Unprecedented stable aqueous semiquinone methide radical formation interferes with adsorptive cathodic stripping voltammetry of cobalt methyl thymol blue

A putatively highly sensitive and selective method for the determination of cobalt in aqueous samples by catalytic adsorptive cathodic stripping voltammetry using methyl thymol blue (MTB) as the ligand has been documented [A. Safavi, E. Shams, Talanta 51 (2000) 1117] and its underlying mechanism has been briefly explored [A. Safavi, E. Shams, Electroanalysis 14 (2002) 708]. In an attempt to adapt the method for application in metalloprotein analysis we obtained erratic results, which were traced down to the redox non-innocence of the free ligand in the potential range prescribed for the metal analysis. On the hanging mercury drop electrode free methyl thymol blue is reversibly one-electron reduced to the semiquinone form with E_m,7.0 = −482 mV versus NHE at 22 °C, and the radical is subsequently quasi-reversibly one-electron reduced to the quinol form with E_m,7 ≈ −0.9 V. This observation invalidates the use of MTB in electrochemical analysis of metal ions. This is also the first observation ever of a stable quinone methide radical in aqueous solution.     

Dimerization of thymol blue in solution: Theoretical evidence

The possibility of dimerization of thymol blue was addressed by ab initio and force field calculations. In agreement with experimental information, a dimer forming symmetrical chemical environments for hydrogen bond formation was determined. This dimer is stable in vacuum and aqueous media and corresponds to the same protonated state proposed by the experiment. A comparison of the CVFF and MM3 force fields and ab initio results shows the suitability of CVFF to qualitatively describe this system.     

Fourth-derivative spectrophotometric determination of neodymium in mixed rare earths with methyl thymol blue and cetylpyridinium chloride

A sensitive and selective method is described for the determination of neodymium in mixed rare earths using fourth-derivative spectrophotometry. The method is based on the absorption spectra of 4f electron transitions of the complex of neodymium with methyl thymol blue and cetylpyridinium chloride. The influence of various instrumental parameters and reaction conditions for maximum colour development are investigated. The calibration curve is linear over the range 0–3.5 g ml^–1 neodymium. The relative standard deviation for determination of 1.4 g ml^–1 neodymium (n = 7) is 1.6%. The detection limit (signal-to-noise ratio = 3) is 0.2 g ml^–1.     

A simple and clean procedure for three-component synthesis of spirooxindoles in aqueous medium

A simple and efficient one-pot three-component synthesis of the biologically important spirooxindoles scaffold was carried out by the reaction of isatin, activated methylene reagent, and 1,3-dicarbonyl compounds in aqueous medium. This method is of great value because of its environmentally benign character, high yield processing, and easy handling.     

Borax-catalyzed thiolysis of 1,2-epoxides in aqueous medium

A convenient, economical, and practical protocol for borax-catalyzed thiolysis of 1,2-epoxides in aqueous medium has been developed, which has greatly expanded the utility scope of borax in organic synthesis.     

Sodium chloride: a proficient additive for the synthesis of pyridine derivatives in aqueous medium

A facile and convenient synthesis of substituted pyridine derivatives catalysed by NaCl in the presence aqueous media under reflux and ultrasound irradiation has been developed via a one-pot multicomponent reaction, in which four new bonds were formed. Particularly valuable features of this protocol including mild conditions, simple execution, broad substrate scope and good yields of products make it an efficient and promising synthetic strategy to build pyridine skeleton.     

Synthesis of aryl-hydrazones via ultrasound irradiation in aqueous medium

The synthesis of aryl-hydrazones from aromatic aldehydes/ketones and hydrazides (semicarbazide, thiosemicarbazide and aminoguanidine) is described using aqueous medium (acid conditions) under ultrasound irradiation with short reaction times (20-30 min), the reactions occurring at room temperature and giving rise to good to excellent yields of the products, along with the diastereoselectivities. The procedure is also simple and clean.     

