Characterization of 11-mercaptoundecanoic and 3-mercaptopropionic acids adsorbed on silver by surface-enhanced Raman scattering

Functionalized n-alkanethiols such as 11-mercaptoundecanoic (MUA) and 3-mercaptopropionic (MPA) acids are likely to adsorb in silver nanoparticles (AgNPs) solely through the thiol group (-SH) or also involving the carboxylate group (−COO⁻) in their structures. The relative tendency is closely related to pH conditions, solvent or the surface potential of the metallic nanoparticles. The SERS effect (Surface Enhancement Raman Scattering) was used for improving the understanding of MUA and MPA group interaction as well as the orientation of these organic compounds adsorbed on AgNPs and the influence of Cu(II) in solution. When analyzing the MPA SERS spectrum, it was verified that the thiol moiety was preferred to adsorb on the AgNPs surface in the thiolate form, presenting both anti and gauche conformations in both acidic and basic media. MUA SERS spectrum however, indicated that solely an anti conformation for the thiol moiety adsorbed on the AgNPs surface in both acidic and basic media. Adding Cu²⁺ ion resulted in coordination to the carboxyl or carboxylate moieties was confirmed by the downshift of the band assigned to OCO stretching. The presence of Cu(II) increased the tendency of gauche conformation for MPA; the coordination of MUA to Cu(II) resulted in a more upright conformation of the carboxylic/carboxylate moieties in both acidic and basic media, respectively.     

Complexing properties of polyhexamethyleneguanidine chemically grafted to a silica surface

Covalent bonding of polyhexamethyleneguanidine amides of maleic and o-phthalic acids to the aminated silica surface was performed. The complexing properties of the obtained composite adsorbents with respect to Zn(II), Cu(II), Fe(III), Co(II), Pb(II), Ni(II), Mn(II), Mo(VI), and Cr(VI) ions were studied. The Mo(VI) and Cr(VI) reduction was detected on the modified silica surface bearing polyhexamethyleneguanidine amide with o-phthalic acid. The formation of different-ligand complexes with transition metal cations adsorbed on the synthesized composite surface was studied.     

Comparative studies of chemically synthesized polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid

Polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid (p-TSA) were synthesized by in situ chemical polymerization method using ammonium per sulphate as an oxidizing agent. This is a novel polymerization process for the direct synthesis of emeraldine salt phase of the polymer. The polymers were characterized by using UV-Vis and FT-IR spectroscopy, SEM, elemental analyzer, TGA/DSC and conductivity measurements. Thermal analysis shows that poly(o-toluidine) is less thermally stable compared to polyaniline. The less conductivity in poly(o-toluidine) is due to the cumulative steric as well as electronic effect of the bulky methyl substituent present on the benzene ring. High temperature conductivity measurements show ‘thermal activated behavior’.     

CuO nano-particles supported on silica,a new catalyst for facile synthesis of benzimidazoles,benzothiazoles and benzoxazoles

A facile synthetic route for benzimidazoles, benzothiazoles and benzoxazoles comprising the reaction of corresponding o-phenylenediamine, o-aminothiophenol and o-aminophenol with various aldehydes using silica supported nano-copper (II) oxide as a catalyst has been described. The catalyst exhibited a clean reaction profile with excellent yields in a short reaction time. The catalyst can be recycled effectively after use.     

Scale-up synthesis of vinyl polymer-grafted nano-sized silica by radical polymerization of vinyl monomers initiated by surface initiating groups in the solvent-free dry-system

For the purpose of the prevention of the environmental pollution and the simplification of reaction process, the scale-up radical graft polymerization of vinyl monomers onto nano-sized silica surface initiated by azo groups and peroxycarbonate groups previously introduced onto the surface in the solvent-free dry-system was investigated. The introduction of azo groups onto the silica surface was achieved by the reaction of surface amino groups with 4,4′-azobis(4-cyanopentanoic acid chloride). On the other hand, the introduction of peroxycarbonate groups onto the silica surface was achieved by Michael addition of surface amino groups to t-butylperoxy-2-methacryloyloxyethylcarbonate. The graft polymerization of vinyl monomers onto the surface was successfully achieved by splaying monomers to nano-sized silica having azo and peroxycarbonate groups in solvent-free dry-system. It is interesting to note that the formation of ungrafted polymer was depressed in comparison with graft polymerization in solution: the grafting efficiency was 90-95%. In addition, in the solvent-free dry-system, the grafting of copolymer having pendant peroxycarbonate groups onto the nano-sized silica surface and the radical postgraft polymerization of styrene initiated by the pendant initiating groups of the grafted copolymer chain on the silica surface was investigated.     

