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The synthetic utility of alkyl-onium salt compounds is widely recognized in the field of organic chemistry. Among the wide variety of onium salts, quaternary ammonium, phosphonium, and tertiary sulfonium salts have been the most useful compounds in organic syntheses. These compounds have been very useful reagents in the construction of organic building blocks. In addition, onium salts are known as reliable catalysts, which are used to promote important organic transformations by serving as phase-transfer and ion-pair catalysts through the activation of nucleophiles. Although phase-transfer catalysis is a major direction for onium salt catalysis, hydrogen-bonding catalysis of alkyl-onium salts, which is promoted via the activation of electrophiles, has recently become a relevant topic in the field of onium salt chemistry. This Minireview introduces new possibilities and future directions for alkyl-onium salt chemistry based on its use in hydrogen-bonding catalysis and on its overall utility.

In the past decade, synthetic oxidized 5-MedC nucleosides and their derivatives have become essential tools for epigenetic research. The low efficacy of both conventional and newly reported BOP methods on C4-amination of these specific oxidized 5-MedU substrates urged us to systematically investigate how the nature of onium salt-based coupling reagents affects the C4-amination of pyrimidine nucleobases and lead us to the findings that different onium coupling reagents result in the formation of distinctive activation intermediates and PyAOP is much more potent than BOP in both activation and aminolysis steps. Direct amination without the need of ribose protection, ultrafast activation, tolerance to aqueous N-nucleophiles, and excellent yields for diverse oxidized 5MedC derivatives are the advantages of this PyAOP-based C4-amination method.

Onium salts, widely used as photoacid generators (PAGs) in the semiconductor industry, are receiving increased regulatory scrutiny due to their potential hazardous properties. Evaluating the environmental impacts of these chemicals requires knowledge of the fate of the onium species during photolithography steps, which remains unclear for many PAGs. The current study investigated the fate of four representative sulfonium PAGs using an irradiation setup simulating industrial photolithography. The photolytic fate for three of the four selected onium cations is reported for the first time. All onium compounds reacted rapidly under 254 nm irradiation, and their half-lives ranged from 51 to 214 s with high quantum yields (0.23−0.85). Multiple highly aromatic and hydrophobic photoproducts were characterized using HPLC-DAD and GC-MS; eight PAG photoproducts were identified for the first time. Authentic commercial standards of some of the photoproducts were available, enabling quantitative estimates of recoveries. The molar recovery of aromatic rings based on these quantified photoproducts was in the range of 4.9–71.4 %. A homolytic reaction mechanisms is proposed and discussed. The results provide insight on the potential environmental impact pertinent to the use of PAGs, e.g., prediction of residual onium levels and the identity of photoproducts in effluents from semiconductor fabrication facilities.

We report the rates of electron transfer (ET) reactions of electronically excited [Ir(COD)(μ-Me2pz)]2 with onium salt photoacid generators (PAGs). The reduction potentials of the PAGs span a large electrochemical window that allows determination of the driving force dependence of the ET reactions. Rate constants of ET from electronically excited [Ir(COD)(μ-Me2pz)]2 to onium PAGs are determined by the reaction driving force until the diffusion limit in acetonitrile is reached.

Cooperative dual catalysis and bifunctional catalysis have emerged as reliable strategies for the development of hitherto difficult asymmetric transformations because they could deliver new reactivity and selectivity, and allow for the employment of substrates not amenable to reaction systems relying on a single, monofunctional catalysts. Furthermore, these modes of catalysis often improve yields and stereoselectivities via the precise recognition and simultaneous activation of nucleophiles and electrophiles. Efforts towards utilizing chiral cationic organic catalysts for asymmetric cooperative catalysis with metal complexes have provided a unique platform to address the challenging issues associated with reaction development. Chiral onium ions, such as tetraalkylammonium, guanidinium, and azolium ions, are employed mainly to control the reactivity and stereochemistry of anionic intermediates through electrostatic and hydrogen-bonding interactions. Metal complexes complement the synergy of the catalysis by activating the substrates via the formation of electrophilic π-allyl complexes, Lewis acid-base adducts, nucleophilic ate complexes, etc. The electrostatic interactions between cations and anions also offer a means to construct complex molecular assemblies, and, thus, onium ions are useful not only for controlling pairing with anionic species, but also for the design of supramolecular catalysts. The combination of onium ions and metal complexes leads to the introduction of novel concepts and powerful strategies for the development of catalysts and chemical transformations.

The cation–π interaction is an attractive noncovalent interaction between a cation and a π-face. Owing to the stronger interaction energy than those of the other π interactions, such as π–π and CH–π interactions, the cation–π interaction has recently been recognized as a new tool for controlling the regio- and stereoselectivities in various types of organic reactions. This chapter attempts to cover a variety of organic reactions assisted by interactions between unreactive onium ions and π-faces, which will provide comprehensive knowledge on the role of cation–π interactions in organic synthesis.

