The use of XPS spectra for the study of reaction mechanisms: the atom inventory method

Castro

Smaniotto

et al. 2014

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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.

Section: Resultsmentioning

confidence: 78%

“…The initial spectra and the spectra calculated through the series of reactions using the atom inventory method, were used to postulate the mechanisms involved.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Castro

Smaniotto

et al. 2014

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“…The XPS spectrum of the sample obtained is presented in Table 1 with the composition calculated using the atom inventory method. [7] The spectrum was calculated considering the internal interconversion of the SO 2 reduction intermediates (reaction 1) followed by sulfur elimination from the matrix (reaction 2) ( Table 1). No decarboxylation occurred at this temperature during the interconversion between the intermediates and the C/O ratio stays constant.…”

Section: Resultsmentioning

confidence: 99%

“…The reactivities of several carbons modified with SO 2 , including MPGO and nanotubes, with respect to the basic hydrolysis, thiolysis, aminolysis, reaction with alkyl halides, and photolysis of phenylalanine and t-butanol [18][19][20] have already been studied. XPS spectra after the reaction calculated by the atom inventory method, [7] assuming reactions already described in the literature, showed that thiol and t-butanol moieties were inserted via oxidized intermediates, while in aminolysis, only the non-oxidized intermediate was involved. These differences in reactivity would allow a selective functionalization of carbon particles.…”

Section: Introductionmentioning

confidence: 99%

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

Smaniotto

Debacher

et al. 2016

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Graphene oxide, MPGO, was obtained by oxidation of graphite microparticles by a H 2 SO 4 /KMnO 4 /H 2 O 2 mixture followed by thermal exfoliation. Non-thermal plasma treatment of MPGO under SO 2 atmosphere resulted in the insertion of the oxidized intermediates only. Refluxing this material in CS 2 (46°C) showed sulfur elimination and interconversion of the oxidized into non-oxidized intermediates with an energetic barrier of ΔG ‡ = 25.81 kcal mol À1 without decarboxylation. The episulfide content in modified MPGO increases with respect to the oxidized intermediates when increasing temperature. Modification of MPGO with SO 2 at 630°C presented exclusively the non-oxidized intermediate. These results support the hypothesis that there are two major reactions with different energetic demand in the SO 2 reduction on carbons: desulfurization and decarboxylation. The selectivity of thiolysis and aminolysis towards the intermediates inserted in the MPGO matrix allowed the aminothiolysis of a sample containing both intermediates with the insertion of the amino group on the episulfide site followed by an intramolecular thiolysis with double functionalization of the matrix.

Kinetics and mechanisms in flow systems: reduction of SO₂ on carbons

Moreira

2012

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Surface‐science studies of some reactions have allowed postulating the mechanisms using a variety of techniques. The surface chemistry of Group IV elements has been particularly studied recently because Si, Ge, and C are semiconductors, and the surface organic chemistry to functionalize these elements has seen immense progress in recent years. In this review article we describe the methodology used to study the mechanism of a solid–gas reaction, the reduction of SO2 on carbons, and the necessary conditions that allowed the measurement of the solid conversion and product distribution when the kinetics was chemically controlled and the reaction had reached the steady state. The reaction was first‐order with respect to SO2 and with respect to carbon and the stoichiometry was determined from the product distribution. The reaction proceeds through two thermally stable reaction intermediates bound to the surface, a six‐membered ring 1,3,2‐dioxathiolane and a five‐membered ring 1,2‐oxathietene 2‐oxide or γ‐sultine, both species being in equilibrium. The reaction was shown to be reversible. The primary product is an episulfide that, after a series of consecutive reactions of atomic sulfur, is able to free sulfur. The reactivity of the intermediates and the episulfide was studied for several reactions and consistent mechanisms were postulated from the X‐ray photoelectron spectroscopy and solid state nuclear magnetic resonance spectra. Aminolysis and the reaction with alkyl halides resulted on the insertion of the alkyl moiety in the episulfide primary product, while the thiolysis and photolytic alcoholysis resulted in the insertion of the alkyl moiety in the oxidized intermediates. Copyright © 2012 John Wiley & Sons, Ltd.