An infrared study of adsorbed metal ions on modified silica: Comparative chelation between mercury, cadmium, and lead divalent ions to silica functionalized with ortho- and para-aminothiophenoles

Chelating selectivity and capacity of silica functionalized 2- and 4-aminothiophenoles (2-ASP-[silica] and 4-ASP-[silica]) toward mercury, lead, and cadmium ions in aqueous medium are studied. In this comparative study, the three metal ions were allowed to interact individually and simultaneously with two aminothiophenol (ASP) derivatives namely, 2- and 4-ASP once as free chelates in solution and secondly as immobilized chelates on silica. Upon individually or simultaneously interacting the three metal ions with 4-ASP-[silica], Hg(II) ions are preferentially adsorbed where 100% of Hg(II) is removed compared to 83.0% of Pb(II) and 76% of Cd(II) ions. In solution, Hg(II) ions are found to be preferentially adsorbed by 2-ASP when compared to 4-ASP. Whereas, anchoring 4-ASP to a silica surface via amide linkage provides a significant enhancement in selectivity and extent of chelation toward Hg(II) over Cd(II) and Pb(II) ions. In the case of 4-ASP-[silica], the existence of a free SH group allows an easy-accessible and strain-free binding site for the incoming Hg(II) ions. Whereas, in 2-ASP-[silica], the SH group is sterically hindered due to proximity to the point of attachment with the surface. As a result, 2-ASP-[silica] showed less potential for Hg(II) binding compared to the modified analogue, 4-ASP-[silica] with less chelation extent observed in solution compared to that observed at the surface.     

Zwitterionic metal carboxylate complexes: In solid state

A flexible dicarboxylic acid having composition [(CH(o-C₅H₄N)(p-C₆H₄OCH₂CO₂H)₂] derived from corresponding bis-phenol reacts with various metal(II) acetates such as manganese(II), cobalt(II) and nickel(II) acetate leads to zwtterionic complexes with compositions [CH(o-C₅H₄N)(p-C₆H₄OCH₂CO₂){p-C₆H₄OCH₂CO₂M(H₂O)₅}].6H₂O (where M = Mn, Co, Ni). The complexes are characterised by X-ray crystallography. These complexes have chiral center due to unsymmetric structure conferred to the ligand through coordination at only one carboxylate group of the ligand. In solid state these complexes are racemic.     

Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies

An unsymmetrical tetradentate Schiff base (H₂L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H₂L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance.     

Bis[n(chlorophenyl)dithiocarbamato] complexes of Cu(II), Zn(II), Cd(II) and Sn(II)

Ammonium[N(o-chlorophenyl)dithiocarbamate], NH₄(OCD), ammonium [N(m-chlorophenyl)dithiocarbamate], NH₄(MCD) and ammonium [N(p-chlorophenyl)dithiocarbamate], NH₄(PCD) and their complexes with Cu(II), Zn(II), Cd(II) and Sn(II) have been synthesised. These complexes have been characterised on the basis of chemical analyses, molecular weight determinations, conductance measurements, electronic and IR spectral studies. Thermal behaviour of the compounds has been studied with the aid of TG and DTA techniques in static air atmosphere. Heats of reaction for different decomposition steps have been calculated from the DTA curves. The end products obtained after thermal decomposition of the complexes were identified by elemental analyses and IR spectral data.     

A one-pot four-component synthesis of N-arylidene-2-aryl-imidazo[1,2-a]azin-3-amines

N-Arylidene-2-aryl-imidazo[1,2-a]azin-3-amines were synthesized via a one-pot, four-component condensation reaction using a 2-aminoazine, toluene-4-sulfonylmethyl isocyanide (TsCH₂NC), and two equivalents of readily available aromatic aldehydes. The reaction was performed in diethyl ether as the solvent, with p-toluenesulfonic acid (p-TSA) as the catalyst at reflux temperature.     

