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1.
ChemSusChem ; 13(4): 707-714, 2020 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-31912979

RESUMO

Biomass-derived surfactants with very good surface tension and critical micellar concentration properties were obtained by conversion of methyl levulinate into methyl 4-alkoxypentanoates through reductive etherification with aliphatic alcohols. Among different bifunctional acid/metal catalysts best results were obtained with Pd on carbon bearing acid sites. The reaction occurred through the formation of an enol ether intermediate followed by hydrogenation. Pd in high-density planes was the active hydrogenation species, and an optimum crystal size was found to be approximately 10 nm. The reductive etherification with aliphatic alcohols was extended to other aliphatic and cyclic ketones and aldehydes obtained from biomass, and excellent results were obtained on supported Pd catalysts with the reaction route and experimental conditions described in this work.

2.
ChemSusChem ; 13(7): 1864-1875, 2020 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-31944622

RESUMO

Biobased plasticizers, as substitutes for phthalates, have been synthesized from 5-hydroxymethylfurfural (HMF) and carboxylic acids (or esters) through a chemoenzymatic cascade process that involves as its first step the reduction of 5-hydroxymethylfurfural into 2,5-bis(hydroxymethyl)furan (BHMF), followed by the esterification of BHMF with carboxylic acids (or esters) by using a supported lipase (Novozym 435). The reduction of HMF into BHMF is performed by using monodisperse metallic Co nanoparticles with a thin carbon shell (Co@C) with high activity and selectivity. After optimization of reaction conditions (temperature, hydrogen pressure, and solvent), it is possible to achieve 97 % conversion of HMF with 99 % selectivity to BHMF after 2 h reaction time. The reduction of HMF and esterification of BHMF using carboxylic acids or vinyl esters as acyl donors by lipase are optimized separately in batch and in fixed-bed continuous reactors. The coupling of two flow reactors (for reduction and subsequent esterification) working under optimized reaction conditions affords the diesters of BHMF in roughly 90 % yield with no loss of activity during 60 h of operation.

3.
J Am Chem Soc ; 141(49): 19304-19311, 2019 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-31774282

RESUMO

Ruthenium nanoparticles with a core-shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide have been synthesized by a mild and easy hydrothermal treatment. The dual structure and composition of the nanoparticles have been determined by synchrotron X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) analysis, and transmission electron microscopy (TEM) imaging. According to depth profile synchrotron XPS and X-ray diffraction (XRD) analysis, metallic ruthenium species predominate in the inner layers of the material, ruthenium carbide species being located on the upper surface layers. The ruthenium carbon catalysts presented herein are able to activate both CO2 and H2, exhibiting exceptional high activity for CO2 hydrogenation at low temperatures (160-200 °C) with 100% selectivity to methane, surpassing by far the most active Ru catalysts reported up to now. On the basis of catalytic studies and isotopic 13CO/12CO2/H2 experiments, the active sites responsible for this unprecedented activity can be associated with surface ruthenium carbide (RuC) species, which enable CO2 activation and transformation to methane via a direct CO2 hydrogenation mechanism. Both the high activity and the absence of CO in the gas effluent confer relevance to these catalysts for the Sabatier reaction, a chemical process with renewed interest for storing surplus renewable energy in the form of methane.

4.
ChemSusChem ; 11(17): 2870-2880, 2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-29975011

RESUMO

A new type of biomass-derived non-ionic surfactants has been obtained by reacting hydroxymethylfurfural (HMF), glycerol, and fatty alcohols. For instance, 5-(octyloxymethyl)furfural glyceryl acetal can be obtained in a one-pot process by etherification of HMF with fatty alcohols followed by acetalization with glycerol. For a successful solid catalyst, acidity and polarity have to be optimized to improve conversion, selectivity, and catalyst deactivation owing to the different adsorption characteristics of the reactant molecules. Accordingly, Beta zeolite with a high Si/Al ratio and practically free of connectivity defects showed good results when dealing with these biomass derivatives, which include a highly polar reactant such as glycerol. The scope of the reaction is good and a variety of new stable surfactant molecules can be obtained that present hydrophilic-lipophilic balance (HLB ) values in the range 4.9 to 6.6, which are of interest for water in oil emulsions.

