Thiocarboxylate Research Articles

Phosphoric Acid Based Heterodimers in Asymmetric Catalysis

Chiral phosphoric acid diesters arguably constitute the most exploited class of catalysts in asymmetric Bronsted acid catalysis. Despite being highly investigated for their acidic properties, these compounds display an amphoteric nature, which has instead been considerably overlooked. The potential of this dichotomous polarity has recently been disclosed and applied to the development of novel reaction modes in organocatalysis. In this account, we present our recent advances in this area, focusing on the establishment of heterodimeric interactions toward the nucleophilic activation of carboxylic acids, thiocarboxylic acids and ketones (via their enols) in asymmetric transformations. 1 Introduction 2 Discovery of Heterodimeric Self-Assemblies 3 Activation of Carboxylic Acids 3.1 The Enantioselective Carboxylysis of Aziridines 3.2 An Asymmetric Hydrolysis of Epoxides 4 Activation of Thiocarboxylic Acids 5 Enol Catalysis 5.1 Asymmetric Michael Addition 5.2 Asymmetric α-Amination 5.3 Asymmetric α-Allylation 6 Concluding Remarks

Fluorescence quenching studies on the interaction of catechin-quinone with CdTe quantum dots. Mechanism elucidation and feasibility studies

Changes of the photoluminescent properties of QD in the presence of oxidized catechin (CQ) were investigated by absorption, steady-state fluorescence, fluorescence lifetime and dynamic light scattering measurements. Photoluminescence intensity and fluorescence lifetime was decreasing with increasing CQ concentration. Dynamic light scattering technique found the hydrodynamic diameter of QD suspension in water is in range of 45nm, whereas in presence of CQ increased to mean values of 67nm. Calculated from absorption peak position of excition band indicated on average QD size of 3.2nm. Emission spectroscopy and time-resolved emission studies confirmed preservation of electronic band structure in QD–CQ aggregates. On basis of the presented results, the elucidated mechanism of QD fluorescence quenching is a result of the interaction between QD and CQ due to electron transfer and electrostatic attraction.The results of fluorescence quenching of water-soluble CdTe quantum dot (QD) capped with thiocarboxylic acid were used to implement a simple and fast method to determine the presence of native antioxidant quinones in aqueous solutions. Feasibility studies on this method carried out with oxidized catechin showed a linear relation between the QD emission and quencher concentration, in range from 1 up to 200μM. The wide linear range of concentration dependence makes it possible to apply this method for the fast and sensitive detection of quinones in solutions.

Application of the Thioacid‐Azide Ligation (TAL) for the Preparation of Glycosylated and Fluorescently Labeled Amino Acids

AbstractThe reaction of thiocarboxylic acids with azides (thioacid‐azide ligation, TAL) is a chemoselective transformation, leading to the formation of amide bonds. Especially in the case of electron‐deficient sulfonyl azides, the reaction occurs in excellent yields, within minutes at room temperature, in a broad range of solvents. In this article, the application of TAL for the synthesis of glycosylated and dansylated amino acids is reported. 2‐Azidosulfonylethyl glycosides were prepared from peracetylated monosaccharides and reacted with thioacid‐containing derivatives of aspartic acid and glutamic acid. Likewise, aromatic sulfonyl azides were employed. Ligation products were obtained in yields of up to 96 %. Different conditions for the generation of the thioacids were compared. Whereas reaction of succinimidyl esters with sodium hydrogen sulfide led to concomitant formation of diacyl disulfides, trityl thioesters turned out to be suitable precursors for the in situ preparation of thioacids by mild acidolysis.

Simple thiol-ene click chemistry modification of SBA-15 silica pores with carboxylic acids

A straightforward approach for anchoring tailored carboxylic groups in mesoporous SiO2 colloidal materials is presented. The thiol-ene photochemical reaction between vinyltrimethoxysilane precursors and various thiocarboxylic acids which has, click chemistry features (i.e. high conversion yields, insensitivity to oxygen, mild reaction conditions), results in carboxylated silane precursors that can be readily used as surface modifiers. The carboxylic groups of acetic, undecanoic and succinic acid were immobilized on the silica mesopore walls of SBA-15 powders employing the synthesized silane precursors. Post-grafting has been confirmed through infrared spectrometry (FTIR), energy dispersive X-ray spectroscopy (EDS), elemental analysis (EA) and zeta potential measurements. Detailed field-emission gun scanning electron microscopy (FESEM) images and small angle X-ray scattering (SAXS) data revealed parallel mesopores and ordered mesostructures. It is shown that the immobilized COOH groups are chemically accessible for acid–base reactions as well as copper adsorption. Immobilization of easily synthesized tailored carboxylic modified alkoxide precursors within mesoporous systems provides a unique chemical nanoenvironment within these ordered frameworks.

