Solid-supported gallium triflate: an efficient catalyst for the three-component ketonic Strecker reaction

Influence of the Weak Nuclear Force on Metal-Promoted Autocatalytic Strecker Synthesis of Amino Acids: Formation of a Chiral Pool of Precursors for Prebiotic Peptide and Protein Synthesis

Natural chiral amino acids typically adopt an L structural configuration. While a preference for specific molecular chiralities is observed throughout biology and cellular chemistry, the origins of this preference are unclear. In a previous report the origin of enantiomeric selectivity was analyzed in terms of an "RNA World" model, and a pathway to a chiral preference for d-ribose was proposed based on the autocatalytic transformation of glyceraldehyde as a precursor to the formation of sugars. Metal-ion-promoted catalysis allows the parity non-conserving (PNC) weak nuclear interaction to influence the chirality of a nascent chiral carbon center. Since the PNC effect is the only natural property with an inherent handedness, it is an obvious candidate to influence enantiomeric preference from a catalytic reaction performed over geologically relevant time scales. The PNC influence requires and emphasizes the important role of catalytic metal ions in primordial chemistry. In this study, the impact of geologically available divalent calcium and higher Z alkaline earth elements are examined as mediators of chiral preference. Detailed calculations of the magnitude of the effect are presented, including the influence of time, temperature, pH, and metal ion identity. It is concluded that metal ions can direct chiral preference for amino acid synthesis via a metal-promoted autocatalytic Strecker reaction within a relatively short geological timeframe, thereby providing a pool of l-amino acids for catalytic chemistry evolving either from an RNA-world model of molecular evolution or alternative pathways to protein synthesis.

Natural halloysite nanotubes as an efficient catalyst in strecker reaction: the synthesis of α-amino nitriles under solvent-free conditions

In this work, a green and cost-effective method based on halloysite as natural catalyst for the synthesis of α-amino nitriles via Strecker three-component reaction is introduced. The chemical and physical structure of natural halloysite has characterized thoroughly, and then the effect of different parameters such as the amount of catalyst, solvent, and temperature was optimized in the synthesis of 2-phenyl-2-(phenylamino)acetonitrile as the model reaction. Then, various substituted benzaldehydes and anilines were converted to the desired α-amino nitriles under the optimized conditions. Electronic properties of substituents on aldehydes and aromatic amines have been affected the reaction efficiency. For all substrates, good to excellent yields of the corresponding α-amino nitriles were obtained under solvent-free conditions at room temperature. The catalyst has been recovered and reused five times in successive Strecker reaction.

N-Acetylation of Amines in Continuous-Flow with Acetonitrile-No Need for Hazardous and Toxic Carboxylic Acid Derivatives

A continuous-flow acetylation reaction was developed, applying cheap and safe reagent, acetonitrile as acetylation agent and alumina as catalyst. The method developed utilizes milder reagent than those used conventionally. The reaction was tested on various aromatic and aliphatic amines with good conversion. The catalyst showed excellent reusability and a scale-up was also carried out. Furthermore, a drug substance (paracetamol) was also synthesized with good conversion and yield.

Divergent Multistep Continuous Synthetic Transformations of Allylic Alcohol Enabled by Catalysts Immobilized in Ionic Liquid Phases

Two individual catalytic platforms (metal- and organo-catalyzed) based on the use of an ionic liquid phase were successfully integrated for the synthesis of α-cyano-amine and cyanohydrin trimethylsilyl ethers from allylic alcohol. The right combination of continuous flow processes enabled access to the divergent preparation of two alternative and interesting intermediate compounds from the same starting material.

Taming hazardous chemistry by continuous flow technology

Over the last two decades, flow technologies have become increasingly popular in the field of organic chemistry, offering solutions for engineering and/or chemical problems. Flow reactors enhance the mass and heat transfer, resulting in rapid reaction mixing, and enable a precise control over the reaction parameters, increasing the overall process selectivity, efficiency and safety. These features allow chemists to tackle unexploited challenges in their work, with the ultimate objective making chemistry more accessible for laboratory and industrial applications, avoiding the need to store and handle toxic, reactive and explosive reagents. This review covers some of the latest and most relevant developments in the field of continuous flow chemistry with the focus on hazardous reactions.

M, Somani RS. Synthesis of aluminium triflate-grafted MCM-41 as a water-tolerant acid catalyst for the ketalization of glycerol with acetone

An aluminium triflate species grafted over MCM-41 (Al(TF)–MS) was synthesized by a novel route as an inexpensive and water-tolerant solid acid catalyst for the ketalization of glycerol with acetone to solketal (solketal synthesis).

Improved catalytic activity and stability using mixed sulfonic acid- and hydroxy-bearing polymer brushes in microreactors

Sulfonic acid-bearing polymer brushes were grown on the inner walls of continuous flow glass microreactors and used in the acid-catalyzed hydrolysis of benzaldehyde dimethyl acetal as a test reaction. Randomly 1:1 mixed polymer brushes of poly-3-sulfopropyl methacrylate (PSPM) and poly-2-hydroxyethyl methacrylate (PHEMA) showed a 6-fold increase of the TOF value compared to the solely PSPM-containing microreactor. This remarkable improvement is attributed to the cooperative stabilizing effect of proximal OH groups on the active sulfonic acid moieties within the brush architecture. In fact, the rational mixing of SPM with methyl methacrylate (MMA) as an OH-free comonomer caused a drop in the activity of the resulting catalytic platform. A 5-fold increase of the TON of the 1:1 PSPM-PHEMA versus the PSPM homopolymer brush systems additionally demonstrates the substantial increase in the stability of the mixed brushes catalytic platform, which could be continuously run over 7 days without significant loss of activity. The 1:1 PSPM-PHEMA mixed brush catalytic system also showed a good activity in the deprotection of 2-benzyl tetrahydropyranyl ether.

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

Polystyrene sulfonate polymer brushes, grown on the interior of the microchannels in a microreactor, have been used for the anchoring of gallium as a Lewis acid catalyst. Initially, gallium-containing polymer brushes were grown on a flat silicon oxide surface and were characterized by FTIR, ellipsometry, and X-ray photoelectron spectroscopy (XPS). XPS revealed the presence of one gallium per 2-3 styrene sulfonate groups of the polymer brushes. The catalytic activity of the Lewis acid-functionalized brushes in a microreactor was demonstrated for the dehydration of oximes, using cinnamaldehyde oxime as a model substrate, and for the formation of oxazoles by ring closure of ortho-hydroxy oximes. The catalytic activity of the microreactor could be maintained by periodic reactivation by treatment with GaCl3.