Bioderived Muconates by Cross‐Metathesis and Their Conversion into Terephthalates

Abstract

Polyethylene terephthalate that is 100 % bioderived is in high demand in the market guided by the ever-more exigent sustainability regulations with the challenge of producing renewable terephthalic acid remaining. Renewable terephthalic acid or its precursors can be obtained by Diels-Alder cycloaddition and further dehydrogenation of biomass-derived muconic acid. The cis,cis isomer of the dicarboxylic acid is typically synthesized by fermentation with genetically modified microorganisms, a process that requires complex separations to obtain a high yield of the pure product. Furthermore, the cis isomer has to be transformed into the trans,trans form and has to be esterified before it is suitable for terephthalate synthesis. To overcome these challenges, we investigated the synthesis of dialkyl muconates by cross-metathesis. The Ru-catalyzed cross-coupling of sorbates with acrylates, which can be bioderived, proceeded selectively to yield diester muconates in up to 41 % yield by using very low catalyst amounts (0.5-3.0 mol %) and no solvent. In the optimized procedure, the muconate precipitated as a solid and was easily recovered from the reaction medium. Analysis by GC-MS and NMR spectroscopy showed that this method delivered exclusively the trans,trans isomer of dimethyl muconate. The Diels-Alder reaction of dimethyl muconate with ethylene was studied in various solvents to obtain 1,4-bis(carbomethoxy)cyclohexene. The cycloaddition proceeded with very high conversions (77-100 %) and yields (70-98 %) in all of the solvents investigated, and methanol and tetrahydrofuran were the best choices. Next, the aromatization of 1,4-bis(carbomethoxy)cyclohexene to dimethyl terephthalate over a Pd/C catalyst resulted in up to 70 % yield in tetrahydrofuran under an air atmosphere. Owing to the high yield of the reaction of dimethyl muconate to 1,4-bis(carbomethoxy)cyclohexene, no separation step was needed before the aromatization. This is the first time that cross-metathesis is used to produce bioderived trans,trans-muconates as precursors to renewable terephthalates, important building blocks in the polymer industry.

Combining Reclaimed PET with Bio-based Monomers Enables Plastics Upcycling

“…Fumaric acid can be produced at high titers from both commodity first-generation sugars as well as lignocellulosic sugars. [98][99][100] Cis,cis muconic acid can be obtained both via the biological conversion of sugars and aromatic compounds directly or catalytically, 101,102 and trans,trans-muconic acid can be obtained from the isomerization of cis,cis-muconic acid. 87,103,89,91 In the case of fumaric acid, its trans configuration (relative to maleic acid's and anhydride's cis configuration) enables higher reactivities and thus better properties at the same cure time, 38,104 while the two double bonds in muconic acid enable additional rigidity and a higher degree of crosslinking.…”

Bioplastics for a circular economy

“…Its identical properties make it suitable for direct application in the beverage (one-third) and textile (two-thirds) markets 56 , as well as PET established recycling streams. Terephthalic acid, which is esterified with ethylene glycol to make PET, can be derived synthetically or microbially from biomass through intermediates such as para -xylene and 2,5-furandicarboxylic acid 136 , 137 .…”

Acetylene and Ethylene: Universal C2 Molecular Units in Cycloaddition Reactions

“…Electron-deficient 1,3-dienes are able to react with acetylene and ethylene via inverse electron-demand Diels–Alder cycloaddition. Ethylene reacted with 1,3-dienes activated by electron-withdrawing groups, such as carbonyl-, 141 alkoxycarbonyl- 142 and carboxyl-substituted dienes 143 and polyhalogen-substituted dienes, 144 affording Diels–Alder adducts (Scheme 73a ). Ethylene also added to substituted anthracenes 156 containing at least one electron-withdrawing group (Scheme 73b ).…”