Polymer-catalyzed hydrolysis of p-nitrophenyl butyrate in an oil/water emulsion

Catalysis of hydrolytic decomposition of p-nitrophenyl butyrate with the copolymer of N-vinylcaprolactam and N-vinylimidazole in an n-dodecane-water emulsion was studied. The reaction rate in the emulsion is higher than that in a solution containing no emulsified dodecane particles. The data obtained indicate that the reactions involving the surface-active substrate and catalyst can be accelerated by interfaces. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2109–2111, December, 2006.     

Homogeneous and biphasic autoxidation of tetralin catalyzed by transition metal salts and complexes

The biphasic autoxidation of tetralin was carried out using various Co, Ni and Mn complexes as catalysts. Cobalt–N,N′-dimethylethylenediamine complex, which is amphiphilic and surface-active, was found to be most effective; it could be easily recovered in a compact emulsion layer after the reaction and could be reused with no apparent loss of activity. The biphasic reaction differs from the homogeneous counterpart in that (1) little hydroperoxide product is formed, (2) there is lesser sensitivity to product inhibition and a greater degree of conversion and (3) there is an easier catalyst recovery and substrate recycle.     

Reactions in surface microreactors: Computer simulation

Chemical transformations of surface-active substrate in the presence of surface-active catalyst are studied by the methods of computer simulation. Reactions occur in emulsion, at whose interfaces reactants are concentrated. It is established that there is an optimal size of emulsion droplets at which the reaction rate is the highest. It is shown that the kinetics of reactions substantially depends on the surface activity of reactants and the potential barrier of reaction. Under specific conditions, the rate of reaction notably increases during the initial time interval.     

A pH-responsive TiO2-based Pickering emulsion system for in situ catalyst recycling

Through tuning the surface wettability of interfacially active TiO₂ particles, a pH-responsive Pickering emulsion system is formed, as in situ separation and recycling of the nano-catalysts system.     

Development of spectrofluorimetric methods for the determination of levosulpiride in pharmaceutical formulation

Simple, accurate, rapid, and sensitive spectrofluorimetric methods for the determination of levosulpiride in pharmaceutical formulation were developed utilizing its fluorescence reaction with Fe³⁺ (method A) and Al³⁺ (method B). The calibration curves were found to be linear in the concentration range 0.239–3.44 μg/mL and 0.310–2.730 μg/mL with limit of detection 0.005 μg/mL and 0.0032 μg/mL, respectively, for method A and method B. The reaction conditions were studied and optimized. In addition, the complexation of Mg²⁺ and Ca²⁺ was also studied. In all cases, an enhancement in fluorescence emission of levosulpiride upon formation of complex with metal ions was observed. A 2: 1 (drug: metal) stoichiometry for all the complexes was established. Benesi-Hildebrand method was applied for calculation of association constant at 25 and 35°C. The thermodynamic parameters obtained in this study revealed that the interaction process was spontaneous and mainly ΔS-driven.     

Structure and Catalytic Properties of a Cu2+-Containing Hydrogel of Zirconium Dioxide

The distribution of Cu²⁺ ions in ZrO₂ and sulfated ZrO₂ hydrogel phases was studied by EPR spectroscopy and voltammetry. The formation of the following three types of copper structures was observed: mononuclear Cu²⁺ complexes (A), magnetic associates (B), and Cu²⁺ compounds (C) that gave no EPR signals under the conditions used in the spectroscopic measurements. The specific catalytic activity of various Cu²⁺ compounds in the liquid-phase reaction of 2,3,5-trimethyl-1,4-hydroquinone oxidation was determined. The copper complexes C were found to exhibit the highest catalytic activity.     

Autocatalytic reaction on low-dimensional substrates

We discuss a model for the autocatalytic reaction A + B→ 2A on substrates where the reactants perform a compact exploration of the space, i.e., on lattices whose spectral dimension d͂ is < 2. For finite systems, the total time τ for the reaction to end scales according to two different regimes, for high and low concentrations of reactants. The functional dependence of τ on the volume of the substrate and the concentration of reactants is discussed within a mean-field approximation. Possible applications are discussed.     

