Recent advances in catalytic oxidation of 5-hydroxymethylfurfural

Highlights

• Catalytic oxidation of 5-hydroxymethylfurfural (HMF).

• Catalytic production of 2, 5-furandicarboxylic acid (FDCA).

• Noble and non noble metal for the heterogeneous catalysis.

• Plausible mechanism for the production of FDCA.

Abstract

5-Hydroxymethylfurfural (HMF) has been considered as one of the most promising versatile biomass based platform molecules. This review discusses recent advances in catalytic oxidation of HMF towards 2, 5-furandicarboxylic acid (FDCA) as well as other HMF oxidation intermediates: 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid (FFCA) deploying noble, non-noble, metal-free and biocatalytic systems in conventional batch protocols; reaction mechanisms and the reaction conditions are well deliberated. Selective HMF downstream oxidation products are obtained via catalyst modifications such as the nature of metal, preparative method as well the property of deployed support. HMF oxidation, an important and integral biomass-based valorization process towards valuable chemicals, deserves more attention.

Introduction

With the rapid development of modern society, the depletion of non-renewable resources, the ensuing greenhouse effect and environmental pollution has garnered more attention, asworldwide environmental issues have started to impact the quality of human life; search for newer and greener strategies and alternative resources for the sustainable development has intensified. Lignocellulosic biomass resources are the most abundant renewable carbon resources on the planet, comprisingcellulose (40–50 %), hemicellulose (20–30 %), lignin (10–25 %) and other negligible groups (Fig. 1) [1]. Among them, cellulose with β-1,4 bonds of anhydrous glucose unit [2], through hydrolysis to glucose, in situ isomerization to fructose, followed by dehydration is converted to an important bio-based platform compound: 5-hydroxymethylfurfural (HMF) [[3], [4], [5], [6]]. Different reviews reported general conversion of biomass such as HMF into bio-based compounds and fuels [[7], [8], [9]] and one is specific on the catalytic oxidation of carbohydrates [10]. Nevertheless, specific advances in catalytic oxidation of HMF were not reviewed in details.

The oxidation of lignocellulosic platform molecules to value-added chemicals has been laid out as an efficient pathway for valorization of biomass-based compounds. Four key platform molecules namely glucose, HMF, furfural and levulinic acid, are recognized asdownstream high value compounds [11,12]. Among them, 2,5-diformylfuran (DFF), 5-hydroxymethyl-2-furancarbonxylic acid (HMFCA), and 5-formyl-2-furancarboxylic acid (FFCA) are the main intermediates of HMF oxidation (Scheme 1); each of them is important biomass-based furan compounds with wide-spread applications. For instance, DFF is used for synthesis of ligands, pesticide, antifungal agents, fluorescent materials and new polymeric materials [13,14]. HMFCA has been reported as an interleukin inhibitor [15], which also showed antitumoral activities [16]. Furthermore, FFCA has some unique structural advantages for the synthesis of drug derivative as attested in two patents; structures of FFCA-based drug derivatives are depicted in Fig. 2.

The final oxidation product, 2,5-furandicarboxylic acid (FDCA), has been considered as the most promising candidate in furan family featuring the unique cyclic furan ring with appended diacid group [17]; DuPont and DSM have commented on FDCA as "a sleeping giant with unlimited potential." In 2004, US Department of Energy identified twelve bio-based platform compounds currently considered most likely to replace more than 300 petroleum-based substitution products. Due to aromatic ring’s plane and rigid structure, FDCA was the only bio-based platform compoundrecommended [18].

2,5-Furandicarboxylic acid (FDCA)has received significant attention due to its wider applications in many fields. For instance, in the synthesis of biochemical compounds such as succinic acid [19], 2,5-dihydroxymethylfuran, 2,5-dihydroxymethytetrahydrofuran, 2,5-bis(aminomethyl)-tetrahydrofuran [18]. FDCA diethyl ester showed strong anaesthetic action similar to cocaine [20], FDCA dicalcium salt was reported to inhibit the growth of Baccillus megatorium spora [21] and FDCA-derived anilides 73 demonstrated anti-bacterial action [22]. FDCA by itself is a strong complexing agent, chelating ions such as Ca²⁺, Cu²⁺ and Pb²⁺ reportedly capable ofremoving kidney stones [23]. In addition, FDCA has been deployed in plasticizers, coatings, adhesives, metal-organic framework materials, among others.

Remarkably, another impressive application of FDCA lies in the bio-based polymer industry as its structural similarity to p-xylene (PX) enables polymerization with diol, diamine or other monomers to produce bio-based polymer materials. For instance, polyethylene 2,5-furandicarboxylate (PEF) is an excellent biopolymer alternative to polyethylene terephthalate (PET) which is obtained from fossil-based monomer terephthalic acid (TPA) [24] (Scheme 2). The starting material for PEF as sourced from biomass reduces the reliance on fossil resources. Furthermore, taking into account the improved salient features such as excellent gas barrier, recyclability and extend mechanical properties than PET [25], PEF is widely employed in food and beverage packaging, and in textile fibers. The Coca Cola company has collaborated with Avantium, Danone, and ALPLA to develop and commercialize PEF bottles. In view of its extensive applications, the price of the high purity FDCA on Sigma-Aldrich is rather expensive at 102 euros (5 g), thus suggestive of extensively studies on catalytic synthesis of FDCA.

5-Hydroxymethylfurfural (HMF) as a promising starting material for FDCA production via chemical catalytic method started in the 19th century. A wide variety of reaction systems have been investigated for the oxidation of HMF ranging from noble metal, non-noble metal, metal-free and biocatalysts, benign oxidants like oxygen, air, H₂O₂, and KMnO₄ as well as homogeneous- and heterogeneous-based approaches under conventional batch conditions. Based on these premises, the aim of this review is centered on the most recent findings with a critical discussion on HMF oxidation to FDCA as well as other HMF oxidation intermediates. The underlying mechanisms in different catalytic systems ranging from noble-metal, non-noble metal, metal-free as well as biocatalysts under diversreaction conditions (HMF/metal molar ratio, oxidant source and pressure, base type and amount, reaction temperature and time) are also discussed.