Artículos de revistas: "Bifunctional solid acids"

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Iglesia, E. "Bifunctional pathways in catalysis by solid acids and bases". Catalysis Today 38, n.º 3 (17 de noviembre de 1997): 339–60. http://dx.doi.org/10.1016/s0920-5861(97)81503-7.

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Rudlof, Jens, Beate Neumann, Hans-Georg Stammler y Norbert W. Mitzel. "Synthesis of a bifunctional boron-Lewis acid and studies on host-guest chemistry using pyridine and TMPD". Zeitschrift für Naturforschung B 77, n.º 2-3 (20 de diciembre de 2021): 141–48. http://dx.doi.org/10.1515/znb-2021-0175.

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Abstract Based on the previously described bifunctional Lewis acid with a functional distance of the boron functions of 4.918(2) Å, the development of a further bifunctional, boron-containing Lewis acid with a wider functional distance is demonstrated. Again, a stannylated precursor was used and the Lewis-acidic boron functions were introduced by means of tin-boron exchange. The general suitability of this class of compounds for the formation of host-guest-complexes is demonstrated by NMR experiments and by solid-state structures using pyridine and TMPD (N 1,N 1,N 4,N 4-tetramethylbenzene-1,4-diamine) as Lewis basic guests. The influence of traces of moisture on the boron-containing, bifunctional Lewis acids was investigated by the structure elucidation of a decomposition product.

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Nishida, Haruo, Hiroshi Morikawa, Takeshi Endo, Takeshi Nakahara, Takayuki Ogata y Koshi Kusumoto. "Solid state reaction of bifunctional bicyclo orthoesters and carboxylic acids and their metal adhesive properties". Polymer 47, n.º 5 (febrero de 2006): 1496–504. http://dx.doi.org/10.1016/j.polymer.2006.01.031.

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Gromov, Nikolay V., Tatiana B. Medvedeva, Ivan A. Lukoyanov, Valentina N. Panchenko, Maria N. Timofeeva, Oxana P. Taran y Valentin N. Parmon. "Formic Acid Production via One-Pot Hydrolysis-Oxidation of Starch over Quaternary Ammonium Salts of Vanadium-Containing Keggin-Type Heteropoly Acids". Catalysts 12, n.º 10 (17 de octubre de 2022): 1252. http://dx.doi.org/10.3390/catal12101252.

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Bifunctional solid acidic quaternary ammonium salts of Keggin-type vanadium-containing heteropoly acids, such as R3.5H0.5PVMo11O40 (R: (C2H5)4N, (C4H9)4N, (C6H13)4N), and [(C4H9)4N]4.5H0.5SiW11VO40, are capable of one-pot hydrolysis-oxidationconversion (OxFA-processing) of starch to biogenic formic acid. The impact of the reaction conditions and catalyst type was revealed. The highest formic acid yield of 50% was achieved over the best [(C2H5)4N]3.5H0.5PVMo11O40 catalyst, which was active and stable in seven reaction cycles. The kinetic computational model, which described formic acid formation well, was proposed in the presence of the most active [(C2H5)4N]3.5H0.5PVMo11O40 catalyst.

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Watanabe, Ryu-ichi, Tetsuo Suzuki y Toshio Okuhara. "Skeletal isomerization of alkanes and hydroisomerization of benzene over solid strong acids and their bifunctional catalysts". Catalysis Today 66, n.º 1 (marzo de 2001): 123–30. http://dx.doi.org/10.1016/s0920-5861(00)00612-x.

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Tyufekchiev, Maksim, Jordan Finzel, Ziyang Zhang, Wenwen Yao, Stephanie Sontgerath, Christopher Skangos, Pu Duan, Klaus Schmidt-Rohr y Michael T. Timko. "A New Method for Solid Acid Catalyst Evaluation for Cellulose Hydrolysis". Sustainable Chemistry 2, n.º 4 (15 de noviembre de 2021): 645–69. http://dx.doi.org/10.3390/suschem2040036.

