Elimination sulfur dioxide

In the presence of aqueous sodium hydroxide, 2-phenylthiirane dioxide gives styrene and the sulfinate 119. These results have been interpreted111 in terms of initial nucleophilic attack of hydroxide ion at the carbon atom in the 3-position of the three-membered ring in addition to sulfur dioxide elimination (see equation 48). 

One procedure for the synthesis of these title ring systems appeared recently <2003S1079>. Yadav and Kapoor described that the transformation of some oxadiazole and thiadiazole derivatives bearing specially substituted methylsulfinyl side chain 131, when reacted with thionyl chloride, give ring-closed compounds 134. The reaction was carried out in pyridine under reflux conditions in 74-79% yield. As shown in Scheme 25, the authors assume that the first step is the formation of the sulfonium salt 132 which undergoes cyclization with hydrogen chloride and sulfur dioxide elimination to 133 and, finally, demethylation of this intermediate leads to the final product 134. 

Ores can be treated without generating sulfur dioxide, eliminating the need to make and market sulfuric acid sulfide sulfur can be recovered in elemental form. 

The mechanism of electron-impact-induced sulfur dioxide elimination from the molecular ions of 4-nitro-2,l-benzisothiazoline and 6-nitro-2,l-benzisothiazoline 2,2-dioxide derivatives has been examined [1359], The light fastness of dyes based on 3-amino-5-nitro-2,l-benzisothiazole was studied in relation to mass spectral data [1251],... 

Interesting results were obtained by pyrolysis of naphtho[l,8-/)c]-l,2-oxathiol 5,5 -dioxide (26) with sulfur dioxide elimination. Depending on the addition to the pyrolyzed mixture of either methanol or carbon monoxide, two pairs of isomeric compounds, 28 and 29 or 30 and 31, respectively, were formed in high yield and in an 1 1 ratio (71TL4093) (Scheme 4). 

When the batch is completed, a slight excess of oleum and chlorine is added to reduce to a minimum the residual SCI2. Because thionyl chloride combines readily with sulfur trioxide to form the relatively stable pyrosulfuryl chloride, it is necessary to maintain the concentration of sulfur trioxide in the reaction mass at a low level hence, the addition of oleum to sulfur chloride rather than the reverse. When all of the reactants are added, heat is appHed to the jacket of the reactor and the batch is refluxed until most of the sulfur dioxide, hydrogen chloride, and chlorine are eliminated. The thionyl chloride is then distilled from the reactor. 

Other methods of preparing tertiary bismuthines have been used only to a limited extent. These methods iaclude the electrolysis of organometaUic compounds at a sacrificial bismuth anode (54), the reaction between a sodium—bismuth or potassium—bismuth alloy and an alkyl or aryl haUde (55), the thermal elimination of sulfur dioxide from tris(arenesulfiaato)bismuthines (56), and the iateraction of ketene and a ttis(dialkylainino)bismuthine (57). 

Another heterocyclic molecule that can serve as a benzyne precursor is benzothiadiazole-1,1-dioxide, which decomposes with elimination of sulfur dioxide and nitrogen. ... 

The high temperature pyrolysis of sulfonyl fluonde results in the elimination of sulfur dioxide, although secondary reactions also occur, depending on the residence tune With perfluorooctanesulfonyl fluonde, long residence times result in perfluoro(Cg-Cig) compounds, and shorter residence times lead to perfluoro-hexadecane [98] (equation 65)... 

The elimination of sulfur dioxide is apparently more difficult than that of either carbon monoxide or carbon dioxide When fluorosulfonyldifluoroacetyl halide (chloride, bromide, or iodide) is photolyzed, carbon monoxide is quantitatively eliminated to give halodifluoromethanesulfonyl fluonde with increasing ease from chloride to bromide to iodide [95, 100] (equation 67)... 

A convenient trap (Fig. 3) devised by John R. Johnson for the absorption of hydrogen chloride, or for the elimination of sulfur dioxide, hydrogen cyanide, etc., may be arranged as shown in the figure. The gases are led into a chamber in which a stream of water (from the reflux condenser in this case) flows downward into a large bottle. The bottle is provided with a... 

Two-component methods represent the most widely applied principles in sulfone syntheses, including C—S bond formation between carbon and RSOz species of nucleophilic, radical or electrophilic character as well as oxidations of thioethers or sulfoxides, and cheletropic reactions of sulfur dioxide. Three-component methods use sulfur dioxide as a binding link in order to connect two carbons by a radical or polar route, or use sulfur trioxide as an electrophilic condensation agent to combine two hydrocarbon moieties by a sulfonyl bridge with elimination of water. 

Hence, one would expect the thermal elimination of sulfur dioxide or of sulfur monoxide... 

The higher strain energy in thiirene dioxides (19) compared to thiirane dioxides (17) is obvious. Yet, the elimination of sulfur dioxide from the latter is significantly faster than one would expect for a thermally allowed concerted process. Consequently, either aromatic-type conjugative stabilization effects are operative in thiirene dioxides2,12 or the relative ease of S02 elimination reflects the relative thermodynamic stability of the (diradical )99 intermediates involved in the nonconcerted stepwise elimination process. 

The elimination of sulfur dioxide from thiirane dioxides leading to the corresponding alkenes is not the only result of base-induced reactions other products are also formed. This fact raises the question of the mechanistic pathway of this reaction. In general, the thiirane dioxide is treated with a large excess of the base in an appropriate solvent for several hours at room temperature or below. Bases commonly used are 2n NaOH (in water), NaOCH3 (in methanol), t-BuO-K + (in f-BuOH) and BuLi (in tetrahydrofuran) or KOH-CCU (in t-BuOH)16-19"112 113. 

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