Nucleophilic Intermolecular Chemistry and Reactivity of Dimethylcarbene

Experimental and computational studies find that dimethylcarbene (DMC), the parent dialkylcarbene, is both predicted to be and functions as a very reactive nucleophilic carbene in addition reactions with five simple alkenes. Activation energies and enthalpies for DMC additions to 2-ethyl-1-butene and methyl acrylate are computed and observed to be negative

Two Equilibria of (<i>N</i>‑Methyl-3-pyridinium)chlorocarbene, a Cationic Carbene

Equilibrium constants and the associated thermodynamic parameters are reported for the equilibria established between the cationic carbene (<i>N</i>-methyl-3-pyridinium)­chlorocarbene tetrafluoroborate (MePyr⁺CCl BF₄^–, <b>3</b>) and 1,3,5-trimethoxybenzene (TMB) to form a carbene–TMB complex, as well as between carbene <b>3</b> and chloride ion to form the zwitterion, <i>N</i>-methyl-3-pyridinium dichloromethide (<b>10</b>). These equilibrium constants and thermodynamic parameters are contrasted with analogous data for several related carbenes, and the influence of the pyridinium unit in carbene <b>3</b> is thereby highlighted. Computational studies augment and elucidate the experimental results

Absolute Reactivity of (<i>N</i>‑Methyl-3-pyridinium)chlorocarbene

(<i>N</i>-Methyl-3-pyridinium)­chlorocarbene tetrafluoroborate (MePyr⁺CCl BF₄^–, <b>4</b>) is generated by laser flash photolysis (LFP) of the corresponding diazirine (<b>5</b>) and reacted with tetramethylethylene, cyclohexene, 1-hexene, 2-ethyl-1-butene, methyl acrylate, and acrylonitrile. Absolute rate constants are measured for these carbene–alkene addition reactions, and activation parameters are obtained for additions of MePyr⁺CCl BF₄^– to tetramethylethylene, cyclohexene, and 1-hexene. MePyr⁺CCl BF₄^– is computed to be a highly reactive, electrophilic, singlet carbene, and experiments are in accord with expectations. Its activation parameters are compared with those of CF₃CCl, CCl₂, CClF, and CF₂. In all cases, enthalpy–entropy compensation is observed, with Δ<i>H</i>^‡ and Δ<i>S</i>^‡ decreasing in tandem as carbenic stability decreases. A qualitative explanation is offered for this phenomenon

Plasma-treated Ce/TiO₂–SiO₂ catalyst for the NH₃-SCR of NO<i>_x</i>

<p>Ce/TiO₂–SiO₂ catalysts with different Ti/Si molar ratios are prepared by the incipient impregnation method and their NH₃-SCR activities are evaluated at 100–500°C on a fixed reactor. The Ce/TiO₂–SiO₂ (3/1) catalyst, modified by non-thermal plasma (NTP) treatment and then activated by thermal treatment at 500°C for 4 h, exhibits best performance. Comprehensive deNO<i>_x</i> performance of the catalyst is evidently improved and its efficiency reaches up to 99.21% at 350°C. NO conversion efficiency of the treated catalyst doped with K remains about 90.23% at 300°C and the catalyst also shows improved activity at lower temperatures. Various characterization methods show that the activity enhancement is correlated only with NTP treatment, as it increases the number of Ce³⁺ species, which generates more chemisorbed oxygen, leads to improved dispersion of Brønsted and Lewis acidic sites and finally has an inherent etching effect.</p