Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

Mechanisms of the reactions of propane with CBr3+ cation and superelectrophilic complex CBr4+·AlBr3- containing a bromine-centered cationic center: a theoretical study

Fragments of the potential energy surfaces (PES) of the systems [C₃H₈ + CBr₃ ⁺] and [C₃H₈ + Br₂CBr⁺·Br₂AlBr₂ ^–] were simulated by the MNDO/PM3 method. Energy minima corresponding to weakly bound adducts of propane molecule with the CBr₃ ⁺ cation or neutral complex CBr₃ ⁺·AlBr₄ ^– were found on the PES's of both systems. These are adducts with the coordination of a H atom of the methylene group of the propane molecule to the electrophile at the Br atom carrying the largest positive charge. As the fragments of the adducts are brought close together, the coordinated H atom migrates to the C atom of the CBr₃ ⁺ fragment. The potential barriers of these migrations were found to be low for both systems. The reactions proceed without formation of cyclic intermediates or transition states typical of the Olah mechanism.     

Kinetics and Mechanism of the Autocatalytic Oxidation of Mn(II) by Bromine

The oxidation of Mn(II) by bromine is an autocatalytic reaction, which seems to be important for a detailed elucidation of chemical oscillators, based on manganese chemistry. With regard to the mechanism proposed previously, an alternative reaction mechanism is proposed, based on a micro-heterogeneous oxidation of Mn(II) ion, adsorbed on a surface of the MnO₂ colloid. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonisothermal thermogravimetry of polymers

The model of weight loss taking place in each step of a scheme of consecutive reactions was applied to nonisothermal thermogravimetric records of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide). The release of HBr was found to be faster in air than in nitrogen. A significant reduction in the apparent activation energy of dehydrobromination as compared with decomposition of the nonbrominated polymer was ascribed not only to a reduction in the activation energy of the initiation reaction, but also to an increase in the order of the termination reaction (from 1 for the nonbrominated polymer to 2 for the highly brominated polymer).     

多硫化钠/溴液流储能电池负极材料的研究

在常规玻璃三电极池中用稳态极化法研究了铁、钴、镍、铅及石墨在 1. 3mol·L-1Na2S4水溶液中的极化行为, 测定了不同材料的交换电流密度.以泡沫镍、镀镍或镀钴碳毡为负极,聚丙腈碳毡为正极组成电池测试了常温下电池的能量效率及循环性能.结果表明:泡沫镍及镀镍或钴的碳毡可做电池负极材料;充放电电流密度为30mA/cm2时,电池的能量效率约 80 %;电池循环性能较好.     

Bromine,arsenic, cadmium,and lead in several key food groups: an assessment of relative risk

ABSTRACT

This study endeavoured to provide an overview of the bromine, Br, arsenic (As, a metalloid) and metal (cadmium, Cd, and lead, Pb) relative risk associated with the consumption of relevant food groups (lean fish, fatty fish, bivalves, cephalopods, fresh fruit, dried fruit, and green vegetables) in Portugal. Though As, Cd, and Pb have been frequently studied, a comprehensive overview applying the same state-of-the-art methodology to a wide array of foods is missing. Besides, there is a large deficit of content information and risk assessment studies on Br. Thus, it is important to apply a mathematically realistic and innovative methodology (extreme value theory) to recent and accurate databases for the aforementioned food groups and elements.

Best fits to Br, As (total), Cd, and Pb concentrations were attained through different functions, ranging from the normal distribution to the Weibull distribution. A semi-probabilistic risk assessment approach on the basis of four alternative scenarios (one monthly meal; one weekly meal; three weekly meals; one daily meal) showed low relative risk regarding Br and Pb in the selected food groups, including bivalves, which contained the highest Br and Pb contents. With respect to total As, high relative risk values were calculated for seafood, but it should be emphasized that this As is overwhelmingly organic, thus presenting low risk. For Cd, substantial relative risk associated with bivalves’ and cephalopods’ consumption, particularly with one or more weekly meal(s), was found. However, the current study enables us to compare between the relative risk of the studied food groups and scenarios, and other studies encompassing the whole diet and following long-term dietary patterns are needed for the assessment of absolute risk.     

Halogenation of the N-Terminus Tyrosine 10 Promotes Supramolecular Stabilization of the Amyloid-β Sequence 7–12

Here, we demonstrate that introduction of halogen atoms at the tyrosine 10 phenol ring of the DSGYEV sequence derived from the flexible amyloid-β N-terminus, promotes its self-assembly in the solid state. In particular, we report the crystal structures of two halogen-modified sequences, which we found to be stabilized in the solid state by halogen-mediated interactions. The structural study is corroborated by Non-Covalent Interaction (NCI) analysis. Our results prove that selective halogenation of an amino acid enhances the supramolecular organization of otherwise unstructured biologically-relevant sequences. This method may develop as a general strategy for stabilizing highly polymorphic peptide regions.     

Oxidative Cyclization of Azo-coupling Products of 3-Isopropenyltropoloneand 3-Cinnamoyltropolone with Bromine

Heterocycle-fusedtroponoidsareakindofcompoundswithphysiologicalactivitysuchasanticancer'.germicide',antiphlogistic',antihypertension'andantidiabetics.Troponoidcompoundscanbesynthesizedinmanyways,amongwhichonewastooxidizethesidechainoftropoloneforcycl...     

Revisiting the Bromination of CH Bonds with Molecular Bromine by Using a Photo‐Microflow System

The photobromination of C?H bonds by using molecular bromine was reinvestigated under microfluidic conditions. The continuous‐flow method suppressed the production of dibrominated compounds and effectively produced the desired monobrominated products with high selectivity. Rapid bromination of benzylic substrates containing a photoaffinity azide group was achieved without any decomposition.