Mar López-González

Hybrid materials: Magnetite-Polyethylenimine-Montmorillonite, as magnetic adsorbents for Cr(VI) water treatment.

Hybrid materials formed by the combination of a sodium rich Montmorillonite (MMT), with magnetite nanoparticles (40 nm, Fe(3)O(4) NPs) coated with Polyethylenimine polymer (PEI 800 g/mol or PEI 25000 g/mol) were prepared. The intercalation of the magnetite nanoparticles coated with PEI among MMT platelets was achieved by cationic exchange. The resulting materials presented a high degree of exfoliation of the MMT sheets and a good dispersion of Fe(3)O(4) NPs on both the surface and among the layers of MMT. The presence of amine groups in the PEI structure not only aids the exfoliation of the MMT layers, but also gives to the hybrid material the necessary functionality to interact with heavy metals. These hybrid materials were used as magnetic sorbent for the removal of hexavalent chromium from water. The effect that pH, Cr(VI) concentration, and adsorbent material composition have on the Cr(VI) removal efficiency was studied. A complete characterization of the materials was performed. The hybrid materials showed a slight dependence of the removal efficiency with the pH in a wide range (1-9). A maximum amount of adsorption capacity of 8.8 mg/g was determined by the Langmuir isotherm. Results show that these hybrid materials can be considered as potential magnetic adsorbent for the Cr(VI) removal from water in a wide range of pH.

Synthesis and Spectroscopic Properties of New Rose Bengal and Eosin Y Derivatives

Abstract Selective esterification of purified Rose Bengal and Eosin Y have been carried out by reaction with methyl iodide, benzyl chloride or p-isopropylbemyl chloride. The lactonic form of each dye reacts with diazomethane producing mixtures of the monomethyl ether and the dimethyl ether of the lactone, and the methyl ether of the methyl ester of the tautomeric quinonoid form. On heating, Rose Bengal decarboxylates in dimethylformamide solution, while Eosin Y loses a bromine atom in dimethylsulphoxide. The structures of all the products obtained have been studied by the usual Spectroscopic techniques. HPLC data are also reported.

Spectrophotometric determination of ionization and isomerization constants of Rose Bengal, eosin Y and some derivatives

Abstract The experimental pK values corresponding to the acid forms of Rose Bengal, Eosin Y, their methyl esters, their methyl ethers, and the decarboxylated compound derived from the first dye, all of them in solution in 1:1 mixtures of dioxane with aqueous buffers, have been determined by applying graphical methods to visible Spectrophotometric data. Assuming the same visible absorption spectra for molecules with similar chromophoric groups, the isomerization constants of the possible equilibria between lactonic and quinonoid tautomeric structures, and the pK values of the ionizations of the molecular forms which can be present, have been estimated. In the quinonoid molecular forms of Rose Bengal and Eosin Y, their phenol groups are ionized first, with estimated pK values of 2·57 and 2·69 respectively, while their carboxylic groups show much less acidity, and pK values of 5·01 and 6·25.

Sequence distribution and stereoregularity in methyl methacrylate-methyl acrylate copolymers at high conversions

Abstract Methyl methacrylate (MMA)-methyl acrylate (MA) copolymerizations have been analysed over a wide range of conversions with the purpose of predicting the changes in copolymer composition and comonomer sequence distribution as a function of conversion. High resolution 1 H n.m.r. spectra (200 MHz) of MMA-MA copolymers, prepared at two overall comonomer concentrations by free radical copolymerization in benzene solution at 50°C at low conversion, have been analysed in terms of comonomer composition, sequence distribution and stereoregularity. Reactivity ratios for the terminal model, statistical parameters, P ij , and co-isotacticity parameters, σ 11 = 0.23 and σ = σ 12 = σ 21 = 0.50, estimated at low conversion were used to describe the changes in copolymer composition and triad fraction intensities with conversion. The experimental sequence distribution intensities were in agreement with the estimated values. From the good agreement found between experimental and calculated values, it can be concluded that the terminal model, through reactivity ratios and Bernoullian statistics, provides a very precise description of copolymerization over the whole range of conversion and composition and overall concentration of monomers.

