Thermally Induced Sigmatropic Isomerization of Pseudosaccharyl Allylic Ether

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2009-04, Vol.113 (15), p.3517-3522
• Main Authors: Gómez-Zavaglia, A, Kaczor, A, Almeida, R, Cristiano, M. L. S, Eusébio, M. E. S, Maria, T. M. R, Mobili, P, Fausto, R
• Format: Article
• Language: English
• Subjects: A: Kinetics, Spectroscopy; Calorimetry, Differential Scanning; Isomerism; Kinetics; Microscopy, Polarization; Oxides - chemistry; Spectrophotometry, Infrared; Temperature; Thiazoles - chemistry
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp8112254

The thermally induced sigmatropic isomerization of the pseudosaccharyl allylic ether [3-(allyloxy)-1,2-benzisothiazole 1,1-dioxide; ABID] has been investigated by a multidisciplinary approach using temperature dependent infrared spectroscopy, differential scanning calorimetry, and polarized light thermomicroscopy, complemented by theoretical methods. Migration of the allylic system from O to N occurs in the melted ABID, and the thermally obtained 2-allyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (ABIOD) starts to be produced at ca. 150 °C, in a process with an activation energy of ∼92 kJ mol−1. From kinetic data, a concerted [3,3′] sigmatropic mechanism is proposed. In the temperature range investigated, ABIOD was found to exhibit polymorphism. Cooling of the molten compound leads to the production of a metastable crystalline form, which upon annealing at room temperature might be transformed to the stable crystalline phase. ABID shows a single crystalline variety. Assignments were proposed for the infrared spectra of the observed neat condensed phases of the two compounds.