Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.

Ionic liquids and catalysis: Recent progress from knowledge to applications

Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 degrees C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, "green" chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected. Because it is impossible to experimentally investigate even a small fraction of the potential cation-anion combinations, a molecular-based understanding of their properties is crucial. However, the unusual complexity of their intermolecular interactions renders molecular-based interpretations difficult, and gives rise to many controversies, speculations, and even myths about the properties that ILs allegedly possess. Herein the current knowledge about the molecular foundations of IL behavior is discussed.

Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies

Recovery and reuse of expensive catalysts after catalytic reactions are important factors for sustainable process management. The aim of this Review is to highlight the progress in the formation and catalytic applications of magnetic nanoparticles and magnetic nanocomposites. Directed functionalization of the surfaces of nanosized magnetic materials is an elegant way to bridge the gap between heterogeneous and homogeneous catalysis. The introduction of magnetic nanoparticles in a variety of solid matrices allows the combination of well-known procedures for catalyst heterogenization with techniques for magnetic separation.

Magnetically Separable Nanocatalysts: Bridges between Homogeneous and Heterogeneous Catalysis

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Polyethylene glycol and solutions of polyethylene glycol as green reaction media

Phase-transfer catalysis. Nucleophilicity of anions in aqueous organic two-phase reactions catalyzed by onium salts. A comparison with homogeneous organic systems

Dramatic effect of the specific solvation on the reactivity of quaternary ammonium fluorides and poly(hydrogen fluorides), (HF)n.cntdot.F-, in media of low polarity

Etude systematique de la stabilite d'une serie de sels d'onium quaternaires R 4 M + Y − en fonction de: la nature de l'heteroatome, de la chaine alkyle R, de l'ion antagoniste Y − associe au cation quaternaire; la concentration de la base dans la phase aqueuse; la presence d'un exces molaire du sel mineral correspondant NaY; la temperature

Stability of quaternary onium salts under phase-transfer conditions in the presence of aqueous alkaline solutions

Nonhydrated anion transfer from the aqueous to the organic phase: Enhancement of nucleophilic reactivity in phase-transfer catalysis.

Using liquid membranes it was shown that in phase-transfer catalysis the transport of anions from one phase into the other does not require the concomitant transfer of the organic cation; kinetic measurements indicate that the effectiveness of the catalyst depends essentially on its organophilicity.

Angelamaria Maia

Papers

Phase-transfer catalysis. Nucleophilicity of anions in aqueous organic two-phase reactions catalyzed by onium salts. A comparison with homogeneous organic systems

Dramatic effect of the specific solvation on the reactivity of quaternary ammonium fluorides and poly(hydrogen fluorides), (HF)n.cntdot.F-, in media of low polarity

Stability of quaternary onium salts under phase-transfer conditions in the presence of aqueous alkaline solutions

Nonhydrated anion transfer from the aqueous to the organic phase: Enhancement of nucleophilic reactivity in phase-transfer catalysis.

Mechanism of phase-transfer catalysis