Metal-bipyridine supported on 3-aminopropyl-functionalized MK10: effect of a metalating agent on the catalytic activity in the transesterification of β-keto ester

The grafting of metal-bipyridine (Bpy-M, M = Mn or Zn) on aminopropyl-modified montmorillonite K10 (NH2-MK10) synthesized via a functionalization-immobilization-metalation route was investigated. Formulated NH2-MK10-Bpy-Mn and NH2-MK10-Bpy-Zn were characterized using BET, FTIR, SEM, XRD, CHNS and NH3-TPD techniques and tested for the synthesis of butyl acetoacetate (BAT) via the transesterification of β-keto ethyl acetoacetate (EAA) with butanol (BTL). The influence of reaction parameters on the BAT yield was investigated using the Taguchi optimization approach. According to characterization data, the samples were mesoporous materials with a considerable number of acidic sites and diverse inorganic and organic functional groups, making them inorganic-organic hybrid catalysts. Optimization results showed that catalyst loading had the most significant impact on the BAT yield, followed by the BTL : EAA molar ratio and temperature, whereas the conversion time had the least impact on the reaction process. NH2-MK10-Bpy-Mn outperformed NH2-MK10-Bpy-Zn in the transesterification of β-keto EAA, achieving 96.1 ± 0.79% conversion compared to 87.3 ± 0.94% at 110 °C for 7 h with a BTL : EAA molar ratio of 1.4 : 1 and catalyst loading of 2.0 wt%. Both catalysts were reusable and maintained good stability, which indicate their great potential for catalyzing the transesterification of β-keto ester.

Expedient approach for trans-esterification of β-keto esters under solvent free conditions using silica supported boric acid (SiO2-H3BO3) as a recyclable catalyst

A highly efficient trans-esterification of β-keto methyl/ethyl esters with primary, secondary, allylic, benzylic and chiral alcohols has been carried out in excellent yields under solvent-free conditions using silica supported boric acid as a heterogeneous catalyst. The surface morphology of the silica-boric acid catalyst (fresh and recycled) has been characterized by SEM and EDX techniques. This sustainable protocol resulted in a remarkable enhancement in the synthetic efficiency (87-95% yield) with high purity and eliminating the use of an environmentally toxic solvent. The work up procedure is very simple and the catalyst has been successfully recovered and recycled. The present methodology is also applicable for trans-esterification with chiral alcohols on a multi-gram scale without compromising the yield. Noteworthy features of this protocol are simple operational procedure, minimizing production of chemical waste, mild reaction conditions, easy preparation of the catalyst and its recyclability up to five cycles without any appreciable loss of catalytic activity.

Magnetic Study of CuFe2O4-SiO2 Aerogel and Xerogel Nanocomposites

CuFe₂O₄ is an example of ferrites whose physico-chemical properties can vary greatly at the nanoscale. Here, sol-gel techniques are used to produce CuFe₂O₄-SiO₂ nanocomposites where copper ferrite nanocrystals are grown within a porous dielectric silica matrix. Nanocomposites in the form of both xerogels and aerogels with variable loadings of copper ferrite (5 wt%, 10 wt% and 15 wt%) were synthesized. Transmission electron microscopy and X-ray diffraction investigations showed the occurrence of CuFe₂O₄ nanoparticles with average crystal size ranging from a few nanometers up to around 9 nm, homogeneously distributed within the porous silica matrix, after thermal treatment of the samples at 900 °C. Evidence of some impurities of CuO and α-Fe₂O₃ was found in the aerogel samples with 10 wt% and 15 wt% loading. DC magnetometry was used to investigate the magnetic properties of these nanocomposites, as a function of the loading of copper ferrite and of the porosity characteristics. All the nanocomposites show a blocking temperature lower than RT and soft magnetic features at low temperature. The observed magnetic parameters are interpreted taking into account the occurrence of size and interaction effects in an ensemble of superparamagnetic nanoparticles distributed in a matrix. These results highlight how aerogel and xerogel matrices give rise to nanocomposites with different magnetic features and how the spatial distribution of the nanophase in the matrices modifies the final magnetic properties with respect to the case of conventional unsupported nanoparticles.

