Micellar effect upon the reaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide in water

Summary Reaction of tris(4,7-diphenyl-1,10-phenanthrolinedisulphonato)iron(II) ion with hydroxide ion is strongly accelerated by cationic micellar systems. Kinetics both in water and in cationic micelles are consistent with a mechanism of consecuive reactions with a reversible step, and the rate constants have been determined. Results in micelles are explained in terms of thepseudo-phase ion-exchange and mass-action kinetics models, and they show that micelles speed the reaction by an authentic catalytic effect by stabilization of transition state of the reaction.     

Effect of the micellar surfactant nanoreactors on the reactions of 2,4-dinitrophenylhydrazine with some aldehydes

By thermogravimetry, the IR and electronic spectroscopy physicochemical characteristics of systems including aromatic aldehydes, 2,4-dinitrophenylhydrazine, and a surfactant were investigated. Selective solubilization effect of the cationic surfactant (cetylpyridinium chloride) micelles on the aci-form of hydrazone arising in the alkaline medium was found. The universal character of solubilization by the cationic surfactant micelles in the aromatic aldehyde—2,4-dinitrophenylhydrazine systems was shown by an example of the benzaldehyde derivatives with substituents of different nature. This effect leads to the increase in solubility of the reaction products and the aggregative stability of solutions.     

The effect of aluminium compounds in the copolymerization of ethylene / α-olefins

Two types of copolymerizations were found with the catalyst system Cp₂ZrCl₂/MAO. One was a less exothermic reaction, and another was a more exothermic one. The former provided a polymer with a single composition distribution because of a single cationic active site. The latter provided a polymer with a bimodal composition distribution, indicating the existence of two active sites. The two active sites were investigated through the comparison of MAO systems and alkylaluminium / borate systems. We speculated that the two active sites were the normal cationic site and the active site where the interaction between a cationic metallocene and an aluminium compound was strong.     

Catalysis of cationic surfactants in organic solvent: Hydrolysis of 2-nitro-4-carboxyphenyl acetate

The hydrolysis reaction of 2-nitro-4-carboxyphenyl acetate was studied in dichloromethane in the presence of an added electrolyte (NaOH) and cationic surfactants systems with varying quantities of added water at 25°C. The kinetic and conductivity data were correlated.     

Synthetic applications in radical/radical cationic cascade reactions

Oxidative photoinduced electron transfer (PET) reactions have been performed with various cyclic cyclopropyl(vinyl) silyl ethers bearing an olefinic or acetylenic side chain. The reactions result in bi- to tetracyclic ring systems via a fragmentation-radical/radical cationic addition reaction pathway with well defined ring juncture. The mode of cyclisation (endo/exo) can be partially controlled by addition of nucleophiles due to the suppression of radical cationic reaction pathways. Quantum chemical calculation of the cyclisation transition states underline the experimentally found selectivities. Additional mechanistic studies concerning the saturation step reveal that the final radical is saturated mostly by the solvent and traces of water in the solvent.     

Competing reactions in anionic gel-poly(propylene imine) dendrimer-surfactant ternary systems

Competitive interactions in ternary systems including a lightly crosslinked polyanionic hydrogel, a protonated Astramol? poly(propylene imine) dendrimer (of first to fifth generation), and an ionic surfactant were studied. It was found that the direction of the substitution reactions in systems containing cationic surfactants depends on the length of the aliphatic radical in the surfactant molecule as well as on the dendrimer generation number. Depending on these parameters, the interpolyelectrolyte complex formed by the network polyanion and the cationic dendrimer is either capable or incapable of sorbing surfactant cations from aqueous solutions, thereby transforming into the network polyanion-cationic surfactant complex with the release of dendrimers to the surrounding solution. It was shown that the substitution reaction in systems containing anionic surfactants leads to the formation of a polyanionic gel reinforced by particles of the dendrimer-anionic surfactant complex.     

Aromatic stabilization energy calculations for the antiaromatic fluorenyl cation. Issues in the choice of reference systems for positively charged species

Aromatic stabilization energy (ASE) calculations for the fluorenyl cation show substantial destabilization in comparison to suitable reference systems (16.3 +/- 1.6 kcal/mol), supporting its categorization as an antiaromatic species. The choice of appropriate reference systems is exacting for cationic systems because of the need to match strain energies, convolved with allylic-type resonance terms and other potential structural effects that stabilize charge. Several homodesmotic ASE reaction systems are examined to demonstrate the role played by these factors in the calculation of an ASE value for the fluorenyl cation. The magnitudes of the derived ASE are quite similar for four very different determinative, homodesmotic reaction systems, giving strong support to the inherent accuracy of the final derived ASE value. The results of nucleus independent chemical shift calculations for the components of each one of the ASE reactions add additional weight to this conclusion.     

