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1. pH-Controlled forms of 1-amino-1-hydrazino-2,2-dinitroethylene (HFOX): selective reactivity of amine and hydrazinyl groups with aldehydes or ketones

   https://doi.org/10.1039/d2ma00307d  

   Chinnam, Ajay Kumar ; Staples, Richard J. ; Shreeve, Jean’ne M. ( May 2022 , Materials Advances)

   1-Amino-1-hydrazino-2,2-dinitroethylene (HFOX) is a potential reactive intermediate for a new class of energetic materials. Now we describe its condensation with various carbonyl compounds in the presence of acidic and basic catalysts. Condensation of HFOX with α-diones and β-diones gives products of much interest. α-Diones undergo cyclization in the presence of base to form six-membered ring products, while β-diones cyclize to five-membered ring products in the presence of acid. One of the exciting reactions is the formation of ammonium (5,6-dimethyl-1,2,4-triazin-3-yl)dinitromethanide salt, 5c, which was isolated by using aqueous ammonia as a nucleophilic base. All new compounds were fully characterized by advanced spectroscopic techniques. The structures of 5, 5c, 5e, 9, 11, and 12a are supported by single crystal X-ray diffraction analysis. Most of the new six membered ring compounds have good thermostabilities (>200 °C), while the fluorinated five membered ring compound, 12b, has the highest density of 2.04 g cm −3 at 25 °C. Heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 software programs. Nearly all new compounds have very good detonation properties, especially, triazine salts, 5e ( D v = 7513 m s −1 ; P = 24.45 G P a), and 5f ( D v = 7948 m s −1 ; P = 26.27 G P a) as well as azide derivative 11 ( D v = 8166 m s −1 ; P = 25.48 G P a), which are superior to TNT ( D v = 6824 m s −1 ; P = 19.40 G P a). These findings provide a new perspective for the synthesis of novel high performing energetic materials. 

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2. Acid Gas Capture by Nitrogen Heterocycle Ring Expansion

   https://doi.org/10.1021/acs.jpca.3c06094  

   Confer, Matthew P ; Dixon, David A ( December 2023 , The Journal of Physical Chemistry A)

   Acid gases including CO2, OCS, CS2, and SO2 are emitted by industrial processes such as natural gas production or power plants, leading to the formation of acid rain and contributing to global warming as greenhouse gases. An important technological challenge is to capture acid gases and transform them into useful products. The capture of CO2, CS2, SO2, and OCS by ring expansion of saturated and unsaturated substituted nitrogen-strained ring heterocycles was computationally investigated at the G3(MP2) level. The effects of fluorine, methyl, and phenyl substituents on N and/or C were explored. The reactions for the capture CO2, CS2, SO2, and OCS by 3- and 4-membered N-heterocycles are exothermic, whereas ring expansion reactions with 5-membered rings are thermodynamically unfavorable. Incorporation of an OCS into the ring leads to the amide product being thermodynamically favored over the thioamide. CS2 and OCS capture reactions are more exothermic and exergonic than the corresponding CO2 and SO2 capture reactions due to bond dissociation enthalpy differences. Selected reaction energy barriers were calculated and correlated with the reaction thermodynamics for a given acid gas. The barriers are highest for CO2 and OCS and lowest for CS2 and SO2. The ability of a ring to participate in acid gas capture via ring expansion is correlated to ring strain energy but is not wholly dependent upon it. The expanded N-heterocycles produced by acid gas capture should be polymerizable, allowing for upcycling of these materials. 

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3. Organosulfates Are Primarily Deprotonated at Atmospheric Aerosol Acidities: pH‐Dependent Protonation State via Raman and Infrared Spectroscopy.