Chelating behavior of new chelating resins derived from n-(o-hydroxybenzyl)iminodiacetic acid

The chelating behavior of a new resin prepared by polycondensation of N-(o-hydroxybenzyl) iminodiacetic acid (o-HDA) with phenol and formaldehyde, is compared with that of the monomer, with p-HDA resin and p-HDA monomer, and with Chelex-100. The order of chelate stability for the o-HDA resin is Cu(II) > Ni(II) > Zn(II) > Co(II). An unusually high stability of the o-HDA and o-HDA resin iron(III) chelates in acidic solution is attributed to the participation of the o-hydroxyl group in the coordination process.     

An Efficient and Odorless Synthesis of Thioethers Using 2‐[Bis(alkylthio)methylene]‐3‐oxo‐N‐o‐tolylbutanamides as Thiol Equivalents

Using 2‐[bis(alkylthio)methylene]‐3‐oxo‐N‐o‐tolylbutanamides 1 as odorless thiol equivalents, an efficient and odorless synthesis of thioethers has been developed. Promoted by NaOH in EtOH, the cleavage of 1 commences to generate thiolate anions, and the generated thiolate anions then react with halides to give various thioethers in good yield. It is noteworthy that only a very faint odor of thiols can be perceived during both the reaction and the workup.     

Preparation and properties of fluorinated carboxylic acid/silica nanocomposite-encapsulated low molecular weight compounds

Perfluoro-2-methyl-3-oxahexanoic acid/silica nanocomposites [R_F-CO₂H/SiO₂] were prepared by the sol–gel reaction of tetraethoxysilane in the presence of silica nanoparticles and the corresponding fluorinated carboxylic acid under alkaline conditions. R_F-CO₂H/SiO₂ nanocomposites were found to exhibit no weight loss in proportion to the contents of fluorinated carboxylic acid in the composites even after calcination at 800 °C. The modified glass surface treated with the R_F-CO₂H/SiO₂ nanocomposites was shown to give a good oleophobicity with superhydrophilicity imparted by fluorinated carboxylic acid in the composites. R_F-CO₂H/SiO₂ nanocomposites were also applied to the encapsulation of a variety of low molecular weight aromatic and aliphatic compounds such as bisphenol AF [BPAF], bisphenol A [BPA], 4,4′-biphenol [BPOH], octafluoro-4,4′-biphenol [FBPOH], 4,4′-bis(triethoxysilyl)-1,1′-biphenyl [BTSBP], 3-(trihydroxysilyl)propane-1-sulfonic acid [THSP], α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD). Encapsulated aromatic compounds possessing acidic hydroxyl groups such as BPAF, BPA, and FBPOH in the R_F-COOH/SiO₂ nanocomposites were found to exhibit no weight loss corresponding to the contents of aromatic compounds in the composites even after calcination at 800 °C. On the other hand, encapsulated aromatic compounds possessing no acidic hydroxyl groups such as BTSBP and aliphatic compounds (THSP, α-, β-, and γ-CD) gave a clear weight loss corresponding to the contents of these compounds in the composites after calcination. In addition, the fluorinated silica nanocomposite-encapsulated these compounds were applied to the surface modification of glass to exhibit a good oleophobicity with superhydrophilicity imparted by fluorinated carboxylic acid on the surface.

Application of p-TSA in the one pot synthesis of N-methyl-3-nitro-aryl-benzo[4,5]imidazo[1,2-a]pyrimidin-2-amine

A simple, efficient, eco-friendly, and cost-effective method has been developed for the synthesis of N-methyl-3-nitro-aryl-benzo[4,5]imidazo[1,2-a]pyrimidin-2-amine derivatives using 2-aminobenzimidazole, aldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine, in the presence of catalytic amount of p-toluenesulfonic acid (p-TSA) in ethanol at 80?°C conditions. The advantages of this method are the use of an inexpensive and readily available catalyst, shorter reaction times, a wide range of functional group tolerance, and high yield of products via a simple experimental and work-up procedure.     

