The production of drop‐in chemicals from bio‐based renewable sources is gaining a lot of momentum due to proven negative impact of fossil‐based economy on environment and society. In this Review, various bio‐derived platform molecules are assessed as renewable alternatives to fossil resources for the catalytic production of acrylates. Acrylic acid and its esters are key building blocks of a large number of high‐value oligomers and polymers in the current industry. In spite of the encouraging successes reported on gram or lab‐scale, real implementation of bio‐based examples remain scarce mainly due to the current high cost and limited availability of the bio‐based substrates. As lactic acid and their derivatives are one of the most promising feedstocks for bio‐acrylate production, they are the main focus of this Review.
Methyl lactate (ML) conversion to methyl acrylate is studied in the gaseous phase over ZSM-5 zeolite catalysts. High acrylate selectivity and catalyst service time were achieved using the K-ZSM-5 catalyst with low content of Brønsted acid sites (below 1 μmol g −1 ) and an overall K-to-Al atom ratio of unity. Feeding of ML in methanol containing 5 to 25 vol % of water improves catalyst stability. As such, up to 80% acrylate yield at complete ML conversion, along with minor deactivation after days-on-stream and fully recoverable catalysis, is presented.
Despite being a simple dehydration reaction, the industrially relevant conversion of lactic acid to acrylic acid is particularly challenging. For the first time, the catalytic cracking of lactide and poly(lactic acid) to acrylic acid under mild conditions is reported with up to 58 % yield. This transformation is catalyzed by strong acids in the presence of bromide or chloride salts and proceeds through simple SN2 and elimination reactions.
The dimeric condensation product of lactic acid, namely (S,S)‐2‐[(2‐hydroxypropanoyl)oxy]propanoic acid, C6H10O5, (I), crystallizes with two independent molecules in the asymmetric unit, which both have an essentially planar backbone. The trimeric condensation product, namely (S,S,S)‐3‐hydroxybut‐3‐en‐2‐yl 2‐[(2‐hydroxypropanoyl)oxy]propanoate, C9H14O7, (II), has one molecule in the asymmetric unit and consists of two essentially planar parts, with the central C—O bond in a gauche conformation. Both molecules of the dimer are involved in intermolecular hydrogen bonds, forming chains with a C(8) graph set. These chains are connected by D(2) hydrogen bonds to form a two‐dimensional layer. The trimer forms hydrogen‐bonded C(10) and C22(6) chains, which together result in a two‐dimensional motif. The Hooft method [Hooft, Straver & Spek (2008). J. Appl. Cryst. 41, 96–103] was successfully applied to the determination of the absolute structure of (I).
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