Benzoxathiete and related structures: experimental and quantum chemical studies
The products, plausible intermediates, and their mechanisms of formation in the aprotic diazotization of 2-[(2-acetoxyethyl)-sulfinyl (and sulfonyl)]anilines with isoamyl nitrate have been investigated by experimental and quantum chemical methods. Oxidation of 1,2,3-benzthiadiazole with hydrogen per...
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Published in | Canadian journal of chemistry Vol. 68; no. 11; pp. 1950 - 1960 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Ottawa, Canada
NRC Research Press
01.11.1990
National Research Council of Canada |
Subjects | |
Online Access | Get full text |
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Summary: | The products, plausible intermediates, and their mechanisms of formation in the aprotic diazotization of 2-[(2-acetoxyethyl)-sulfinyl (and sulfonyl)]anilines with isoamyl nitrate have been investigated by experimental and quantum chemical methods. Oxidation of 1,2,3-benzthiadiazole with hydrogen peroxide in acetic acid affords 1,2,3-benzthiadiazole-1-oxide,
13
. The thermal stability of
13
up to 135 °C, together with EPR evidence which disfavors an aryldiazenyl radical precursor, discount
13
as an intermediate in the formation of benzoxathiete
14
or its valence tautomer
17
during aprotic diazotization of the sulfinylanilines. Electron paramagnetic resonance evidence in conjunction with spin trapping indicates an intermediate arylaminyl radical. This evidence, taken together with abinitio calculations of optimized geometries energies and energy differences for biradical intermediate
15
, favors a mechanism of formation of benzoxathiete
14
via aryldiazoate anhydride
5
thence to rapid ring closure of carbon-centered radical
8
. Further oxidation of 1,2,3-benzthiadiazole-1-oxide,
13
, with hydrogen peroxide in methanol - acetic acid affords biphenylene and dibenzo-1,4-oxathiane-S-oxide,
38
. Rose bengal sensitized photooxidation of 1,2,3-benzthiadiazole affords
13
, biphenylene, and
38
. Formation of the latter, in which one of the original SO bonds has been broken, requires the formation of benzoxathiete-S-oxide,
34
, and its rapid valence tautomerism to ketosulfine
36
and (2 + 4) cycloaddition of
36
to the simultaneously generated dehydrobenzene to give
38
. Both ring closure of singlet biradical
35
to
34
and valence tautomerism of the latter to
36
are predicted by abinitio calculations to be facile and exothermic. In contrast to the aprotic diazotization of 2-[(2-acetoxyethyl)sulfinyl]anilines, the reaction of isoamyl nitrite with the corresponding sulfonyl anilines may plausibly follow a mechanism via 1,2,3-benzthiadiazole-1,1-dioxide
33
owing to the thermal instability of the latter and supported by abinitio treatments of the energetics of the processes involved. In addition EPR evidence, in conjunction with spin trapping of carbon centered radicals, support the viability of the pathway via
23
,
25
,
28
, and
16
to biphenylene
20
. The abinitio calculations of the energy differences between the reaction intermediates and estimates of the activation energies elucidated several aspects of these novel reactions. Keywords: benzoxathiete, abinitio calculations, valence tautomerism. |
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ISSN: | 0008-4042 1480-3291 |
DOI: | 10.1139/v90-300 |