Sulfur trioxide, addition compounds dioxane

See also Sulfuryl chloride) Sulfur trioxide, addition compounds with pyridine, dimethylaniline, and dioxane, 2 173, 174 for synthesis of deuterosulfuric acid, 6 121... 

Fuming sulfuric acid and sulfur trioxide are more reactive than sulfuric acid, frequently leading to polysulfonation. Formation of addition compounds of sulfur trioxide with suitable Lewis bases (nitromethane, pyridine, 1,4-dioxane), however, moderates its reactivity allowing clean monosulfonation. 

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. 

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