Jaime Primo

Zeolites as base catalysts: Condensation of aldehydes with derivatives of malonic esters

Abstract The condensations of benzaldehyde with ethyl cyanoacetate, ethyl malonate, and ethyl acetoacetate were carried out with high activity and selectivity on lithium-, sodium-, potassium- and caesium-exchanged X and Y zeolites. The activity of the zeolites increased with decrease in the framework silicon-to-aluminium ratio of the zeolite and increase in the radius of the counter cation. Under reaction conditions, it was found that most of the basic sites in alkaline X and Y zeolites have pKb⩽10.3, and sites with pKb⩽13 were present only in the CsX sample. This catalyst is more active than pyridine, and less active but more selective than piperidine. It is shown that, on these catalysts, in the condensation reactions studied, the controlling step is not proton abstraction but attack of the carbonyl group by the carbanion.

Cu2+-phthalocyanine and Co2+-perfluorophthalocyanine incorporated inside Y faujasite and mesoporous MCM-41 as heterogeneous catalysts for the oxidation of cyclohexane

Abstract A series of Cu 2+ -phthalocyanine and Co 2+ -perfluorophthalocyanine has been prepared inside the pores of MCM-41 (MPcMCM-41) by synthesis from o -dicyanobenzene. The complexes were characterized by comparison of the UV–Vis diffuse reflectance and IR spectra with that of the same unsupported complexes. Transition metal ion exchange levels higher than 40% were found necessary for the success of the synthesis. o -Cyanobenzoic acid and phthalic anhydride were isolated as byproducts. Differential scanning calorimetry indicates that the complexes are more stabilized inside MCM-41 than within the supercages of Y faujasite. This has been interpreted as a reflection of the different conformations (planar for MCM-41 and distorted for Y faujasite) depending on the pore size of the host. The catalytic performance of novel MPcMCM-41 for cyclohexane oxidation was compared with that of the same unsupported complexes or when encaged within Y faujasite. tert -Butyl hydroperoxide was found as a more convenient oxidizing reagent than hydrogen peroxide. No leaching of the MPc or uncomplexed metal ions was observed. It was found that CoF 16 PcMCM-41 was more active and selective than CoF 16 PcY or unsupported CoF 16 Pc. However, in the case of the CuPc complex, the highest activity and selectivity was achieved using CuPcY. Our work shows the influence that the void dimensions of the porous host can play in the performance of metallophthalocyanines as oxidation catalysts.

Acid zeolites as catalysts in organic reactions. tert-Butylation of anthracene, naphthalene and thianthrene

Liquid phase tert-butylation of anthracene, naphthalene and thianthrene to afford 2-tert-butyl plus 2,6- and 2,7-di tert-butyl derivatives were carried out at atmospheric pressure and moderate temperatures (below 100°C) in the presence of a series of large pore zeolites and mesoporous aluminosilicates including HY-100 (Si/Al 2.6), HY-D1 (Si/Al 2.75), HY-D2 (Si/Al 15), Hβ, HMor and MCM-41. The activity increases from MCM-41 and Mor to β and Y zeolites, the latter being the most active catalysts. In addition, HY zeolites are much more efficient as catalysts than p-toluenesulfonic acid under the same reaction conditions. As alkylating reagent tert-butyl alcohol was employed in isooctane or carbon tetrachloride. It was found that isooctane itself is a powerful and convenient reagent for the tert-butylation. Mechanistic studies using radical scavengers indicates that in the isooctane alkylation tert-butyl cation is the sole intermediate involved. In the case of thianthrene, the concomitant formation of the thianthrenium radical cation during the alkylation reaction has been observed.

Gentisic Acid As a Pathogen-Inducible Signal, Additional to Salicylic Acid for Activation of Plant Defenses in Tomato

Citrus exocortis viroid (CEVd) and tomato mosaic virus (ToMV), which produce a systemic non-necrotizing infection in tomato (Lycopersicon esculentum cv. Rutgers), strongly induced the accumulation of a phenolic compound that we have characterized as 2,5-dihydroxybenzoic acid (gentisic acid, GA) by nuclear magnetic resonance, following purification by high-performance liquid chromatography. Levels of free and total GA increased more than 150-fold in response to CEVd and ToMV infections. Unlike these non-necrotizing infections, the necrotizing reaction elicited by Pseudomonas syringae pv. syringae in this host did not produce any accumulation of GA. It is also shown that, in healthy leaf tissues, benzoic acid (BA) and salicylic acid (SA) were rapidly converted to GA, SA being the immediate precursor of GA, according to radiolabeling studies. Interestingly, exogenous GA elicited accumulation of the previously described CEVd-induced antifungal pathogenesis-related (PR) proteins P23, P32, and P34. These protei...

One-step synthesis of citronitril on hydrotalcite derived base catalysts

Abstract Citronitril was obtained starting from ethyl cyanoacetate and benzylacetone using solid base catalysts. Hydrotalcites were found to carry out this reaction efficiently. The hydrotalcite catalyst was optimized from the point of view of its textural properties, composition ,i.e. Ca, Mg, and Zn as divalent cations, and Al/(Al+Mg) in the case of the magnesium-aluminium hydrotalcites. The influence of water, reaction temperature and polarity of the solvent on conversion and selectivity was studied.

