Sulfur K-Edge X-ray Absorption Spectroscopy of Aryl and Aryl–Alkyl Sulfides

Abstract

Aryl and mixed aryl−alkyl organic sulfides are important species in a variety of fields, including the drug and food industries. They also are present in fossil fuels, where they contribute to the range of sulfur compounds that must be removed by the fuel industry. We have used sulfur K-edge X-ray absorption spectroscopy, in combination with density functional theory calculations, to study the aryl sulfide diphenyl sulfide and two different aryl−alkyl sulfides. The sulfur K near-edge X-ray absorption spectra are strongly affected by the coordination of the phenyl ring and are distinct from spectra of the alkyl sulfides. For diphenyl sulfide the spectra are predicted to be sensitive to rotation about the S−C bonds, with experimental spectra corresponding to a sum of thermally accessible conformations. We also have investigated the vapor-phase spectrum of diphenyl sulfide, which is found to be very similar to that of toluene solutions of the compound.

X-ray absorption spectroscopy of organic sulfoxides

“…The spectra show a low energy feature marked (*) at about 2470 eV, which increased in intensity upon exposure to the X-ray beam. We interpret this as small amounts of a photo-reduced species, most probably phenylsulde, 51 that accumulated with exposure. agreement with this the feature is most intense in the last spectrum collected (q ¼ 75 ) and shows no intensity in the rst spectra of the series that were collected (q ¼ 90 and 60 ).…”

“…In previous studies of the XAS of compounds in which sulfur is bound to an aromatic ring it has been shown that the spectra can be substantially inuenced by the aromatic ring. 51 For example, the spectrum of diphenylsulde shows a pronounced peak at $1.5 eV above the lower-energy main peak, 51 which is only observed in arylsuldes and not in alkyl or aryl-alkyl suldes. 50,51 Likewise, the aliphatic sulfoxides lack the intense transition 3, suggesting that this involves the aromatic rings.…”

“…51 For example, the spectrum of diphenylsulde shows a pronounced peak at $1.5 eV above the lower-energy main peak, 51 which is only observed in arylsuldes and not in alkyl or aryl-alkyl suldes. 50,51 Likewise, the aliphatic sulfoxides lack the intense transition 3, suggesting that this involves the aromatic rings. The crystal structure of diphenylsulfoxide shows that the phenyl rings are oriented in two different aspects, with the plane of one phenyl ring oriented at 28 and the other at 68 to the crystallographic b axis.…”

“…In the case of diphenyl sulde we found previously that conformational exibility could dramatically change the computed spectra. 51 Although diphenyl sulfoxide lacks the exibility of diphenyl sulde, some rotation about the C-S bonds can occur in solution 5 and inspection of the crystal structure indicates that a more limited extent of phenyl rotation should still be possible. Preliminary calculations (not illustrated) show that even subtle phenyl ring rotations can effect substantially different computed spectra.…”

“…41 Other applications of sulfur Kedge XAS include studies of geological, 42 environmental, [43][44][45] and archeological samples. 46 In previous work we have reported upon the sulfur K-edge XAS of thiophenes, [47][48][49] organic suldes 50,51 and organic disul-des. 52 Here we report upon the sulfur K-edge XAS of selected aliphatic and aromatic sulfoxides, and use a combination of density functional theory calculations and single crystal polarized XAS to develop an understanding of their spectra.…”