Cation CpFeC5H4–C+=CH2 was obtained by protonation of FcC CH with Nafion superacid in DMF or scCO2 and characterized by NMR spectroscopy. The protonation in the presence of SMe2 or PPh3 affords new onium derivatives, which were isolated as the tetrafluoroborate salts.

Asymmetric 1,2-additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al-F-salen complex. This allowed for unprecedented turnover numbers of up to 104 . DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results.

The catalytic coupling of oxetane, the symmetric isomer of propylene oxide, with carbon disulfide has been investigated utilizing (salen)CrCl in the presence of various onium salts. Oxygen and sulfur atom exchange was observed in both the polymeric and cyclic carbonate products. The coupling of oxetane and CS2 was selective for copolymer formation over a wide range of reaction conditions. Five different polymer linkages and two cyclic products were determined by 1H and 13C NMR spectroscopy, and these results were consistent with in situ infrared spectroscopic monitoring of the process. The major cyclic product produced in the coupling process was trimethylene trithiocarbonate, which was isolated and characterized by single crystal X-ray crystallography. Upon increasing the CS2/oxetane feed ratio, a decrease in the O/S scrambling occurred. The reaction temperature had the most significant effect on the O/S exchange process, increasing exchange with increasing temperature. The presence of the onium salt ini...

Data of potentiometric, redox, and conductometric studies of interactions in the sulfur(IV) oxide-ethylenediamine (or its analogs)-water systems, being in fair agreement, have showed the formation of onium sulfites, hydrosulfites, and pyrosulfites. The absorbance capacity of aqueous solutions of ethylenediamines with respect to sulfur dioxide depends on the amino groups amount. Ion and molecular compositions of the studied solutions have been computed, and the relative stability of onium sulfites of ethylenediamine and piperazine has been estimated.

Density functional theory (DFT) calculations have been employed on 165 complexes of onium ions (NH4+, PH4+, OH3+, SH3+) and methylated onium ions with CO2, aromatic (C6H6) and heteroaromatic (C5H5X, X = N, P; C4H5Y, Y = N, P; C4H4Z, Z = O, S) systems. The stability of CO2⋯onium, CO2⋯π and onium⋯π complexes was shown to be mediated through various noncovalent interactions such as hydrogen bonding, NH–π, PH–π, OH–π, SH–π, CH–π and π–π. We have discussed 17 complexes wherein the proton transfer occurs between the onium ion and the heteroaromatic system. The binding energy is found to decrease with increasing methyl substitution of the complexes containing onium ions. Binding energy components of all the noncovalent complexes were explored using localized molecular orbital energy decomposition analysis (LMO-EDA). The CO2⋯π complexes were primarily stabilized by the dispersion term followed by contributions from electrostatic and polarization components. In general, for onium ion complexes with CO2 or π systems, the electrostatic and polarization terms primarily contribute to stabilize the complex. As the number of methyl groups increases on the onium ion, the dispersion term is seen to have a key role in the stabilization of the complex. Quantum theory of atoms in molecules (QTAIM) analysis and charges based on natural population analysis (NPA) in various complexes have also been reported in order to determine the nature of noncovalent interactions in different complexes.

Although quaternary onium salt-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles proceeded smoothly in the presence of lipophilic quaternary onium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate additions, aldol reaction, sulfenylation, and chlorination under the influence of chiral bifunctional onium bromides as key catalysts.

Two novel redox initiator systems have been developed for carrying out the cationic polymerizations of vinyl and heterocyclic monomers. The initiators are based on various onium salts as the oxidant together with an alkylborane or an organosilane as the reducing agent. Using both redox cationic initiator systems, the polymerizations of a wide variety of monomers can be carried out at or below room temperature in the presence or absence of unreactive solvents. Also described in this communication is the novel use of a two-component redox system in which the reducing agent, a silane, is delivered to the monomer sample in the vapor state. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor the polymerizations in real-time. A study of the effects of variations in the structures of the onium salt, the silane and the type of noble metal catalyst were carried out. The use of these initiator systems for carrying out commercially attractive crosslinking polymerizations for coatings, composites and electronic encapsulations is discussed.

International audience; Palladium nanoparticles, simply and briefly generated in commercial and cheap onium salts using supercritical carbon dioxide, have been found to be an effective catalytic system for additive free N-alkylation reaction using alcohols via cascade oxidation/condensation/reduction steps.