Formation and hydrolysis of acetals catalysed by acid Faujasites

Abstract Dimethyl and cyclic ethylene acetals can be obtained in the presence of HY zeolites by treatment of the corresponding carbonyl compound with trimethyl orthoformate at room temperature or with ethylene glycol using a Dean-Stark system, respectively. The relationship between the percentage of Na + exchange of the zeolite and the initial reaction rates shows that only strong acid sites are active in the dimethyl acetal formation. Similarly, regeneration of the parent carbonyl compound was accomplished by simply heating suspensions of the appropriate acetal in carbon tetrachloride with HY catalysts. Evidence supporting the implication in the hydrolysis of the adsorbed water remaining on the zeolite after thermal activation was drawn from the results obtained using a dried solvent and a highly dealuminated zeolite. The possibility of using hydrolytic cleavage of acetals as a chemical activation procedure for zeolites was tested.

Evaluation of Traps and Lures for Mass Trapping of Mediterranean Fruit Fly in Citrus Groves

Abstract Mass trapping has proven to be a powerful weapon in the control of Ceratitis capitata (Wiedemann), and its application in Mediterranean countries has currently increased notably as a control method. In this study, the efficacy of newly developed traps and dispensers of attractants were assessed with the aim of finding the best trap and set the lifetime of the dispensers, thus improving the total efficacy of mass trapping. Efficacy trials with six different types of traps and six different types of female dispensers were carried out. Moreover, the lifetime of three female dispensers, including a new attractant composition dispenser with n-methyl pyrrolidine, were studied. Results show significant differences among the trap types using female attractants, with an advantage of nearly 3 times more catches in best trap. Tested female dispensers showed no significant differences in efficacy between trimethylamine and putrescine attractants regard n-methyl pyrrolidine, however we observed differences in lifetime between dispensers. Thus, there are significant differences among different types of traps and dispensers in efficacy, and the appropriate selection of the trap and dispenser will improve the mass trapping results.

Induction of p-Coumaroyldopamine and Feruloyldopamine, Two Novel Metabolites, in Tomato by the Bacterial Pathogen Pseudomonas syringae

Inoculation of tomato plants (Solanum lycopersicum cv. Rutgers) with Pseudomonas syringae pv. tomato led to the production of a hypersensitive-like response in this pathovar of tomato. Accumulation of hydroxycinnamic acid amides (HCAA) of tyramine (p-coumaroyltyramine and feruloyltyramine) and dopamine (p-coumaroyldopamine and feruloyldopamine) was detected after bacterial infection. Two of them, p-coumaroyldopamine and feruloyldopamine, are described for the first time. The accumulation of HCAA was preceded by an increment of hydroxycinnamoyl-CoA:tyramine N-hydroxycinnamoyl transferase (THT) gene expression. HCAA also accumulated in transgenic NahG tomato plants overexpressing a bacterial salicylic hydroxylase. However, treatment of plants with the ethylene biosynthesis inhibitor, aminoethoxyvinilglycine, led to a reduction in the accumulation of THT transcripts and HCAA. Together, the results suggest that pathogen-induced induction of ethylene is essential for HCAA synthesis, whereas salicylic acid is not required for this response. In addition, notable antibacterial and antioxidant activities were found for the new HCAA, thus indicating that they could play a role in the defense of tomato plants against bacterial infection.

Beckmann rearrangement of cyclohexanone oxime on zeolites

The Beckmann rearrangement of cyclohexanone oxime (1) was carried out in the liquid phase in the presence of a series of acid zeolites (HY-20, HY-50, HY-100, HYD, and HZSM-5) at different reaction temperatures. Together with e-caprolactam ( 2 ), 5-cyano-1-pentene ( 3 ), and cyclohexanone ( 4 ) were present in the reaction mixtures. From the selectivity curves of 2 and 3, it can be concluded that a Ritter equilibrium between 2 and 3 occurs under our experimental conditions, the direction of the process depending strongly on the hydrophobicity of the catalyst. The influence of the level of Na + exchange and of the framework Si/Al ratio on the total conversion and the selectivity of 2 reveals that medium and strong acid sites (p K a

Zeolites in organic reactions: Condensation of formaldehyde with benzene in the presence of HY zeolites

Alkylation of benzene with formaldehyde to give diphenylmethane was carried out at 30–80°C in the presence of a series of HY zeolites at three levels of Na+ exchange (HY-21, HY-50 and HY-100), several framework Si-to-Al ratios from 4 to 90 and two zeolite crystal sizes (0.30 and 0.80 μm). Only strong acid sites, i.e., those with p Ka < 0, which correspond to centres with 0 and 1 aluminium in the next nearest neighbours, are active in catalysing this reaction. The turnover number of the acid zeolites increases steadily with increasing framework Si-to-Al ratio. Under the conditions studied there is no diffusion control of the reaction in the pores of the zeolite. There is a decay in the catalyst activity during the course of the formaldehyde condensation, which is greater for samples with higher Al content. This catalyst decay is due not only to poisoning by oligomers, but also to the strong adsorption of polar products.