Metal ion complexes of 2-acetylpyridine 3-(4-methyl)piperazinyl-thiosemicarbazone

Metal complexes of stoichiometries, [M(HLppz4M)X₂] and [M(Lppz4M)X], are formed from nickel(II) and copper(II) halides and 2-acetylpyridine 3-(4-methyl)piperizinylthiosemicarbazone, HLppz4M. The [M(Lppz4M)X] complexes involve tridentate N(pyridyl), N(azomethinyl) and S(thiolate) coordination with a halo ligand completing the bonding. Neutral HLppz4M coordinatesvia the two nitrogen donors. Spectral evidence indicates the presence of a thiol hydrogen in Hppz4M complexes, the first to be reported for a coordinated thiosemicarbazone.     

Synthesis and structural study of two decanuclear cobalt(II) cages incorporating pyridonates and benzoate-based carboxylates

In this paper, we report the synthesis and the structures of two new decanuclear cobalt(II) cages including carboxylate and pyridonate ligands. The carboxylates are related to benzoic acid. Complex 1 has the formula [Co₁₀(OH)₆(chp)₆(o-MeBz)₇(n-C₃H₇OH)₅][o-MeBz] where chp = 2-chloro-6-pyridonate and o-MeBz = 2-methylbenzoate. The second cage, 2, has the formula [Co₁₀(OH)₆(mhp)₆(p-tBuBz)₈(Hmhp)₂(CH₃CN)₂], where mhp = 2-methyl-6-pyridonate, Hmhp = 2-methyl-6-hydroxypyridine and p-tBuBz = 4-tertbutylbenzoate. The cobalt ions of 1 form a centred-tricapped-trigonal prism, whereas the metal core of 2 is based on a centred tetraicosahedron where five metal ions are missing. To cite this article: C. Cadiou et al., C. R. Chimie 6 (2003).     

Protolytic properties of silica modified with maleinized linseed oil

The protolytic equilibria on the surface of silicas coated with a layer of maleinized linseed oil (MLO), a new type of carboxylic cation exchangers, were studied using potentiometric titration. The ionexchange capacity of the sorbents was determined, a parameter that first increases and then decreases with increasing concentration of MLO on the silica surface. For the dibasic carboxy groups of MLO, pK _a=3.99±0.04 and 4.73±0.04, values close to pK _a for succinic acid, a homogeneous analogue of the system under study.     

Copper catalyzed Gomberg-Buchmann-Hey reaction using aryldiazonium tosylate

Copper catalyzed modification of Gomberg-Bachmann-Hey reaction to synthesize symmetrical/unsymmetrical biaryls via diazotization of anilines with p-TSA and NaNO₂ system at 50 °C, in aromatic liquids as solvents and second partners was successfully developed. Aniline and 3-nitronaniline gave biphenyl and 3-nitrobiphenyl, respectively, with moderate yields. All para-substituted anilines gave comparatively higher yields while in the other cases including ortho-substituted anilines yields were lower. Except anilines with o-NHCOCH₃ and o-CONH₂ which gave symmetrical biaryls, all others gave selectively unsymmetrical biaryls.     

p-Toluenesulfonic acid mediated hydroarylation of cinnamic acids with anisoles and phenols under metal and solvent-free conditions

Hydroarylation of cinnamic acids with anisoles and phenols mediated by p-toluenesulfonic acid (p-TSA) under metal and solvent-free conditions gave 3-(4-methoxyphenyl)-3-phenylpropanoic acids and dihydrocoumarins, respectively, in high yields and excellent selectivity.     

Formation of the bismuth thiolate compound layer on bismuth surface

The structure and composition of thiolate multilayers formed at bismuth monocrystal electrodes from solutions of 1-octadecanethiol and 1-decanethiol in ethanol at open circuit potential are characterized by cyclic voltammetry, electrochemical impedance and infrared reflectance spectroscopy, optical microscopy and AFM methods. Analysis of results demonstrates that after holding of Bi(h k l) electrodes during some hours in solution of thiol in ethanol bismuth is covered with a thick porous layer of bismuth thiolate compound. For the verification of formed thiolate layers the new compounds tris(1-octadecylthio)bismuthine and tris(1-decylthio)bismuthine were also synthesised from bismuth(III)oxide and thiol in hexane solution and a similarity of properties with the bismuth thiolate compounds, formed at the bismuth electrode surface, has been demonstrated.