Multidisciplinary Study of the Molecular Structure, Vibrational Spectra and Thermal Isomerization of Simple Ethers of Pseudosaccharin

A. GÓMEZ-ZAVAGLIA, A. KACZOR, R. ALMEIDA, L. CRISTIANO, T. ROSEIRO, E. EUSÉBIO, R. FAUSTO.

Buenos Aires

Congreso; International Workshop on Infrared Spectroscopy Applied to Biological and Biomimetic Systems: From the Isolated Molecule to the Cell" (FTIR 2007); 2007

Facultad de Farmacia y Bioquímica. Catedra de Química General e Inorgánica

Saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide) is the oldest artificial sweetener and has received much attention during the last decades. Pseudosaccharins (substituted 1,2-benzisothiazole 1,1-dioxides) are also biologically important compounds, which also receive applications in organic synthesis. Pseudosaccharyl ethers, in particular, have been used as intermediates for reductive cleavage of the C-O bond in hydroxylic compounds due the peculiar electronic and structural properties of their C-O-C moiety [1]. In this work, two representantive simple pseudosaccharyl ethers have been studied by matrix-isolation infrared spectroscopy, differential scanning calorimetry (DSC) and quantum chemical calculations: 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide (3MBID) and 3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide (3ABID). For 3MBID, a single conformer was isolated in argon, krypton and xenon matrices, and its infrared spectra were subsequently asigned and interpreted with the help of extensive DFT calculations performed at the B3LYP/6-311++G(3df,3pd) level of theory. Isolation of 3ABID in the same matrices enabled the observation of several conformers, which could also be identified and spectroscopically characterized with the help of the theoretical data. The thermal reactivity of both ethers in the neat condensed phases was investigated by variable temperature FT-IR spectroscopy and DSC. For both compounds isomerization was found to take place according to the scheme below. The rearrangement of 3ABID is intramolecular, of sigmatropic type. However, for 3MBID, a sigmoid type kinetics was observed, indicating that the rearrangement is intermolecular in nature and starts to take place for the compound in the solid phase.