Instituto Nacional de Ciência e Tecnologia de Catálise em Sistemas Moleculares e Nanoestruturados

Abstract This paper describes the use of imidazolium‐based ionic liquids {1‐ n ‐butyl‐3‐methylimidazolium tetrafluoroborate [BMI‐BF 4 ], 1‐ n ‐butyl‐3‐methylimidazolium hexafluorophosphate [BMI‐PF 6 ], and 1‐ n ‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide [BMI‐NTf 2 ]} as efficient supports for Lewis and Brønsted acids ,which are promoters of the aminolysis of some esters, fatty acids, and fatty acid esters (among others) to form amide derivatives. Some esters and carboxylic acids were tested to demonstrate the generality of the methodology, and the corresponding amides were obtained in high yields. Recycling reactions (at least eight reuses) without a notable loss in activity could be performed by using CdO and SnCl 2 as catalysts in BMI‐NTf 2 as the ionic medium. Brønsted acids, such as H 2 SO 4 and HCl, were also tested with impressive results; however, it was not possible to perform recycling reactions because of catalyst leaching. The same was true when using BF 3 ⋅OEt 2 as the catalyst. Mechanistic insights and the ionic‐liquid effect were investigated by using 13 C{ 1 H} NMR spectroscopy, which showed that there is a strong interaction of the imidazolium cation with the CO and CC bonds of methyl oleate, most likely through CH⋅⋅⋅π interactions, π‐stacking interactions, and ion‐pair formation in the presence of a metal catalyst. Electrospray ionization–quadrupole time‐of‐flight experiments allowed a better understanding of the reaction mechanism. The results could explain the enhanced ionic‐liquid effect on the stabilization of the formed intermediates, which facilitated the amide bond formation.

Er 2 O 3 /Al 2 TiO 5 and Al 2 TiO 5 were evaluated as catalysts for the propanolysis of the organophosphate pesticide dimethyl 4-nitrophenyl phosphate (methyl paraoxon). The solid catalysts were characterized by energy-dispersive X-ray fluorescence (EDXRF), N 2 physisorption (BET and BJH methods), and scanning and transmission electron microscopy (SEM and TEM). Physical–chemical characterizations revealed that the erbium content is 11.7% w/w in the novel solid and results in improved catalyst performance when compared with Al 2 TiO 5, with textural properties favorable for methyl paraoxon diffusion in agglomerates composed of polydisperse spherical nanoparticles. Kinetic measurements at 80 °C show that the Er 2 O 3 /Al 2 TiO 5 catalyst promotes a catalytic effect of at least 7 × 10 5 -fold when compared with the first-order rate constant of the spontaneous propanolysis of methyl paraoxon.

Bioinspired catalysts were obtained by assembling poly(acrylic acid) (PAA) of different molecular weights and cetyltrimethylammonium bromide. For PAA, the proximity between the carboxylate groups led to the appearance of two distinct mean pKa values of 4.6 and 6.8. The increase in pKa is a consequence of the destabilization of the conjugate base due to the proximity of the negative charges, mimicking the catalytic carboxylate–carboxylate dyads of aspartic proteases and glycosidases. The nanostructured polymer/surfactant complexes accelerated the hydrolysis reaction of the diethyl 2,4-dinitrophenyl phosphate by four orders of magnitude compared to the spontaneous hydrolysis. In the absence of a surfactant, the polymer containing the carboxylate–carboxylate dyad did not show a significant catalytic effect. This demonstrates the importance of structural organization and the formation of hydrophobic microenvironments for the approach of the substrate to the active site. Mechanistic studies have shown that the phosphate transfer reaction occurred through a carboxylate nucleophilic attack. It is worth mentioning that the enzyme-like patterns observed in this work open the way for fundamental studies in the understanding of natural enzymes. Moreover, the application of polymer-based nanostructured supramolecular complexes with bioinspired functional groups enables the development of environmentally friendly methodologies for the catalysis of phosphate transfer reactions.

Silica-borax pearl samples impregnated with 0.17 and 0.64% Cr 3+ were characterized by specific surface area measurements, UV-Vis spectroscopy, energy-dispersive X-ray fluorescence and laser-scanning confocal microscopy. Pearl stability against oxidizing conditions was tested by adding samples to an aqueous hydrogen peroxide solution. The reaction was examined by UV-Vis spectroscopic measurements of the supernatant and laser-scanning confocal microscopy images of the substrate. Overall, hydrogen peroxide-induced Cr 3+ to Cr 6+ oxidation across the solid-liquid interface promoted solid matrix cleavage pearl degradation and concomitant formation of multiple scattering centers was observed. A dual-detection scheme was employed in the confocal microscopy measurements allowing us to separate scattering and absorptive contributions to the observed signals. The confocal microscopy images indicate that Cr 3+ oxidation induced by hydrogen peroxide solutions occurs throughout the entire pearl sample and indicate that oxidation reactions induce leakage of chromate ion into aqueous solutions.