Sulfinate thermal decomposition

The H and 13C CIDNP studies have shown that not only the sulfone 14, but also the sulfmic ester 15, is generated as cage products from the phenyl/p-toluenesulfonyl radical pair during the thermal decomposition of phenylazo aryl sulfone (13)54 (Scheme 2). The cross-termination of arenesulfonyl and triethylgermyl radicals was found to occur exclusively via the formation of germyl sulfinate, ArS(0)0GeEt333. 

Pyrazino sulfolenes 495 have been derived from a cycloaddition reaction of intermediate 494 with SO2. This intermediate is produced by the thermal decomposition of the sulfine 493 (Scheme 39) <2000JOC3395>. 

The stable dithiirane 5-oxide (4) is converted to sulfine (15) and triphenylphosphine sulfide upon treatment with triphenylphosphine (93JA4914). When heated, (4) decomposes to give thioketone (16), sulfine (15), and dicarbonyl compound (17). Compounds (16) and (15) result from loss of sulfur monoxide and sulfur, respectively, from (4). Thioketone (16) exists in equilibrium with oxathietane (18). The rate of thermal decomposition of (4) was found to be dependent on its concentration, with higher rates at higher concentrations. The authors suggest that this observation is indicative of a decomposition pathway involving the sulfur and sulfur monoxide products. Thermolysis of (4) also leads to isomerization of (12) in addition to the products described above. 

The reaction is believed to involve homolysis of the S—S bond to give a biradical which is intermediate to isomerization and product formation. Thermal decomposition of (4a) gives elemental sulfur and thioketone (16) <94AG(E)777>. Treatment of (4a) with triphenylphosphine also leads to (16) plus triphenylphosphine thiooxide. Oxidation of the dithiirane with MCPBA gives the sulfine (15). Heating of a dilute solution of (4a) in 1,2-dichloroethane gives the bicyclic 1,3,4-oxadithiolane (19) along with (16) and (18). 

Thermal Decomposition of Sulfinate (XVI). Heating sulfinate (XVI) in o-dichlorobenzene at 150°C, XVI completely decomposed within 5 min. No styrene was formed. 4-Methoxy-2,6-diphenylphenol (Vila) is isolated from the reaction mixture together with other products, which proved to be thiosulfonate (XVIII), sulfonate (XIX), and sulfide (XX). Reaction Scheme 4 gives possible routes for the formation of products XVIII, XIX, and XX. 

Thermal Decomposition of Sulfinate (XVI) in the Presence of an Excess of 4-Methoxy-2,6-Diphenylphenoxyl (XVa). Besides the products formed as indicated in Scheme 4 an increasing amount of 4-methoxy-2,6-diphenylphenol (Vila) is formed. Moreover styrene is formed in equi-molecular amount with the sulfite (XXI). In Scheme 5 a possible explanation is given for the formation of the above-mentioned products. 

Thermal Decomposition of Sulfinate (XVI). A solution of 0.12 mmol of sulfinate (XVI) in 1 mL of o-dichlorobenzene was heated at 150°C. In the liquid chromatograms several peaks rose and disappeared during the reaction. Three main products were isolated 4-methoxy-2,6-diphenyl-phenol (Vila) was identified by its ir spectrum thiosulfonate (IXVIII), the vmax 1200 s (S02), 750 s, and 700 s cm-1 (aromatic monosubstitution), (mass spectrometry parent peak (M) m/e 306, peak m/e 242 (M-S02), m/e 105 (CeH5C2H4 fragment), and a molecule ion peak m/e 136, which was assigned to sulfide XX) and sulfonate XIX (the vmax 2830 w (OCH3), 1200 s (S02), and strong bands between 700 and 800 cm-1 (two types of aromatic substitution) mass spectrometry parent peak (M) m/e 444, peak m/e 380 (M-S02)). 

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