Photoredox pairs consisting of dyes based on diazobenzo[a]fluorene derivatives and commercially available onium salts (diaryliodonium and triphenylsulfonium salts) are tested as effective initiator systems for the cationic polymerization of cyclohexene oxide using visible light. The efficiency of these initiator systems is discussed based on the free energy change for the electron transfer from examined dyes to the onium compounds. The most efficient sensitizers are the dyes with the lowest oxidation potential and the highest −ΔGel. A linear relationship between the quantum yields of acid release Φ(H+) and the conversion of CHO is observed.

Quaternary onium salts of halides can be efficiently converted into the corresponding quaternary onium salts of various anions [NO3–, BF4–, PF6–, CF3SO3–, CH3SO3–, ClO4–, p-CH3C6H4SO3–, CF3CO2–, 2,4-(NO2)2C6H3O–] by treating the onium halide with trimethyl phosphate under neat condition in the presence of an equivalent amount of conjugate acid of the desired anion.

Relations were investigated between the structure of a series of onium salts, rates of alkaline hydrolysis catalyzed by the salts of 4-nitrophenyl N-benzyloxycarbonylglycinate in a two-phase liquid-liquid system, and the value of the standard exchange enthalpy of anions in ion pairs with the catalyst cation calculated by the semiempiric PM3 method. The catalytic activity of ammonium, phosphonium, pyridinium, imidazolium, and benzimidazolium salts in a wide range of cation structures varies in parallel with the enthalpy of formation of the active form of the catalyst by the exchange of the anion with a hydroxide ion.

A review of our work on two- and-three component photoinitiator systems is presented. The emphasis is in on visible light polymerization in aqueous media. The systems discussed comprise a synthetic dye as sensitizer and an onium salt as coinitiator, or a dye-amine-onium salt with the amine as coinitiator and the onium salt as an enhancer of the polymerization efficiency. The effect of the composition of the system on the photopolymerization kinetics was analyzed. To this end, the photophysics and photochemistry of the dye under polymerization conditions was explored by means of stationary and time-resolved spectroscopic methods. Different dyes and onium salts were investigated. The action mechanism of the different photoinitiators systems is discussed.

In this work, diversified quaternary onium salt-type triphase catalysts (TPC) were prepared based on crosslinked polystyrene (CPS) microspheres, and the relationship between their chemical structures and catalytic activities in liquid-solid-liquid reaction system were investigated in depth by using the esterification reaction of benzyl chloride with sodium acetate as a model system. The experimental results indicate that the chemical structures of the TPC affect their catalytic activity greatly and there are four basic points: (1) the quaternary phosphonium-type TPC have higher activity than quaternary ammonium-type catalyst; (2) the TPC with more lipophilic substitutes at N atom have higher catalytic activity; (3) the TPC with longer spacer arm, which links quaternary onium salt group to the matrix microsphere, have higher catalytic activity; (4) the bonding density of quaternary onium salt group on the polymeric carrier affects the hydrophilic and hydrophobic property of the TPC, and consequently, influences the catalytic activity significantly. For a given triphase catalysis system, there is an optimal bonding density of quaternary onium salt group on the solid catalysts. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Long wavelength free radical photopolymerization of (meth) acrylic monomers using a conjugated thiophene derivative, namely 3,5-diphenyldithieno[3,2-b: 2-,3--d]-thiophene (DDT) and one of the following compounds, namely diphenyliodonium hexafluorophosphate (Ph(2)I(+)PF(6)(-)), triphenylsulfonium hexafluorophosphate (Ph(3)S(+)PF(6)(-)) and N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP(+)PF(6)(-)), as photosensitizer and coinitiator, respectively, was described. Polymerization occurred only when DDT, in the presence of the onium salts, was irradiated at wavelengths where the salts have no absorption. A feasible initiation mechanism involves intermolecular electron transfer from photoexcited thiophene compound to the onium salt. The relative initiation efficiencies of the salts were investigated and evaluated in terms of their redox potentials.

Task specific ionic liquids and onium salts have been used as soluble supports for peptide synthesis. These new supports combine easy monitoring, high loading capacities, large scale preparation, and homogeneous kinetics characteristics while keeping advantages of solid-phase synthesis including easy purification and workup. Careful structural design of these supports allowed for fine tuning of physical properties leading to better yields, kinetics, and purities.

In this article, a new route for the synthesis of N-aryl heteroaromatic onium salts by the direct copper catalyzed arylation of pyridine, substituted pyridines, isoquinoline, and acridine with diaryliodonium salts is described. It was demonstrated that these N-aryl heteroaromatic onium salts undergo facile platinum or rhodium-catalyzed reduction by silanes bearing Si—H groups. The reduction of N-aryl heteroaromatic onium salts generates Bronsted acids. When this redox reaction was carried out in situ in the presence of an appropriate monomer, cationic polymerization was observed. Using this approach, the cationic polymerizations of epoxides, oxetanes, 1,3,5-trioxane, styrene, and vinyl ethers were carried out. The use of optical pyrometry to monitor the redox initiated cationic polymerizations of some representative multifunctional monomers is described.

