AROMATIC SULFONATION .131. FORMATION OF SULFONIC-ACIDS AND SULFONIC ANHYDRIDES IN THE SULFUR-TRIOXIDE SULFONATION OF SOME DIALKYLBENZENES AND 1,OMEGA-DIARYLALKANES

An exploratory study has been made on the SO3 sulfonation of a number of alkylarenes in [D-2]dichloromethane as an aprotic solvent, mostly i n the presence of [D-8]1,4-dioxane as a reactivity moderator, in order to obtain information on sulfonic acid and sulfonic anhydride formati on. 1,2-Dimethylbenzene (1) with 1.0 mol-equiv, of SO3 yields predomin antly the 4-sulfonic acid (1-4-S), whereas with 4.0 mol-equiv, of SO3, 18 mol-% of the corresponding (intermolecular) sulfonic anhydride (1- 4-SO2)(2)O is additionally formed. 1,4-Dimethylbenzene (2) with 0.8 mo l-equiv. of SO3 yields predominantly 2-2-S, whereas with 4.0 mol-equiv . of SO3 the sulfonic anhydride (2-2-SO2)(2)O and its 6-S and 6,6'-S-2 derivatives are formed, the eventual main product being (6-S-2-2-SO2) (2)O. Reaction of 1-ethyl-4-methylbenzene (3) with 2.0 mol-equiv. of S O3-[D-8]dioxane at -78 --> -40 degrees C leads to the predominant form ation of the 2- and 3-S derivatives in a molar ratio of 26:74, with sm all amounts of the three corresponding intermolecular anhydrides. Upon performing the sulfonation of 3 at 0 --> 22 degrees C, the relative a mounts of the anhydrides are larger, and in addition the 3,5-S-2 deriv atives of the intermolecular anhydrides are formed. The absence of the isomeric 2,6-S, derivative is ascribed to the buttressing effect of t he 2-sulfo on the 1-ethyl group, hampering the sulfonation at C(6). Re action of diphenylmethane (4) with 4.2 mol-equiv, of SO3 at -20 --> 25 degrees C yields initially 4-4'-S and subsequently 4-4',4 ''-S-2. Sul fonation of 1,2-diphenylethane (5) with 4.0 mol-equiv. of SO3 at -78 - -> 22 degrees C for 4.5 h leads mainly to the cyclic dimeric disulfoni c anhydride [5-4',4 ''(-SO2)(2)O](2), which upon hydrolysis affords 9% of 5-2',4 ''- and 91% of 5-4',4 ''-S-2. However, sulfonation of 5 at 0 --> 22 degrees C for ca. 0.8 h was found to lead to the formation of the intermolecular sulfonic anhydride (4'-S-5-4 ''-SO2)(2)O. On sulfo nation of 1,2-di-p-tolylethane (6) with 1.0 mol-equiv, of SO3, only ca . 20% of the substrate was sulfonated to give, after hydrolysis, 3% of the 2'- and 12% of the 3'-sulfonate, whereas with 4.0 mol-equiv. of S O3 the initial monosulfonic acids are almost completely converted to y ield the 2',3 '',5 ''-S-3, 3',3 '',5 ''-S-3, and 3',3 '',5',5 ''-S-4.