Electrochemical Behavior of Diphenyl Disulfide and Thiophenol on Glassy Carbon and Gold Electrodes in Aprotic Media

The investigation of the electrochemical reduction processes of C₆H₅SSC₆H₅ and C₆H₅SH in CH₃CN using cyclic voltammetry indicates a different behavior on GC and Au electrodes. On GC surface adsorption phenomena are absent, the electrochemical reduction process is irreversible and diffusion controlled. For both the starting molecules the same species, C₆H₅S^?, is formed upon reduction. The E° values of the reduction processes were determined by convolution method and the standard free energy of the S? S bond of C₆H₅SSC₆H₅ estimated. On Au surface instead, a self‐assembled monolayer of C₆H₅SAu_ads originated after the S? S or S? H bond breaking can be observed by simply dipping the electrode in solution of C₆H₅SSC₆H₅ and C₆H₅SH, respectively. The properties of the SAM were investigated by electrochemical reduction of the adsorbed thiolates. On Au electrode the reduction processes involve C₆H₅SAu_ads and give rise to desorbed C₆H₅S^?. A neutral radical is obtained by electrochemical oxidation of thiolate anion. It reacts rapidly with the electrode surface to give the S‐Au bond again.     

Thiol-mediated radical cyclization: regioselective formation of indole-annulated sulfur heterocycles by tandem cyclization

Indole-2-yl-prop-2-ynyl sulfides, under thiophenol-mediated alkenyl radical cyclization conditions, afforded exclusively 4-thiophenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indoles or 3-thiophenylmethyl-2,3,8-trihydrothieno[2,3-b]indoles depending on the substituent at the indole nitrogen.     

Visible‐Light‐Driven Iron‐Promoted Thiocarboxylation of Styrenes and Acrylates with CO2

The first thiocarboxylation of styrenes and acrylates with CO₂ was realized by using visible light as a driving force and catalytic iron salts as promoters. A variety of important β‐thioacids were obtained in high yields. This multicomponent reaction proceeds in an atom‐ and redox‐economical manner with broad substrate scope under mild reaction conditions. Notably, high regio‐, chemo‐, and diasteroselectivity are observed. Mechanistic studies indicate that a radical pathway can account for the unusual regioselectivity.     

Thiol derivatives of arylnaphthylmethane as novel anti-osteoporotic agents

(Mercaptophenyl)naphthylmethane derivatives were synthesized as novel estrogen receptor binding ligands. [4-(Methylsulfonyl)phenyl](naphth-1-yl)ketone shows a very promising activity towards osteoporosis. Correspondence: Sangita, Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001, India.     

Boric acid catalyzed convenient synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines in aqueous media

A one-pot three-component condensation of an aldehyde, malononitrile, and thiophenol has been achieved by conventional and ultrasound method. The reaction has been catalyzed by boric acid in aqueous medium. This protocol afforded corresponding 2-amino-3,5-dicarbonitrile-6-thio-pyridines in shorter reaction times and high yields with the green aspects by avoiding toxic catalysts and solvents.     

Thiophenol and thiophenol radical and their complexes with gold clusters Au5 and Au6

The longstanding controversy between experiment and theory regarding which conformer of thiophenol, planar or perpendicular, is the most stable and what is the magnitude of the corresponding rotational barrier of the S–H group is discussed. We propose a variety of rather modest high-level computational methods within the density theory, which corroborate the experimental data. These methods demonstrate that the planar structure of thiophenol is the most stable and the magnitude of the rotational barrier falls within the experimental range of 3.35±0.84 kJ mol⁻¹. However, the barrier is of the order of RT at room temperature, which might prevent to clearly identify the most stable conformer of thiophenol in experiments and leads to a large-amplitude motion of the thiolic hydrogen. On the other hand, such low value of the barrier may lead to some error in evaluating the thermodynamic properties of thiophenol within the rigid-rotor-harmonic oscillator model, in particular for the bond dissociation enthalpy. We also show the existence of a large entropy contribution to the Gibbs free energy difference between the planar and perpendicular conformers which is the order of the rotational barrier (≈4 kJ mol⁻¹). This might be of interest for experimental study. The most stable complexes of thiophenol with the gold clusters Au₅ and Au₆ are also investigated. It is shown that the sulfur atom prefers to anchor to two- and three-coordinated atoms of gold in these clusters to form a strongly directional gold–sulfur bond. The hydrogen abstraction from the S–H group of thiophenol bonded to the two-coordinated gold atom in Au₅ yields the bridging Au–S dibond and results in a spectacular reduction of the bond dissociation energy of thiophenol by nearly a factor of three.     