磺酸基功能化有机聚苯乙烯/无机磷酸氢锆催化环氧大豆油

首先制备了2种磺酸功能化的有机聚苯乙烯/无机磷酸氢锆非均相催化剂,运用傅里叶红外光谱(FT-IR)、N2吸附-脱附测试、X射线衍射(XRD)、扫描电子显微镜(SEM)等测试技术对催化剂进行了表征,提出了催化剂可能的模型。其次,考察了非均相催化剂催化合成环氧化大豆油的催化性能。结果表明:以叔丁基过氧化氢(TBHP)为氧化剂,固体催化剂对大豆油的环氧反应具有良好的催化性能,相比于催化剂1(磺酸化低聚苯乙烯基膦酸-磷酸氢锆),在相同的条件下,催化剂2(磺酸化聚(苯乙烯-苯乙烯膦酸)-磷酸氢锆)表现出更高的催化活性(产率:58.6%vs 53.3%),这主要归因于催化剂2拥有更大的比表面积、孔容以及孔径,为底物和催化剂的接触提供足够的催化场所。催化剂2重复使用7次后,催化活性未见明显降低。第8次反应结束后,将其置于2 mol·L-1稀盐酸中静置过夜后,在进行第9和10次循环时,催化活性又得以恢复。     

Investigation of A New Catalytic Reaction of Complex Formation of Cobalt (III) With Nitroso-R-Salt for the Determination of Microquantities of Phosphate-Ions

ABSTRACT

The catalytic action of phosphate-ions on the reaction of complex formation of cobalt (III) with nitroso-R-salt in a weakly acid medium has been found. The dependence of the rate of the catalytic reaction on temperature, concentrations of reagents and catalyst, pH of the medium, as well as on the presence of some anion and non-ion surface-active substances and accompanying inorganic minerals was studied. The optimum conditions for the determination of 0.1 μg/ml PO^3- ₄ in water were determined. A technique for the determination of phosphate-ion impurity up to 9×10^-5% in the high-purity sodium iodide and 2×10^-4% cesium iodide used for the single crystals growth is suggested.     

Influence of the force interaction on accumulation of macroscopic correlations in elementary reaction <Emphasis Type="Italic">A</Emphasis> + <Emphasis Type="Italic">B</Emphasis> → <Emphasis Type="Italic">C</Emphasis>

The applicability of the Encounter Theory (ET) (the prototype of the Collision Theory) concepts for widely occurring diffusion assisted irreversible bulk reaction A + B →C (for example, radical reaction) in dilute solutions taking account of initial microscopic correlations and force interactions between reactants has been treated theoretically with modern many-particle method for the derivation of non-Markovian binary kinetic equations. The method shows that taking into consideration initial correlations and force interactions leads to the redefinition of the Markovian rate constant only in the expressions derived earlier. Thus, just as in the reaction A + A →C and the reaction A + B →C neglecting force and initial correlations, the Modified Encounter Theory (MET), when reduced to equations of a Regular Form, both extends the time applicability range of ET homogeneous rate equation, and yields the inhomogeneous equation of the Generalized Encounter Theory (GET). It reveals macroscopic correlations induced by the encounters in the reservoir of free walks in full agreement with physical considerations. Time accumulation of macroscopic correlations obeys the same time law as in the previously considered case neglecting force interactions. Just the rate of the process will change, according to traditional redefinition of the steady-state constant of the reaction.     

Vitamin B1 as a metal-ion-free natural catalyst for sustainable quinoxaline ring condensation under sonochemical conditions

Abstract  

The role of vitamin B₁ as a catalyst is investigated for the quinoxaline ring condensation under various mild reaction conditions. The results revealed that the combination of vitamin B₁ and ultrasonic irradiation promotes the reaction more efficiently. The salient features of this environmentally benign method are fast conversions, excellent yields for a wide range of substrates, and the use of a low-cost, readily available, nontoxic, and metal-ion-free natural catalyst. The wide range of turnover frequency values (6–400 h⁻¹) shows that the reaction rate is highly dependent on the nature of the functional groups on the aromatic ring of substrates. Moreover, a plausible mechanism for the catalytic action of vitamin B₁ has been introduced.     