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A systematic and structure-agnostic method for identifying heterogeneous activity of solid acids for catalyzing cellulose hydrolysis is presented. The basis of the method is preparation of a supernatant liquid by exposing the solid acid to reaction conditions and subsequent use of the supernatant liquid as a cellulose hydrolysis catalyst to determine the effects of in situ generated homogeneous acid species. The method was applied to representative solid acid catalysts, including polymer-based, carbonaceous, inorganic, and bifunctional materials. In all cases, supernatant liquids produced from these catalysts exhibited catalytic activity for cellulose hydrolysis. Direct comparison of the activity of the solid acid catalysts and their supernatants could not provide unambiguous detection of heterogeneous catalysis. A reaction pathway kinetic model was used to evaluate potential false-negative interpretation of the supernatant liquid test and to differentiate heterogeneous from homogeneous effects on cellulose hydrolysis. Lastly, differences in the supernatant liquids obtained in the presence and absence of cellulose were evaluated to understand possibility of false-positive interpretation, using structural evidence from the used catalysts to gain a fresh understanding of reactant–catalyst interactions. While many solid acid catalysts have been proposed for cellulose hydrolysis, to our knowledge, this is the first effort to attempt to differentiate the effects of heterogeneous and homogeneous activities. The resulting supernatant liquid method should be used in all future attempts to design and develop solid acids for cellulose hydrolysis.

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El Fergani, Magdi, Natalia Candu, Iunia Podolean, Bogdan Cojocaru, Adela Nicolaev, Cristian M. Teodorescu, Madalina Tudorache, Vasile I. Parvulescu y Simona M. Coman. "Catalytic Hydrotreatment of Humins Waste over Bifunctional Pd-Based Zeolite Catalysts". Catalysts 12, n.º 10 (9 de octubre de 2022): 1202. http://dx.doi.org/10.3390/catal12101202.

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The catalytic hydrotreatment of humins, the solid byproduct produced from the conversion of C6 sugars (glucose, fructose) to 5-hydroxymethylfurfural (HMF), using supported Pd@zeolite (Beta, Y, and USY) catalysts with different amounts of Pd (i.e., 0.5, 1.0 and 1.5 wt%) was investigated under molecular hydrogen pressure. The highest conversion of humins (52.0%) was obtained on 1.5Pd@USY catalyst while the highest amount of humins oil (27.3%) was obtained in the presence of the 1Pd@Beta zeolite sample, at PH2 = 30 bars and T = 250 °C. The major compounds in the humins oil evidenced by GC-MS are alcohols, organic acids, ethers, and alkyl-phenolics. However, although all these classes of compounds are obtained regardless of the nature of the catalyst used, the composition of the mixture differs from one catalyst to another. Furanic compounds were not identified in the reaction products. A possible explanation may be related to their high reactivity under the reaction conditions, in the presence of the Pd-based catalysts these compounds lead to alkyl phenolics, important intermediates in the petrochemical industry.

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Kingsbury, Christopher J., Marc Kielmann, Brendan Twamley y Mathias O. Senge. "Self-Organization of Porphyrin–POM Dyads: Nonplanar Diacids and Oxoanions in Low-Dimensional H-Bonding Networks". Molecules 27, n.º 20 (19 de octubre de 2022): 7060. http://dx.doi.org/10.3390/molecules27207060.

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Coordinating the spatial arrangement of electroactive partners is crucial to designable molecular electronics and photonics. Porphyrins are ubiquitous reaction centers in nature; synthetic porphyrins, in the crystallographic solid state, are often coerced into monolithic stacks, inhibiting reactivity. Using the principles of self-organization, and by exploiting charge-balance principles, we can manipulate nonplanar porphyrins into one- and two-dimensional hydrogen-bonded polymers, with polyoxometalate (POM) and bifunctional counter-anions serving as linkers. Herein, we report 11 crystal structures as a systematic study of the interactions between dodecasubstituted porphyrin acids and nonstandard counterions, as well as the induced conformations in the porphyrin core. We can show that this hydrogen bond chelate is a viable method of organizing electroactive centers into filaments and monolayers for surface deposition and ultrathin devices.

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9

Elias, Samya, Ademola M. Rabiu, Benjamin I. Okeleye, Vincent Okudoh y Oluwaseun Oyekola. "Bifunctional Heterogeneous Catalyst for Biodiesel Production from Waste Vegetable Oil". Applied Sciences 10, n.º 9 (1 de mayo de 2020): 3153. http://dx.doi.org/10.3390/app10093153.

