dominant functionalities are closely related. The carbon skeleton (e.g., its hydrophobicity, length, and bond structure) also governs the fate and climate-relevant properties of dicarbonyls in the atmosphere. If other dicarbonyls behave like butenedial, their reaction with NHx could constitute a regional source of brown carbon to the atmosphere. 

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