Structural investigation of cellulose Iα and Iβ by 2D RFDR NMR spectroscopy: determination of sequence of magnetically inequivalent d-glucose units along cellulose chain

In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) ¹³C–¹³C INADEQUATE, it was revealed that cellulose I_α contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose I_β contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose I_α and that of residues B and B′ in I_β were investigated by 2D ¹³C–¹³C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly ¹³C₆-labeled (U−¹³C₆) bacterial cellulose and the same [U−¹³C₆] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled ¹³C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled ¹³C spin pairs as well as strongly coupled ¹³C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−¹³C₆] cellulose recorded with a mixing time of 15 ms, the inter-residue ¹³C–¹³C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose I_β, however, inter-residue ¹³C–¹³C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−¹³C₆] cellulose. From these findings, that cellulose I_α was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose I_β, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain.     

Catecholase biomimetic catalytic activity of copper(II) complexes with 2-methyl-3-amino-(3H)-quinazolin-4-one

The oxidation of catechol by molecular oxygen in the presence of a catalytic amount of copper(II) complex with 2-methyl-3-amino-(3H)quinazoline-4-one (MAQ) and various anions (Cl⁻, Br⁻, ClO ₄ ⁻ , SCN⁻, NO ₃ ⁻ and SO ₄ ^– ) was studied. The catecholase biomimetic catalytic activity of the copper(II) complexes has been determined spectrophotometrically by monitoring the oxidative transformation of catechol to the corresponding light absorbing o-quinone (Q). The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time, concentration of catalyst and substrate and finally solvent effects. Addition of pyridine or Et₃N showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation reaction has a first order dependence with respect to the catalyst and catechol concentration and obeying Michaelis–Menten Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the nature of counter anions bound to copper(II) ion in the complex molecule and follows the order: Cl⁻ > NO ₃ ⁻ > Br⁻ > SO ₄ ^– > SCN⁻ > ClO ₄ ⁻ . To further elucidate the catalytic activity of the complexes, their electrochemical properties were investigated and the catecholase mimetic activity has been correlated with the redox potential of the Cu²⁺/Cu⁺ couple in the complexes.     

Glycol modified titanosiloxane as molecular precursor for homogenous titania–silica material: synthesis and characterization

Ti(OPrⁱ)₄ reacts with HOSi(O^tBu)₃ in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPrⁱ)₃{OSi(O^tBu)₃}] (A) and [Ti(OPrⁱ)₂{OSi(O^tBu)₃}₂] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPrⁱ)(O–G–O){OSi(O^tBu)₃}] (1A–3A) and [Ti(O–G–O){OSi(O^tBu)₃}₂] (1B–3B), respectively [where G = (CH₂)₂ (1A, 1B); (CH₂)₃ (2A, 2B) and {CH₂CH₂CH(CH₃)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and ¹H, ¹³C & ²⁹Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors. Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO₂·SiO₂ in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO₂·SiO₂. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses.     

Model Studies for the Coenzyme-B12-Catalyzed Methylmalonyl→Succinyl Rearrangement. The Importance of Hydrophobic Peripheral Associations

The interaction between a vitamin B₁₂ derivative containing a peripheral C₁₈ alkyl chain (see 1a ) and a (methyl)thiomalonate substrate bearing alkyl chains of various length at the thioester group (see 5 ) was investigated. A catalytic cycle was established for the methylmalonyl→succinyl rearrangement by using electrochemistry and photolysis (see Scheme 3). Increased yields of the succinate relative to the reduction product were obtained (2:3 ratio), when the reaction was run in MeOH/H₂O, and when both the substrate and the catalyst had an octadecyl substituent capable of hydrophobic interactions.     

