Enantioselective reactions of tert-butyl glycinate-benzophenone Schiff base catalyzed by chiral phase-transfer catalyst in aqueous media without any organic solvent

Chiral phase-transfer catalyzed enantioselective alkylations of tert-butyl glycinate-benzophenone Schiff base were investigated in aqueous media without any organic solvent. Reactions in aqueous media smoothly proceeded to give the desired product in higher yield than under standard liquid-liquid biphasic conditions. In aqueous media the formation of benzophenone, which was caused by in situ hydrolysis of Schiff base, was depressed.     

Direct organocatalytic asymmetric Mannich-type reactions in aqueous media: one-pot Mannich-allylation reactions

The first direct organocatalytic asymmetric Mannich-type reactions in aqueous media are demonstrated herein. l-Proline-catalyzed reactions in aqueous media to provide β-formyl substituted α-amino acid derivatives with excellent diastereoselectivities (dr up to 19:1, syn/anti) and high enantioselectivities (ee between 72 and >99%). These conditions provided for the development of novel one-pot asymmetric syntheses of cyclic γ-allyl substituted α-amino acid derivatives (ee up to >99%). This was accomplished by combining the proline-catalyzed Mannich-type reactions with indium promoted allylations in aqueous media.     

Extraction and separation of gallium, indium and thallium with several carboxylic acids from chloride media

A method is proposed for the extraction and individual separation of trivalent gallium, indium and thallium with sec-octylphenoxy acetic acid (CA-12), sec-nonylphenoxy acetic acid (CA-100) and naphthenic acid (NA) from chloride media. The distribution equilibria of gallium (III), indium (III), thallium (III) and thallium (I) between carboxylic acids (CA-12, CA-100 and NA) dissolved in kerosene and acidic aqueous chloride media has been investigated as a function of the concentration of extractants and the concentration of hydrogen ion in aqueous phase. A possible mechanism of the extraction is discussed. The method permits rapid and precise individual separation of gallium (III), indium (III) and thallium (III), and is applicable to the analysis of alloy samples.     

A versatile and convenient route to ketone C-pyranosides and ketone C-furanosides from unprotected sugars

Both ketone C-pyranosides (in up to 97% yields) and C-furanosides (in 83–97% yields) could be prepared, respectively, from the condensations of pentane-2,4-dione and various unprotected sugars in sodium carbonate aqueous media by adjusting the reaction conditions.     

Asymmetric Mannich reactions catalyzed by proline and 4-hydroxyproline derived organocatalysts in the presence of water

The ability of amphiphilic catalysts based on proline and 4-hydroxyproline to catalyze the Mannich reaction in aqueous media is reported. With a 4-tert-butyldimethylsiloxy-substituted organocatalyst derived from N-prolylsulfonamide, the reaction of cyclohexanone with iminoglyoxylate proceeds with high enantioselectivity (>99% ee for the syn-diastereomer). This catalyst was also successfully applied in a reaction of an iminoglyoxylate with an aqueous tetrahydro-2H-pyran-2,6-diol to give the corresponding 2,3-disubstituted tetrahydropyridine with up to 95:5 dr and 98% ee.     

Sine-wave polarographic determination of zirconium or niobium in aqueous media

The sine-wave polarographic determination of zirconium in aqueous media was investigated using solutions which were 0.55 – 5.5·10^-3M in zirconyl chloride and 1 M in potassium chloride and had been adjusted to pH 2.0 with hydrochloric acid. It was possible to determine zirconium in the concentration range of 0.05 to 0.4 mg per ml. The sine-wave polarographic behavior of zirconium in aqueous solutions in the pH range 2–3 is discussed. The sine-wave polarographic determination of niobium in aqueous media was investigated using concentrated sulfuric acid containing 5 to 0.1 mg of niobium per ml in a supporting electrolyte of citric acid; the determination of niobium was possible down to 0.1 mg of niobium per ml of concentrated sulfuric acid although the D.C. polarographic method was impractical for the determination of less than 0.5 mg of niobium per ml.     

A structural remedy toward bright dipolar fluorophores in aqueous media

The donor–acceptor (D–A) type dipolar fluorophores, an important class of luminescent dyes with two-photon absorption behaviour, generally emit strongly in organic solvents but poorly in aqueous media. To understand and enhance the poor emission behaviour of dipolar dyes in aqueous media, we undertake a rational approach that includes a systematic structure variation of the donor, amino substituent of acedan, an important two-photon dye. We identify several factors that influence the emission behaviour of the dipolar dyes in aqueous media through computational and photophysical studies on new acedan derivatives. As a result, we can make acedan dyes emit bright fluorescence under one- and two-photon excitation in aqueous media by suppressing the liable factors for poor emission: 1,3-allylic strain, rotational freedom, and hydrogen bonding with water. We also validate that these findings can be generally extended to other dipolar fluorophores, as demonstrated for naphthalimide, coumarin and (4-nitro-2,1,3-benzoxadiazol-7-yl)amine (NBD) dyes. The new acedan and naphthalimide dyes thus allow us to obtain much brighter two-photon fluorescent images in cells and tissues than in their conventional forms. As an application of these findings, a thiol probe is synthesized based on a new naphthalimide dye, which shows greatly enhanced fluorescence from the widely used N,N-dimethyl analogue. The results disclosed here provide essential guidelines for the development of efficient dipolar dyes and fluorescence probes for studying biological systems, particularly by two-photon microscopy.     