Dimethylcuprate-Mediated Transformation of Acetate to Dithioacetate

Dithiocarboxylic acids, RCS2H, and their esters, RCS2R′, are useful reagents that can be synthesized by the reaction of carbon disulfide with organometallic reagents. Here the coinage-metal-mediated transformation of acetate to dithioacetate is explored in the gas phase using multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with density functional theory (DFT) calculations. The ion–molecule reactions between coinage-metal dimethylmetalate anions [CH3MCH3]− (M = Au, Ag, Cu), formed via double decarboxylation of the metal acetate anions, [CH3CO2MO2CCH3]−, and carbon disulfide, were examined. Only [CH3CuCH3]− reacts with CS2 with a reaction efficiency of 0.8% of the collision rate to yield the adduct [CH3CuS2CCH3]− (77.5%) as well as CH3CS2– (22.5%). Collision-induced dissociation (CID) of the adduct [CH3CuS2CCH3]− gives CH3CS2– as the major product, with a small amount of [CuS2CCH2]− being formed via loss of methane. DFT calculations reveal the following. (i) [C...

Sulphur-functionalized graphene towards high performance supercapacitor

To enhance the energy densities, pseudocapacitive materials are usually added to electric double layer carbonaceous materials. However in the process of energy densities enhancement, power densities are usually lowered which creates a dilemma situation for researchers. Thus to obtain high energy and power densities, a new pseudocapacitive mechanism, to the best of our knowledge, is introduced in this paper. High supercapacitive performance can be obtained by the redox mechanism of thiocarboxylic acid ester to sulphone with the aid of external current. The specific capacitance of the material is enhanced to as high as 1089Fg−1 at 1Ag−1, and even at high current density of 50Ag−1, it is able to discharge a respectable 833Fg−1. The material is able to exhibit high energy density of 43Whkg−1 at high power density of 38kWkg−1 which validates the possibility of a harmonious coexistence between high energy density and high power density.

Synthesis, characterization and electrochemical properties of meso-thiocarboxylate-substituted porphyrin derivatives

Considering the versatility of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPPF20) to react with nucleophiles we highlight here the synthesis and characterization of several mono- and tetra-thiocarboxylate derivatives. The selective displacement of the para-fluorine groups in TPPF20 by thiocarboxylic acids demonstrates that TPPF20 is an ideal platform for the rapid formation of thiocarboxylate porphyrins. The optical and electrochemical features of the thiocarboxylate derivatives were also examined thinking on their potential use in photovoltaic devices. From their electrochemical characterization the following parameters were taken into account: (i) electronegative induced effect of the thiocarboxylate dyes owing the presence of the fluorine and sulfur atoms on the molecular structure of the porphyrin; and (ii) the free rotation and flexibility features that such S atom gives to the porphyrin relatively to the semiconductor.

Exploring water catalysis in the reaction of thioformic acid with hydroxyl radical: a global reaction route mapping perspective.

Hydrogen abstraction pathways, in the gas-phase reaction of tautomers of thioformic acid (TFA), TFA(thiol), and TFA(thione), with hydroxyl radical in the presence and absence of single water molecule acting as a catalyst, is investigated with high-level quantum mechanical calculations at CCSD(T)/6-311++G(2d,2p)//MP2/6-311++G(2d,2p), CCSD(T)/6-311++G(d,p)//DFT/BHandHLYP/6-311++G(d,p), and DFT/B3LYP/6-311++G(2df,2p) levels of the theory. A systematic and automated search of the potential energy surface (PES) for the reaction pathways is performed using the global reaction route mapping (GRRM) method that employs an uphill walking technique to search prereaction complexes and transition states. The computations reveal significant lowering of the PES and substantial reduction in the activation energy for the hydrogen abstraction pathway in the presence of water, thereby proving water as an efficient catalyst in the reaction of both the TFA tautomers with OH radical. The hydrogen-bonding interactions are observed to be responsible for the large catalytic effect of water. Notably, in the case of TFA(thiol), formyl hydrogen abstraction is observed to be kinetically more favorable, while acidic hydrogen abstraction is observed to be thermodynamically more feasible. Interestingly, in the case of TFA(thione), reaction pathways involving only formyl hydrogen abstraction were observed to be feasible. The water-catalyzed hydrogen abstraction reaction of TFA with hydroxyl radical, investigated in this work, can provide significant insights into the corresponding reaction in the biological systems.

