Arene In Water Research Articles

Direct C-H Trifluoromethylation of (Hetero)Arenes in Water Enabled by Organic Photoredox-Active Amphiphilic Nanoparticles.

Photoredox‐catalyzed chemical conversions are predominantly operated in organic media to ensure good compatibility between substrates and catalysts. Yet, when conducted in aqueous media, they are an attractive, mild, and green way to introduce functional groups into organic molecules. We here show that trifluoromethyl groups can be readily installed into a broad range of organic compounds by using water as the reaction medium and light as the energy source. To bypass solubility obstacles, we developed robust water‐soluble polymeric nanoparticles that accommodate reagents and photocatalysts within their hydrophobic interior under high local concentrations. By taking advantage of the high excited state reduction potential of N‐phenylphenothiazine (PTH) through UV light illumination, the direct C−H trifluoromethylation of a wide array of small organic molecules is achieved selectively with high substrate conversion. Key to our approach is slowing down the production of CF3 radicals during the chemical process by reducing the catalyst loading as well as the light intensity, thereby improving effectiveness and selectivity of this aqueous photocatalytic method. Furthermore, the catalyst system shows excellent recyclability and can be fueled by sunlight. The method we propose here is versatile, widely applicable, energy efficient, and attractive for late‐stage introduction of trifluoromethyl groups into biologically active molecules.

Stabilization of Antitumor Agent Busulfan through Encapsulation within a Water-Soluble Pillar[5]arene.

The complexation of the antitumor agent busulfan by negatively charged carboxylatopillar[5]arene in water is reported. The encapsulation within carboxylatopillar[5]arene reduces the hydrolytic degradation of busulfan from 90.7% to 25.2% after 24 days and accordingly enhances its stability by providing a hydrophobic shelter for busulfan in water. Moreover, the complexation results in 12 times improvement of water solubility for busulfan. Our result provides a supramolecular approach for stabilizing the anticancer agent busulfan.

Photoredox-Catalyzed Reduction of Halogenated Arenes in Water by Amphiphilic Polymeric Nanoparticles.

The use of organic photoredox catalysts provides new ways to perform metal-free reactions controlled by light. While these reactions are usually performed in organic media, the application of these catalysts at ambient temperatures in aqueous media is of considerable interest. We here compare the activity of two established organic photoredox catalysts, one based on 10-phenylphenothiazine (PTH) and one based on an acridinium dye (ACR), in the light-activated dehalogenation of aromatic halides in pure water. Both PTH and ACR were covalently attached to amphiphilic polymers that are designed to form polymeric nanoparticles with hydrodynamic diameter DH ranging between 5 and 11 nm in aqueous solution. Due to the hydrophobic side groups that furnish the interior of these nanoparticles after hydrophobic collapse, water-insoluble reagents can gather within the nanoparticles at high local catalyst and substrate concentrations. We evaluated six different amphiphilic polymeric nanoparticles to assess the effect of polymer length, catalyst loading and nature of the catalyst (PTH or ACR) in the dechlorination of a range of aromatic chlorides. In addition, we investigate the selectivity of both catalysts for reducing different types of aryl-halogen bonds present in one molecule, as well as the activity of the catalysts for C-C cross-coupling reactions. We find that all polymer-based catalysts show high activity for the reduction of electron-poor aromatic compounds. For electron-rich compounds, the ACR-based catalyst is more effective than PTH. In the selective dehalogenation reactions, the order of bond stability is C-Cl > C-Br > C-I irrespective of the catalyst applied. All in all, both water-compatible systems show good activity in water, with ACR-based catalysts being slightly more efficient for more resilient substrates.

Bioinspired photocatalysed C–H fluoroalkylation of arenes in water promoted by native vitamin B12 and Rose Bengal

Fluoroalkylation of activated arenes was accomplished in water employing the dyad Rose Bengal and unmodified vitamin B12 as photocatalyst and co-catalyst respectively, with fluoroalkyl bromides as radical sources, under green LEDs irradiation.

Cu(I)/sucrose-catalyzed hydroxylation of arenes in water: the dual role of sucrose.

A protocol for the hydroxylation of aryl halides catalyzed by copper(i) and sucrose in neat water has been developed. The dual role of sucrose, the reaction pathway, and the high selectivity for hydroxylation were investigated using a combination of experimental and theoretical techniques.

Enthalpies of Solution of C-Alkylresorcin[4]arenes in Water and Acetonitrile: Hydrophilic and Hydrophobic Effects.

