Intramolecular Amino-thiolysis Cyclization of Graphene Oxide Modified with Sulfur Dioxide: XPS and Solid-State NMR Studies

Graphite microparticles were oxidized to graphene oxide (MPGO) by Hummers' method followed by thermal exfoliation (C/O ratio 1.53). Graphene oxide was modified with SO2 (mMPGO) at 600 °C and by subsequent treatment at 200 °C having a sulfur content of 10.9% (C/O ratio 16.94) and manganese content 9.39 μmol·g–1. The XPS spectrum of MPGO showed the presence of carbonyl and epoxide groups. The reactivity of mMPGO toward alkyl thiol and alkyl amine showed the same selectivity as other carbons and suggested that oxidation did not modify deeply the edging structure of graphite. Therefore, the tetradehydrogenated-benzo[α]anthracene (TBA) reactive site model is valid. From XPS and solid-state NMR, amino-thiolysis occurred via cyclization. On the basis of the joint analysis of solid-state 1H and 13C NMR spectra of mMPGOs treated with mono- and difunctionalized alkanes, a preferred conformation of the alicyclic moiety of aminothiol over the graphene matrix occurred via binding to mMPGO at both amine and thiol ends. It was found that paramagnetic manganese ions in mMPGO can lead to cross-polarization inefficiency in the 13C CPMAS detection of alkyl chains bound to mMPGO, while ring currents from graphene aromatic layers can shift alkyl 1H NMR signals to lower frequencies by up to 4 ppm.