Amberlite IR-120 catalyzed,microwave-assisted rapid synthesis of 2-aryl-benzimidazoles

An expeditious synthesis of 2-aryl-benzimidazoles by the condensation of o-phenylenediamine with various araldehydes is described. This greener protocol is catalyzed by Amberlite IR-120, and proceeds efficiently in the absence of any organic solvent under microwave irradiation within 3–5 min.     

Hydrophobic Vitamin B12. X. Steric Effect in Electrochemical Carbon-Skeleton Rearrangement Catalyzed by Hydrophobic Vitamin B12 in Nonaqueous Media

Abstract

A steric effect in the carbon-skeleton rearrangement catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C₁ester]C10₄, was investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides having two carboxylic ester groups of different bulkiness on the same carbon atom, such as 2,2-bis(ethoxycarbonyl)-l-bromopropane, l-bromo-2-tert-butoxycarbonyl-2-ethoxy-carbonylpropane, l-bromo-2-cyclohexyloxycarbonyl-2-ethoxycarbonylpropane, and l-bromo-2-ethoxy-carbonyl-2-phenoxycarbonylpropane, were carried out in N,N-dimethylformamide, as catalyzed by [Cob(II)7C₁ester]CIO₄, to give the corresponding ester-migrated products in the dark at—1.5 V vs SCE in the presence of acetic acid and at—2.0 V vs SCE without acetic acid. As regards a correlation between bulkiness of an ester group and a migration aptitude, a smaller ester group tends to migrate to the adjacent carbon atom more readily than a larger one. The origin of such a steric effect is discussed with attention to the rate-determining step.     

Synthesis and characterization of 1-phenyl-3-alkylbenzimidazol-2-ylidene salts and their catalytic activities in the Heck and Suzuki cross-coupling reactions

The synthesis and characterization of 1-phenyl-3-alkyl-substituted carbene precursors that were prepared from 1-phenyl substituted benzimidazole and various alkyl halides are reported. The new benzimidazolium salts (1a–e) were characterized by ¹H NMR, ¹³C NMR, FT-IR spectroscopic methods and elemental analyses. New in situ generated palladium-benzimidazolium complexes were tested for catalytic activity in the Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions.     

Copper‐catalyzed Clauson–Kass pyrroles synthesis in aqueous media

An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Rate processes on fractals: Theory,simulations, and experiments

Heterogeneous kinetics are shown to differ drastically from homogeneous kinetics. For the elementary reaction A + A products we show that the diffusion-limited reaction rate is proportional tot ^– h[A]² or to [A]^x, whereh=1- d _s/2, X=1+2/d _s =(h-2)(h-1), andd _s is the effective spectral dimension. We note that ford = d _s =1, h =1/2 andX = 3, for percolating clustersd _s = 4/3,h = 1/3 andX = 5/2, while for dust ds <1, 1 >h > 1/2 and >X > 3. Scaling arguments, supercomputer simulations and experiments give a consistent picture. The interplay of energetic and geometric heterogeneity results in fractal-like kinetics and is relevant to excitation fusion experiments in porous membranes, films, and polymeric glasses. However, in isotopic mixed crystals, the geometric fractal nature (percolation clusters) dominates.     

碱存在下二烷基硼酸甲酯与氯仿的相转移反应研究

由烯烃经一氯硼烷甲硫醚（Ｈ２ＢＣｌ·ＳＭｅ２）硼氢化和甲醇解制得的二烷基硼酸甲酯６，在５０％ＮａＯＨ和相转移催化剂（ＴＥＢＡ）存在下与氯仿反应，继之氧化，获得了相应的二烷基酮１，二环烷基酮２和３以及脂环酮４．考查了各种参数对反应的影响．讨论了反应机理，为从烯烃出发合成各种类型的酮提供了一条简便新途径．     

Nonequilibrium dynamics of a diffusion-limited reaction driven by a cluster-memory mechanism

The diffusion-limited reaction A+AA+B is studied in general dimension. The asymptotic decay of the system is found to depend nontrivially upon the initial concentration of A particles for certain ranges of the diffusion constant, backward reaction rate, and total concentration of particles. This nonequilibrium behavior is due to the formation of clusters centered about the initial A particles. A perturbative analysis ind=1 shows that the transition to the nonequilibrium dynamics is sharp and is quite similar to another previously studied reaction A+AA. Ford>1, a scaling argument is presented which describes the dependence of the asymptotic decay on the initial concentration of A particles and the equilibrium concentration for large backward reaction rates. Monte Carlo data are shown which confirm the analytic work ind=1, 2, and 3.