Enthalpies of solution, Δsln H, of six C-alkylresorcin[4]arene ( C-ARA) solids, with alkyl substituents varying systematically from methyl (Me) to hexyl (Hx), have been measured in water, using solubility data, and in acetonitrile, by direct calorimetry. For all of the C-ARAs studied, the values of Δsln H were highly favorable (exothermic) for dissolution into water but were strongly unfavorable (endothermic) for dissolution into acetonitrile (ACN). The differences between the two solvents varied systematically with increasing carbon chain length, from about 100 kJ·mol-1 (for Me) to 140 kJ·mol-1 (for Hx). These extraordinary variances can be attributed to the loss of hydrophilic hydration of the eight -OH groups on the rim of the C-ARAs and also by the loss of (enthalpically favorable) hydrophobic hydration of the alkyl chains upon transfer from the highly structured, strongly H-bonding water to the aprotic, relatively weak donor/acceptor ACN. Although Δsln H values for the present C-ARAs in H2O are strongly favorable, they are more than counteracted by even larger negative changes in the entropy of dissolution, Δsln S. This enthalpy/entropy compensation effect is consistent with the low aqueous solubilities (<10-3 mol·kg-1) of the C-ARAs and their slight increase with increasing carbon chain length, which is opposite to typical behavior of the homologous series of organic molecules.

Group 9 [Cp*MIII] complex-catalyzed C–H olefination of arenes in water at room temperature: a study on the catalytic activity

Herein, we report our discovery of group 9 [Cp*MIII] complexes catalyzing the olefination of arenes in water at ambient temperature.

Guest-length driven high fidelity self-sorting in supramolecular capsule formation of calix[5]arenes in water

Only homocapsules 1⊃NC8N⊂1 and 2⊃NC10N⊂2 are selectively formed out of ten potentially different products.

Green synthesis of imidazo[1,2-a]pyridines using calix[6]arene-SO3H surfactant in water

In this research, green synthesis of imidazo[1,2-a]pyridines in the presence of calix[n]arenes-SO3H as a Brønsted acid catalyst and surfactant is described. Using of calix[n]arenes in water provided a hydrophobic cavity that successfully carried out the synthesis reactions at short times with high yields. This catalyst system is recoverable with a simple extraction using an organic solvent and reusable for at least for 5 cycles without any losses of its activity.

Volumetric and acoustic properties of two sodium sulfonateresorcin[4]arenes in water and dimethylsulfoxide

Apparent molal volumes, apparent isentropic compressibilities and solvation numbers of two sodium sulfonateresorcin[4]arenes, Na4BRA and Na4SRA in aqueous and DMSO solutions, were determined from density and speed of sound measurements, over the temperature range (278.15 to 308.15) K, at 5K intervals. The dependence of the volumes on the molality was correlated to the Redlich-Rosenfeld-Meyer equation for aqueous solutions and the Masson type equation for DMSO solutions. The parameters derived from these equations were interpreted according to hydrophobic and hydrophilic hydration and the ion-ion interactions. The standard (infinite dilution) partial molar properties and their dependence on the temperature were determined. In addition, the transfer properties of the ions from DMSO to water were evaluated. The properties calculated are discussed in terms of solute-solvent and solute-solute interactions.

Catalytic Hydrogenation of Arenes in Water Over In Situ Generated Ruthenium Nanoparticles Immobilized on Carbon

AbstractWe describe a tandem process to generate active Ru nanoparticles (≈7 nm) immobilised in situ on carbon from an organometallic precursor and formic acid to afford the hydrogenation of a wide range of arenes and heteroarenes in yields up to 72 % with high conversions and selectivities for the desired products. The hydrogenation of several substrates analogous to lignin‐derived fragments to the corresponding alicyclic products was also achieved. Our experimental investigations evidenced that the observed enhanced activity for arene hydrogenation was driven by the unique structural advantages of the organometallic precursor to activate formic acid, in which the presence of a nitrogen ligand is crucial to achieve a high catalytic activity. TEM analysis revealed the formation of Ru0 nanoparticles, and Hg0 poisoning experiments support the heterogeneous nature of the active catalyst.

Magnetically Retrievable Rh(0) Nanocomposite as Relevant Catalyst for Mild Hydrogenation of Functionalized Arenes in Water

A Rh0@γ-Fe2O3 nanocomposite was easily prepared by straightforward deposit of metal nanoparticles on the nonfunctionalized magnetic support through a wet impregnation method. This nanomaterial proved to be highly active and magnetically retrievable in room-temperature hydrogenation of various arenes under atmospheric hydrogen pressure in neat water. The catalytic applications were extended to the selective reduction of nitroarenes into aniline, a relevant synthon for industrial applications, and to the dechlorination of chloroarenes, which could be of great interest for wastewater treatment. Finally, these Rh0@γ-Fe2O3 nanocomposites were compared to their Pd analogs, thus affording complementary catalytic activities.

Catalyst-free direct C–H trifluoromethylation of arenes in water–acetonitrile

An efficient, practical, catalyst-free direct C–H trifluoromethylation of arenes using readily available and inexpensive CF3SO2Na as a CF3-source in water–acetonitrile is described.

Tubular Structures Self-Assembled from a Bola-Amphiphilic Pillar[5]arene in Water and Applied as a Microreactor.

Various nanomorphologies were obtained by simply changing the fabrication conditions, such as the pH of the system, different solvent, or different concentration, of bola-amphiphilic pillar[5]arene Bola-AP5. Importantly, hybrid microtubules as a microreactor were successfully prepared by directly reducing AuCl4(-) on the surface of Bola-AP5-based tubular structures in water.