An efficient access to N-tert-butanesulfinyl aldimines in water: Application to one-pot synthesis of homoallylic amines, (+)-crispine A and (−)-coniine

An Efficient method for the syntheses of N-tert-butanesulfinyl aldimines in water was developed using Amberlyst-15 as catalyst. Subsequently, chiral homoallylic amines were synthesized in one pot from aldehydes by combining with In-promoted allylation in aqueous media. The total syntheses of (+)-Crispine A and (?)-Coniine were conducted to demonstrate the utility of this one-pot approach.     

Copolymers of <Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam with 1-vinyl- and 1-methacryloyl-3,5-dimethylpyrazole as sorbents of essential α-amino acids in liquid- and solid-phase extraction

Radical copolymerization of N-vinylcaprolactam with 1-vinyl- and 1-methacryloyl-3,5-dimethylpyrazole was performed with the aim of development of effective extraction systems based on nontoxic copolymers for the recovery of essential amino acids histidine, threonine, and tryptophan from aqueous media. Water-soluble and water-insoluble products were obtained. As follows from the copolymerization data, N-vinylcaprolactam exhibits relatively high activity, and the copolymerization constants r₁ and r₂ for both pairs of comonomers are lower than unity. The influence of the composition and structure of copolymers on the quantitative characteristics (degree of recovery R and distribution coefficient D) of liquid- and solid-phase extraction was studied. The probable mechanism of the interaction of the polymers with α-amino acids was considered. The synthesized copolymers show high performance in recovery of α-amino acids from aqueous media.     

Pulse polarographic determination of nitrosamines: Part 2. Methods for the Determination of N-Nitrosodiphenylamine and N-Nitrosodibutylamine

Differential pulse polarographic methods are reported for the determination of N-nitrosodiphenylamine and N-nitrosodibutylamine in aqueous media. Optimum conditions for analysis were obtained with acetate buffer (pH 3.74) and 0.01 M H₂SO₄, where reduction peak separations were of the order of 300 mV and 200 mV, respectively. Detection limits were approximately 3×10^-8 M for each compound. Methods for the extraction of these nitrosamines from iso-octane to aqueous solutions were quantitatively examined.     

Kinetics and nature of the slow stage of cathodic hydrogen evolution on iron in aqueous and water-ethylene-glycol solutions of HCl in the presence of o-fluorophenylbiguanidine

The influence of the concentration of o-fluorophenylbiguanidine (FF) (0.5–40 mM) on the kinetics of hydrogen evolution on iron in aqueous and ethylene glycol (10 wt % H₂O) solutions with an electrolyte x M HCl + (1 ? x) M LiCl was studied. In aqueous media, the introduction of increasing concentrations of FF led to a transition from one slow stage to other stages in a series: slow discharge → slow recombination → slow lateral diffusion → slow discharge. In ethylene glycol media, the series is formally the same, but there is no initial slow discharge and hydrogen evolution (HER) in supporting solutions is limited by chemical recombination, which shifts to slow lateral diffusion already in the presence of 0.1 mM FF. In aqueous solutions, this change in the nature of the rate-limiting stage requires a 50-fold increase in the FF concentration. Finally, at a certain FF concentration, HER occurs under the conditions of slow discharge.     

Ethylenediamine diacetate-catalyzed three-component reaction for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones and their spirooxindole derivatives

Ethylenediamine diacetate (EDDA)-catalyzed one-pot syntheses of biologically interesting 2,3-dihydroquinazolin-4(1H)-ones and their spirooxindole derivatives from isatoic anhydride, amines, and benzaldehydes or isatins via a three-component condensation in aqueous media have been described. This method is of great value because of high yields and ease of handling.     

Indoles

A new method is proposed for the synthesis of 1,2-disubstituted tryptophols by reaction of N_α-substituted arylhydrazines with α-acyl-γ-butyrolactones by refluxing the components in an acidic aqueous alcohol media.     