Novel redox initiators for cationic polymerizations were developed consisting of an onium salt together with a SiH functional silane or siloxane. The reduction of the onium salt by the silane is catalyzed by noble metal complexes or certain transition metal compounds and takes place spontaneously at room temperature. The redox reaction of the onium salt with the silane results in the liberation of a strong Bronsted acid that can be subsequently used to initiate cationic polymerizations. Typical onium salts that have been employed in these redox initiator systems are diaryliodonium salts, triarylsulfonium salts and S,S-dialkyl-S-phenacylsulfonium salts. Studies of the effects of variations in the structures of the onium salt, the silane and the type of noble metal catalyst were carried out. In principle, the redox initiator systems are applicable to all types of cationically polymerizable monomers and oligomers, including the ring-opening polymerizations of such heterocyclic monomers as epoxides and oxetanes and, in addition, the polymerization of vinyl monomers such as vinyl ethers, N-vinylcarbazole and styrenic monomers. The use of these novel initiator systems for carrying out commercially attractive crosslinking polymerizations for coatings, composites and encapsulations is discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Various zinc halide-based ionic liquids were prepared from zinc halides and onium halides as catalysts for the synthesis of styrene carbonate (SC) from styrene oxide and carbon dioxide. The effects of the ionic liquid catalyst composition (types of onium cation and halide, onium cation/zinc ratio) and CO2 pressure on the reaction were investigated. The effectiveness of the onium cation as the active catalyst component was in the order of tetrabutylammonium > 1-butylpyridinium > 1-butyl-3-methylimidazolium ≫ choline. The type of halide atom originating from the zinc salt affected the catalytic activity of the ionic liquid more significantly than that of the one originating from the onium salt. The onium cation/zinc ratio also affected the SC yield, but its manner was different depending on the type of onium cation. Influence of CO2 pressure was not significant. Various zinc halide-based ionic liquids were prepared from zinc halides and onium halides as catalysts for the synthesis of styrene carbonate from styrene oxide and CO2. Effects of types of onium cations and halides, the molar ratio of onium cation to zinc, and CO2 pressure on the carbonate yield were investigated.

Efficient catalytic systems based on the combination of cobalt(II)/onium salts for the coupling reaction of CO 2 and epoxides are reported. The catalytic systems work under mild reaction conditions (e.g. 10 bar and 120 °C) and produce cyclic carbonates with high turnover frequencies (TOF) and selectivity. From a series of onium salts, bis(triphenylphosphoranylidene)ammonium chloride proved to be the most active cocatalyst (TOF = 2314), while tetrabutyl ammonium chloride (TOF = 2223) and 1,3-bis(2,4,6trimethylphenyl)imidazolium chloride (TOF = 2174) provided only slightly reduced activities under similar conditions. The influence of various reaction parameters including CO 2 pressure, reaction temperature and loading of onium salt was determined. In order to obtain an insight into the catalytic process, the reaction was followed by electrospray ionisation-mass spectrometry. Additionally, in situ FT-IR measurements show that the catalyst is stable even with low loading (0.025 mol%) and as a result, the reaction proceeds steadily over several hours.

Using the HF, B3LYP, and MP2 methods in the 6−31+G(d) basis with zero-point energy corrections, quantum chemical calculations of energy characteristics were carried out for the model molecules CH2=XH+ (X = NH, O, S, Se) formed from the molecules YCH2XH (Y = NH2, OH, SH, SeH, Cl) either through the elimination of Y-anions or as a result of the abstraction of neutral species YH from these molecules upon their interaction with a proton. Stabilities of the onium states of nitrogen atom were shown to be considerably higher than those of the onium states of chalcogen derivatives, with the lowest stability shown by the models with the Cl atom being in the onium state. The results have been formulated in the form of stability series of the onium compounds and allowed one to interpret certain features of the aminomethylation reaction (the Mannich reaction), hydroxy- and alkoxymethylation, thio- and selenomethylation, and chloromethylation (the Blanc reaction).

Examples of the effects of interionic H-bonds on the structural features and properties of onium fluorosilicates are analyzed and systematized. Potential applications of these effects are ascertained.

