The formation of carbon-carbon bonds is a quest that has required a lot of research throughout the last 125 years of history of chemistry. The creation of these bonds is key to producing a wide variety of advanced products with great societal importance. In the past, the Knoevenagel reaction entailed a big part of these reactions. All the Knoevenagel reactions are performed with nitrogen-based catalysts, categorized as tertiary amines, secondary amines, primary amines, and ammonium salts. These catalysts operate through different reaction paths, with very deviant intermediates concerning each category. Subsequently, these intermediates create new research opportunities considering their catalytic activity. Some remarks are made in the context of green chemistry, with quantitative analysis using e-factor calculations. In this perspective, the importance of Knoevenagel chemistry exemplified, which is repeatedly overlooked throughout history.
Katritzky salts have
emerged as effective alkyl radical sources
upon metal- or photocatalysis. These are typically prepared from the
corresponding triarylpyrylium ions, in turn an important class of
photocatalysts for small molecules synthesis and photopolymerization.
Here, a flow method for the rapid synthesis of both pyrylium and Katrizky
salts in a telescoped fashion is reported. Moreover, several pyrylium
salts were tested in the photoinduced RAFT polymerization of vinyl
ethers under flow and batch conditions.
The design of molecularly recyclable polymers contributes to a possible solution to the end‐of‐use issue of polymeric materials and gives a closed‐loop approach toward a circular materials economy. The biobased semi‐aromatic polyesters (e.g., poly(phloretic acid), poly(dihydroferulic acid), and poly(dihydro‐sinapinic acid)), described in this paper, can be derived entirely from biomass (mainly lignin). The described polyesters exhibit thermal properties similar to those of certain commodity polymeric materials. These polyesters with ligno‐phytochemicals as monomer have so far demonstrated complete and almost infinite molecular recyclability with a loss of total mass less than 5% per cycle. Moreover, molecular weight and thermal properties (Tg, Tm, and Tcryst) of the tenth generation polymeric material are identical to those of the first generation.
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