Metal-free catalytic systems based on imidazolium chloride and strong bases for selective oxidative esterification of furfural to methyl furoate

• Published in: Applied catalysis. A, General General, 2023-03, Vol.654, p.119088, Article 119088
• Main Authors: Fuerte-Díez, Beatriz, Rangel-Rangel, Elizabeth, Iglesias, Marta, Maya, Eva M.
• Format: Article
• Language: English
• Subjects: Oxidative Esterification – 2-Methyl furoate – oxygen- Ionic hypercrosslinked network-DBU-metal-free catalyst
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2023.119088

Homogeneous and heterogeneous catalytic systems based on 1-benzyl-3-methylimidazolium chloride (BzmimCl) assisted by strong bases (Cs2CO3 or 1, 8-diazabicyclo [5.4.0] under-7-ene (DBU)) were applied in the oxidative esterification of furfural, to obtain 2-methyl-furoate (MF). The reaction was carried out in one step, using oxygen as a unique source of oxidation and methanol as an esterification reagent. Commercial BzmimCl was used as a homogeneous ionic catalyst whereas the heterogeneous ionic one (HCP-BzmimCl) was prepared through a Friedel-Crafts reaction between biphenyl and BzmimCl. The catalytic systems here reported yield MF with a selectivity > 92% and furfural conversions > 82% after 24 h. The homogeneous catalyst systems have better catalytic activity than the similar ionic liquid systems assisted by bases published so far. Besides, HCP-BzmimCl is the first heterogeneous metal-free catalyst containing imidazole chloride groups for this reaction. HCP-BzmimCl can be recycled up to 5 times using both bases, obtaining quantitatively methyl furoate. [Display omitted] •Synthesis of 2-methyl furoate with 100% yield from furfural using basic-imidazolium chloride catalytic systems.•Metal-free catalytic systems using O2 as a unique oxidizing agent, 60 °C and 24 h of reaction.•Homo- and heterogeneous catalytic systems based on benzyl-3-methylimidazolium chloride and Cs2CO3 or DBU.•Cs2CO3 improves the recyclability of the heterogeneous systems.•Hypercrosslinked polymer, HCP-BZmimCl, is the first heterogeneous ionic network reported for this reaction.