In the recent past, it has been found that the use of onium salts as acid-generating species has improved the performance of photoresists, particularly for microelectronic applications. However, little research has been dedicated to the use of these photo-initiators in aqueous-developable resists. This work describes the synthesis and characterization of some water-soluble polymers and investigates the feasibility of employing one of the onium salts in the formulation of a resist polymer for use in aqueous conditions. The ability of this onium salt to photo-initiate the cationic polymerization of epoxies residues was exploited using water-soluble copolymers, containing glycidyl methacrylate (GMA). The comonomers included methacrylic acid. Various copolymers were prepared by radical copolymerization typically in methyl ethyl ketone. It was found that the copolymer containing 85 mol.% of GMA unit in feed was soluble in aqueous base and crosslinked in the presence of photogenerated acid caused by acid-initiated ring opening polymerization of the pendant epoxide groups. A good pattern with reasonable resolution was attained by exposure to a UV lamp with λ = 365 nm light followed by a post exposure bake at 80° C for 1 min.

International audience; Metal nanocrystals have been prepared in onium salts using supercritical carbon dioxide assisted synthesis. During the process, metal salts precursors are reduced by H2 in an organic solvent free media, the onium salts allowing both the stabilization of the nanostructured material and the preparation of an air and moisture stable powder made of embedded metal nanocrystals. Those catalysts proved to be highly effective in the hydroboration of alkyne process.

A coating consisting of an ionic liquid (1,3-butylmethylimidazolium hexafluorophosphate [BMIM][PF6]) was deposited on silica gel as well as on a new polyvinylimidazolium phase and treated with a task specific onium salt (TSOS). The activity and stability of both immobilised Pd-species were studied and compared in Mizoroki-Heck cross coupling reactions.

A new two-component system, consisting of a matrix and an onium salt as comatrix, is described for detection of sulfo-peptides in the positive mode by matrix-assisted desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Binary iodonium salts were superior to quaternary phosphonium salts in terms of suppression of desulfation and salt formation with the carboxyl group. Of the iodonium salts examined, bis(4-tert-butylphenyl)iodonium (BTI) hexafluorophosphate and bromide were most effective in giving intensive molecular ion signals in the form of [M(BTI)+BTI]+. The conditions optimized for O-sulfated tyrosine-containing peptides could be applicable for O-sulfated serine- and threonine-containing peptides. In the case of a phospho-peptide, a molecular ion appeared more intensively as a proton adduct than as a BTI adduct. Copyright © 2006 John Wiley & Sons, Ltd.

N-Alkylation of anilines by dimethyl carbonate (DMC) catalyzed by onium salts has been demonstrated. The work presented here shows that a simple catalytic system consisting of onium salts in the presence of a small amount of water is extremely effective in enhancing the DMC mediated N-alkylation of anilines to dialkylated products. The effect of reaction conditions, on the synthesis of N,N-dimethyl aniline (NNDMA) from aniline and DMC has been investigated. Under the optimized conditions highest yield of NNDMA obtained was 99.8%, which is the best reported for liquid phase N-alkylation of aniline using DMC. The role of water in enhancing the yield of NNDMA is explained and a reaction-networking scheme is constructed, which summarizes the chemistry behind liquid phase N-alkylation of anilines by DMC. The catalyst has been shown to recycle up to five times and at the end of fifth recycle almost 98% of NNDMA yields were obtained.

The heterogeneous atom transfer radical polymerization of styrene using various onium salts as ligands in the presence of (1‐chloroethyl or 1‐bromoethyl) benzene [PEX (X = Cl, Br)] was investigated. The rate of polymerization using these onium salts as ligands exhibited non‐linear first‐order kinetics with respect to the monomer. The experimental molecular weights increased linearly with monomer conversion and were close to the calculated values for most of these catalytic systems. The polydispersities of the resulted polymers were around 1.1–1.5. Allylic substituent on the phosphorus favored the control of polymerization. The FeCl2 · 4H2O/hexadecyl trimethyl ammonium bromide yield the lowest rate of polymerization, which maybe due to the excess of Fe3+. Using mixed halogen initiation system PEBr/FeCl2, poor control of ATRP of styrene in the presence of onium salts was observed except for triphenylbutyl phosphonium bromide.

A novel visible photosensitized system, squaraine dye (SQ)/iodonium salt (On) combination, used as a radical photogeneration source has been suggested and studied. The thermodynamic data and experimental results show that the SQ/On combination readily undergoes photoreaction via fast intramolecular ion-pair electron transfer within the short time scale of excited lifetime of SQ, simultaneously resulting in a photobleaching of SQ dye and a generation of active radical species released by subsequent decomposition of onium product. Some important factors that affect the formation of ion-pair complex between SQ dye and onium salts, such as solvent polarity, nature of counter anion, concentration of SQ dye and onium salt, show a large influence on the photoreaction kinetics. Based on the results of primary photoreaction, the visible photopolymerization using SQ/On combination as photoinitiator was studied in the solution and film. The synchronous photopolymerization and photobleaching behaviors were found in the polymerization process. The dye-sensitized photoreaction mechanism of SQ/On system was also proposed and discussed.

