Hello,

I have essentially no experience with sufonation rxns, except for the one I recently successfully completed using conc H2SO4-20% SO3. I thought about using a Sigma product with advertised 65% SO3, but it seems nobody is making/selling anything more than 20% SO3 in sulfuric acid. Just as well, because the precautions (Tyvek suit, respirator, goggles, face shield, and the anti-anything gloves-can't recall the product) was fairly cumbersome, and still dangerous. As a diversion, let me say that the first attempt was done with a heating mantle and a variac control. Heating control escaped me and I recovered very hard char. The successful effort was done using a jacketed flask and I circulated temp controlled water (with one circulator), from RT to 90 deg C for 8 hr, while keeping the Friedrich condenser at minus 10 deg C. 90 C was the upper limit on the heating device. Anyway, I was able to control temperature very well, but never brought it to reflux. Now, what's the question? Can anyone recommend reaction and recovery conditions for sulfonation conditions using the less dangerous methods; those where sulfur trioxide is complexed with pyridine, DMF, triethyl or trimethyl amine? [LONG DIVERSION: I did attempt the same sulfonation using the pyridine-SO3 complex, 45-50% SO3. I placed 100 cc of pyridine in the same 250 cc jacketed flask as above and controlled temperatures similarly using the heating and the chilling circulators. I added my starting compound and it was a fluffy solid at RT, with stirring. I then added pyridine-SO3 complex in a balanced stoichiometry. (At least with H2SO4-SO3 great care is taken not only in avoiding excessive heat-leading to char; but also with equivalent moles of SO3, for concern about unwanted side reactions.) Anyway, starting at 0 deg C there appeared to be no rxn, as there continued to be a fluffy white solic. But by the time the temp was 70-80 deg C all was in solution and the color light tan, as with the prior rxn using H2SO4. After 24 hr at 90 deg and cooling there was a heavy ppt, filtered on a Buchner. It was washed 1X with cold pyridine and then the pyridine removal was attempted using an azeotrope with toluene, 3X; and next with heptane, 2X (recommendations I've seen in this forum). Could still get a slight whiff of pyridine, so did a phase separation using ethyl acetate. All appears to be gone now. However, when I attempt to dry in vac oven at only 120 deg C all melts, and it almost took a hammer (well, a steel mortar) to break and crush the pieces. My product above has a mp >300 deg as do many/most sulfonates. Another phase extraction and azeotrope effort and still melts. No pyridine left, but probable considerable starting product contaminating, an aryl carboxylic acid. So, at an impasse. Will do a TLC tonight. Oddly, the UV spectrum looks very much like the successful synthesis of this product, using H2SO4-SO3.] OK, now I'm really serious about the question now. So, can anyone help regarding the reaction conditions when doing sulfonation rxns using SO3 complexed either with pyridine, dimethylformamide, trimethyl- or triethylamine; and suggestions regarding the "cleanup" or purification of the products. Again, the starting compound is a carboxylic acid with a phenyl at a beta position sp3 carbon. Many sincere 'Thanks.'