High selective hydrogenation of furfural catalysed by recyclable Pd-nanoparticles

The investigation and deveiopment of new non-fossi) carbon energy sources are urgentiy needed due to the increasing energy consumption, decreasing reserves of fossi) resources, and global ecologica) degradation. In this regards, biomass conversion is a promising way to overcome the dependence of society on tossii hydrocarbons (oil, gas, etc), especially in fuel production and energy areas. The effective conversion of lignocellulosic biomass into valuable chemicais and fueis has gained much attention during the past few decades. As a result of the oxygen-rich nature of bio-mass-derived molecules, the selective removal of the oxygenated groups is a primary challenge for the use of these molecules. An important example is the conversion of hemicellulose in 2-methyltetrahydrofuran (2-MTHF) using furfural as piatform. 2-MTHF, as well as 2-methylfuran, is a good liquid fuel additive with a high energy density, boiling point, and octane number and it can be partiy mingied into gasoline for engineering purposes [1]. In particular, furfural has been recognized as a crucial bio-based platform molecule, and therefore, its valorisation has been attracting researchers' attention. In this contest, here we report a selective hydrogenation of furfural catalysed by recyclable Pd¬nanocatalyst under mild reaction conditions. Mcderials e methods Ali chemicais were purchased from commerciai sources and used as received. Palladium cataiyst (Pd-poi) was synthesized as reported in the literature [2,3]. Palladium content in Pd-poi was assessed after sample mineralization by atomic absorption spectrometry using a Perkin¬Elmer 3110 instrument. Catalyst mineralization prior to Pd analyses was carried by microwave irradiation with an ETHOS E-TOUCH Milestone applicator, atter addition of 12 mL HCl/HNO3 (3:1, v/v) soiution to each weighted sampie. The products were identified by comparison of their GC-MS features with those of authentic samples. Reactions were monitored by GLC analyses, which was performed using a HP 6890 instrument equipped with a FID detector and a Supelcowax-10 capillary column (30.0 m x 0.25 mm x 0.25 pm). Conversions and yields were calculated by GLC analysis as moles of hydrogenated product per mole of starting substrate by using biphenyi as internai standard. P19 XII CONGRESSO NAZIONALE Procedures In a typical run, a 50 mL stainless steel autoclave equipped with a transducer for online pressure monitoring was charged, under air, of Pd-pol (43.3 mg, Pd: 2.45 mollo), the substrate (0.5 mmol), and CH3OH (5.0 mL) or water (5.0 mL). The autoclave was then purged three times with hydrogen, then pressurized with 8 bar H2, set on a magnetic stirrer at room temperature. After the minimum time needed to reach reaction completion, the hydrogen was vented and the autoclave opened. The catalyst was recovered by easy filtration while the organic product was extracted with ethyl ether (3 mL), the water phase was washed with ethyl ether (3 x 5 mL)and the organic layers were collected. The yields were assessed by GLC analysis of the ethyl ether solution with the internai standard (biphenyl) method. Results and discussion An efficient and clean approach is proposed for mild and easy full hydrogenation of furfural to 2-methyltetrahydrofuran (Scheme 1) using a polymer supported palladium catalyst in aqueous solvent. The same results were gained by using methanol or water as solvents; this permits to select the greenest methodology to respect the green chemistry principles. Of fundamental practical significance is the fact that the catalyst can be easily recovered at the end of the reaction and recycled for at least ten times, keeping the same activity and selectivity. TEM analyses showed that the active species are Pd nanoparticles, which do not aggregate with reuses and do not suffer of metal leaching during reaction. The benchmark reaction was scaled up to 3.0 mmol of substrate achieving the same high selectivity for the hydrogenation of furfural to 2-methyltetrahydrofuran. //O Pd-pol' H2O —(13-barjrRoF H2 Scheme 1. Hydrogenation of furfural catalysed by Pd-nanocatalyst. Bibliography [1] R. Mariscal, P. Maireles-Torres, M. Ojeda, I. Sadaba, M. Lopez Granados, "Furfural: a renewable and versatile platform molecule for the synthesis of chemicals and fuels", Energy Environ. Sci., 9, 1 144-1 189 (2016) [2] M.M. Dell'Anna, P. Mastrorilli, F. Muscio, C.F. Nobile, G.P. Suranna, "A polymer-supported 13- ketoesterate complex of palladium as an efficient, phosphane-free, air-stable, recyclable catalyst for the heck reaction", Eur. J. lnorg.Chem., 8, 1094-1099 (2002) [3] M.M. Dell'Anna, M. Mali, P. Mastrorilli, P. Cotugno, A. Monopoli, "Oxidation of benzyl alcohols to aldehydes and ketones under air in water using a polymer supported palladium catalyst", J. Mol. Catal. A: Chem., 386, 114-119 (2014).