Thermally induced sigmatropic isomerization of pseudosaccharyl allylic ether.
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 degrees C, in a process with an activation energy of approximately 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.
Gómez-Zavaglia
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Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal.
Kaczor
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Almeida
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Cristiano
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Eusébio
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Maria
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Mobili
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Fausto
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