Synthesis and reactivity of a novel hydridocobalt(III) complex containing trimethylphosphine and thiophenolato ligands

The novel hydridocobalt(III) complex [mer-Co(H)(SPh)₂(PMe₃)₃] (1) was prepared by reaction of thiophenol with [Co(PMe₃)₃Cl], [Co(PMe₃)₄] and [Co(PMe₃)₄Me]. A dinuclear cobalt dithiophenolato complex [Co(PMe₃)₂(SPh)]₂ (2) was obtained from the reaction of thiophenol with [Co(PMe₃)₄Me]. Reaction of 1 with iodomethane afforded complex [Co(PMe₃)₃(I)₂] (3). Reaction of complex 2 with carbon monoxide gave a mononuclear dicarbonyl cobalt(I) complex [Co(PMe₃)₃(CO)₂(SPh)] (4). The crystal structures of 1-4 were determined by X-ray diffraction. Formation mechanism of 1 is discussed.     

Catalytic Oxidation of Ascorbic Acid on 2D and 3D Monolayers of 4‐Hydroxythiophenol

Monolayers of 4‐hydroxythiophenol (4‐HTP) immobilized on gold electrode (2D SAMs) or gold nanoclusters (3D SAMs) lead to catalytic oxidation of ascorbic acid (AA). The catalytic role of the modified clusters was revealed by comparing the electrodes covered by 1,9‐nonanedithiol and the same nonanedithiol monolayer decorated by 4‐HTP protected clusters. The 4‐HTP protected gold nanoclusters supported on a metal surface using a monolayer of 1,9‐nonanedithiol as the bridge, transferred charge to ascorbic acid (AA) molecule in the solution more efficiently than when the same 4‐HTP monolayer was formed directly on the gold electrode.     

Unexpected transformations of 3-(bromoacetyl)coumarin provides new evidence for the mechanism of thiol mediated dehalogenation of α-halocarbonyls

The mechanism for the thiol mediated dehalogenation of α-halogenated carbonyls has remained an unresolved problem, despite its ongoing application in synthetic organic chemistry. Nakamura and co-workers first proposed that net dehalogenation occurs via sequential nucleophilic substitutions, while Israel and co-workers concluded that the rate at which dehalogenation occurred suggested that dehalogenation proceeds in a single concerted step. In this study, we investigated the debromination and nucleophilic substitution of 3-(bromoacetyl)coumarin with a variety of thiophenols, whose electron donating or withdrawing natures resulted in large variations in the degree of nucleophilic substitution and dehalogenation products, respectively. Results from these experiments, in addition to an unexpected formation of thioether containing dibenzo[b,d]pyran-6-ones from a Robinson annulation, has provided new evidence for this disputed mechanism.     

Development of ion-sensitive field-effect transistor-based sensors for benzylphosphonic acids and thiophenols using molecularly imprinted TiO2 films

Molecularly imprinted polymeric membranes, containing artificial recognition sites for a number of benzylphosphonic acid derivatives, were prepared by the polymerization of titanium(IV) butoxide in the presence of a titanium(IV) phosphonate complex. Reference polymers were prepared in the same manner but in the absence of the phosphonate template. FTIR spectroscopy was used to follow the formation of a benzylphosphonic acid-Titanium(IV) oxide complex during the imprinting process, and upon the association of the substrate in the imprinted TiO₂ thin film. The imprinted polymers were examined as sensing membranes in an ion-sensitive field-effect transistors (ISFETs). The sensors reveal selectivity towards analyzing the imprinted substrates, yet the recognition ability of the sensors strongly depends on the substituents associated with the phosphonic acid structures. The response time of the sensors is ca. 45 s, and the sensors reveal unaffected stability for at least 2 weeks. Also, imprinted TiO₂ films for thiophenol, and para-nitrothiophenol were generated on ISFET devices, and the respective substrates were selectively sensed by the functional devices.