5.
ChemSusChem ; 10(1): 119-128, 2017 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-27860418

RESUMO

N-substituted 5-methyl-2-pyrrolidones were prepared in a one-pot process starting from ethyl levulinate and nitro compounds in the presence of a nanosized Pt-based catalyst. Pt supported on TiO2 nanotubes (Pt/TiO2 -NT) catalyzed the synthesis of N-substituted 5-methyl-2-pyrrolidones through a cascade process involving the reduction of nitro compounds, formation of the intermediary imine, hydrogenation, and subsequent cyclization. A bifunctional metal-acid system was a suitable catalyst for the process. Pt supported on TiO2 showed lower catalytic activity than Pt/TiO2 -NT owing to the strong adsorption of nitro compounds during the first reaction step that poisoned the acidic sites and strongly decreased the rate of amination and cyclization. However, Pt/TiO2 -NT with milder acid sites was less affected by the adsorption of nitro compounds and the full cascade process could proceed. The results indicate that the prepared Pt/TiO2 -NT is a chemoselective and reusable catalyst that can be applied to the synthesis of a variety of N-substituted 5-methyl-2-pyrrolidones starting from nitro compounds with excellent yields in absence of an additional organic solvent under mild reaction conditions.


Assuntos
Ácidos Levulínicos/química , Nitrocompostos/química , Pirrolidinonas/química , Pirrolidinonas/síntese química , Adsorção , Catálise , Técnicas de Química Sintética , Hidrogenação , Nanotubos/química , Platina/química , Especificidade por Substrato , Propriedades de Superfície , Titânio/química
6.
ChemSusChem ; 9(24): 3492-3502, 2016 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-27882684

RESUMO

Alkyl glucosides surfactants are synthesized by a cascade process that involves the methanolysis of cellulose into methyl glucosides followed by the transacetalization with n-octanol. The first step was performed using methanol as solvent and acid catalysts (such as, inorganic acids, heteropolyacids, ionexchange resins, or modified carbon materials). Subsequently, long-chain alkyl glucosides are obtained in the second step by transacetalization, which involves the reaction of methyl glucosides with a fatty alcohol using the same acid catalyst. The overall process was performed under mild conditions. Amorphous sulfonated carbon catalyst achieved the best results for the complete conversion of cellulose in methanol at 200 °C with methyl α,ß-glucopyranosides yields higher than 80 %. Moreover, this material containing -SO3 H groups is ideal to perform the second step to obtain octyl and decyl glucosides in yields higher than 73 % at 120 °C. In addition, the sulfonated carbon catalyst (C-SO3 H) can be reused with only a slightly decrease of its activity after four consecutive cycles.


Assuntos
Celulose/química , Tensoativos/química , Catálise , Glicosídeos/química , Hidrólise , Metanol/química , Reciclagem , Enxofre/química , Temperatura
7.
ChemSusChem ; 8(19): 3270-82, 2015 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-26333197

RESUMO

The dehydration of aldoximes to the corresponding nitriles can be performed with excellent activity and selectivity by using iron trimesate as a homogeneous catalyst. Iron trimesate has been heterogenized by synthesizing metal-organic frameworks (MOFs) from iron trimesate, that is, Fe(BTC), and MIL-100 (Fe). These materials were active and selective aldoxime dehydration catalysts, and postsynthesis-treated MIL-100 (Fe) produced the desired nitriles with 100 % conversion and selectivities >90 % under mild reaction conditions and in short reaction times. X-ray photoelectron spectroscopy showed the presence of different Fe species in the catalyst, and in situ IR spectroscopy combined with catalytic results indicates that the catalytic activity is associated with Fe framework species. The postsynthesis-treated MIL-100 (Fe)-NH4 F can be recycled several times and has an excellent reaction scope, which gives better catalytic results than other solid acid or base catalysts.


Assuntos
Ferro/química , Nitrilos/química , Compostos Organometálicos/química , Adsorção , Catálise , Ácidos de Lewis/química , Compostos Organometálicos/síntese química , Oximas/química , Água/química
8.
ChemSusChem ; 7(4): 1177-85, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-24616280

RESUMO

1,5-Benzothiazepines derivatives were obtained first by starting from 1,3-diphenylpropenone derivatives (chalcones) and 2-aminothiophenol by using aluminosilicate solid catalysts. However, diffusional limitations and the strong adsorption of products on the catalyst are deleterious for catalyst activity and life. Then a structured amorphous mesoporous catalyst with large pores and mild acidity that works at higher temperatures allowed us to obtain high conversions (99 %) and selectivities (98 %) of the desired product. A one-pot synthesis of 1,5-benzothiazepines that starts from benzaldehyde, acetophenone, and 2-aminothiophenol with 95 % yield was performed by combining optimized solid base and acid catalysts in batch mode as well as in a continuous-flow reactor system. Much better conversion and selectivity as well as process intensification has been achieved with the structured mesoporous materials by avoiding intermediate and final neutralization and purification steps required in the synthesis reported previously that uses homogeneous catalysts.


