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Browsing by Author "Maria, T. M. R."

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  • First observation of Chapman rearrangement of a pseudosaccharyl ether in the solid state: the thermal isomerization of 3-(methoxy)-1,2-benzisothiazole 1,1-dioxide revisited
    Publication . Almeida, R.; Gómez-Zavaglia, A.; Kaczor, A.; Cristiano, Maria Lurdes Santos; Eusébio, M. E. S.; Maria, T. M. R.; Fausto, R.
    3-(Methoxy)-1,2-benzisothiazole 1,1-dioxide, a pseudosaccharyl ether, was long ago known to undergo a thermal Chapman-like [1,30]-isomerization to the corresponding N-methyl pseudosaccharin at temperatures above its melting point (ca. 184 C) [Hettler H., Tetrahedron Lett. 1968, 15, 1793]. In the present study, it is shown that this rearrangement can also take place in the solid state, at temperatures as low as 150 C. This was the first observation of a Chapman-like [1,30]-isomerization in pseudosaccharyl ethers in the solid state. The study has been carried out by a multidisciplinary approach using temperature dependent infrared spectroscopy, differential scanning calorimetry (DSC), and polarized light thermomicroscopy, complemented by theoretical methods.
    2008Journal article Restricted access Show more
  • The thermal sigmatropic isomerization of pseudosaccharyl crotyl ether
    Publication . Cabral, Lília; Maria, T. M. R.; Martelo, L.; Eusébio, M. E. S.; Cristiano, Maria Lurdes Santos; Fausto, R.
    The thermally induced sigmatropic isomerization of the pseudosaccharyl crotyl ether, 3-(E)-but-2-enoxy)-1,2-benzisothiazole 1,1-dioxide (CBID), has been investigated by using temperature dependent infrared spectroscopy, differential scanning calorimetry (DSC), and polarized light thermomicroscopy. The reaction can take place in both melted and crystalline phases, affording the product resulting from the [3,30] migration of the allylic system from O to N, 2-(E)-1-methylprop-2-en-1,2-benzisothiazol-3(2H)-one 1,1-dioxide (CBIOD). In the melt, the activation energy of the process was determined as being 49.1 5.3 kJ mol 1, with k¼(22.2 0.6) 104 s 1 at 140 C. In the solid state, at 110 C, the rate constant drops by one order of magnitude [k¼(1.46 0.07) 104 s 1]. The enthalpy of reaction, determined by DSC, is DrxH¼ 27.0 0.8 kJ mol 1. Assignments were proposed for the infrared spectra of the observed neat condensed phases of the two compounds.
    2013Journal article Restricted access Show more
  • Thermally induced sigmatropic isomerization of pseudosaccharyl allylic ether
    Publication . Gómez-Zavaglia, A.; Kaczor, A.; Almeida, R.; Cristiano, Maria Lurdes Santos; Eusébio, M. E. S.; Maria, T. M. R.; Mobili, P.; Fausto, R.
    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.
    2009Journal article Restricted access Show more