Vasilii A. Mikhailov

Sequential transformations of molecular complexes and ionic intermediates lead to ionic products of nonionic bromine and alkylacetamides interaction. Molecular geometry, electron structure and thermodynamic parameters were evaluated at ωB97xV/dgdzvp level for all final products and supposed intermediates. A number of intra- and intermolecular noncovalent interactions such as Br···O, C-H···O, C-H···Br, H···O···H and other were revealed with combined use of spectral and computational methods, and defining role of these interactions in products and intermediates stabilization was demonstrated.

Reaction of nonionic N,N-dimethylformamide (DMF) with bromine under controllable conditions leads to a number of ionic compounds, mainly to bis(N,N-dimethylformamide)hydrogen dibromobromate. Computations with DFT (ωB97xV/dgdzvp) were made for geometry, thermochemistry and electron configuration of products and supposed intermediates. Two labile particles [bis(N,N-dimethylformamide)hydrogen cation and dibromobromate-anion] form stable highly conductive ionic liquid that can be distilled in vacuo without losses or decomposition. A number of molecular complexes of DMF with bromine and water presumed to be intermediates of this reaction. It is a set of halogen and hydrogen bonding that provide an intramolecular binding in these complexes.

The micellar effects in the perhydrolysis and base-catalyzed hydrolysis of 4-nitrophenyl esters of phosphoric, phosphonic, and toluenesulfonic acids in organized microheterogeneous systems based on dicationic [Gemini surfactant AlkIm⁺–(CH₂)₃–Im⁺Alk∙2Br^–, where Alk = C₁₂H₂₅ or C₁₄H₂₉ (GS)] and monocationic (AlkIm⁺CH₃∙Br^–, where Alk=C₁₂H₂₅ or C₁₄H₂₉) surfactants have been analyzed. The reagent concentrations have been found to be the main factor responsible for micellar catalysis. The hydroperoxide α-effect defined as the ratio of the second-order rate constants of perhydrolysis and base-catalyzed hydrolysis is preserved and, depending on the nature of the surfactant and the substrate, may reach ~ 100.

Stretched all-trans conformations were found preferable in computed structures of bis-imidazolium dications with short aliphatic (С1-С4) and hydroxyl substituted -СН2-СНОН-СН2- spacers. Maxima of molecular electrostatic potential were established near С2Н imidazolium and spacer hydrogens, for α,ω-alkenyl spacers, and close to hydroxyl hydrogen for hydroxypropane spacer. Sufficiently higher rotational barrier around С1-C2 bond in -СН2-СНОН-СН2- spacer compared with polymethylene is supported with intramolecular hydrogen bonds С-Н···О-Н between imidazolium hydrogens and hydroxyl oxygen.

Stretched all-trans conformations were found preferable in computed structures of bis-imidazolium dications with short aliphatic (С₁–С₄) and hydroxyl substituted –СН₂–СНОН–СН₂– bridges. The molecular electrostatic potential is distributed unevenly in the dications: maxima of molecular electrostatic potential are located near С²Н imidazolium and bridge hydrogens for the α,ω-alkenyl bridges, and close to hydroxyl hydrogen for the hydroxypropane bridge. Intramolecular hydrogen bonds С–Н···ОН contribute to a significantly higher rotational barrier around С¹–C² bond in dications with a hydroxypropane bridge compared with polymethylene bridges.

Design of organized microheterogeneous systems for fast disrupting (disintegration) of acylcontaining substrates (including organophosphorus compounds) is based on the use of highly reactive compounds. Reagents (catalysts) ability to provide “turnover” is of great impotence. Kinetic regularities for 4- nitrophenylacetate (PNPA) deacylation with 1-methyl-3-(2-hydroximinoethyl)-imidazolium chloride (oxime), chloral, and their mixtures were studied in water and cetyltrimethylammonium bromide (CTAB) solutions, under pH = const and [CTAB] = 10-2 M. Rate constants dependences upon nucleophile (catalyst) and detergent concentration are typical for reactions in water and micellar pseudophase. Transferring of PNPA deacylation from water into surfactant micelles leads to three orders rate enhancement. Kinetic experiments at different substrate concentrations indicate that a) first order rate constant in the chloral-CTAB system does not change up to tenfold excess of PNPA; b) first order rate constant in the oxime-CTAB system decreases for approx. 40% at PNPA excess; c) all advantages of “turnover” are achievable in the system chloral-oximeCTAB, where chloral provides first disintegration of acylated oxime with generation of highly reactive oximate-ion. Results obtained pave the way to modifying organized microheterogeneous systems, first of all, by surfactant structure changes.