Assuntos
Tiazepinas/química , Tiazepinas/síntese química , Adsorção , Catálise , Técnicas de Química Sintética , Difusão , Concentração de Íons de Hidrogênio
9.
ChemSusChem ; 7(1): 210-20, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24106062

RESUMO

A new class of biodegradable anionic surfactants with structures based on 5-alkoxymethylfuroate was prepared starting from 5-hydroxymethylfurfural (HMF), through a one-pot-two-steps process which involves the selective etherification of HMF with fatty alcohols using heterogeneous solid acid, followed by a highly selective oxidation of the formyl group with a gold catalyst. The etherification step was optimized using aluminosilicates as acid catalysts with different pore topologies (H-Beta, HY, Mordenite, ZSM-5, ITQ-2, and MCM-41), different active sites (Bronsted or Lewis) and different adsorption properties. It was shown that highly hydrophobic defect-free H-Beta zeolites with Si/Al ratios higher than 25 are excellent acid catalysts to perform the selective etherification of HMF with fatty alcohols, avoiding the competitive self-etherification of HMF. Moreover, the 5-alkoxymethylfurfural derivatives obtained can be selectively oxidized to the corresponding furoic salts in excellent yield using Au/CeO2 as catalyst and air as oxidant, at moderated temperatures. Both H-Beta zeolite and Au/CeO2 could be reused several times without loss of activity.


Assuntos
Silicatos de Alumínio/química , Éteres/química , Furaldeído/análogos & derivados , Dióxido de Silício/química , Tensoativos/química , Biomassa , Catálise , Cério/química , Furaldeído/química , Ouro/química
10.
ChemSusChem ; 6(7): 1224-34, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23754795

RESUMO

Glycerol carbonate esters (GCEs), which are valuable biomass-derivative compounds, have been prepared through the direct esterification of glycerol carbonate and long organic acids with different chain lengths, in the absence of solvent, and with heterogeneous catalysts, including acidic-organic resins, zeolites, and hybrid organic-inorganic acids. The best results, in terms of activity and selectivity towards GCEs, were obtained using a Nafion-silica composite. A full reaction scheme has been established, and it has been demonstrated that an undesired competing reaction results in the generation of glycerol and esters derived from a secondary hydrolysis of the endocyclic ester group, which is attributed to water formed during the esterification reaction. The influence of temperature, substrate ratio, catalyst-to-substrate ratio, and the use of solvent has been studied and, under optimized reaction conditions and with the adequate catalyst, it was possible to achieve 95% selectivity for the desired product at 98% conversion. It was demonstrated that the reaction rate decreased as the number of carbon atoms in the linear alkyl chain of the carboxylic acid increased for both p-toluenesulfonic acid and Nafion-silica nanocomposite (Nafion SAC-13) catalysts. After fitting the experimental data to a mechanistically based kinetic model, the reaction kinetic parameters for Nafion SAC-13 catalysis were determined and compared for reactions involving different carboxylic acids. A kinetic study showed that the reduced reactivity of carboxylic acids with increasing chain lengths could be explained by inductive as well as steric effects.


Assuntos
Carbonatos/química , Polímeros de Fluorcarboneto/química , Glicerol/química , Dióxido de Silício/química , Ácidos Carboxílicos/química , Catálise , Esterificação , Ésteres , Cinética , Água/química
11.
ChemSusChem ; 6(1): 123-31, 2013 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-23303623

RESUMO

The selective acetalization of 5-hydroxymethylfurfural (HMF) with long-chain alkyl alcohols has been performed to obtain precursors of molecules with surfactant properties. If direct acetalization of HMF with n-octanol is performed in the presence of strong acids (homogeneous and heterogeneous catalysts), an increase in etherification versus acetalization occurs. Beta zeolite catalyzes both reactions. However, if the acidity of a zeolite (Beta) was controlled by partial exchange of H(+) with Na(+), the dioctyl acetal of HMF can be achieved in 95% yield by transacetalization. It is possible to achieve a high yield in a very short reaction time through a two-step one-pot process, which includes the synthesis of the dimethyl acetal of HMF followed by transacetalization with n-octanol. The one-pot process could be extended to other alcohols that contain 6-12 carbon atoms to afford 87-98% yield of the corresponding dialkyl acetal with a selectivity higher than 96%. The optimized catalyst with an adequate Na content (1.5NaBeta) could be recycled without loss of activity or selectivity.