Organocatalysis in aqueous micellar medium: a new protocol for the synthesis of [1,2,4]-triazolyl-thiazolidinones

A new environmentally friendly methodology for the efficient synthesis of biologically significant triazole thiazolidinone hybrids in aqueous medium, using acetic acid as an organocatalyst in the presence of cetyltrimethylammonium bromide (CTAB) surfactant has been developed for the first time. The effect of several surfactants on the yield and completion time of the reaction was investigated and it was found that the use of CTAB at 60 °C gave the best results (79–96% in 20 min–35 min) for the synthesis of the target compounds.     

[Cp2TiCl2] as polymerization catalyst in aqueous medium: polymerization of styrene in water

The contrary to the general idea, an early transition metal organometallic compound, [Cp₂TiCl₂] has been found to be active catalyst for aqueous medium polymerization of styrene.     

Poly(4-vinylpyridinium)hydrogen sulfate: An efficient heterogeneous catalyst for the one-pot synthesis of polyhydroquinolines via unsymmetrical Hantzsch reaction in aqueous medium

A facile and highly efficient protocol for the synthesis of polyhydroquinolines via Hantzsch multicomponent condensation of dimedone, aryl/heteryl aldehydes, ethylacetoacetate and ammonium acetate utilizing poly(4-vinylpyridinium)hydrogen sulfate as a catalyst in aqueous medium has been described. The method offers several advantages such as high yield, short reaction time, simple workup, easy separation of the catalyst and its reusability.     

A new strategy for basic drug extraction in aqueous medium using electrochemically enhanced solid-phase microextraction

This work describes an electrochemically enhanced solid-phase microextraction (EE-SPME) method using a mild negative potential (-0.6 V) for the enhanced extraction of the selected basic drugs in a pure aqueous matrix and urine samples. The EE-SPME method gave a more effective extraction of drugs (primarily via electrophoresis and complementary charge interaction) compared to that obtained with SPME (without applying a potential, and which is based on passive partitioning). The EE-SPME method eliminated the need for alkalizing, derivatizing the drugs, or modifying the fiber coating before extraction. The analysis of methamphetamine (MA) and amphetamine (AM) was selected as a typical example to demonstrate in detail the advantages of EE-SPME over SPME. Based on the results obtained, 3-min extraction efficiency for both the amphetamines using EE-SPME was better than that of 30-min using SPME. The developed EE-SPME-GC method exhibited wide linear ranges (2-1000 ng mL(-1)) for both the amphetamines with R(2) larger than 0.99, and the method detection limits (MDLs) for AM and MA were 0.26 and 0.12 ng mL(-1), respectively. In addition, the EE-SPME method developed was also successfully applied to enhance the extraction of several other basic drugs (ephedrine, 3,4-methylenedioxyamphetamine (MDA), atropine, methadone, cocaine, codeine, acetylcodeine and papaverine) with preconcentration factors from 157 to 2199, indicating the potential applicability of this method in the field of forensic, clinical and pharmaceutical analysis.     

Green chemical synthesis of fluorinated 1,3,5-triaryl-s-triazines in aqueous medium under microwaves as potential antifungal agents

Reasonable pure fluorinated s-triazines were synthesized in quantitative yield (96-99%) in 2-3 min in aqueous medium under microwaves, by reaction of fluorinated anilines and aqueous formaldehyde. All synthesized compounds have been screened in vitro for their antifungal activity against Rhizoctonia solani, Fusarium oxysporum, and Collectotrichum capsici.     

Greener and rapid access to bio-active heterocycles: room temperature synthesis of pyrazoles and diazepines in aqueous medium

An expeditious room temperature synthesis of pyrazoles and diazepines by condensation of hydrazines/hydrazides and diamines with various 1,3-diketones is described. This greener protocol was catalyzed by polystyrene supported sulfonic acid (PSSA) and proceeded efficiently in water in the absence of any organic solvent within 1-2 min.     

Palladium(II) chloride/EDTA-catalyzed biaryl homo-coupling of aryl halides in aqueous medium in the presence of ascorbic acid

Both electron-deficient and electron-rich aryl bromides undergo biaryl homo-coupling in a basic aqueous-ethanolic medium in the presence of PdCl₂-EDTA (1:1 molar ratio, 3 mol %) as catalyst and ascorbic acid as reductant (1 mol equiv) in acceptable to good yields.     