Dicationic imidazolium surfactants of the 1,1′-(2-hydroxypropan-1,3-diyl)bis(3-alkyl-1H-imidazol-3-ylium)chloride series with a variable hydrophobic chain length have been synthesized and characterized. The values of their critical micelle concentration have been determined by tensiometry, conductometry and spectrophotometry. Significant antimicrobial activity of these surfactants against a number of pathogenic bacteria and fungi was revealed. It was found that decyl and dodecyl derivatives turned out to be leader compounds, which surpassed reference antibiotics in their action and showed activity against resistant strains. The kinetic parameters reflecting the high catalytic effect of the tested dicationic imidazolium surfactants in the alkaline hydrolysis of 4-nitrophenyl esters of phosphonic, phosphoric, and toluenesulfonic acids have been obtained.

Ascertaining regularities in the effects of organized media on reactivity of organic compounds, establishing of quantitative relationships «structure - property - micellar effects», and searching for efficient ways of structure modifications and functionalization of microorganized systems offer broad potentials for governing the reaction rates. A good choice for decomposition of ecotoxic substrates is the use of reaction media agreeable to “green chemistry” criteria. Solutions of surfactants can serve these purposes. Three approaches were used in designing highly efficient organized microheterogeneous systems (OMS) suitable for development of catalytic systems on the basis of dimeric surfactants. The first involves structure variations in cationic surfactants for alkaline hydrolysis (length of spacer and tail, the nature of head group, and so on). The second consists in design of surfactants with reactive counterion; dihalogenohalogenates are the sources of nucleophilic-oxidizing species with a broad spectrum of activity. The third approach involves design of functionalized surfactants which are several orders of magnitude more efficient than their non-functionalized counterparts. Micellar effects in decomposition of 4-nitrophenyl esters of diethylphosphonic, diethylphosphoric and toluenesulfonic acids reach ~ 100 in alkaline hydrolysis, and 10000 times in the systems involving functionalized surfactants. The reagent concentrating and change in nucleophilic reactivity by transferring the reaction from water into the micellar pseudophase contribute significantly to the observed rate acceleration. Hydrophobic properties of surfactant and substrate, mainly the nature of the head group and spacer are essential. Выяснение закономерностей влияния организованных сред на реакционную способность органических соединений, установление количественных закономерностей «структура-свойство-мицеллярные эффекты» и поиск путей модификации и функционализации микроорганизованных систем открывают широкие перспективы управления скоростями химических реакций. Решение такой задачи напрямую связано с минимизацией актов террористического воздействия и техногенных аварий. Разложение субстратов-экотоксикантов предполагает использование реакционной среды, удовлетворяющей критериям «Green chemistry», что является необходимым условием, и таковыми выступают растворы ПАВ. Для создания высокоэффективных организованных микрогетерогенных систем (ОМС) для катализа на основе димерных ПАВ были реализованы три следующих направления. Первое - варьирование структуры катионных ПАВ в реакциях щелочного гидролиза. Второе - конструирование ПАВ с реакционноспособным противоионом (дигалогенгалогенат) - системы широкого спектра действия, одновременно выступающей источником нуклеофильно-окислительного реагента и реализующей преимущества ОМС. Третье - формирование функционализированных наноразмерных ансамблей, обладающих на порядки более высокой эффективностью, чем не функционализированные. Мицеллярные эффекты в реакциях разложения 4-нитрофениловых эфиров диэтилфосфоновой, диэтилфосфорной и толуолсульфоновой кислот достигают ~ 100 (щелочной гидролиз) - 10000 раз (системы на основе функционализированных ПАВ). При этом основной вклад в наблюдаемое ускорение при переносе процесса из воды в мицеллярную псевдофазу вносят эффекты концентрирования реагентов и изменение нуклеофильной реакционной способности. В этом случае важное значение имеют гидрофобные свойства ПАВ и субстратов, природа катионной части головной группы и мостикового звена.