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Bifunctional solid catalysts facilitate the esterification of free fatty acids (FFA) into alkyl esters alongside the transesterification reaction, which allows for the use of waste vegetable oils with high water and FFA contents for biodiesel production. This makes the process economically viable and greener, as the waste fats and oils are readily available. The concurrent esterification and transesterification of waste palm oil (WPO) and waste sunflower oil (WSO) with methanol was investigated in the presence of calcium oxide on alumina catalyst in a conventional batch process. The catalyst characterization showed the existence of calcium oxide aluminates (calcined at 750 °C), which exhibited crystalline phases with porous/spongy-like particles. The high concentration of CaO in CaO/Al2O3 was a favorable support material in the heterogeneously-catalyzed transesterification reactions. The optimum catalyst parameters for the production of fatty acid methyl esters (FAMEs) were observed at 65 °C for 4 h with a methanol-to-oil ratio of 9:1, 60% (waste palm oil, or WPO) and 80% (waste sunflower oil, or WSO), CaO/Al2O3 (% wt/wt) catalyst ratio as well as 4% CaO/Al2O3 concentration (% wt.) for WSO and WPO. The simultaneous esterification/transesterification reactions at optimum conditions on WPO and WSO led to high yield of FAMEs of 89, 61 and 55% for WPO and 54, 75 and 98% for WSO at catalyst ratios (wt %) of 60, 70 and 80% respectively. The use of bifunctional heterogeneous catalyst (CaO/Al2O3) with waste vegetable oil can result in high performance and the upscaling of biodiesel production.

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Yang, Qiang y Xuejun Pan. "Synthesis and Application of Bifunctional Porous Polymers Bearing Chloride and Sulfonic Acid as Cellulase-Mimetic Solid Acids for Cellulose Hydrolysis". BioEnergy Research 9, n.º 2 (junio de 2016): 578–86. http://dx.doi.org/10.1007/s12155-015-9702-2.

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11

Echizen, Tsuneo, Tetsuo Suzuki, Yuichi Kamiya y Toshio Okuhara. "Mechanistic study on skeletal isomerization of n-butane using 1,4-13C2-n-butane on typical solid acids and their Pt-promoted bifunctional catalysts". Journal of Molecular Catalysis A: Chemical 209, n.º 1-2 (febrero de 2004): 145–53. http://dx.doi.org/10.1016/j.molcata.2003.08.021.

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12

Sekine, Mitsuo y Tsujiaki Hata. "Chemical Synthesis of Oligonucleotides by Use of Phenylthio Group". Current Organic Chemistry 3, n.º 1 (enero de 1999): 25–66. http://dx.doi.org/10.2174/1385272803666220130205329.

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This review deals with recent studies of oligonucleotide synthesis using the phenylthio group as the phosphate protecting group. Several fundament! properties of the P-S bond in phosphorothioate compounds are described in detail. The chemical synthesis and properties of nucleoside phosphorothioate derivatives, which can be prepared via silyl phosphite intermediates, are described. Several interesting and unique properties of a new useful phosphorylating reagent, S, S-diphenyl phosphorodithioate (PSS) are described with some examples involving an application to oligodeoxyribonucleotide synthesis using the phenylthio group as the 5'-terminal or internucleotidic phosphate protecting group. The potential utility of pyridinium phosphonate (PPN) has been demonstrated as an efficient catalyst for dephenylthiolation of bis(phenylthio)phosphorylated nucleoside derivatives, which is required for stepwise condensation in these oligonucleotide syntheses via the phosphotriester approach. Further application of this thiophosphotriester method to the solid-phase synthesis of oligodeoxyribonucleotides is described. The background of developments of bifunctional condensing reagents such as MDS and DDS and their application to the liquid phase synthesis of oligonucleotides are also reviewed. Several methods using oximate reagents and (Bu3Sn)20 are exemplified for removal of the phenylthio group from fully protected oligonucleotides. The application of the phenylthio group as an activatable protecting group to the chemical synthesis of 7-methylguanosine (MMG)- and trimethylguanosine (TMG)-capped oligonucleotides. Other applications of this activation strategy to the synthesis of naturally occurring nucleic acids are also described. Finally, a plausible mechanism of the present thiophosphotriester method is discussed.