Comparative study of copper complexes with different anchoring groups by molecular modeling and its application to dye-sensitized solar cells

Copper complexes with different anchoring groups (based on biquinoline ligands with acetylacetone, catechol, hydroxamic acid, phosphonic acid and thiocarboxylic acid groups) have been studied by Density Functional Theory and Time-Dependent Density Functional Theory, also the integral equation formalism of the polarizable continuum model has been extended to the calculation of solvent effects. Maximum absorption wavelength reaches the highest value for the complex with hydroxamic acid as anchoring group but a low oscillator strength; the rest of the complexes fulfill both properties. In general, the molecular orbitals energy levels and the schematic representation of them suppose an appropriate electron transfer between the sensitizer and the semiconductor (TiO2), emphasizing more clearly for the copper complex with the thiocarboxylic acid. Chemical reactivity parameters like chemical hardness shows similitude for all molecular systems; but not so in the case of the electrophilicity index and electroaccepting power.

ChemInform Abstract: Copper‐Catalyzed Synthesis of Benzo[b]thiophenes and Benzothiazoles Using Thiocarboxylic Acids as a Coupling Partner.

AbstractSubstrates with a methyl group in α‐position of the PPh3‐group do not react under these conditions to yield the corresponding 3‐methylbenzothiophene.

The mechanism of tautomerisation and geometric isomerisation in thioformic acid and its water complexes: exploring chemical pathways for water migration.

A systematic and automated search for chemical pathways of isomerisation between geometric and tautomeric forms of gas-phase thioformic acid (TFA) and its water complexes is performed using a global reaction route mapping (GRRM) method, and an uncovered pathway for cis-trans isomerisation in the thiol form of TFA has been explored through computations performed at CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(2d,2p) level of the coupled cluster and density functional theories. To explore the routes for water migration, a detailed analysis of complexes of TFA with a single-water molecule is presented. Notably, during the isomerisation process in TFA, a positive catalytic effect of water was observed that can arise either by the stabilization of the reactant and/or of the transition state through extensive hydrogen bonding. Interesting behavior of isomeric forms of TFA along the pathways analysed is revealed through the Gibbs free-energy change and its temperature-dependence. The cis form of TFA(thiol) in the complexes of TFA with a single-water molecule is found to be thermodynamically equally feasible as the trans form which though is known to be the most dominating among the isomeric forms of TFA. Besides these, various complexes of TFA with two-water molecules have also been explored to study the hydrogen-bonding interaction through natural bond-orbital (NBO) analysis. The complexes of TFA with two-water molecules have also been characterized using spectral features including vibrational frequency analysis, and the effect of complexation has been observed by noting frequency shift.

Copper-Catalyzed Synthesis of Benzo[b]thiophenes and Benzothiazoles Using Thiocarboxylic Acids as a Coupling Partner

An efficient copper-catalyzed approach to benzo[b]thiophene and benzothiazole derivatives using thiocarboxylic acids as a sulfur source has been developed. In the presence of CuI and 1,10-phen, and n-Pr3N as the base, (2-iodobenzyl)triphenylphosphonium bromide and (2-iodophenylimino)triphenylphosphorane reacted smoothly with thiocarboxylic acids to give benzo[b]thiophene and benzothiazole derivatives in good yields via sequential Ullmann-type C-S bond coupling and Wittig condensation.

Synthesis, Characterization, and Relative Stabilities of Self-Assembled Monolayers on Gold Generated from Bidentate n-Alkyl Xanthic Acids

A series of self-assembled monolayers (SAMs) on gold were generated by the adsorption of n-alkyl xanthic acids (NAXAs) having the general formula CH3(CH2)nOCS2H (n = 12-15). The structural features of these SAMs were characterized by optical ellipsometry, contact angle goniometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). This series of xanthate SAMs were compared to SAMs generated from the corresponding n-alkanethiols and aliphatic dithiocarboxylic acids (ADTCAs). The collected data indicate that the NAXAs generate densely packed and well-ordered monolayers. The contact angles of hexadecane on the xanthate monolayers exhibited a large "odd-even" effect similar to that produced by the ADTCA SAMs. The relative stability of these bidentate xanthate SAMs was evaluated by monitoring the changes in ellipsometric thicknesses and wettability as a function of time under various conditions. The results demonstrate that SAMs formed from NAXAs are much less stable than analogous n-alkanethiolate and ADTCA SAMs.

Effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution by modified polyethyleneimine

A novel flocculant with the capacities of reduction and chelation was prepared in this paper. The flocculant, called polyethyleneimine–sodium xanthogenate (PEX), was synthesized by modifying polyethyleneimine with carbon disulfide and sodium hydroxide. The effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution with PEX was investigated by using flocculation experiments. The results showed that in the single-ion system (only including Cr(III) or Cr(VI) in the solution), the final Cr(III) decreased with the increase in pH from 2.0 to 10.0, while the final Cr(VI) increased at first and then decreased with the increase in this pH range studied. The removal of Cr(III) was not desirable at pH lower than 7.0, whereas the final Cr(VI) concentration reached the minimum value of 0.145mg/L at pH2.0. In the mixture system of Cr(III) and Cr(VI), the variation tendency for the removal of Cr(III) or Cr(VI) was very similar to that obtained in the single-ion system. The oxidation–reduction potential, zeta potential, and final pH in the supernatant were also measured to analyze the above results. Furthermore, FTIR spectra revealed that dithiocarboxylic acid groups on the macromolecular chains of PEX played a major role in the Cr(VI) reduction and Cr(III) chelation.

Syntheses and structures of three Mn(II) coordination polymers assembled from a dithiocarboxylic acid and N-donor ligands

Three new complexes, {[Mn(dtb)(bpe)·2H2O]·H2O} n (1), {[Mn(dtb)(bpa)·2H2O]·H2O} n (2), and {[Mn(dtb)(phen)]} n (3) [H2dtb = 5,5′-dithiobis(2-nitrobenzoic acid), bpe = 1,2-bis(4-pyridyl)ethene, bpa = 1,2-bi(4-pyridyl)ethane, phen = 1,10-phenanthroline], have been synthesized under hydrothermal conditions with Mn(OAc)2·4H2O, dtb, and different N-donor ligands. X-ray structure analyses of 1 and 2 reveal analogous structures with 1D helical chains and 2D 44 chiral layers. The structure of 3 shows a 1D chain which is outwardly decorated with phen ligands. These neutral polymeric complexes exhibit structural diversity due to the different coordination modes of the flexible dtb ligand and the N-donor ligands. The thermogravimetric analyses and X-ray powder diffractions of 1–3 are also presented.

Metathetic sulfur transfer mediated by N-(2-aminophenyl)-4-methyl-thiazolin-2-thione derivatives. Part III: An alkylthiol- and thioacid-free route to diversely substituted S-alkyl thioesters

A metal free synthesis of S-alkyl thioesters, which does not involve alkylthiol or thiocarboxylic acid as sulfur source is disclosed. The process involves first an acylation at the nitrogen of the readily available N-(2-aminophenyl)-4-methyl-thiazolin-2-thione, second an alkylation at sulfur of the resulting amides and finally a base catalyzed metathetic reaction, which provides under very mild conditions and in high isolated yields the S-alkyl thioesters. An ion-pair intermediate (9-acyl-3-methyl[1,3]thiazolo[3,2-a][3,1]benzimidazol-9-ium alkylthiolate) accounts for the formation of mixed thioesters during cross-coupling experiments.S-Alkyl diversity is provided by the alkylating agent and the acyl diversity comes from the acylating agent, while the sulfur atom is provided by the heterocycle.

Removal of Cr(VI) from aqueous solution by flocculant with the capacity of reduction and chelation

A novel agent polyethyleneimine-sodium xanthogenate (PEX) with the multifunction of reduction, chelation, flocculation and precipitation was synthesized by using polyethyleneimine (PEI), carbon disulfide (CS2), and sodium hydroxide (NaOH). The effects of different important parameters, such as pH value, initial Cr(VI) concentration, coexisting ions and turbidity etc., on the removal of chromium from aqueous solution by PEX were investigated in flocculation experiments. The experiments results demonstrated that PEX could efficiently remove Cr(VI) and total Cr (Cr(VI)+Cr(III)) in strongly acidic media. It was proved that the presence of coexisting ions (Na+, Ca2+, F−, Cl−, and SO42−) in the solution had a little influence on the removal of chromium. Furthermore, it was conformed that Cr(VI) ions and turbidity could be simultaneously removed when water samples contained both Cr(VI) ions and turbidity. Finally, the mechanism of interaction between chromium and PEX was further confirmed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results reveal that dithiocarboxylic acid groups on PEX macromolecule play a major role in Cr(VI) reduction and Cr(III) chelation, and the flocs formation is attributed to the interparticle bridging mechanism of PEX.

