Edge functionalization of graphene layers with a 2-pyrone

Conversion of hydrolyzed biomass, mainly composed by carbohydrates, into suitable building blocks is one of the major purposes of Green Chemistry, defined as ‘‘the design of chemical products and processes to reduce or eliminate the use and generation of hazardous substances”. 2-pyrones are a class of unsaturated heterocyclic C-6 sugar derivatives, prevalent in many natural products and, due to their versatile chemical reactivity, intriguing building blocks in organic and polymer chemistry. In this work, a green and efficient procedure for the preparation of 2-pyrone is presented, starting from galactaric acid, also known as mucic acid, easily obtained from galactose or galacturonic acid. A 2-pyrone derivative, 5-hydroxy-6-oxo-6H-pyran-2-carboxylic acid ethyl ester (Pyr-COOEt) was used for the functionalization of nano-sized graphite with high surface area (HSAG). Adducts of Pyr-COOEt with HSAG were prepared by means of a simple and sustainable method, with the help of either thermal or mechanical energy. Functionalization yield was in all cases larger than 90%. After the functionalization reaction, the bulk structure of HSAG remained substantially unaltered, thanks to the edge functionalization. Few layers graphene were easily obtained by means of a mild sonication of a water dispersion of the HSAG/Pyr-COOEt adducts.