Synthesis,crystal, and molecular structures of HIDA and its monomethyl ester

A simple procedure for synthesis of HIDA (2,6-dimethylphenylcarbamoylmethyl iminodiacetic acid) is described. It was obtained in better yield by reaction of 2,6-dimethylphenylcarbamoylmethyl chloride with iminodiacetic acid in carbon tetrachloride. The HIDA (A) was identified by IR and¹H NMR spectroscopy. Two types of crystals were detected in the crystal final product. Since they could be separated, the crystals:A andB were investigated by X-ray analysis. Crystal and molecular structures were solved by direct methods and refined by full-matrix least-squares technique toR=0.047 andR=0.056, respectively. In the structure ofA, the N2 atom is protonated and the molecule exists as a zwitterion. The crystal structure of compoundA is stabilized by strong hydrogen bonds, which are reflected in higher close-packing coefficient, density, and melting point, compared to compoundB. CompoundB is a monomethyl ester of HIDA, which is present as an impurity in the final recrystallized product.     

Synthesis,Characterization and Catalytic Behaviour of Silica Supported Zinc Salicylaldimine Complex

Zinc salicylaldimine complex immobilized on silica gel was used as a promising catalyst for the transesterification reaction of dimethyl terephthalate (DMT) and ethylene glycol (EG).The catalyst was characterized by Fourier transform infra‐red spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and atomic absorption spectroscopy (AAS). The product bis‐(2‐hydroxyethyl)terephthalate (BHET)was confirmed by mass and ¹H‐NMR studies. In comparison to zinc acetate i.e., homogeneous catalyst, a polymer supported catalyst showed better stability, catalytic activity and ease of separation from the reaction product. The catalyst can be reutilized during successive catalytic cycles.     

XPS study of the surface composition of modified nickel-cobalt powder catalysts for enantioselective ethyl acetoacetate hydrogenation

The surface cobalt concentration in the powder bimetallic Ni-Co catalysts (ratio Co/Ni ≈ 0.25) was shown by X-ray photoelectron spectroscopy to be 2–4 times that of the volume content. Both Ni and Co exist in mixed valent states, viz., M⁰ and M²⁺, even after catalyst reduction. After ethyl acetoacetate hydrogenation, the cobalt content on the surface increases 16 times compared to that in the bulk. In addition, the metals are partially oxidized, and the amount of Ni⁰ and Co⁰ in the surface layers of the catalyst decreases 2–3 times. It was assumed that the increase in the cobalt content indicates an increase in the amount of cobalt complexes that involve the modifier, substrate, and reaction product, and which shield the nickel active sites. As a result, the enantioface differentiating ability of the catalyst decreases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2265–2268, November, 2007.     

Enantioselective Catalysis of the Intermolecular [2+2] Photocycloaddition between 2‐Pyridones and Acetylenedicarboxylates

Intermolecular [2+2] photocycloadditions represent the most versatile and widely applicable of photochemical reactions. For the first time, such intermolecular reactions have been carried out in a catalytic fashion using a chiral triplet sensitizer, with high enantioselectivity (up to 92 % ee). The low catalyst loading (2.5–5 mol %) underlines the high efficiency of the process both in terms of reaction acceleration and differentiation of the enantiotopic faces of the substrate. The substrate is anchored to the chiral catalyst through noncovalent interactions (hydrogen bonds), thus providing a chiral environment in which the enantioselective photocycloaddition proceeds. The densely functionalized products present numerous possibilities for further synthetic transformations.     

间位苯基桥联的锰（Ⅲ）双咔咯的合成、表征及催化氧化性质

通过间苯二甲醛与5-氟苯基二吡咯甲烷反应合成了一种新的间位苯基桥联的双咔咯1,并利用锰盐与自由咔咯反应制备了其锰的金属配合物2。采用紫外、质谱、核磁、XPS等手段对化合物进行了表征。以苯乙烯为底物考察了锰双咔咯2的催化氧化性质,探讨了时间、溶剂、氧源、轴向配体对催化反应的影响。结果表明以亚碘酰苯和间氯过氧苯甲酸为氧源时催化的主要产物为环氧苯乙烷,而以双氧水和叔丁基过氧化氢为氧源时则主要产物为苯甲醛;在极性溶剂中的催化氧化产率较高。轴向配体对催化氧化有促进作用,不同轴向配体对催化反应产率提高的顺序是：1-甲基咪唑 >吡啶 >咪唑。