The oxidations of cyclohexene (Ch) and tetralin (T) are induced by insertion of O 2 into their activated CH groups and primarily hydroperoxides are formed. The onium salts promote the homolysis of the hydroperoxides formed. The efficiency of the catalysts depend on the polarizing power (partial charge) of the onium cations, the polarizability of the counteranions and the concentration of the catalyst. During the catalysed oxidation of substrates and during the catalysed decompositions of their hydroperoxides radical formation was detected by means of a spin trap, and some singlet O 2 was also evolved. The catalysed cooxidations demonstrated that the oxidation products mutually influence the transformations of these hydrocarbons. The onium-decavanadate ion-pair complexes are more effective catalysts than the pure onium salts. The Arrhenius parameters of the oxidations were determined and a possible mechanism is outlined.

The primary objective of this study was to improve montmorillonite clay-platelet separation in vinyl ester resin matrix by organically modifying the nanoclay platelet with a partially reactive onium salt. The reactive onium salt (ω-undecylenyl amine hydrochloride) was synthesized from commercial ω-undecylenyl alcohol through a series of synthetic conversions. Nonreactive onium salt (undecyl amine hydrochloride) was made from commercial undecyl amine. These salts were characterized with 1H and 13C NMR and Fourier transform infrared techniques. The relative amounts of exfoliated, intercalated, and as-treated clay and the size of the clay particle aggregates depended significantly on the composition of clay and the processing conditions. When the clay was ion-exchanged with a mixture of reactive and nonreactive onium salts, a partially exfoliated vinyl ester resin polymer nanocomposite was formulated. The addition of a comonomer styrene and high-intensity ultrasonic mixing produced vinyl ester nanocomposite with the highest degree of clay-platelet exfoliation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1310–1321, 2004

A new approach to the preparation of epoxy−clay nanocomposites is reported based on the intercalation and exfoliation of homostructured mixed inorganic/organic cation exchanged forms of a commercially available montmorillonite (PGW) and a synthetic fluorohectorite (FH) clay. In these mixed-ion homostructures both the organic onium ions and the inorganic exchange ions co-occupy the gallery surfaces of the clay, thereby dramatically reducing the amount of organic modifier needed to access the galleries for nanocomposite formation. The homostructures were prepared by ion exchanging the inorganic H+ and Li+ forms of the smectite clays with diprotonated primary α,ω-diamines of the type H2NCH(CH3)CH2[OCH2CH(CH3)]xNH2 (denoted Jeffamine D2000 with x = 33.1). Varying the ratio of inorganic cations to onium ions afforded homostructured mixed-ion intercalates with basal spacings ranging from ∼17 A (25% onium ion exchange) to ∼46 A (65% onium ion exchange), indicating the Jeffamine D2000 modifier adopted extended ch...

To synthesize an epoxy–montmorillonite nanocomposite, the intercalation of clay layers with acid onium ions {[H3N(CH2)n−1COOH]+, [H3N(CH2)n−1CH3]+, [H3N(CH2)−NH2]+, and [H3N(CH2)nNH3]2+} by different methods were studied. The intercalated clay was characterized by XRD, ICP, and CHN elemental analysis. An acid onium ion [H3N(CH2)17CH3]+ enlarged the d-spacing of CWC–, AMS–, and Kunipia–montmorillonite to 21.6, 18.1, and 20.7 A, respectively. The results of CHN elemental analysis confirmed that onium ions were intercalated between the clay layers. Ion exchange of montmorillonite with onium ions is a better way to intercalate more onium ions. Among those onium ions mentioned above, [H3N(CH2)nNH3]2+ displaced more sodium ions from the clay layers than did the others. An epoxy–montmorillonite nanocomposite was synthesized by heating a mixture of [H3N(CH2)17CH3]+–montmorillonite (CWC) with an epoxy monomer and curing agent. The nanocomposite was characterized by XRD, TEM, DSC, UV, TGA, and Instron testing. TEM photographs showed that the spacing between the clay layers was further enlarged to about 50 A and no segregation between the clay particle and the polymer was observed. The glass transition temperature of the nanocomposite containing 20 phr of [H3N(CH2)17CH3]+–montmorillonite (CWC) increased from 108.4 to 146.1°C. Especially, the nanocomposite possesses higher water resistance than that of the epoxy resin or of the physical mixture of epoxy and montmorillonite (CWC). According to the transmittance measurement (λ = 550 nm), the nanocomposite shows good light transmittance. Although, we cannot improve the mechanical properties, improvements of other properties can be evidenced for the formation of nanoscale composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 414–421, 2002