Experimental and simulation studies on the transport of gaseous diatomic molecules in polycarbonate membranes

Measurements on the pure transport of oxygen, nitrogen, and carbon monoxide in membranes prepared from poly[bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene) diphenol carbonate] are reported. The isotherms representing the variation of the permeability coefficient with the upstream pressure can be described by assuming that the diffusants are retained in the matrix by Henry and Langmuir mode sorptions. The values of the permeability coefficient of oxygen, nitrogen and carbon monoxide at 35 °C and p0=1 atm are 8.75, 1.87, and 2.91 barrers, respectively. The values of the diffusion coefficient in 10−8 cm2/s, measured in the same conditions, are 8.26, 2.81, and 3.08, respectively. These membranes exhibit higher permeability than polycarbonate membranes with the two methyl groups of bisphenol A replaced by other different molecular groups, without a substantial diminution of permselectivity. The permeability and the diffusion coefficients obey Arrhenius behavior. The application of the transition...

Free-radical copolymerization of methyl acrylate with methyl methacrylate in benzene solution

Abstract Methyl acrylate and methyl methacrylate have been copolymerized using the initiator 2,2′-azobisisobutyronitrile over a wide composition and conversion range. Free-radical copolymerization has been carried out in benzene solution using 3 and 5 mol1 −1 as the overall concentrations of monomers. Reactivity ratios do not, apparently, change by dilution. Cumulative copolymer composition was independent of total monomer concentration, being described satisfactorily by the integrated Mayo-Lewis equation. The overall copolymerization coefficients are not affected by total monomer concentration. They were analysed on the basis of a penultimate effect on the propagation reaction.

Thermal decarboxylation of rose bengal dye

Abstract The xanthene dye rose bengal undergoes decarboxylation when heated in dimethylformamide or cyclohexanone.

Synthesis and gas transport properties of new polynorbornene dicarboximides bearing trifluoromethyl isomer moieties

This work reports on the synthesis and ring-opening metathesis polymerization (ROMP) of new structural isomers based on norbornene dicarboximides bearing trifluoromethyl moieties, specifically, N-2-trifluoromethylphenyl-exo-endo-norbornene-5,6-dicarboximide (2a) and N-3-trifluoromethylphenyl-exo-endo-norbornene-5,6-dicarboximide (2b) using tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (I), bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (II), and bis(tricyclohexylphosphine) p-fluorophenylvinylidene ruthenium (II) dichloride (III). It is observed that the –CF3 moiety attached to the ortho position of the aromatic ring increases the thermal and mechanical properties of the polymer, whereas the meta substitution has the opposite effect. A comparative study of gas transport in membranes based on these fluorinated polynorbornenes showed that the –CF3 ortho substitution increases the permeability of the polymer membrane as a consequence of the increase of both the gas solubility and the gas diffusion. In contrast, the gas permeability coefficients of the meta-substituted polymer membrane are rather similar to those of the non-fluorinated one attributed to a lower fractional free volume. The meta-substituted polymer membrane besides showing the largest permselectivity coefficients of all the isomers studied here was also found to have one of the largest permselectivity coefficients reported to date for separating hydrogen/propylene in glassy polynorbornene dicarboximides.

Synthesis of polyesters as binders for deinkable inks. V. Structural analysis of the polyesterification between o-phthalic anhydride and trimethylolpropane in bulk at 165°C by high resolution 13C and 1H nuclear magnetic resonance

Structural analysis of the polyesterification in bulk without external catalyst at 165°C between o-phthalic anhydride (P) and trimethylolpropane (1,1, 1-tri(hydroxymethyl)propane) (T) with a mole ratio ([-COOH]/[-OH]) = 0.70 has been carried out by high resolution 13 C nuclear magnetic resonance ( 13 C NMR) in DMSO-d 6 and CDCl 3 solutions and by 1 H nuclear magnetic resonance ( 1 H NMR) in CDCl 3 solution. The use of CDCl 3 as NMR solvent has allowed us to identify several signals, which have been assigned to trimethylolpropane monoesters with different esterification degree in the o-phthalate residue. Identically, we have detected signals assignable to chain-end monoesters in structures with different chain lengths. These monoesterified structures have also been confirmed by analysing, by the same procedures, samples modified by diazomethane addition to the samples in chloroformic solution. These modified samples have also been used to determine free acid groups as their methoxylic derivatives by 1 H NMR in CDCl 3 solution. The values compare very well with those obtained by 13 C and 1 H NMR spectroscopies in both solvents in some other regions of the spectra. It has been found that NMR allows quantitative determination as a function of the reaction time, of the conversion of acid P and alcohol T functions, as well as monoester and diester of P distributions and those of free, mono- di- and tri-esterified T. We have not observed any detectable signs of gelation.

Dye-sensitized photooxidation of 1-methylindolyl-3-acetic acid

Abstract The structure of the products constituting the complex mixture afforded by the entitled reaction is similar to that proceeding from the N-unmethylated acid and supports the presumed mechanistic analogy with the enzymatic oxidation.