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13

Viollier, P. H., K. T. Nguyen, W. Minas, M. Folcher, G. E. Dale y C. J. Thompson. "Roles of Aconitase in Growth, Metabolism, and Morphological Differentiation of Streptomyces coelicolor". Journal of Bacteriology 183, n.º 10 (15 de mayo de 2001): 3193–203. http://dx.doi.org/10.1128/jb.183.10.3193-3203.2001.

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ABSTRACT The studies of aconitase presented here, along with those of citrate synthase (P. H. Viollier, W. Minas, G. E. Dale, M. Folcher, and C. J. Thompson, J. Bacteriol. 183:3184–3192, 2001), were undertaken to investigate the role of the tricarboxylic acid (TCA) cycle in Streptomyces coelicolor development. A single aconitase activity (AcoA) was detected in protein extracts of cultures during column purification. The deduced amino acid sequence of the cloned acoA gene constituted the N-terminal sequence of semipurified AcoA and was homologous to bacterial A-type aconitases and bifunctional eukaryotic aconitases (iron regulatory proteins). The fact that an acoA disruption mutant (BZ4) did not grow on minimal glucose media in the absence of glutamate confirmed that this gene encoded the primary vegetative aconitase catalyzing flux through the TCA cycle. On glucose-based complete medium, BZ4 had defects in growth, antibiotic biosynthesis, and aerial hypha formation, partially due to medium acidification and accumulation of citrate. The inhibitory effects of acids and citrate on BZ4 were partly suppressed by buffer or by introducing a citrate synthase mutation. However, the fact that growth of an acoA citA mutant remained impaired, even on a nonacidogenic carbon source, suggested alternative functions of AcoA. Immunoblots revealed that AcoA was present primarily during substrate mycelial growth on solid medium. Transcription ofacoA was limited to the early growth phase in liquid cultures from a start site mapped in vitro and in vivo.

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Miranda, Luis F. C., Rogéria R. Gonçalves y Maria E. C. Queiroz. "A Dual Ligand Sol–Gel Organic-Silica Hybrid Monolithic Capillary for In-Tube SPME-MS/MS to Determine Amino Acids in Plasma Samples". Molecules 24, n.º 9 (27 de abril de 2019): 1658. http://dx.doi.org/10.3390/molecules24091658.

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This work describes the direct coupling of the in-tube solid-phase microextraction (in-tube SPME) technique to a tandem mass spectrometry system (MS/MS) to determine amino acids (AA) and neurotransmitters (NT) (alanine, serine, isoleucine, leucine, aspartic acid, glutamic acid, lysine, methionine, tyrosine, and tryptophan) in plasma samples from schizophrenic patients. An innovative organic-silica hybrid monolithic capillary with bifunctional groups (amino and cyano) was developed and evaluated as an extraction device for in-tube SPME. The morphological and structural aspects of the monolithic phase were evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption experiments, X-ray diffraction (XRD) analyses, and adsorption experiments. In-tube SPME-MS/MS conditions were established to remove matrix, enrich analytes (monolithic capillary) and improve the sensitivity of the MS/MS system. The proposed method was linear from 45 to 360 ng mL−1 for alanine, from 15 to 300 ng mL−1 for leucine and isoleucine, from 12 to 102 ng mL−1 for methionine, from 10 to 102 ng mL−1 for tyrosine, from 9 to 96 ng mL−1 for tryptophan, from 12 to 210 ng mL−1 for serine, from 12 to 90 ng mL−1 for glutamic acid, from 12 to 102 ng mL−1 for lysine, and from 6 to 36 ng mL−1 for aspartic acid. The precision of intra-assays and inter-assays presented CV values ranged from 1.6% to 14.0%. The accuracy of intra-assays and inter-assays presented RSE values from −11.0% to 13.8%, with the exception of the lower limit of quantification (LLOQ) values. The in-tube SPME-MS/MS method was successfully applied to determine the target AA and NT in plasma samples from schizophrenic patients.