A mixed-ion, amphiphilic fluorohectorite heterostructure, wherein the galleries are regularly interstratified by hydrophilic inorganic ions (Na + ) and lipophilic onium ions, is shown to be an efficient electrochemical sensor for the specific determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and the pollutant 2,4-dicholorophenol (2,4-DCP) when incorporated at the 5 wt % level into a carbon paste electrode (CPE). The clay-modified electrode was substantially less sentive to herbicides that lack the aromatic hydroxyl groups needed for oxidation to a quinone (e.g., Illoxan and Furore). Conventional homoionic organoclays with all galleries exclusively occupied by an onium ion surfactant exhibited a lower electrochemical response to 2,4-D and 2,4-DCP oxidation when incorporated into a CPE. Similarly, low current responses were observed for a CPE modified with a homostructured mixed-ion montmorillonite clay with both inorganic ions and organic onium ions cooccuping each clay gallery. The electrochemical response observed for the mixed-ion fluorohectorite heterostructure was attributed to the ability of this unique clay intercalate to achieve electrical neutrality upon oxidation of the dichlorophenoxy moiety through the facile ejection of sodium ions from the segregated inorganic galleries.

International audience; M(0) nanocatalysts stabilised in Onium Salt were synthesised using an original preparation and their effectiveness in catalysing the challenging selective sterodivergent alkyne hydrosilylation reaction was studied. Four metal based nanocrystals, namely Pt, Ir, Rh and Ru stabilised by three Onium Salts (quaternary ammonium salts with different anions and cations), were successfully prepared by supercritical CO2 assisted synthesis. The Onium Salts with three different structures were chosen considering their effect on nanocrystals morphology and surface properties but without interference in the selectivity towards hydrosilylation reaction. It was found that the stereochemical outcome can be adjusted either by varying the metal but preserving the same Onium Salt stabilizer, or varying the metal NCs surface properties by changing the stabilizer structure.

A new system for efficiently carrying out cationic photopolymerizations with visible and long-wavelength UV light is described. This system is based on the principle that certain onium salt cationic photoinitiators can be reduced by free radicals produced by the hydrogen abstraction reactions of photoexcited ketones. Thus, when camphorquinone, benzil, 2-isopropylthioxanthone, and 2-ethylanthraquinone are irradiated in the presence of a monomer that can serve as a hydrogen donor, the resulting monomer-bound radical rapidly reduces a diaryliodonium salt or a dialkylphenacylsulfonium salt, and the resulting monomer-centered cations initiate the polymerizations of epoxides, vinyl ethers, and heterocyclic compounds. Onium salts with high reduction potentials, such as triarylsulfonium salts, do not undergo sensitization by this new system.

The oxidation of tetralin and cyclohexene by O2 was investigated in the presence of cationic phase-transfer catalysts (PTCs). It was found that the oxidation takes place analogously to the recently investigated catalysed decompositions of hydroperoxide initiator molecules. The natures of both the onium cation and the counteranion are determining factors. The catalytic activity of the onium salt is determined by the effective charge on the onium ion and by the size and polarizability of the anion. For both hydrocarbons, the primary product of oxidation is the corresponding hydroperoxide, which may undergo further oxidation. For tetralin, tetralyl hydroperoxide underwent disproportionation into O2 and tetralol, and reuse of the O2 thus produced resulted in a considerable “overoxidation” in the closed reactor. Tetralone was formed in a smaller amount. The main products in the oxidation of cyclohexene were its hydroperoxide, cyclohexene oxide and 2-cyclohexen-1-ol. In contrast to the oxidation of tetralin, “overoxidation” did not occur here, and the formation of 2-cyclohexen-1-one was never observed. The oxidations of these hydrocarbons in the presence of cationic PTCs proved to be strongly influenced by the concentration of homogeneously dissolved water. The oxidation products of these hydrocarbons also exerted considerable influence on the progress of the oxidation.

The progress of developer base into films of terpolymers of norbornene−maleic anhydride and acrylic acid was shown to be a percolation process with a critical site concentration of x(c) = 0.084, implying that every acrylic acid site in the terpolymer makes 12 monomer units of the polymer water compatible. Using these terpolymers, the dissolution inhibition mechanism for two types of common additives, tert-butyl carboxylate (e.g., cholates, cyclohexanecarboxylates, and malonates) dissolution inhibititors and onium salt photoacid generators (PAG's), were examined. Additionally, the dissolution promotion mechanism of carboxylic acids released from acidolysis of tert-butyl esters was investigated. For a wide range of cholates and other tert-butyl carboxylate derivatives, increasing hydrophobicity is a good predictor of increased dissolution inhibition. The molar dissolution promotion ability of a carboxylic acid increases with increasing number of both carboxyl and hydroxyl ester functional groups. For onium ...

