Reactivity of the intermediates of the reduction of SO2. Functionalization of graphite, graphite oxide and graphene oxide

Abstract

dGraphite particles (0.505 mm) were oxidized to graphite oxide with KClO3 in a H 2 SO 4 /HNO 3 mixture. Graphite and graphite oxide particles were modified by reaction with SO 2 at 630°C. Thiolysis with sodium dodecane-1-thiolate and aminolysis with dodecane-1-amine of these particles occurred with the insertion of the organic moiety in the carbon matrix. Graphite microparticles (6.20 μm) were oxidized by H 2 SO 4 / KMnO 4 / H 2 O 2 mixture and were exfoliated to graphene oxide sheets (MPGO). MPGO was modified by reaction with SO 2 at 630°C. The modified MPGO was refluxed in DMSO with dodecane-1-thiol, dodecane-1-amine, and hexadecane-1-bromide. The reactions occurred with the insertion of the organic moiety in the carbon matrix, according to the X-ray photoelectron and nuclear magnetic resonance spectra. Mechanisms for the reactions were postulated using the atom inventory technique. Despite the structural differences, graphite, graphite oxide, and graphene oxide present the same selectivity for aminolysis and thiolysis reactions, with respect to the oxidized and non-oxidized intermediates of the reduction of SO 2 , as was found for the activated carbon.

Interconversion and selective reactivity of sulfur dioxide reduction intermediates inserted on graphene oxide

“…MPGO presented only non-oxidized sulfur before the reaction, and after the thiolysis performed refluxing in DMSO (200°C), the interconversion to oxidized intermediates was observed. [19] Interconversion of the intermediates during thermal treatment is plausible SO 2 because according to the theoretical calculations [5] and experimental results [18] , the primary product episulfide is more stable than the oxidized intermediates, and the energetic barrier, as shown in this work, is only 25.81 kcal mol…”

“…[18][19][20] In all cases, the thiolysis proceeded through the oxidized intermediate, while reaction with amine took place through the primary product episulfide. These results suggest the possibility of a double functionalization of the matrix through an amino-thiolysis reaction if both reactive sites would be near enough as assumed by the primary mechanism.…”

“…[4,19] The exfoliated oxidized MPG, denominated MPGO, showed the following bands in the FTIR spectrum: 3400 cm Scanning electron microscope images revealed the typical fluffy and wrinkled morphology of oxidized and exfoliated graphite, unlike the compact layered structure of pristine graphite. Surface area measurements via nitrogen gas absorption indicated a 20-fold surface area expansion, which denotes that exfoliation took place.…”

“…It has been observed previously that when MPGO containing only non-oxidized intermediate was submitted to thiolysis, the oxidized intermediate was generated by interconversion followed by thiol insertion and extrusion of SO 2 from the matrix. [19] The formation of episulfide is associated with formation of a peroxide intermediate C(CO 2 ) that allows the retroconversion of the episulfide to the oxidized intermediate dioxathiolane.…”

“…The 13 C NMR spectrum of modified MPGO showed the alkyl peak after thiolysis at 29.0 ppm and after aminolysis at 28.8 ppm, too close to distinguish the double substitution by NMR. [19] However, the calculations of the XPS spectrum (Table 5) allows the description of the reaction.…”