Assuntos
1-Octanol/química , Furaldeído/análogos & derivados , Tensoativos/química , Zeolitas/química , Biomassa , Catálise , Furaldeído/química , Dióxido de Silício/química , Sódio/química
13.
Chemistry ; 16(4): 1221-31, 2010 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-20013773

RESUMO

Bifunctional acid-base ionic liquid organocatalysts with different distances between the two sites have been synthesised, and their activity for the Knoevenagel condensation has been tested. As has been found to be the case with enzymes, the distance between the acidic and basic sites determines the activity of the bifunctional organocatalyst, and at the optimal distance the reaction rate increases by two orders of magnitude with respect to the purely acidic or basic counterpart organocatalysts. The experimental results have been rationalised through the study of the reaction mechanism of the Knoevenagel condensation between malononitrile and benzaldehyde by means of DFT calculations. It has been found that it consists of two consecutive steps. First, deprotonation of malononitrile on the basic site to obtain a methylene carbanion intermediate takes place, and second, co-adsorption and activation of benzaldehyde on the acid centre of this intermediate followed by the C-C bond-formation reaction. The calculations and the kinetic study indicate that there is an inversion of the rate-controlling step when the distance between the acidic and the basic sites is modified, with a direct implication on the reaction rate.

14.
Chemistry ; 15(35): 8834-41, 2009 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-19621393

RESUMO

Substituted 1,5-benzodiazepines are selectively synthesized in one pot from substituted nitroaromatics and ketones. The reaction is performed in the presence of hydrogen and in the absence of solvent by using a bifunctional solid catalyst with a chemoselective hydrogenation functional group capable of reducing the nitro group to a diamino group and an acid functional group, which catalyzes the cyclocondensation of the amino group with the ketone.


Assuntos
Benzodiazepinas/síntese química , Nitrocompostos/química , Benzodiazepinas/química , Catálise , Estrutura Molecular , Oxirredução , Estereoisomerismo
15.
ChemSusChem ; 2(6): 500-6, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19396883

RESUMO

Catscade reactions: Heterogeneous catalysis can enable sustainability by carrying out multistep reactions in one step. It is shown that single- and multisite solid catalysts can be designed to carry out cascade reactions for the synthesis of fine chemicals.


Assuntos
Catálise , Fenômenos de Química Orgânica , Química Verde/métodos , Compostos Orgânicos/síntese química
16.
Org Lett ; 10(20): 4409-12, 2008 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-18808126

RESUMO

Photolysis of the title dyads under aerobic conditions leads to a 2-deoxyribonolactone derivative. Laser flash photolysis reveals that the process occurs from the short-lived benzophenone-like triplet excited state. A mechanism involving intramolecular electron transfer with the purine bases (adenine, guanine, or 8-oxoadenine) as donors is proposed.


Assuntos
Benzofenonas/química , Cetonas/química , Purinas/química , Açúcares Ácidos/síntese química , Radicais Livres/química , Estrutura Molecular , Fotoquímica , Espectrofotometria , Açúcares Ácidos/química
17.
J Phys Chem B ; 111(28): 8277-82, 2007 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-17590040

