Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction

Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals.This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species(denoted as Fe-reactor).Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2(ethane,ethylene and acetylene) and 31.8% toward BTX(benzene,toluene and xylene),respectively.The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene,which provides an additional route of methane activation apart from catalytic activation.

Enantioselective cyanation of benzylic C—H bonds via copper-catalyzed radical relay

With the support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,the research team led by Prof.Liu Guosheng(刘国生)at Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences,and Prof.Shannon Stahl at the University of Wisconsin-Madison,discovered a copper-catalyzed radical relay pathway for enantioselective conversion of benzylic C—H bonds

Mechanism and rate constants for complete series reactions of 19 fluorophenols with atomic H

Fluorine-containing halogenated fluorophenol may have effect as intermediate species involved in the formation of polyfluorinated dibenzo-p-dioxin/dibenzofurans （PFDDs/Fs）. The mechanism for the atomic H initiated reactions with complete series of nineteen fluorophenol congeners was studies using the density functional theory. At the MPWB1K,/6-31＋G（d,p） level, the geometries and frequencies of reactants, transition states, and products were obtained, and the accurate energetic values were acquired at the MPWB 1K/6-311 ＋G（3df,2p） level. The rate constants were evaluated by the canonical variational transition-state theory with the small curvature tunneling contribution over a wide temperature range of 600-1000 K. The study shows that the intramolecular hydrogen-bond in the ortho-substituted FPs as well as the inductive effect of the electron-withdrawing fluorine and steric repulsion of multiple substitutions may ultimately be responsible for the relative strength of the O-H bonds in FPs. The results can be used for further studies on PFDD/Fs formation mechanism.

Computational Study on Mechanisms of C2H5O2＋OH Reaction and Properties of C2H5O3H Complex

A comprehensive theoretical study on the bimolecular reaction of C2H502 with OH radicals was performed at the CCSD（T）/6-311＋＋G（2df2p）//B3LYP/6-311＋G（d,p） level of theory. The calculation results show that C2H5O2 ＋ OH reaction proceeds on both the singlet and the triplet potential energy surfaces（PESs）. On the singlet PES, the favorable pathway is the addition of OH radical to the terminal oxygen atom of C2H5O2 radical, leading to the formation of trioxide C2H5O3H with a barrierless process. Then, the trioxide directly decomposes to the products C2H50 and HO2 radicals. On the triplet PES, the predominant pathways are a and β hydrogen atom abstractions of C2H5O2 radical by OH radical-forming products 3CH3CHO2＋H2O and 3CH2CH2O2＋H2O, and the corresponding bar- tiers are 12.02（3TS8） and 19.19 kJ/mol（3TS9）, respectively. In addition, the comprehensive properties of trioxide C2H503H were investigated for the ftrst time. The results indicate that the trioxide complex RC1 can exist stably in the atmosphere owing to a significantly large and negative enthalpy of formation（-118.44 kJ/mol） as well as a high first excitation energy（5.94 eV）.