Rosa M. Martín-Aranda

Study of oxygen-containing groups in a series of graphite oxides: Physical and chemical characterization

Some graphite oxides with different degrees of oxidation have been prepared by using a modified Staudenmaier method. The oxidation process has been studied by using different techniques: elementary analysis, gas adsorption, X-ray diffraction, FT-IR, XPS and 13C-NMR. The influence of the oxidation degree on the appearance and evolution of new chemical groups in the samples has been analyzed. The oxidation process produces a development of porosity, especially microporosity. FT-IR, XPS and 13C-NMR are complementary techniques, which confirm the existence of hydroxyl, carbonyl, ether, epoxy, and peroxy groups in the more oxidized samples. These surface groups may play an important role in the acid-base bifunctional catalysis.

Novel Basic Mesoporous Catalysts for the Friedländer Reaction from 2‐Aminoaryl Ketones: Quinolin‐2(1H)‐ones versus Quinolines

The quinoline ring is present in a number of natural and synthetic products often exhibiting interesting pharmacological activities or physical properties. Different synthetic approaches for the preparation of quinolines have been reported; the Friedl nder reaction (FR) being one of the simplest and most efficient methods. FR is a baseor acid-catalyzed condensation of an aromatic 2-amino-substituted carbonyl compound (aldehyde or ketone) with a carbonyl derivative containing a reactive a-methylene group followed by cyclodehydration (Scheme 1). Generally, the annulation takes place

Knoevenagel condensation reaction in a membrane microreactor

A multi-channel membrane microreactor was fabricated and tested for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate using Cs-exchanged faujasite NaX as the catalyst; the membrane microreactor achieves supra-eqiulibrium conversion at higher product purity.

Characterization of basic sites of alkaline carbons by Knoevenagel condensation

The characterization of the carbon surface basicity by condensation of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate, diethyl malonate and ethyl bromoacetate as test reactions were studied with a series of lithium, sodium, potassium and cesium exchanged activated carbon (Norit RX 1 Extra). The importance of active sites and the measurement of the surface area in determining the reactivity of the carbons is emphasized. The activity of the carbons increases when the ionic radius of the alkali cation increases; the activity increases in the order Li < Na < K < Cs. Under reaction conditions, it was found that most of the basic sites in alkaline carbons have 10.7 ≤pK a ≤ 13.3 and there are a few sites in the range of 13.3 ≤ pKa ≤ 16.5. The treated activated carbon that had not been subjected to exchange by alkali metal cations exhibited mostly basic sites able to abstract protons with 9 ≤ pKa ≤ 10.7.

Ultrasound enhanced reactions involving activated carbons as catalysts: synthesis of α,β-unsaturated nitriles

Abstract α,β-Unsaturated nitriles have been synthesized by sonochemical activated reactions of carbonylic compounds with malononitrile using two basic carbons (Na+– and Cs+–Norit) as catalysts. The catalysts were characterized by thermal analysis, X-ray photoelectron spectroscopy and nitrogen adsorption isotherms. Under the experimental conditions, unsaturated nitriles can be prepared with a high activity and selectivity. The role of alkaline promoters (Na+ and Cs+) in the carbon has been studied. It is evidenced that the greater the basicity and the amount of catalyst, the higher is the conversion. For comparison, the condensation reaction has also been carried out in a batch reaction system and the influence of the temperature in both (batch and ultrasonic) systems has been studied.

Sonocatalysis and Basic Clays. Michael Addition Between Imidazole and Ethyl Acrylate

Under ultrasound activation, imidazole was condensed with ethyl acrylate using two basic clays (Li+ and Cs+ montmorillonites). The clay catalysts were characterized by chemical analyses, nitrogen adsorption isotherms, and X-ray diffraction. Under sonochemical conditions N-substituted imidazole can be obtained with a high activity and selectivity. The conversion increases with the basicity of the clays and the ultrasonic exposition time. The yield presents a maximum for 0.1 g of Cs+ montmorillonite after 60 min of sonication.

Application of basic clays in microwave activated Michael additions: Preparation of N-substituted imidazoles

Abstract Imidazole (C 3 H 4 N 2 ) was condensed with ethyl acrylate (C 5 H 8 O 2 ) using two basic clays (Li + and Cs + montmorillonites) as catalysts in a microwave oven. The catalysts were characterized by chemical analyses, nitrogen adsorption isotherms and X-ray diffraction. Under these experimental conditions N -substituted heterocycles can be obtained with a high activity and selectivity. The role of alkali promoters (Li + and Cs + ) in the montmorillonite for the Michael addition was studied. It was evidenced that the greater the basicity and the irradiation time and power of irradiation were, the higher were the conversion. The yield of the N -substituted imidazole presents a maximum for 0.1 g of Cs-montmorillonite at 850 W in only 5 min of irradiation.

Zeolite membrane microreactors and their performance

Knoevenagel condensation reactions between benzaldehyde and ethyl cyanoacetate, ethyl acetoacetate and diethyl malonate were carried out in the microreactors. Membrane microreactor consistently performed better than the microreactor. The water produced by the condensation reaction was selectively pervaporated through a zeolite micromembrane. The best reaction yield was obtained by locating the CsNaX catalyst immediately adjacent to the membrane.

Alkaline carbons as base catalysts: Alkylation of imidazole with alkyl halides

Abstract Anionic alkylation of imidazole with alkyl halides to produce intermediates in the synthesis of pharmaceutically important antiviral products, such as famciclovir and acyclovir, have been carried out using alkaline carbons as base catalysts. Previously to the alkylation of imidazole, the condensation of benzaldehyde with malonic esters has been used as test reaction of basicity on a series of lithium, sodium, potassium and cesium exchanged Norit RX 1 Extra activated carbon. The importance of active sites and the measurement of surface basicity have been emphasized. Under reaction conditions, it has been found that most of the basic sites in alkaline carbons have 10.7⩽p K a ⩽13.3, but there is a considerable number of sites able to abstract protons of 13.3 ⩽p K a ⩽16.5. Norit RX 1 Extra which was not subject to alkaline exchange retains most of its basic sites capable of abstracting protons of 9 ⩽p K a ⩽10.7. Taking into account that the p K a . of the NH group of imidazole is 14.5, the alkaline carbons present the required basic strength to catalyze the alkylation of this N -heterocycle with alkyl halides.

Acid-activated carbon materials: Cheaper alternative catalysts for the synthesis of substituted quinolines

We describe the first examples of Friedländer reactions efficiently catalyzed by carbon materials. We report herein a series of acidic activated carbon materials, which can be considered as an environmentally friendly, cheaper alternative to the traditional acidic mesoporous silicates or even zeolites for the synthesis of quinolines/quinolones. Textural parameters of the acidic activated carbon materials together with their acidic properties are important factors that affect the reaction selectivity. Some mechanistic details have been addressed by computational calculations.