Selective hydroconversion of levulinic acid to γ-valerolactone or 2 methyltetrahydrofuran over silica-supported cobalt catalyst

Solvent-free hydroconversion of levulinic acid (LA) was studied over Co/silica catalysts applying flow-through fixed-bed microreactor. Consecutive hydrogenation/hydrogenolysis and dehydration reactions proceeded over the catalyst having Co0 metal and CoOx Lewis acid active sites. As a first step, LA was dehydrated to form angelica lactone (AL) intermediate. Because dehydration of LA is a facile reaction, the selectivity was controlled by the hydrogenation/hydrogenolysis activity of the catalyst. At 200 °C and 30 bar total pressure in the steady state, the catalyst could only saturate the double bond of AL ring. Thus, γ-valerolactone (GVL) was obtained with 98 mol% yield at full LA conversion. However, at temperature 225 °C the hydrogenation activity was high enough to cleave the GVL ring and obtain 2-methyltetrahydrofuran (2-MTHF) with a stable yield of about 70 mol %. FT-IR spectroscopic examination of the adsorbed LA showed the formation of H-bound LA and also surface carboxylate. 4-Hydroxy-3-pentenoate and 4-hydroxypentanoate were substantiated as surface intermediates of lactone formation by dehydration

Synthesis of Semiochemicals via Olefin Metathesis

Semiochemicals are substances or mixtures that carry messages and are used for communication between individuals of the same or different species. Semiochemicals that are used in pest control are called biopesticides. Conventional pesticides, which are generally synthetically derived and unnatural, inactivate or kill the pests, whereas biopesticides are naturally occurring compounds that attract insects to a trap or interfere with their reproduction. There are several advantages to biopesticides. Compared with conventional pesticides, biochemical-based pesticides are often less toxic and therefore have a significantly lower impact on human health and the environment. Moreover, biopesticides are pest-selective and as such do not negatively impact other organisms such as insects, mammals, or birds. Other advantages of biopesticides include high potency, meaning that smaller amounts of biopesticide are required, less resistance by target organisms, and the ability to biodegrade more quickly than conventional pesticides. Although biochemical-based pesticides are very promising materials, their production is often cumbersome, and their application is often limited. To date, most biopesticides have been synthesized by multistep, classical organic reactions that are not economical and have high environmental impact. However, in recent decades many efforts have been made to implement cost-effective and safer chemical procedures for the widespread application of biochemical-based pesticides. The purpose of this Perspective is to draw the attention of the green chemistry community to the applicability of olefin metathesis reactions in environmentally benign and cost-effective biopesticide synthesis. We review seminal work on the total synthesis of biopesticides using olefin metathesis as a key reaction step, and in doing so, we hope to inspire new ideas for forthcoming olefin-metathesis-based biopesticide development

Synthesis and characterization of novel PEPPSI type bicyclic (alkyl)(amino)carbene (BICAAC)-Pd complexes

A series of bicyclic alkylamino carbenes (BICAAC) (where N-aryl = dipp, mes, 2,6-dimethyl-4-(dimethylamino)phenyl, 5a–d) and their novel air- and moisture-resistant pyridine (pyridine, 4-dimethylaminopyridine) containing palladium Pd(II) complexes (6a–e) were synthetized and characterized. As novel examples of the PEPPSI (“pyridine enhanced precatalyst preparation stabilization and initiation”)-Pd compounds, the reported complexes have shown high activity in Mizoroki–Heck coupling reaction even at as low as 100 ppm loading (TON up to 10000). Kinetic studies revealed that reactions carried out in the presence of elemental mercury resulted decrease in activity. It indicates that the coupling reaction may have both molecular and Pd(0)-mediated catalytic paths. © 2022 The Author

Preparation of cubic-shaped sorafenib-loaded nanocomposite using well-defined poly(vinyl alcohol alt-propenylene) copolymer

Vinyl alcohol (VA) copolymers having fine tunable polarities are emerging materials in drug delivery applications. VA copolymers rendering well-defined molecular architecture (C/OH ratio = 2, 4, 5 and 8) were used as carriers for model drug compound, fluorescein exhibited significantly different release characteristics depending on the polarity of the polymers. Based on the preliminary drug release tests the well-defined VA copolymer having C/OH = 5 ratio, poly(vinyl alcohol alt-propenylene) copolymer (PVA-5) was selected for nanocomposite synthesis. Sorafenib anticancer drug was embedded into PVA-5 (C/OH = 5 ratio) nanoparticles by nanoprecipitation resulting in nanoparticles exhibiting unusual cubic shape. The sorafenibloaded nanocomposites showed continous release during a day and concentration-dependant cytotoxicity on HT-29 cancer cells. This might be interpreted by the sustained release of the drug

Catalytic Decomposition of Long‐Chain Olefins to Propylene via Isomerization‐Metathesis Using Latent Bicyclic (Alkyl)(Amino)Carbene‐Ruthenium Olefin Metathesis Catalysts

One of the most exciting scientific challenges today is the catalytic degradation of non‐biodegradable polymers into value‐added chemical feedstocks. The mild pyrolysis of polyolefins, including high‐density polyethylene (HDPE), results in pyrolysis oils containing long‐chain olefins as major products. In this paper, novel bicyclic (alkyl)(amino)carbene ruthenium (BICAAC−Ru) temperature‐activated latent olefin metathesis catalysts, which can be used for catalytic decomposition of long‐chain olefins to propylene are reported. These thermally stable catalysts show significantly higher selectivity to propylene at a reaction temperature of 75 °C compared to second generation Hoveyda–Grubbs or CAAC−Ru catalysts under ethenolysis conditions. The conversion of long‐chain olefins (e.g., 1‐octadecene or methyl oleate) to propylene via isomerization‐metathesis is performed by using a (RuHCl)(CO)(PPh(3))(3) isomerization co‐catalyst. The reactions can be carried out at a BICAAC−Ru catalyst loading as low as 1 ppm at elevated reaction temperature (75 °C). The observed turnover number and turnover frequency are as high as 55 000 and 10 000 mol(propylene) mol(catalyst) (−1) h(−1), respectively