A new organocatalyst derived from abietic acid and 4-hydroxy-l-proline for direct asymmetric aldol reactions in aqueous media

Enantioselective direct aldol reactions were carried out in aqueous media with a new organocatalyst that was derived from 4-hydroxy-l-proline and abietic acid via a simple and convenient synthetic protocol with a high overall yield (75%). The new organocatalyst was used for aldol reactions between substituted aromatic aldehydes and various ketones in the presence of several acid additives in aqueous media. The corresponding aldol products were obtained in high isolated yields (up to 99%) and with high anti-diastereoselectivities (up to 94%) and enantioselectivities (>99.9%). The catalyst loading can be efficiently reduced to only 1 mol %. The aldol reactions were found to be extremely fast which is very unusual in organocatalyzed reactions in water.     

Poly (3-substituted) thiophenes electroactive in water

Three thiophene rings bearing n-ethoxy arylsulfonamide pendant groups were synthesized and their electropolymerization was performed at a platinum electrode. The electrochemical behaviour of the polythiophene matrix was studied both in organic and in aqueous solvent. If all polymers present a reversible n- and p-doping process in organic solvents, only one of them particularly possess a reversible p-doping in aqueous media. This phenomenon was shown to be directly related to the nature of the spacer between the thiophene ring and the aryl sulfonamide unit.     

Synthesis of a paraffin phase change material microencapsulated in a siloxane polymer

The coemulsification method suitable for the formulation of microcapsules of n-eicosane coated with a polysiloxane is developed. This method allows to synthesize core–shell microcapsules of paraffin which have the shape of spheres or distorted spheres and are designed for the use as phase change materials. The microcapsules are formed in aqueous phase by the precipitation of n-eicosane together with modified polyhydromethylsiloxane from a common solvent which is miscible with aqueous media. The polysiloxane is modified by the attachment of silylvinyl and alkoxy functions before coemulsification with the paraffin. It also contains the Pt(0) Karstedt catalyst. The microcapsules formed by coemulsification are stabilized by the in situ cross-linking of the polysiloxane shell. The shell is additionally modified by the in situ generation of silanol groups which provide colloidal stabilization of microspheres in aqueous phase. Microcapsules were studied by DSC, SEM, optical polarized microscope, and by thermooptical analysis (TOA).     

One-pot chemoenzymatic synthesis of protected cyanohydrins

In a chemoenzymatic one-pot reaction of ethyl cyanoformate with benzaldehyde catalyzed by the hydroxynitrile lyase from Prunus amygdalus ethoxycarbonylated (R)-mandelonitrile is formed in a highly enatioselective manner. The reaction was performed both in aqueous and organic media. ¹H NMR investigations revealed a two-step procedure consisting of an enzyme-catalyzed addition of HCN, generated by hydrolysis of ethyl cyanoformate, to the aldehyde followed by ethoxycarbonylation of the free cyanohydrin in a second step     

Reaction of thiourea S,S-dioxides with dyes containing carbonyl or azo groups

The kinetics of decomposition of thiourea and N-methylthiourea S,S-dioxides in alkaline aqueous medium and their reactions with oxygen, Indigo Carmine, and Acid Yellow 11 were studied. The decomposition of thiourea S,S-dioxides in weakly alkaline media was found to follow two pathways leading to the formation of ammonia and sulfoxylate ion, respectively. The second pathway predominates in strongly alkaline media. Thiourea S,S-dioxides can be used for selective reduction of azo compounds to the corresponding hydrazo derivatives.     

Fluorescence investigation of isochlorotetracycline: ground-state and excited-state acid-base equilibria

The fluorescence emission from isochlorotetracycline is shown to be associated with the hydroxyphthalide portion of the molecule. Neutral, anionic, zwitterionic and cationic forms of the fluorophore are proposed to account for the fluorescent behaviour in aqueous and organic media of different acidities. In strongly acidic aqueous solution intermolecular photoautomerism is observed, while in chloroform intramolecular phototautomerism occurs. In aqueous solution an excited-state pK_a of 3.3 was observed for the fluorophore. From a study of the pH vs. fluorescence profile with excitation at 350 nm, the ground-state microscopic dissociation constants for isochlorotetracycline hydrochloride were calculated. The optimum conditions for the fluorimetric determination of isochlorotetracycline are an alkaline medium (pH > 10) with κ_ex = 350 nm and κ_em = 415 nm.     

Synthesis of β-fluoroenones and their reductive rearrangement in aqueous media

In this paper, a simple and efficient preparation of β-fluoroenones, as a mixture of E/Z isomers with the E-isomer as the main product, from 1,2-allenic ketones by using TBAF·3H₂O in water as a nucleophilic fluorination agent has been developed. Moreover, in exploring the synthetic applications of β-fluoroenones, an unprecedented reductive defluorination rearrangement of β-fluoroenones toward enones under mild conditions in aqueous media was also discovered.