Sulfur trioxide-1,4-dioxane

Sulfonation with sulfur trioxide, pyridine sulfur trioxide, pyridine bis-sulfur trioxide, and dioxane sulfur trioxide, which are useful sul-fonating agents for acidophobic substances, have been applied to the thiophene seriesd At room temperature the 2-monosulfonic acid (isolated as the barium salt) is obtained in 86% yield. Higher temperatures lead to a disulfonic acid. However, sulfonation with chloro-sulfonic acid appears to be more convenient,as the sulfonyl chloride obtained can be used directly for the preparation of derivatives. 

The sulfonating actions of pyridine-sulfur trioxide, pyridine-bis sulfur trioxide and dioxane sulfur trioxide on 2,5-dimethyIthiophene have been compared. Yields of 95% monosulfonic acid were obtained with the latter two reagents, whereas pyridine sulfur trioxide yielded only 75%. 2-Methyl-3,5-diphenylthiophene resists formylation and SnCl4 Catalyzed acylation in contrast to 2,3,5-trimethylthiophene, which is formylated and acylated quite easily. 

The dioxane-sulfur trioxide complex reacts with 2,3-dimethylbutadiene to give the sultone... 

S03Na2 (and + 7H20) Sodium sulfite, 2 162, 164, 165 S03-0(CH2CH2)20 Dioxane sulfur trioxide, 2 174... 

The reaction of alkenes with sulfur trioxide is an important synthesis of 1,2-oxathiolane 2,2-dioxides. The best conditions involve the use of a dioxane-sulfur trioxide complex at low temperature. The initial addition involves formation of the most stable cation followed by ring closure, as shown in Scheme 31 (74JOC2459). 

When selenophene-2-aldehyde or its diacetate is sulfonated with dioxane-sulfur trioxide, 5-sulfoselenophene-2-aldehyde is formed. The 2-carboxylic acid with oleum gives 5-sulfoselenophene-2-car-boxylic acid containing an admixture ( 20%) of the 4-sulfo isomer. The sulfo group is readily replaced by nitro by the action of fuming nitric acid.51... 

The dioxane-sulfur trioxide adduct is prepared as follows 101 In an all-glass apparatus sulfur trioxide is distilled out of 60% oleum into a tared flask containing dry ethylene dichloride and cooled in cold water. To this solution is added, with vigorous stirring, an equivalent amount of dioxane (previously boiled over sodium and distilled) while the internal temperature is kept always below 59. 

Acetophenone-co-sulfonic acid 100 Acetophenone (42 g, 0.35 mole) is added to the dioxane-sulfur trioxide reagent (exactly 0.35 mole) whilst the temperature is not allowed to rise above 35°. Addition is complete in 1 h, and after a further 2 hours stirring the mixture is hydrolysed by being poured into water (300 ml). The organic layer is removed and the aqueous layer is brought to pH 7 by cold sodium hydroxide solution and evaporated in a stream of air. The solid residue is extracted with a boiling 60% ethanol-water mixture. Sodium acetophenone-co-sulfonate (54 g, 70%) crystallizes from the extract as it cools. 

Phenylalkanoic acids and dioxan-sulfur trioxide afford their -sulfonic acids,102 whereas direct sulfonation by sulfuric acid leads to substitution in the ring. 

Aromatic hydrocarbons such as toluene, xylenes, mesitylene, and methyl-naphthalenes can be sulfonated in dichloroethane almost quantitatively by the dioxan-sulfur trioxide complex under very mild conditions (2 h at 20°).179... 

The use of sulfur trioxide as a sulfonating agent is often inconvenient, and reactions carried out with it are usually vigorous and difficult to control. The addition compounds-that sulfur trioxide forms with tertiary amines and other strong electron donors, however, have been found to be very convenient sulfonating agents. Procedures for the preparation of three typical compounds, pyridine-sulfur trioxide, CsHsN-SOa dimethylaniline-sulfur trioxide, CeHs-N(CH3)2 SOs and dioxane-sulfur trioxide, 0(CH2 CH2)20 -SO3, are presented here. 

Less than an equivalent quantity of sulfur trioxide is distilled from 60 per cent oleum into a solution of 88 g. of redistilled dioxane in 300 ml. of ethylene chloride, which is chilled and stirred mechanically. The white crystalline addition compound precipitates where the sulfur trioxide strikes the surface of the solution. The compound is filtered and dried as in the previous cases. It usually contains considerable sulfate, J since dioxane-sulfur trioxide is very sensitive to moisture. 

Dioxane-sulfur trioxide is stable at room temperature under anhydrous conditions but is decomposed on heating to 75° in carbon tetrachloride. It is much more reactive than is pyridine-sulfur trioxide and is hydrolyzed instantly by water to form sulfuric acid and dioxane. Its use as a sulfonating agent for a wide variety of organic compounds has been the subject of an extensive investigation by Suter, Evans, and Kiefer. ... 

Different sulfonating agents have been used for the a sulfonation of fatty acids and their esters stabilized liquid SO3, sulfur trioxide vapor, chlorosul-fonic acid, and dioxane-sulfur trioxide complex. Stirton tried all of them and preferred liquid SO3. The other agents are used for special applications [29]. 

Dioxane/sulfur trioxide Sulfonation of olefins Sultones from ethylene derivs. 

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