   Fankhauser, Allison ; Lei, Ziying ; Daley, Kimberly ; Xiao, Yao ; Zhang, Zhang ; Gold, Avram ; Ault, Bruce ; Surratt, Jason ( October 2021 , 2021 AAAR 39th Annual Conference)

   Secondary organic aerosol (SOA) is a significant component of atmospheric fine particulate matter (PM2.5) globally that can form through multiphase chemistry of oxidized volatile organic compounds (VOC) leading to lower‐volatility particulate species. Condensed phase reactions of certain SOA constituents with inorganic sulfate derived from SO2 oxidation will lead to the formation of organosulfates, which can account for up to 10 – 15% of the organic mass within PM2.5. Despite the ubiquitous presence of atmospheric fine particulate organosulfates, our fundamental understanding of the molecular structure of organosulfates is limited, including for 2‐methyltetrol organosulfates (2‐MTSs), which are typically the single most abundant organosulfates measured in PM2.5, formed from isoprene oxidation products. As atmospheric aerosol pH varies widely (0 – 6), it is important to know whether organosulfates exist primarily in their protonated (ROSO3H) or deprotonated (ROSO3 ‐) forms. In this study, vibrational modes of synthetically‐pure 2‐MTSs were spectroscopically probed using Raman and infrared (IR) spectroscopies, supported by density functional theory (DFT) of the protonated and deprotonated structures. Vibrational bands at 1035 and 1059 cm‐1 were seen in both the IR and Raman spectra, and were associated with the ROSO3 ‐ anion by comparison to DFT calculations. Analysis of Raman spectra across a range of acidities (pH = 0 – 10) shows that 2‐MTSs are deprotonated (ROSO3 ‐) at those pH values. Additional DFT calculations for organosulfates derived from isoprene, α‐pinene, β‐caryophyllene, and toluene suggest that most organosulfates exist in their deprotonated form (ROSO3 ‐) in atmospheric particles. These charged species may have significant implications for our understanding of aerosol acidity and should be considered in thermodynamic model calculations. 

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4. Chemical Structure Regulates the Formation of Secondary Organic Aerosol and Brown Carbon in Nitrate Radical Oxidation of Pyrroles and Methylpyrroles

   https://doi.org/10.1021/acs.est.2c02345  

   Mayorga, Raphael ; Chen, Kunpeng ; Raeofy, Nilofar ; Woods, Megan ; Lum, Michael ; Zhao, Zixu ; Zhang, Wen ; Bahreini, Roya ; Lin, Ying-Hsuan ; Zhang, Haofei ( June 2022 , Environmental Science & Technology)

   Nitrogen-containing heterocyclic volatile organic compounds (VOCs) are important components of wildfire emissions that are readily reactive toward nitrate radicals (NO3) during nighttime, but the oxidation mechanism and the potential formation of secondary organic aerosol (SOA) and brown carbon (BrC) are unclear. Here, NO3 oxidation of three nitrogen-containing heterocyclic VOCs, pyrrole, 1-methylyrrole (1-MP), and 2-methylpyrrole (2-MP), was investigated in chamber experiments to determine the effect of precursor structures on SOA and BrC formation. The SOA chemical compositions and the optical properties were analyzed using a suite of online and offline instrumentation. Dinitro- and trinitro-products were found to be the dominant SOA constituents from pyrrole and 2-MP, but not observed from 1-MP. Furthermore, the SOA from 2-MP and pyrrole showed strong light absorption, while that from 1-MP were mostly scattering. From these results, we propose that NO3-initiated hydrogen abstraction from the 1-position in pyrrole and 2-MP followed by radical shift and NO2 addition leads to light-absorbing nitroaromatic products. In the absence of a 1-position hydrogen, NO3 addition likely dominates the 1-MP chemistry. We also estimate that the total SOA mass and light absorption from pyrrole and 2-MP are comparable to those from phenolic VOCs and toluene in biomass burning, underscoring the importance of considering nighttime oxidation of pyrrole and methylpyrroles in air quality and climate models. 

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5. Mono- N -oxidation of heterocycle-fused pyrimidines

   https://doi.org/10.1039/d0dt03260c  

   Tang, Yongxing ; Li, Kejia ; Chinnam, Ajay Kumar ; Staples, Richard J. ; Shreeve, Jean'ne M. ( February 2021 , Dalton Transactions)

   null (Ed.)

   Three nitrogen-rich heterocyclic compounds containing the diamino-pyrimidine mono- N -oxide moiety were synthesized via mild oxidation reactions. Oxidation of the furazano-pyrimidine compound ( 1 ) with a mixture of trifluoroacetic anhydride (TFAA) and hydrogen peroxide (50%) gave the nitrate salt ( 3 ). All of the compounds were characterized by NMR spectra, elemental analysis, and single-crystal X-ray diffraction. They show high thermal stability and good detonation performance as well as low sensitivity. 

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