Ni(II)-oxalate on plastic-derived carbon: a green platform for furfural diacetal synthesis

An efficient and environmentally benign method for the synthesis of diacetals from furfural (FF) and heavy aliphatic (1-hexanol) or alicyclic (cyclohexanol) alcohols is reported for the first time. A novel catalyst comprising 2.5 wt% Ni(II) oxalate deposited on carbon char derived from the pyrolysis of plastic waste was synthesized and employed under microwave-assisted conditions. The catalyst effectively promoted the acetalization of FF with heavy alcohols at 130-170 °C, achieving up to 70% FF conversion and 99% selectivity toward diacetals within one hour in both binary (FF + single alcohol) and ternary (FF + mixed alcohols) systems. Reactions involving mixed alcohols resulted in a notable 40-50% increase in total productivity, yielding furfurylhexyl diacetal, furfurylcyclohexyl diacetal, and the hybrid furfurylhexyl/cyclohexyl diacetal. The addition of n-hexane as a co-solvent further enhanced yields, particularly at lower temperatures and when using the sterically hindered secondary alcohol (cyclohexanol). Under optimized conditions (150-170 °C, 40-45 vol% n-hexane), the yield of furfurylcyclohexyl diacetal increased five- to sixfold compared with reactions conducted in the absence of co-solvent. These findings highlight the catalytic potential of plastic-derived Ni(II) oxalate/carbon systems for sustainable diacetal synthesis from biomass-derived aldehydes.