Molecular Structures of the Metastable Charge-Transfer Complexes of Benzene (and Toluene) With Bromine as the Pre-Reactive Intermediates in Electrophilic Aromatic Bromination

Successful crystallization and X-ray crystallographic analyses of the highly metastable (1∶1) complexes of bromine with benzene and toluene establish the unique (localized) structure B that differs in notable ways from the long-accepted (delocalized) structure A. Furthermore, we demonstrate the (highly structured) charge-transfer complexes [C6H6,Br2] and [CH3C6H5,Br2] to be the pre-reactive intermediates that are converted (via an overall Br+ transfer) to the Wheland intermediates in electrophilic aromatic bromination. The role of the dative ion pairs [C6H6˙+ Br2˙−] and [CH3C6H5˙+ Br2˙−] in the rate-limiting activation processes is underscored

Noncovalent Binding of the Halogens to Aromatic Donors. Discrete Structures of Labile Br\u3csub\u3e2\u3c/sub\u3e Complexes with Benzene and Toluene

Precise molecular structures resulting from the noncovalent interaction of Br2 with benzene (and toluene) reveal the unusual localized bonding to specific (one or two) carbon centers in prereactive complexes leading directly to the transition states for electrophilic aromatic brominations

New Type of Detachable Contact Joints for Aluminium Cell Busbar Arrangement

The new type of detachable contact joints (DJC) for the aluminium industry is offered. It is shown, that DJC with cylindrical split contact inserts allow to provide stability of electrotechnical characteristics of connection from -50 to + 40ºC

Shok-free Dismounting of Cathode Assembly Lining of Aluminum Cells

Рассматривается технология демонтажа футеровки катодного устройства при капитальном ремонте алюминиевых электролизеров непосредственно в корпусах электролиза. Для ускорения процесса разрушения футеровки и снижения воздействия ударно-вибрационных нагрузок при выполнении демонтажных работ на соседние с ремонтируемым катодным устройством электролизеры, демонтаж выполняется с использованием гидропрессового оборудования для безударного разрушения материалов с применением инструментов алмазной резки и бурения. Ускорение процесса демонтажа достигается за счет использования гидропрессового оборудования, позволяющего создать в материале футеровки катодного устройства электролизера локально неоднородное распределение давления, обеспечивающего образование трещин, разрушающих целостность футеровки.The technology of dismantle of the cathodic device of electrolytic furnaces is considered. Lining destruction in the cathodic device of an electrolytic furnace is made by a special hydraulic press. In a lining material locally non-uniform loadings causing occurrence of cracks are created. The technology allows to exclude with great dispatch-vibrating influence on near electrolytic furnaces and to increase term of their operation

New Type of Detachable Contact Joints for Aluminium Cell Busbar Arrangement

The new type of detachable contact joints (DJC) for the aluminium industry is offered. It is shown, that DJC with cylindrical split contact inserts allow to provide stability of electrotechnical characteristics of connection from -50 to + 40ºC

Shok-free Dismounting of Cathode Assembly Lining of Aluminum Cells

Рассматривается технология демонтажа футеровки катодного устройства при капитальном ремонте алюминиевых электролизеров непосредственно в корпусах электролиза. Для ускорения процесса разрушения футеровки и снижения воздействия ударно-вибрационных нагрузок при выполнении демонтажных работ на соседние с ремонтируемым катодным устройством электролизеры, демонтаж выполняется с использованием гидропрессового оборудования для безударного разрушения материалов с применением инструментов алмазной резки и бурения. Ускорение процесса демонтажа достигается за счет использования гидропрессового оборудования, позволяющего создать в материале футеровки катодного устройства электролизера локально неоднородное распределение давления, обеспечивающего образование трещин, разрушающих целостность футеровки.The technology of dismantle of the cathodic device of electrolytic furnaces is considered. Lining destruction in the cathodic device of an electrolytic furnace is made by a special hydraulic press. In a lining material locally non-uniform loadings causing occurrence of cracks are created. The technology allows to exclude with great dispatch-vibrating influence on near electrolytic furnaces and to increase term of their operation

Transformations of Conjugated Enynones in the Superacid CF₃SO₃H. Synthesis of Butadienyl Triflates, Indanones, and Indenes

Conjugated 1,5-diarylpent-2-en-4-yn-1-ones add the superacid CF₃SO₃H to the acetylenic bond with formation of the corresponding butadienyl triflates. Under superacidic reaction conditions, these triflates are transformed into indanone or indene derivatives depending on which substituents on the aromatic ring are conjugated with the butadiene fragment. In a less acidic system (10% vol pyridine in CF₃SO₃H) only the formation of butadienyl triflates takes place. Cationic reaction intermediates were studied by means of NMR and DFT calculations

Friedel–Crafts Alkylation of Arenes with 2‑Halogeno-2-CF₃‑styrenes under Superacidic Conditions. Access to Trifluoromethylated Ethanes and Ethenes

The formation of the corresponding benzyl cations [ArHC⁺–CH­(X)­CF₃] takes place under protonation of <i>E</i>-/<i>Z</i>-2-halogeno-2-CF₃ styrenes [ArCHC­(X)­CF₃, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel–Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoro­propanes [Ar­(Ar′)­CH–CH­(X)­CF₃] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of <i>E</i>-/<i>Z</i>-trifluoro­methylated diarylethenes [Ar­(Ar′)­CCCF₃] (in yields up to 96%) by dehydrohalogenation with base (KOH or <i>t</i>-BuOK). The mechanism of elimination (E₂ and Ecb) depends on the nature of the leaving group and reaction conditions

Study of Structure of Industrial Acid Hydrolysis Lignin, Oxidized in the H₂O₂-H₂SO₄ System

<p>Products of oxidation of industrial acid hydrolysis lignin in the H₂O₂-H₂SO₄ system were studied using ¹³C NMR (in solution and solid state), MALDI-MS, and MS(ESI) techniques. Oxidation of hydrolysis lignin leads to the opening of aromatic rings of lignin, yielding carboxylic groups. Alkyl aryl ether linkages (β-O-4-bonds) between lignin phenyl propane units are not significantly affected by the oxidation. The structure of oxidized hydrolysis lignin is proposed. The basic structural unit of oxidized hydrolysis lignin is a muconic acid derivative.</p