Tandem bis-aza-Michael addition reaction of amines in aqueous medium promoted by polystyrenesulfonic acid

An efficient and environmentally benign tandem bis-aza-Michael addition of amines catalyzed by polystyrenesulfonic acid (PSSA) is described. This operationally simple high yielding microwave assisted synthetic protocol proceeded in water in the absence of any organic solvent.     

A simple and clean procedure for the synthesis of polyhydroacridine and quinoline derivatives: reaction of Schiff base with 1,3-dicarbonyl compounds in aqueous medium

A clean and simple synthesis of benzo[c]acridine, benzo[a]acridine, pyrido[2,3-c]acridine and benzo[f]quinoline derivatives was accomplished in good to excellent yields via the reaction of Schiff base with 1,3-dicarbonyl compounds in aqueous medium catalyzed by TEBA. The structures were characterized by ¹H NMR, IR and elemental analysis, and confirmed by X-ray diffraction study.     

The methods of determination of critical micellar concentrations of the amphiphilic systems in aqueous medium

Science is the attempt to make the chaotic diversity of our sense-experience to a logically unified system of thought. A sound theoretical basis and a rational physicochemical understanding based on experimental findings lead to a proper understanding of a topic. Colloid chemistry strengthened its footing by the extensive studies on gold sols by Michael Faraday in 1850s, however, the term “colloid” was coined by Thomas Graham in 1861. Historically, the Stone Age paintings in the Lascaux cave in France and the written records of Egyptian pharaohs were produced with stabilized colloid pigments. The part of colloid science dealing with amphiphilic molecules is so diverse on its own that it is dealt in a separate branch called the “association colloid”. A key development in the study of association colloids was the observation by James McBain that the osmotic pressure of salts of alkali metal fatty acid displayed a pronounced break in the concentration beyond a specific characteristic concentration, after which the osmotic coefficient remained almost constant (Evans and Wennerstrom, 1994). McBain attributed this fact to the self-association of these molecules among themselves (McBain, 1913, McBain, 1944) in solution. Here, we are providing a molecular as well as thermodynamic approach toward the micellization process.     

Resorcinarene supramolecular organocatalyst for functionalized 1-tetralone synthesis in aqueous medium

An efficient, straightforward and environmentally benign process has been developed for the synthesis of fluorenone and 1-tetralone derivatives using cyclic 1,3-dione, malononitrile and dialkylacetylenedicarboxylate as starting materials in aqueous medium. The reaction is favoured in presence of resorcin[4]arene which is effective as a reusable organocatalyst. The catalyst has been easily synthesized and characterized by ¹H, ¹³C NMR, IR, XRD and HRMS analyses. Resorcin[4]arene afforded the resulted products in a shorter time and in good yields. The recyclability of the catalyst was established up to 6th cycle by FT-IR and SEM images.     

Polystyrene sulfonic acid catalyzed greener synthesis of hydrazones in aqueous medium using microwaves

An environmentally benign aqueous protocol for the synthesis of cyclic, bi-cyclic, and heterocyclic hydrazones using polystyrene sulfonic acid (PSSA) as a catalyst has been developed; the simple reaction proceeds efficiently in water in the absence of any organic solvent under microwave irradiation and involves basic filtration as the product isolation step.     

Stereoselective adduct formation of α-acylcamphorato-copper(II) chelates with some chiral Lewis bases

The formation constants of the mono-adducts of α-acylcamphorato-copper(II) chelates such as (+)-Cu(facam)₂, (?)-Cu(facam)₂, (+)-Cu(hfbc)₂ and (?)-Cu(hfbc)₂ with some chiral Lewis bases were determined spectrophotometrically in benzene. In order to compare the adduct formation constants obtained with the (+)- and (?)-forms, some pairs of chiral Lewis bases such as 1-amino-2-propanol [(R)(?), (S)(+)], 1-(α-naphthyl)ethylamine [(R)(+), (S)(?)], α-phenyl ethylamine [(R)(+), (S)(?)] and also quinine and quinidine were examined as neutral ligands. Although not very pronounced, the effects of combinations obtained for (+)- or (?)-Cu(II) chelates and (+)- or (?)-ligands indicate that formation constants obtained by the formation of adducts with the ligands having different directions of the optical rotation seems to be superior to those with the same direction.