Highly sulfonated graphene and graphene oxide nanosheets as heterogeneous nanocatalysts in green synthesis of bisphenolic antioxidants under solvent free conditions

Sulfonated functionalized graphene and graphene oxide nanosheets were prepared via chemical approaches and their catalytic activities were investigated in the green synthesis of 6,6'-(arylmethylene) bis(2,4-dialkylphenol) antioxidants. In this research, three types of the catalysts including sulfonated reduced graphene oxide nanosheets (catalyst 1a), sulfonated graphene oxide nanosheets (catalyst 1b), and sulfonated propylsilane graphene oxide nanosheets (catalyst 1c) were synthesized and used in the synthesis of target molecules. The catalysts were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction spectroscopy (XRD), and back acid-base titration. The catalyst 1a showed excellent catalytic activity in the green synthesis of 6,6'-(arylmethylene) bis(2,4-dialkylphenol) antioxidants under solvent free conditions and was reused several times without any appreciable loss of its catalytic activity even after eight consecutive cycles. In addition, the high yield of the products and non-toxicity of the catalysts are other worthwhile advantages of the present methods.