Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop p-Sulfonic acid calix[4]arene: A highly efficient organocatalyst for dehydration of fructose to 5-hydroxymethylfurfural Sarah de Paiva Silva Pereira a , Jodieh Oliveira Santana Varejão a , Ângelo de Fátima b , Sergio Antonio Fernandes a, ⁎ a Grupo de Química Supramolecular e Biomimética (GQSB), Departamento de Química, Universidade Federal de Viçosa, Viçosa, MG, 36570-900, Brazil b Grupo de Estudos em Química Orgânica e Biológica (GEQOB), Departamento de Química, Universidade Federal de Minas Gerais, Belo Horizonte, MG, 31270-901, Brazil ARTICLE INFO Keywords: Fructose 5-Hydroxymethylfurfural Organocatalysis Calixarenes Biorefinery ABSTRACT Biomass is an attractive renewable source of carbon since it has a huge potential as a substituent of the scarce fossil fuels and has been widely exploited to obtain important chemicals such as 5-hydroxymethylfurfural (HMF). Fructose, one of the main components of biomass, has been widely explored as precursor for obtaining HMF. Several efforts have been expended in the search for efficient and reproducible methodologies for the synthesis of HMF, a chemical platform important in the production of fuels and other value-added chemicals. In this work, the organocatalyst p-sulfonic acid calix[4]arene (CX4SO 3 H) was for the first time employed as a catalyst for fructose dehydration reaction to produce HMF. Various parameters such as temperature, reaction time, catalyst load, fructose concentration and catalytic efficiency of other Brønsted acids were investigated. 1 H NMR spectroscopy was successfully used as qualitative and quantitative method in all steps of optimization. Using only 1 mol% of CX4SO 3 H as the catalyst (DMSO-i-PrOH 20% V/V, 140 °C, 50 mg mL -1 of fructose), 92% yield HMF could be obtained in a relatively short time (45 min). Thus, the present work was able to produce HMF from fructose with high efficiency and metal-free conditions. 1. Introduction Growing concern about environmental issues and the scarcity fossil resources, which are the principal source of essential chemicals and fuels, has led to a flood of research for renewable resources that have the potential to minimize environmental impacts. In this context, the use of biomass for the production of biofuels and high value-added chemical products has aroused great interest, mainly non-edible and/or residual biomass (Corma et al., 2007; Alonso et al., 2010; Aristizábal et al., 2015). Carbohydrates glucose and fructose are present in large amounts in vegetable biomass and they can be also obtained from agricultural and/ or forest residues, what make them attractive sources as renewable resources and with low environmental impact (Vandermeersch et al., 2014; Xia et al., 2016; Haque et al., 2017; Yu et al., 2018). Many studies have reported the conversion of carbohydrates into the chemical 5-hydroxymethylfurfural (HMF). This interest is mainly due to the achievement of several high value-added products from HMF, mainly as an alternative to precursors derived from petroleum. For example, HMF can be used in the synthesis of levulinic acid, formic acid, 2,5-dimethylfuran, 2,5-furandicarboxaldehyde, 2,5-di(hydro- xymethyl)furan, 2,5-furandicarboxylic acid, 2,5-diformylfuran among others chemicals. These substances are extensively used, for example, to obtain polymers, fuel cells, biofuels, resins, solvents, pharmaceuticals and agrochemicals (Boisen et al., 2009; Swift et al., 2013; Mukherjee et al., 2015; Yu and Tsang, 2017; Khan et al., 2018; Kong et al., 2018). In addition to serving as a chemical platform, HMF has potential as a drug acting, for example, as antisickling agent (Abdulmalik et al., 2005; Xu et al., 2017), antioxidant- (Zhao et al., 2013), antiproliferative (Zhao et al., 2013), nematicide (Ntalli et al., 2010) and cardioprotective (Wölkart et al., 2017). Several efforts have been expended in the search for a simple, ef- ficient, rapid, environmentally friendly and reproducible on a large scale for the conversion of carbohydrates into HMF. To this end, nu- merous homogeneous and heterogeneous catalysts, Brønsted acids and Lewis acids, have been employed to obtain HMF in higher yields and less by-product formations such as 5,5′-oxy(bismethylene)-bis-2-fur- aldehyde ether (OBMF), humins and other polymeric structures (Khokhlova et al., 2013; Mukherjee et al., 2015; Agarwal et al., 2018). Despite the great advances obtained, many of the catalysts https://doi.org/10.1016/j.indcrop.2019.111492 Received 2 May 2019; Received in revised form 5 June 2019; Accepted 18 June 2019 ⁎ Corresponding author. E-mail addresses: santonio@ufv.br, sefernandes@gmail.com (S.A. Fernandes). Industrial Crops & Products 138 (2019) 111492 0926-6690/ © 2019 Elsevier B.V. All rights reserved. T