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Cubo, Teresa, Francisco Romero, Jose M. Vinardell y Jose E. Ruiz-Sainz. "Expression of the Rhizobium leguminosarum biovar phaseoli melA Gene in Other Rhizobia Does Not Require the Presence of the nifA Gene". Functional Plant Biology 24, n.º 2 (1997): 195. http://dx.doi.org/10.1071/pp96076.

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Many different Rhizobium strains produce melanin (Mel+) when grown on solid media supplemented with L-tyrosine. The composition of the media and the culture conditions are of great importance for pigment production. Previous reports showed that some Rhizobium leguminosarum biovar phaseoli strains that produce the pigment in complete solid media (TY) failed to produce the pigment in minimal media (SY) supplemented with L-tyrosine or in TY liquid media. In this paper we have investigated different R. fredii, R. meliloti, R. etli and R. leguminosarum bv. trifolii and phaseoli strains (all of them Mel+ in solid media) for their ability to produce the pigment in liquid media. All Rhizobium species tested, except Rhizobium etli, were Mel+ in liquid media and in all cases the pigment yielded maximum absorption peaks at 280 and 315 nm. Melanin production by other bacteria (such as Vibrio, Streptomyces or Azospirillum) is enhanced by the presence of amino acids other that tyrosine. In this paper we show that the addition of L-methionine, which is not a precursor of rhizobial melanins, stimulated pigment production by Rhizobium cultures supplemented with L-tyrosine. The role of melanin production by Rhizobium strains is unclear. One hypothesis is that the Rhizobium tyrosinase, a bifunctional copper-containing enzyme that is essential for melanin biosynthesis, could detoxify polyphenolic compounds which might accumulate in senescing nodules. We show here that R. etli and R. fredii bacteroids produced melanin, which supports the idea that bacteroids contain the enzyme tyrosinase. Previous reports showed that, in R. leguminosarum bv. phaseoli strain 8002, the expression of the tyrosinase gene (melA) is dependent on the presence of nifA, a regulatory gene that is located in the symbiotic plasmid. However, transfer of R. leguminosarum bv. phaseoli melA gene to pSym-cured derivatives of R. leguminosarum bv. trifolii and viciae, R. fredii and Rhizobium sp. (Hedysarum) produced Mel+ transconjugants. DNA-hybridisation experiments showed that the pSym-cured strains did not contain any copy of nifA. Therefore, in contrast to the results reported on R. leguminosarum bv. phaseoli strain 8002, the expression of the melA gene in other rhizobia is not nifA-dependent. Key words: Rhizobium, melanin.

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Wang, Shuai, Iker Agirrezabal-Telleria, Aditya Bhan, Dante Simonetti, Kazuhiro Takanabe y Enrique Iglesia. "Catalytic routes to fuels from C1 and oxygenate molecules". Faraday Discussions 197 (2017): 9–39. http://dx.doi.org/10.1039/c7fd00018a.

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This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C₁ and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C–C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C–C bond from C₁ molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O₂ and H₂O molecules. These gaseous OH species act as strong H-abstractors and activate C–H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C–H bonds in larger alkane products than in CH₄ reactants. Anhydrous carbonylation of dimethyl ether forms a single C–C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni²⁺ active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C–C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C₁ homologation selectively forms C₄ and C₇ chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C–C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid–base site pairs on TiO₂ and ZrO₂ catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid–base pairs. Ketonization is mediated instead by C–C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H₂ and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal–alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C–C bonds as skeletal isomers unattainable by other routes. Their respective transition states are of similar size, leading to selectivities that cannot sense the presence of a confining host. Prins condensation reactions benefit from weaker acid sites because their transition states are less charged than those for oligomerization and consequently less sensitive to conjugate anions that become less stable as acids weaken.

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17

Flores-Ramírez, Nelly, Erandini Guzmán-Mejía, Salomón R. Vásquez-García, Lada Domratcheva-Lvova, Leandro Garcia-Gonzalez y Julián Hernández-Torres. "Development of an ecological varnish from the resin of pine". MRS Advances 3, n.º 63 (2018): 3827–32. http://dx.doi.org/10.1557/adv.2018.599.