Polymerizations with contribution of covalent and ionic species

The similarities and dissimilarities between the ring-opening and vinyl cationic polymerizations are discussed for systems with simultaneous presence of covalent and ionic species. The common denominator in comparing kinetics of polymerization of these systems is the comparison of the total times of polymerization with the time elapsing when a given macromolecule is active (i.e. ionic) and inactive (e.g. covalent in cationic vinyl and ring-opening polymerization). In the cationic ring-opening polymerization the reactivation of covalent species proceeds mostly by intramolecular nucleophilic dipole-dipole reaction (conformationally assisted) involving the chain unit adjacent to growing ester chain end. This reaction is fast (e.g. in THF polymerization) and is responsible for covalent ion-pair interconversion. In the cationic vinyl polymerization this path does not exist but covalent species (esters) can be faster ionized by using of the nucleophile, increasing thus the rate of exchange between esters and ions. This process provides one of the possible ways for converting the non-living polymerization into the living-dormant process. The cationic polymerizations are then compared with covalent (pseudoanionic) polymerization of cyclic esters, initiated with covalent metal alkoxides like R₂AlOR' or Al(OR)₃.     

Electrochemical reduction of p-nitrosodiphenylamine in, a cationic micellar system

The electroreduction of p-nitrosodiphenylamine (p-NDPA) in an alkaline aqueous solution containing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was investigated by polarography, cyclic and rotating disc voltammetry. It was found that the reduction of p-NDPA in cationic micellar systems takes place by the ECE mechanism, and, compared to the reduction of the same compound in a homogeneous water solution, has a somewhat lower rate of the overall electrode reaction. The lower reaction rate of p-NDPA reduction in micellar medium is probably due to three main factors: solubilization of p-NDPA in CTAB micelles, adsorption of monomeric surfactant species at the electrode surface and a lower rate of the base catalyzed dehydration reaction (C-step) in the micellar system.     

Triflic acid promoted synthesis of polycyclic aromatic compounds

The triflic acid (CF₃SO₃H) promoted cyclizations of 2-styrylbiaryls are found to be useful for the synthesis of polycyclic aromatic compounds, including functionalized derivatives of polycyclic aromatic compounds and heterocyclic systems. The reaction involves cationic cyclization followed by an elimination of benzene from the intermediate product.     

Reactivity of phosphorus esters in supramolecular systems based on surfactants containing an uracil residue and polyethylenimine

The reactivity of phosphorus esters with different hydrophobicities was studied in aqueous solutions of cationic surfactants containing an uracil residue, as well as in binary systems based on polyethylenimine. Pronounced substrate specificity was revealed in all supramolecular systems examined; in particular, acceleration of the hydrolysis of more hydrophobic substrate and inhibition of the reaction with less hydrophobic analog were observed. Aggregation in the examined systems was confirmed by tensiometric and conductometric measurements. The aggregation threshold considerably decreased in going from monocationic amphiphile to more hydrophobic dicationic analog due to the presence in the latter of two additional alkyl radicals.     

烯烃可控/活性正离子聚合新方法与新工艺及其应用

<正>离子聚合是高分子科学中重要的聚合方法之一,也是制备聚异丁烯或丁基橡胶等关键材料不可或缺的聚合方法.本文总结了异丁烯、苯乙烯及其衍生物等单体可控/活性正离子聚合的新引发体系、聚合反应特征的调节与转化、水相介质中正离子聚合新方法与新工艺、微观分子混合与正离子聚合新工艺及其用于设计合成异丁烯基聚合物.这些方法与技术是发展高效节能与绿色减排先进聚合物生产技术的重要途径,部分研究成果已在产业化中得到应用与验证.发展可控/活性正离子聚合新体系、新方法与新工艺,为实现绿色低碳高分子化工过程及相关产品工程(新结构、新功能、高性能与高品质)提供了新思路与新技术.     

Cationic intermediates in the Pd-catalyzed negishi coupling. kinetic and density functional theory study of alternative transmetalation pathways in the Me-Me coupling of ZnMe2 and trans-[PdMeCl(PMePh2)2

The complexity of the transmetalation step in a Pd-catalyzed Negishi reaction has been investigated by combining experiment and theoretical calculations. The reaction between trans-[PdMeCl(PMePh(2))(2)] and ZnMe(2) in THF as solvent was analyzed. The results reveal some unexpected and relevant mechanistic aspects not observed for ZnMeCl as nucleophile. The operative reaction mechanism is not the same when the reaction is carried out in the presence or in the absence of an excess of phosphine in the medium. In the absence of added phosphine an ionic intermediate with THF as ligand ([PdMe(PMePh(2))(2)(THF)](+)) opens ionic transmetalation pathways. In contrast, an excess of phosphine retards the reaction because of the formation of a very stable cationic complex with three phosphines ([PdMe(PMePh(2))(3)](+)) that sequesters the catalyst. These ionic intermediates had never been observed or proposed in palladium Negishi systems and warn on the possible detrimental effect of an excess of good ligand (as PMePh(2)) for the process. In contrast, the ionic pathways via cationic complexes with one solvent (or a weak ligand) can be noticeably faster and provide a more rapid reaction than the concerted pathways via neutral intermediates. Theoretical calculations on the real molecules reproduce well the experimental rate trends observed for the different mechanistic pathways.     

