Theoretical and experimental studies on oxidation and interactions of mono- and dithioethers and their derivatives.

Abstract

The potential energy surface of naphtho (1,8-b,c) -1,5-dithiocin and its mono-, di-, tri-, and tetraoxides was analyzed by dynamic ¹H NMR spectroscopy, AM1 semiempirical calculations, and x-ray crystallography. The lowest energy conformers of these compounds in the solid state, the gas state, and in solution, as well as the energy barriers for the interconversion between their conformers are reported. The electronic structure of naphtho (1,8-b,c) -1,5-dithiocin was analyzed by the AM1 semiempirical method. An experimental method was developed to verify these calculations. Comparison of the relative intensities of the bands observed in the He I and He II photoelectron spectra of aromatic thioethers provides an effective means for assigning bands to ionizations from specific molecular orbitals. Such methodology confirmed the calculations which showed that naphtho (1,8-b,c) -1,5-dithiocin has a large sulfur-sulfur lone pair splitting of 1.6-2.0 eV. Dissolution of naphtho (1,8-b,c) -1,5-dithiocin-1-oxide in concentrated sulfuric acid produced the corresponding disulfide dication, which upon hydrolysis regenerated the sulfoxide. The mechanism of this reaction sequence was investigated using 2-monodeuterated naphtho (1,8-b,c) -1,5-dithiocin-1-oxide. This stereochemical probe showed that both the formation of the disulfide dication and its hydrolysis occurred with retention of stereochemistry at the sulfoxide sulfur. The molecular structure of naphtho (1,8-b,c) -1,5-dithiocin-1-oxide, determined by x-ray crystallographic methods, showed evidence of transannular interaction between the sulfur atoms. Vibronic analysis on naphtho (1,8-b,c) -1,5-dithiocin and naphtho (1,8-b,c) -1,5-dithiocin-1-oxide using the Hartree-Fock method with the STO-3G basis set showed no evidence of bond formation in naphtho (1,8-b,c) -1,5-dithiocin-1-oxide compared with naphtho (1,8-b,c) -1,5-dithiocin. Thus this transannular interaction in the sulfoxide must be due to electrostatic interaction and not incipent sulfurane formation. The mechanism of the photodecompositions of perester and aldehyde compounds with β substituted sulfur moieties was investigated. The photodecomposition of these compounds produced their corresponding alkenes without stereocontrol. These results suggest that the decompositions occur via a stepwise non-stereoselective mechanism. Flash photolysis of peresters β substituted with sulfonium salt groups was shown to produce thioether cation radicals, e.g., the 1,5-dithiocane cation radical. This demonstrated that the photodecomposition of β sulfonium salt peresters is potentially a powerful and novel method for making cation radicals.