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ABSTRACTRosin resin is constituted by rosin acids, in particular, abietic acid, which is an inexpensive substance. This paper concerns the study of the molecular interactions between a bifunctional monomer of abietic acid with isocyanate to form polyurethane. Polyurethane is a varnish that can be applied to any timber surface protecting it from chemical and environmental factors. Furthermore, the polar groups (OH´s) of the diol have a direction along the molecular axis thus, increasing their intermolecular interactions with the isocyanate groups. The varnish named as (PAR), was synthesized in the laboratory and applied to a timber surface whereby its functionality was evaluated. Morphological and spectroscopic studies were carried out on the diol obtained and the polyurethane. Likewise, we behaved several of physical and chemical analyses of vanish. The comparative SEM showed a homogeneous phase on the PAR surface and FTIR between the diphenylmethane, 4-4, diisocyanate (MDI) and the varnish from hydroxylated rosin resin (HAA) showed that the reaction was carried out in its entirety, exhausting the limiting reagent (MDI). The obtained varnish which was labelled as PAR has very suitable characteristics for indoor use. It has a transparent and bright appearance, a solids percentage of 44-45%, a drying time for application between layers and layers of 15-20 minutes.

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Antonio, Mark R., J. Malinsky y L. Soderholm. "Synthesis and Properties of Lanthanide-Exchanged Preyssler's Heteropolyanions". MRS Proceedings 368 (1994). http://dx.doi.org/10.1557/proc-368-223.

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ABSTRACTNa+ in the Preyssler heteropolytungstate anion [NaP5W30O110]14− can be exchanged for a trivalent lanthanide ion. The potential significance of this new class of lanthanide heteropolyanions relates to their applications in catalysis science. This view follows from the fact that Keggin heteropolyanions and their free acids are used as heterogeneous solid catalysts and homogeneous solution catalysts. We describe synthetic conditions that lead to the incorporation of Ce3+ and Pr3+ within the Preyssler anion, and the coprecipitation of Ce3+ and the Preyssler anion. Initial studies indicate that the latter, coprecipitated, material deserves study for bifunctional catalytic activity.

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Zinchenko, V. F. y V. V. Menchuk. "ELECTRONEGATIVITY AND STRENGTH OF ACIDS AND BASES IN AQUEOUS SOLUTIONS". Odesa National University Herald. Chemistry 27, n.º 1(81) (5 de junio de 2022). http://dx.doi.org/10.18524/2304-0947.2022.1(81).255831.

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Сoncepts of acidity-basicity for systems of different types are considered. The application of the parameter of effective electronegativity for estimating the acidity is proposed, the value of which is calculated from the thermochemical data of acid-base reactions in the condensed state (liquid, solid). The basis is the value of electronegativity of SO3, which should be equal to 3.00. Its values are in the range of 2.0 ÷ 3.1 for acid oxides and 0.3 ÷ 1.6 for oxides of basic nature. A significant group consists of oxides of bifunctional nature (amphoteric oxides) whose electronegativity values are 1.7 ÷ 1.9. A characteristic feature of amphoteric oxides is the manifestation of two values of electronegativity, corresponding to acid and basic functions. It is shown that the behavior of water as a characteristic amphoteric oxide is similar. Some predominance of acidic properties of water over the basic ones is shown and the possible reason for such behavior is discussed. To take into account this phenomenon, a method of converting the electronegativity of water to its value for the oxide partner during hydration is proposed. The values of electronegativity of hydroxides of elements (acidic, basic and amphoteric) were carried out by averaging them for components on the principle of additivity, the correctness of which is confirmed by direct calculations for individual hydroxides. It is shown that in the formation of hydroxides of elements there is a convergence between the values of electronegativities of acidic and basic oxides, ie the reduction of the former and the growth of the latter. Instead, in the case of amphoteric hydroxides, no noticeable changes in electronegativities compared to the original oxides occur. There is a qualitative correlation between the electronegativity of the hydroxides of the elements and the acidity (basicity) constants of their aqueous solutions, which is a reflection of their strength. This allows predicting the strength of acids and bases based on the electronegativity of hydroxides.

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Artículos de revistas sobre el tema "Bifunctional solid acids"

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