ChemInform Abstract: Bimolecular Formation of Radicals by Hydrogen Transfer. Part 15. New Hydrogen Transfer Catalysts.

Morgenthaler, Jens; Ruechardt, C.

doi:10.1002/chin.199947126

Cited by 2 publications

(7 citation statements)

References 2 publications

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“…The C–H bonds on the 9 and 10 positions of 9,10-dihydroanthracene were sufficiently weak to initiate the reaction, and the conversion of α-methylstyrene and 9,10-dihydroanthracene proceeded even in the absence of asphaltenes, which is consistent with a previous report . The dominant product in the methanol extract was the dimerization product of α-methylstyrene and 9,10-dihydroanthracene, and the selectivity to cumene was only 15%, which was contrary to what was anticipated from literature, which reported the near complete selectivity to cumene, albeit with 6 H -benzo[cd]pyrene also present in the reaction mixture.…”

Section: Resultssupporting

confidence: 84%

“…In these experiments the industrial asphaltenes feed was mixed with selected model compounds, and some model compound mixtures were studied on their own. Diphenylether was employed as insert solvent, subsequent to a report that it was not degraded during reaction of a mixture of α-methylstyrene, 6 H -benzo[cd]pyrene, and 9,10-dihydroanthracene in diphenylether at 250 °C . A list of the experiments that were performed is shown in Table .…”

Section: Methodsmentioning

confidence: 99%

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Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

2017

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The reactivity and reactions of asphaltenes were explored over the temperature range 100−250°C following reports of reactivity and meaningful free radical content in asphaltenes. This study employed industrial pentane precipitated asphaltenes from Athabasca oilsands bitumen. The presence of free radicals in the asphaltenes feed was confirmed. On heating the asphaltenes to 150°C, the aromatic hydrogen content increased relative to the feed by a factor 1.12. It was also found that on heating the asphaltenes to 150°C the n-heptane insoluble fraction increased from 67% to 75%. Almost no gas phase products were produced. The observed changes were ascribed to hydrogen transfer reactions and addition products formed by combination reactions. Direct evidence of hydrogen transfer reactions taking place in the asphaltenes was obtained through the use of the model systems, α-methylstyrene and cumene, as well as anthracene and 9,10-dihydroanthracene. The extent of hydrogen transfer was of the order 1.8 mg H/g asphaltenes in 1 h at 250°C. Asphaltenes also caused dimerization of model compounds, providing indirect evidence that free radical combination reactions took place in the asphaltenes. Interpretation relying on thermodynamic arguments combined with experimental results indicated that at 250°C the reactive species in asphaltenes were incapable of abstracting hydrogen by hydrogen transfer that had bond strengths (based on homolytic bond dissociation energy) exceeding around 353 kJ mol −1 . Using similar arguments, it was deduced that the ratio of reactive species in asphaltenes capable of abstracting hydrogen with bond strengths in the range around 315−353 kJ mol −1 , compared to transferable hydrogen in asphaltenes with a bond strength less than 315 kJ mol −1 was about 2:1.

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Section: Resultssupporting

confidence: 84%

Section: Methodsmentioning

confidence: 99%

Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

2017

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“…The use of less sterically hindered nucleophiles such as hexynyl lithium and reduction of 4 with LiAlH 4 /AlCl 3 led to the recovery of the starting material. 26 Nevertheless, this unexpected 1,4addition provided the possibility for the substitution at 5-and 7-positions, which is of interest for functionalization in the future. OR1 and OR2 appeared dark green in color in solution and black in color as solids, and the structures were unambiguously determined by X-ray crystallography (vide infra), ESI-MS and MALDI-TOF-MS.…”

Section: ■ Results and Discussionmentioning

confidence: 98%

“…The synthesis of 6-position-protected olympicenyl radical derivative OR1 was realized by treatment of 6 H -benzo[ cd ]pyren-6-one ( 1 ) with lithiated triisopropylsilyl (TIPS) acetylene, followed by reduction with H 2 SnCl 4 . To further functionalize the periphery, we conducted Ir-catalyzed borylation reaction which selectively activated 4- and 8-positions with the least steric hindrance .…”

Section: Results and Discussionmentioning

confidence: 99%

“…Further reaction with organolithium reagent failed to give desired compound 5 , probably due to severe steric congestion. The use of less sterically hindered nucleophiles such as hexynyl lithium and reduction of 4 with LiAlH 4 /AlCl 3 led to the recovery of the starting material . Nevertheless, this unexpected 1,4-addition provided the possibility for the substitution at 5- and 7-positions, which is of interest for functionalization in the future.…”

Section: Results and Discussionmentioning

confidence: 99%

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Stable Olympicenyl Radicals and Their π-Dimers

Xiang

Guo

et al. 2020

J. Am. Chem. Soc.

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An olympicenyl radical, a spin 1/2 hydrocarbon radical with C 2v symmetry and uneven spin distribution, remains elusive despite the considerable theoretical research interest. Herein, we report syntheses of two air-stable olympicenyl radical derivatives, OR1 and OR2, with half-life times (τ1/2) in air-saturated solution of 7 days and 34 days. The high stability was ascribed to kinetic blocking of reactive sites with high spin densities. X-ray crystallographic analysis revealed unique 20-center–2-electron head-to-tail π-dimer structures with intermolecular distances shorter than the sum of van der Waals radius of carbon. The ground state of the π-dimers was found to be singlet, with singlet–triplet energy gaps estimated to be −2.34 kcal/mol and −3.28 kcal/mol for OR1 and OR2, respectively, by variable-temperature electron spin resonance (ESR) spectroscopy. The monomeric radical species were in equilibrium with the π-dimer in solution, and the optical and electrochemical properties of the monomers and π-dimers in solution were investigated by UV–vis–NIR spectroscopy and cyclic voltammetry, revealing a concentration-dependent nature. Theoretical calculations illustrated that upon formation of a π-dimer the local aromaticity of each monomer was enhanced, and spatial ring current between the monomers was present, which resulted in an increment of aromaticity of the interior of the π-dimer.

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ChemInform Abstract: Bimolecular Formation of Radicals by Hydrogen Transfer. Part 15. New Hydrogen Transfer Catalysts.

Cited by 2 publications

References 2 publications

Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

Uncatalyzed Hydrogen Transfer during 100–250 °C Conversion of Asphaltenes

Stable Olympicenyl Radicals and Their π-Dimers

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