Green synthesis of three- to five-membered O-heterocycles using ionic liquids

Thermal Stability of Protic Ionic Liquids

While protic ionic liquids (ILs) have found great success as solvents for a broad range of applications, little is known about their degradation when exposed to temperatures above ambient for extended periods of time. Here, we report the thermal stability of six protic ILs, namely, ethylammonium nitrate, ethylammonium formate, ethylammonium acetate, ethanolammonium nitrate, ethanolammonium formate, and ethanolammonium acetate. The effect of heating each ionic liquid to 60 °C for 1 h or 1 week (sealed or open to the atmosphere) was evaluated by considering the changes to water content, pH, mass, thermal phase transitions, and molecular structure after each treatment. Heating each of the six ILs when sealed led to measurable shifts in their water content and 10 wt % pH, but there was no significant change in their mass, thermal phase transitions according to differential scanning calorimetry (DSC), or molecular structure using proton nuclear magnetic resonance (1H NMR) spectra, indicating that the samples were largely unchanged. The samples that were heated open to the atmosphere also displayed no significant changes after 1 h but displayed significant changes after 1 week.

From Conventional to Sustainable Catalytic Approaches for Heterocycles Synthesis

Synthesis of heterocyclic compounds is fundamental for all the research area in chemistry, from drug synthesis to material science. In this framework, catalysed synthetic methods are of great interest to effective reach such important building blocks. In this review, we will report on some selected examples from the last five years, of the major improvement in the field, focusing on the most important conventional catalytic systems, such as transition metals, organocatalysts, to more sustainable ones such as photocatalysts, iodine-catalysed reaction, electrochemical reactions and green innovative methods.

Thermal Stability of Ionic Liquids: Current Status and Prospects for Future Development

Ionic liquids (ILs) are the safest solvent in various high-temperature applications due to their non-flammable properties. In order to obtain their thermal stability properties, thermogravimetric analysis (TGA) is extensively used to analyze the kinetics of the thermal decomposition process. This review summarizes the different kinetics analysis methods and finds the isoconversional methods are superior to the Arrhenius methods in calculating the activation energy, and two tools—the compensation effect and master plots—are suggested for the calculation of the pre-exponential factor. With both parameters, the maximum operating temperature (MOT) can be calculated to predict the thermal stability in long-term runnings. The collection of thermal stability data of ILs with divergent cations and anions shows the structure of cations such as alkyl side chains, functional groups, and alkyl substituents will affect the thermal stability, but their influence is less than that of anions. To develop ILs with superior thermal stability, dicationic ILs (DILs) are recommended, and typically, [C4(MIM)2][NTf2]2 has a decomposition temperature as high as 468.1 °C. For the convenience of application, thermal stability on the decomposition temperature and thermal decomposition activation energy of 130 ILs are summarized at the end of this manuscript.

Synthesis of indoles from alkynes and a nitrogen source under metal-free conditions

This review deals with the methodologies published in the last ten years, which used metal-free conditions to prepare indoles starting from alkynes and nitrogen compounds.