Dimethylaniline-sulfur trioxide

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. 

Dimethylaniline-sulfur trioxide is very similar to pyridine-sulfur trioxide in appearance. However, it is much more easily hydrolyzed even by atmospheric moisture. This is in accordance with the general rule that compounds of the type formula RsN-SOs, become less stable when one of the alkyl groups is replaced by an aryl radical. Dimethylaniline-sulfur trioxide reacts with absolute ethyl alcohol, phenol, aniline, and aqueous or liquid ammonia. ... 

Because phenolic compounds are easily sulfonated, their sulfation must be accomplished with milder sulfating agents, eg, complexes of sulfur trioxide or chlorosulfonic acid with trimethylamine, dimethylformamide, pyridine, or dimethylaniline, in anhydrous or aqueous medium below 100°C (86-89). 

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

The orientation of phenylsulfamic acid would be expected to be orthopara, since there is an unshared electron pair on the nitrogen atom adjacent to the benzene ring. Dimethylaniline forms no complex with sulfur trioxide 48 and consequently the formation of the para isomer may be interpreted as a reaction proceeding through the small amount of dimethylaniline in equilibrium with the substituted ammonium salt ... 

The same reducing agent can be nsed for the removal of the phenolic hydroxy group via prior transformation into monoarylsulfates by reaction with the complex of sulfur trioxide with dimethylaniline (Scheme... 

---