RESUMO

The aim of the present work was to find a ketoprofen (KP) equivalent suitable for time-resolved studies on the interactions of its KP-like triplet state with biomolecules or their simple building blocks, under physiologically relevant conditions. Such a compound should fulfill the following requirements: (i) it should be soluble in aqueous media; (ii) its triplet lifetime should be longer than that of KP, ideally in the microsecond range; and (iii) its photodecarboxylation should be slow enough to avoid interference in the time-resolved studies associated with formation of photoproducts. Here, the glycine derivative of ketoprofen (KPGly) has been found to fulfill all the above requirements. In a first stage, the attention has been focused on the photophysical and photochemical properties of KPGly, and then on its excited-state interactions with key amino acids and nucleosides. In acetonitrile, the typical benzophenone-like triplet-triplet absorption (3KPGly) with lambda(max) at 520 nm and a lifetime of 5.3 micros was observed. This value is very close to that of 3KP (5.6 micros) obtained under the same conditions. In methanol, the 3KPGly features were also close to those of 3KP with detection of a short-lived triplet state that evolves to give a ketyl radical. By contrast with the behavior of KP, in deaerated aqueous solutions at pH = 7.4, the transient detected in the case of KPGly displayed two bands at lambda(max) at 330 and 520 nm, very similar to those observed in acetonitrile solution but with a lifetime of 7.5 micros at 520 nm. Hence, it was assigned to the KPGly triplet. In the case of KP, efficient decarboxylation occurs in the subnanosecond time scale, via intramolecular electron transfer. This process gives rise to a detectable carbanion intermediate (lifetime approximately 250 ns) and prevents detection of the shorter-lived 3KP signal. In a second stage, the attention has been focused on the excited-state interactions between 3KPGly and amino acids or nucleosides; for this purpose, 2'-deoxyguanosine (dGuo), thymidine (Thd), tryptophan (Trp), and tyrosine (Tyr) have been chosen as photosensitization targets. In general, efficient quenching (rate constant kq > 109 M(-1) x s(-1)) was observed; it was attributed for dGuo, Tyr, and Trp to a photochemical reaction involving initial electron transfer from the biological target to 3KPGly, followed by proton transfer from the amino acid or the nucleoside radical cation to KPGly-*. As a matter of fact, ketyl radical together with guanosinyl, tyrosinyl, or tryptophanyl radicals were detected; this supports the proposed mechanism. The results with Thd were somewhat different, as the efficient 3KPGly quenching was ascribed to oxetane formation by a Paterno Büchi photocycloaddition.


Assuntos
Aminoácidos/química , Anti-Inflamatórios não Esteroides/química , Cetoprofeno/análogos & derivados , Cetoprofeno/química , Nucleosídeos/química , Transferência de Energia , Glicina/química , Lasers , Fotólise , Soluções , Fatores de Tempo
18.
Chemistry ; 12(2): 553-61, 2005 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-16173098

RESUMO

Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Büchi cycloaddition to give oxetanes 3-6; however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.


Assuntos
Benzofenonas/química , Timidina/análogos & derivados , Timina/química , Benzofenonas/efeitos da radiação , Éteres Cíclicos/síntese química , Éteres Cíclicos/química , Fotoquímica , Timidina/química , Timidina/efeitos da radiação
19.
Chem Commun (Camb) ; (20): 2572-4, 2005 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-15900330

RESUMO

Using two diastereomeric dyads containing naphthalene and thymine units, significant chiral discrimination has been found in the photophysical processes involving the naphthalene excited states: singlet deactivation by hydrogen bonding molecules, singlet-singlet energy transfer from thymine and triplet decay.


Assuntos
Naftalenos/química , Termodinâmica , Timina/química , Ligação de Hidrogênio , Conformação Molecular , Fotoquímica , Estereoisomerismo
20.
Chemphyschem ; 5(11): 1704-9, 2004 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-15580930

RESUMO

Two thymidine-derived nucleosides 1 and 2 were prepared by attaching a chiral naphthalene to the positions 5' and 3' of the sugar. The resulting dyads, which contain key substructures present in drugs and nucleic acids, exhibit different spatial arrangements (transoid or cisoid) of the fluorophore relative to the thymine unit. Emission measurements on these compounds in the presence of ROH molecules revealed a remarkable intramolecular prescence quenching for dyad 1. The obtained results are consistent with quenching of the singlet excited state of 1 by hydrogen-bond donor solvents. Thus, a physical deactivation process (vibronically induced internal conversion) would be the pathway responsible for the accelerated decay of 1*, favorably competing with fluorescence and intersystem crossing to the triplet. This effect appears to be strongly dependent on the relative spatial arrangement between the naphthalene and thymine units, together with the hydrogen-bonding ability of the employed ROH.


Assuntos
Naftalenos/química , Timina/química , Cristalografia por Raios X , Lasers , Modelos Moleculares , Conformação Molecular , Fotólise , Espectrometria de Fluorescência , Espectrofotometria Ultravioleta
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