Pyridinium-type salts containing an N-ethoxy group belong to the family of onium salts and are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers which are not polymerizable by a free radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the onium ion, with the former being restricted to the wavelength range of self absorption, the latter being applicable at wavelengths of visible light, An additionally useful tool, namely free radical-mediated generation of initiating species enlarges the versatility of pyridinium salts as photoinitiators. In this connection, the oxidation of free radicals by pyridinium-type ions and the free radical-induced fragmentation of alkoxy pyridinium ions are addressed in this article. Moreover, an interesting application is noted concerning the synthesis of novel block copolymers with the aid of the onium salt-based photopolymerization technique.

Experimental and theoretical evidence is presented that cationic phase-transfer catalysts promote the homolytic decomposition of hydroperoxide initiators into radicals, this being a fundamental step in the catalysis of the oxidation of hydrocarbons by O2. Such decomposition of the model substance tert-butyl hydroperoxide (t-BHP) results in O2, tert-butanol (90–95%) di-tert-butyl peroxide (5–10%) and traces of CO2. The stoichiometric ratio Δ[t-BHP]/ΔO2 was found to have a value of 2, independently of the nature of the counteranion present. It is assumed that the interaction between hydroperoxide and onium cation is mainly electrostatic in nature and that its effectivity depends on the positive charge density on the onium cation, which is controlled by the nature and dimensions of the counteranion. The role of water in the decomposition of t-BHP is also elucidated.

A series of single component chemically amplified molecular resists were made using an onium salt cation core of tris(4-(tert-butoxycarbonyloxy)-3,5-dimethylphenyl)sulfonium (TAS) with five different acid anions: chloride (Cl), hexafluoroantimonate (SbF"6), triflate (Tf), nonaflate (Nf), and tosylate (Ts). The counter-ion had a large effect on both the performance and physical characteristics of the resists. TAS-SbF"6 and TAS-Tf imaged as positive tone resists with good LER, but suffered from acid diffusion problems which limited resolution. TAS-Ts and TAS-Cl had high water solubility that prevented their use as positive tone resists. TAS-Nf had poor wetting and adhesion that prevented it from being spin-coated into films. Using onium salts as single molecule resists places great restriction on the choice of anion used because of the large effect it has on the properties of the resist. Using extreme ultraviolet lithography, TAS-SbF"6, the best performing derivative, was able to resolve 50nm 1:1 line/space patterns with LER ([email protected]) of 5.2nm.

The story of the discovery and development of onium salt photoinitiators for cationic polymerization is chronicled. The chemistry of the synthesis of these compounds is outlined, and the mechanisms of their initiation are discussed briefly. Among the most useful of these types of photoinitiators are diaryliodonium and triarylsulfonium salts, which are used widely for photoinduced cationic crosslinking reactions. From the very beginning, onium salt photoinitiated cationic polymerizations have found use in a multitude of practical applications. Specifically discussed in this article are the use of onium salts in coatings, adhesives, printing inks, release coatings, stereolithography, holographic recording, photocurable composites, and microelectronic photoresists. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4241–4254, 1999

Amphiphilic mixed ion smectite clays have been prepared by the reaction of inorganic ion exchanged forms of synthetic fluorohectorite with [C16H33EBu3+] onium ions, where E is N or P. Regardless of the initial inorganic exchange cation (Li+, Na+, Ca2+, Ba2+, Al3+, Ce3+), heterostructures with regularly stacked galleries of organic and inorganic ions were formed at fQ = 0.50, where fQ is the fraction of surfactant onium ions. The stagelike segregation of cations into separate galleries is attributable to the steric restrictions of the headgroup and to hydrophobic interactions between the alkyl groups of the onium ions. The same 1:1 mixed ion intercalates were formed by ion redistribution reactions of the homoionic end-member clays, indicating their thermodynamic stability. Decreasing the fraction of onium ions from fQ = 0.50 to 0.33 resulted in the displacement of up to 30% of the onium ions (C16H33PBu3+) in the organic galleries by inorganic cations (Na+). The same gallery stacking sequence as in a 1:1 mi...

p-Terphenyl (TP) sensitizes photocatalytic reduction of water to H2 under UV irradiation of homogeneous aqueous acetonitrile solution in the presence of triethylamine (TEA) as an electron donor and Ru3+ as a precursor of cocatalyst, Ru metal colloid. The addition of quaternary onium salts enhances the H2 evolution, where the onium salts with longer alkyl groups become more effective. Dynamics studies of TP photosensitization reveal that the presence of the salts contributes to stabilization of the radical anion of TP (TP•-) formed through reductive quenching of the singlet state of TP (1TP*) and the triplet state of TP (3TP*) by TEA. The TP photosensitization accompanies competitive photo-Birch reduction via TP-. , but the presence of onium salts enhances the lifetime of TP•- through the specific interaction, leading to the effective TP-photosensitized H2 evolution.