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1. Multigram Synthesis of a Combustion‐Relevant δ‐Ketohydroperoxide through Sulfonylhydrazine Substitution

   https://doi.org/10.1002/chem.202202266  

   Ke, Yan‐Ting; Gall, Bradley_K; Dewey, Nicholas_S; Rotavera, Brandon; Ferreira, Eric_M (September 2022, Chemistry – A European Journal)

   Abstract A synthesis of a δ‐ketohydroperoxide is described, addressing potential functional‐group compatibilities in these elusive species relevant to combustion and atmospheric chemistries. The hydroperoxide is installed via sulfonylhydrazine substitution, which was found to be more effective than displacement of secondary halides. As part of this protocol, it was observed that 1,2‐dimethoxyethane is an advantageous medium for the reaction, avoiding the formation of a tetrahydrofuran hydroperoxide side product. This discovery facilitated the multigram synthesis (6 steps, 41 % yield overall) and discrete characterization of the target δ‐ketohydroperoxide. 

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2. Role of curvature in acridone for ¹O₂ oxidation of a natural product homoallylic alcohol: A novel iso ‐hydroperoxide intermediate

   https://doi.org/10.1111/php.13843  

   Lapoot, Lloyd; Jabeen, Shakeela; Durantini, Andrés M.; Greer, Alexander (August 2023, Photochemistry and Photobiology)

   Abstract A density functional theoretical (DFT) study is presented, implicating a¹O₂oxidation process to reach a dihydrobenzofuran from the reaction of the natural homoallylic alcohol, glycocitrine. Our results predict an interconversion between glycocitrine and aniso‐hydroperoxide intermediate [R(H)O⁺–O⁻] that provides a key path in the chemistry which then follows. Formations of allylic hydroperoxides are unlikely from a¹O₂‘ene’ reaction. Instead, the dihydrobenzofuran arises by¹O₂oxidation facilitated by a 16° curvature of the glycocitrine ring imposed by a pyramidalN‐methyl group. This curvature facilitates the formation of theiso‐hydroperoxide, which is analogous to theisospecies CH₂I⁺–I⁻and CHI₂⁺–I⁻formed by UV photolysis of CH₂I₂and CHI₃. Theiso‐hydroperoxide is also structurally reminiscent of carbonyl oxides (R₂C=O⁺–O⁻) formed in the reaction of carbenes and oxygen. Our DFT results point to intermolecular process, in which theiso‐hydroperoxide's fate relates to O‐transfer and H₂O dehydration reactions for new insight into the biosynthesis of dihydrobenzofuran natural products. 

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3. SSZ-70 borosilicate delamination without sonication: effect of framework topology on olefin epoxidation catalysis

   https://doi.org/10.1039/c8dt03044h  

   Okrut, Alexander; Aigner, Martina; Schöttle, Christian; Grosso-Giordano, Nicolás A.; Hwang, Son-Jong; Ouyang, Xiaoying; Zones, Stacey; Katz, Alexander (October 2018, Dalton Transactions)

   We report a scalable delamination procedure for a SSZ-70-framework layered-zeolite precursor, which for the first time does not involve either sonication or long-chain surfactants. Our approach instead relies on the mild heating of layered zeolite precursor B-SSZ-70(P) in an aqueous solution containing Zn(NO 3 ) 2 and tetrabutylammonium fluoride. Powder X-ray diffraction data are consistent with a loss of long-range order along the z -direction, while 29 Si MAS NMR spectroscopy demonstrates preservation of the zeolite framework crystallinity during delamination. The resulting delaminated material, DZ-2, possesses 1.4-fold higher external surface area relative to the nondelaminated three-dimensional zeolite B-SSZ-70, based on N 2 physisorption data at 77 K. DZ-2 was functionalized with cationic Ti heteroatoms to synthesize Ti-DZ-2 via exchange with framework B. Ti-DZ-2 contains isolated titanium centers in its crystalline framework, as shown by UV-Vis spectroscopy. The generality of the synthetic delamination approach and catalyst synthesis is demonstrated with the synthesis of delaminated material DZ-3, which is derived from layered zeolite precursor ERB-1(P) with MWW framework topology. Upon catalytic testing for the epoxidation of 1-octene with ethylbenzene hydroperoxide as oxidant, under harsh tail-end conditions that deactivate amorphous Ti-silica-based catalysts, Ti-DZ-2 exhibits the highest per-Ti-site activity, selectivity, and stability for 1-octene epoxidation of all catalysts investigated. This testing includes the prior benchmark delaminated zeolite catalyst in this area, Ti-UCB-4, which possesses similar external surface area to Ti-DZ-2 but requires sonication and long-chain surfactants for its synthesis. The synthesis of DZ-2 is the first example of an economical delamination of layered zeolite precursor SSZ-70(P) and opens up new doors to the development of delaminated zeolites as commercial catalysts. 

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4. Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study

   https://doi.org/10.1063/5.0219431  

   Roy, Tarun Kumar; Qian, Yujie; Sojdak, Christopher A; Kozlowski, Marisa C; Klippenstein, Stephen J; Lester, Marsha I (July 2024, The Journal of Chemical Physics)

   Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010 cm−1 (∼10–20 kcal mol−1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products. 

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5. Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

   https://doi.org/10.1073/pnas.1916711117  

   Caravan, Rebecca L.; Vansco, Michael F.; Au, Kendrew; Khan, M. Anwar H.; Li, Yu-Lin; Winiberg, Frank A. F.; Zuraski, Kristen; Lin, Yen-Hsiu; Chao, Wen; Trongsiriwat, Nisalak; et al (April 2020, Proceedings of the National Academy of Sciences)

   Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester,J. Chem. Phys.149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only thesyn-conformers are observed;anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction ofsyn-MVK-oxide with SO₂and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO₃and identifying organic hydroperoxide formation from reaction with SO₂and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model. 

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