Metal- and Solvent-Free Transesterification and Aldol Condensation Reactions by a Homogenous Recyclable Basic Ionic Liquid Based on the 1,3,5-Triazine Framework

A new recyclable basic ionic liquid was introduced as an efficient catalyst for aldol condensation and transesterification reactions under environmentally friendly conditions. The catalyst was prepared based on methyl imidazolium moieties bearing hydroxide counter anions via the Hofmann elimination on a 1,3,5-triazine framework. The ionic liquid with two functionalities including anion stabilizer and high basicity, was used as an efficient catalyst for aldol condensation as well as transesterification reaction of a variety of alkyl benzoates. All reactions were performed in the absence of any external reagent, co-catalyst, or solvent, in line with environmental protection. The kinetics isotope effect (KIE) was conducted for the transesterification reaction to elucidate the mechanism and rate determining step (RDS). It worth noted that, the homogeneous catalyst could be recycled from the reaction mixture and reused for several consecutive runs with insignificant drop of basicity and conversion.

Recent advances in the transesterification of β-keto esters

The ability to selectively transesterify β-keto esters is a useful transformation in organic synthesis. The increasing interest in transesterification for the synthesis of compounds of pharmaceutical importance, as well as for biodiesel production, has led to the development of a variety of different approaches. This article aims to summarise recent advances in the transesterifications of β-keto esters. Particular interest has been paid to methodologies with minimal environmental impact.

This review summarises the many advances in the selective transesterification of β-keto esters, with a particular focus on the past 30 years.

Synthesis of 3-Carbonyl Trisubstituted Furans via Pd-Catalyzed Aerobic Cycloisomerization Reaction: Development and Mechanistic Studies

Herein, we report the synthesis of 3-carbonyl-trisubstituted furans via Pd-catalyzed oxidative cycloisomerization reactions of 2-alkenyl-1,3-dicarbonyl scaffolds, using molecular oxygen as the sole oxidant to regenerate active palladium catalytic species, featuring good functional tolerance and mild reaction conditions. Deep investigation of intermediates and transition states of the reaction mechanism were conducted via experimental and DFT studies, providing a detailed mechanistical profile. The new developed methodology presents a greener alternative to Wacker-type cycloisomerizations and avoids the use of stoichiometric amounts of oxidants and strong acid additives.

Greener Route for Synthesis of aryl and alkyl-14H-dibenzo [a.j] xanthenes using Graphene Oxide-Copper Ferrite Nanocomposite as a Recyclable Heterogeneous Catalyst

A facile, efficient and environmentally-friendly protocol for the synthesis of xanthenes by graphene oxide based nanocomposite (GO-CuFe2O4) has been developed by one-pot condensation route. The nanocomposite was designed by decorating copper ferrite nanoparticles on graphene oxide (GO) surface via a solution combustion route without the use of template. The as-synthesized GO-CuFe2O4 composite was comprehensively characterized by XRD, FTIR, Raman, SEM, EDX, HRTEM with EDS mapping, XPS, N2 adsorption-desorption and ICP-OES techniques. This nanocomposite was then used in an operationally simple, cost effective, efficient and environmentally benign synthesis of 14H-dibenzo xanthene under solvent free condition. The present approach offers several advantages such as short reaction times, high yields, easy purification, a cleaner reaction, ease of recovery and reusability of the catalyst by a magnetic field. Based upon various controlled reaction results, a possible mechanism for xanthene synthesis over GO-CuFe2O4 catalyst was proposed. The superior catalytic activity of the GO-CuFe2O4 nanocomposite can be attributed to the synergistic interaction between GO and CuFe2O4 nanoparticles, high surface area and presence of small sized CuFe2O4 NPs. This versatile GO-CuFe2O4 nanocomposite synthesized via combustion method holds great promise for applications in wide range of industrially important catalytic reactions.

Magnetically separable CuFe2O4/reduced graphene oxide nanocomposites: as a highly active catalyst for solvent free oxidative coupling of amines to imines

Solvent free aerobic oxidative coupling of amines to imines in presence of CuFe₂O₄/RGO nanocomposites.

Ag–Cu nanoparticles as efficient catalysts for transesterification of β-keto esters under acid/base-free conditions

For the first time transesterification of β-keto esters, conventional acid- or base-catalyzed reactions, has been catalyzed by Ag–Cu bimetallic nanoparticles with high activity.