Gold Catalysis: Catalyst Oxidation State Dependent Dichotomy in the Cyclization of Furan–Yne Systems with Aromatic Tethers

Four different synthetic strategies led to a variety of furan–yne systems that contained an aryl system in the tether. Due to the short routes to these systems (four steps or less), a small library of substrates could easily be prepared. These were treated with AuCl₃ or with the Gagosz’s catalyst Ph₃PAuNTf₂ complex. The AuCl₃‐catalyzed reactions delivered highly substituted fluorene derivatives, a class of compounds of great importance as precursors for luminophores with extraordinary abilities. Conversely, a different mechanistic pathway was observed with the cationic gold(I) catalyst. In the latter case, a mechanistically interesting reaction cascade initiated a formal alkyne insertion into the furyl‐sp³‐C bond, which gave indene derivatives as the final products. This new reaction pathway depends on the aromatic moiety in the tether, which stabilizes a crucial cationic intermediate as a benzylic cation.     

Diaryliodonium salts as thermal initiators of cationic polymerization

Diaryliodonium salts (I) undergo efficient thermal decomposition in the presence of copper (II) compounds. Such systems can be employed as a novel class of latent thermal initiators for cationic polymerization. An investigation of the mechanism of the reaction demonstrated that the copper (II) compound is first reduced to the corresponding copper (I) compound, which subsequently reduces the diaryliodonium salt. The cationic polymerization of some typical monomers using these new initiators was carried out to demonstrate the scope of their utility.     

The Spectrophotometric Determination of gallium (III) Using O-Hydroxyhydroquinonephathalein in the Presence of Surfactant Micellar

Abstract

The color reaction systems between various metal ions and o-hydroxyhydroquinonephthalein(Qnph) as a xanthene dye, in the presence of various water soluble surfactants(cationic. anionic, non-ionic surfactants) alone or in combination, were systematically investigated at various pH areas. The coexistence of cationic and non-ionic surfactants, such as Zephiramine (Zp) and Brij 35, was most effective for the color reaction systems between Qnph and gallium(III), as a metal ion, at weakly acidic media. By using the color reaction between Qnph and gallium(III) in the coexistence of Zp and Brij 35, an improved and sensitive spectrophotometric determination of gallium(III) was proposed as method 1, and the calibration curve was rectilinear in the range of 0～7.0 μg of gallium(III) in a final solution of 10ml at pH 6.4. The apparent molar absorptivity was 1.5 × 10⁵ 1 mol^?1 cm^?1 at 560 nm, and the interference of foreign ions was decreased by ½～ ¼-fold in comparison with other methods; method 3—in the presence of Zp alone at pH 6.4, method 2—in the presence of Tween or Brij 35 alone, without Zp, at pH 8. Thus, the use of Qnph as a xanthene dye and the combination of cationic and non-ionic surfactants, such as Zp and Brij 35(perhaps, on the mixed micellar media), was most effective and its color reaction was used for the separative assay of gallium(III).     

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.     

A theoretical study on the mechanisms of intermolecular hydroacylation of aldehyde catalyzed by neutral and cationic rhodium complexes

In this paper, we used density functional theory(DFT) computations to study the mechanisms of the hydroacylation reaction of an aldehyde with an alkene catalyzed by Wilkinson's catalyst and an organic catalyst 2-amino-3-picoline in cationic and neutral systems. An aldehyde's hydroacylation includes three stages: the C–H activation to form rhodium hydride(stage I), the alkene insertion into the Rh–H bond to give the Rh-alkyl complex(stage II), and the C–C bond formation(stage III). Possible pathways for the hydroacylation originated from the trans and cis isomers of the catalytic cycle. In this paper, we discussed the neutral and cationic pathways. The rate-determining step is the C–H activation step in neutral system but the reductive elimination step in the cationic system. Meanwhile, the alkyl group migration-phosphine ligand coordination pathway is more favorable than the phosphine ligand coordination-alkyl group migration pathway in the C–C formation stage. Furthermore, the calculated results imply that an electron-withdrawing group may decrease the energy barrier of the C–H activation in the benzaldehyde hydroacylation.     

Sonogashira reaction on quinolizium cations

The four isomeric bromoquinolizium bromides reacted with aryl- and heteroarylacetylenes under Sonogashira conditions. The reactions proceed with moderate-to-high yields to afford aryl- and heteroarylethynyl quinolizium cations. This is the first reported example of the Sonogashira reaction on heteroaromatic cations, and it allowed easy access to potential pi-donor pi-acceptor systems bearing cationic units.     

CH Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3−

Although early transition metal (ETM) carbides can activate C?H bonds in condensed‐phase systems, the electronic‐level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, C?H activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC₃^?) under thermal‐collision conditions has been identified by using high‐resolution mass spectrometry, photoelectron imaging spectroscopy, and high‐level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC₃^? with C₂H₆. The C?H activation follows a mechanism of oxidative addition that is much more favorable in the carbon‐stabilized low‐spin ground electronic state than in the high‐spin excited state. The reaction efficiency between the MoC₃^? anion and C₂H₆ is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt⁺+C₂H₆) was made. It turned out that the potential‐energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.