Photolysis of an amphiphilic assembly by calixarene-induced aggregation.

Photosensitizers generally show great tendency for self-aggregation in aqueous media, leading to quenched fluorescence and lower photosensitizing ability. Herein, we report that amphiphilic anthracene is highly photoreactive after aggregation induced by p-sulfonatocalix[4]arene in water. The formation of a host-guest supramolecular assembly and the photolysis of the anthryl core are identified by UV-vis and NMR spectroscopy, dynamic light scattering, and transmission electron microscopy. Additionally, the assembly exhibited efficient photolysis with visible light in the presence of exogenous photosensitizers. This approach could be extended to various photoresponsive self-assemblies and applications in phototherapy and the design of photodegradable materials.

The difference between the aggregates of short-tailed and long-tailed cationic calix[4]arene in water as detected using fluorescein dyes

Water-soluble cationic calixarenes readily form aggregates in water. The properties of these aggregates, however, markedly vary along with alterations in the molecular structure. In a set of our recent studies, such aggregates were examined by various methods, and first of all using acid–base indicator dyes. The latter acted in fact as monoprotic acids exhibiting one color transition, and their pKa shifts against the values in water were relatively close for different calixarenes. In the present paper, we report the behavior of a much more complicated dye, fluorescein, and two relative compounds, in aqueous solutions of two cationic calix[4]arenes. The last named possess four choline groups on the upper rim and the sole difference is the length of the alkoxy groups at the lower rim: O(CH2)2CH3 and O(CH2)7CH3. In water, both calixarenes form aggregates of similar size and with similar zeta-potential. However, their influence on the acid–base and tautomeric equilibria of fluorescein clearly demonstrate that the aggregates of the long-tailed calixarene resemble the common micelles of colloidal surfactants to a higher degree than those of tetrapropyloxy compound.

Complex formation of MnII with tetra(p-tert-butyl)thiacalix[4]arene acid in aqueous solutions of surfactants and polymers

The formation of manganese(II) complexes with different stereoisomers of tetraacid based on p-tert-butylthiacalix[4]arene in water, in micellar solutions of nonionogenic surfactants, and in polymer solutions was studied. The formation of complexes with different degrees of ligand protonation was revealed by pH-metric titration and nuclear magnetic relaxation. On the basis of experimental data, the composition and stability constants of the solubilized complexes of stereoisomers of thiacalixarene acid with manganese(II) ions were determined using mathematical simulation methods. The manganese thiacalixarene complexes are unstable in solutions, especially upon the addition of calcium cations and in the presence of nitrilotriacetic acid.

Deprotonation of para-sulphonatocalix[4]arene in water–methanol mixtures

The deprotonation of para-sulphonatocalix[4]arene was investigated in some aqueous methanol solutions by spectrophotometric method. Principal component analysis was performed on the spectral data matrices in order to determine the number of light absorbing species which are involved in the deprotonation process. The equilibrium constant of the deprotonation reaction together with the pure spectrum and concentration profile of each species were extracted by STAR programme utilising the multivariate curve fitting. The effect of specific and non-specific solute–solvent interactions on the pK a values was examined upon the basis of the linear solvation energy relationship concept. Thus, a multiple linear regression analysis was used to correlate the pK a variation with the macroscopic (dielectric constant) and microscopic Kamlet–Taft parameters (α, β and π*) of binary mixtures. Results indicate that the deprotonation of para-sulphonatocalix[4]arene in water–methanol mixtures is highly related with the non-specific long-range electrostatic solute–solvent interactions.

Neutral guest capture by a cationic water-soluble pillar[5]arene in water

A cationic water-soluble pillar[5]arene offering a well-defined cavity with hydrophobic inner surface can capture neutral guests, even water-insoluble guests, into its cavity via hydrophobic forces. The binding ability depends upon guest hydrophobicity. The higher guest hydrophobicity contributes to the higher host affinity. Methanol and ethanol do not show any affinity for the host at all, because they are too hydrophilic for the host to compete with water.

The oxidative halogenations of arenes in water using hydrogen peroxide and halide salts over an ionic catalyst containing sulfo group and hexafluorotitanate

An ionic compound, bis[1-methyl-3-(3′-sulfopropyl)imidazolium] hexafluorotitanate (1), was proved to be the efficient and recyclable catalyst for the oxidative halogenations of arenes in water using H2O2 as the oxidant and halide salts as the halogenation sources. The mono-halogenated products were obtained selectively by this method. The synergetic catalytic effect coming from the two incorporated functionalities of SO3H and [TiF6]2− was manifested in 1. The halogenation rate catalyzed by 1 was in the ranking of NaBr≫NaCl>KI. The UV–vis and FT-IR analyses indicated that the successful formation and regeneration of the active peroxo-Ti species (1A) with the aid of proton acid guaranteed the recycling uses of 1.