Anti-Leishmanial Activity of Novel Homo- and Heteroleptic Bismuth(III) Thiocarboxylates

Two new thiocarboxylic acids, p-bromothiobenzoic BTA and thionaphthoic acid TNA, and five new homo- and heteroleptic bismuth(iii) compounds derived from thiocarboxylic acids: [Bi{S(C=O)C6H4Br}3] 1, [PhBi{S(C=O)C6H4Br}2] 2, [Bi{S(C=O)C10H7}3] 3, [PhBi{S(C=O)C10H7}2] 4, and [Ph2Bi{S(C=O)C10H7}] 5 were synthesised and fully characterised. The solid-state structure of complex [PhBi{S(C=O)C6H4Br}2] 2 was confirmed by X-ray crystallography. In complex 2, the two thiocarboxylate ligands are coordinated to the bismuth(iii) centre in a didentate fashion, forming a distorted octahedral geometry in which the phenyl group and the lone pair are oriented axial to the plane formed by the two thiocarboxylate ligands. Long-range Bi–S interactions (3.54 Å) link these monomeric units to form a one-dimensional polymer. These compounds, in addition to six previously synthesised complexes: [Bi{SC(=O)C6H5}3] 6, [PhBi{SC(=O)C6H5}2] 7, [Ph2Bi{SC(=O)C6H5}] 8, [Bi{SC(=O)C6H4NO2}3] 9, [PhBi{SC(=O)C6H4NO2}2] 10, and [PhBi{SC(=O)C6H4SO3}] 11, and the thiocarboxylic acids themselves, were assessed for their in vitro activity against Leishmania major promastigotes, and for general toxicity against human fibroblast cells. The thiocarboxylic acids, with the exception of thiobenzoic acid and sulfothiobenzoic acid, were toxic to both L. major parasites and the mammalian cells at high concentrations of 50–100 μM. The bismuth(iii) thiocarboxylate derivatives proved to be more active than the corresponding acids. Among these, the heteroleptic phenyl-substituted bismuth(iii) complexes 2, 4, 5, and 7 were highly active, showing IC50 (half maximal inhibitory concentration) values ranging from 0.39 to 4.69 μM, and a clear ligand dependence on activity.

Self-assembly mechanism of thiol, dithiol, dithiocarboxylic acid, disulfide and diselenide on gold: an electrochemical impedance study

The self-assembly mechanism of normal aliphatic thiol (RSH), disulfide (RSSR), diselenide (RSeSeR), dithiol (R(SH)2) and dithiocarboxylic acid (RS2H) onto a gold surface was studied in real time by electrochemical impedance spectroscopy (EIS). The different stages of adsorption could be clearly followed from the interfacial capacitance variation. An initial very fast adsorption, varying from a few seconds to several minutes depending on concentration, is the major adsorption step. This fast step is followed by long-term additional adsorption and self-assembled monolayer (SAM) consolidation. However, an intermediate step, probably due to transformation from the initial physisorbed state to the self-assembled state, could be identified with RSH and R(SH)2. An intermediate rearrangement of RS2H molecules after their initial diffusion controlled Langmuir (DCL) adsorption through the thiol functional group was also recognized. Initial adsorption of RSH and R(SH)2 followed either purely diffusion controlled or DCL kinetics for a very short time. Their continuing fast adsorption followed DCL kinetics. The fast adsorption step of RSSR and RSeSeR also followed the same mechanism. The findings made with EIS on the SAM organization were analyzed by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The R(SH)2 based SAMs had comparatively poor organization.

Solid-to-Solid Oxidation of a Vanadium(IV) to a Vanadium(V) Compound: Chemisty of a Sulfur-Containing Siderophore

Visible light facilitates a solid-to-solid photochemical aerobic oxidation of a hunter-green microcrystalline oxidovanadium(IV) compound (1) to form a black powder of cis-dioxidovanadium(V) (2) at ambient temperature. The siderophore ligand pyridine-2,6-bis(thiocarboxylic acid), H(2)L, is secreted by a microorganism from the Pseudomonas genus. This irreversible transformation of a metal monooxo to a metal dioxo complex in the solid state in the absence of solvent is unprecedented. It serves as a proof-of-concept reaction for green chemistry occurring in solid matrixes.