Pyrosulfonic acid

The reaction of organic feedstock (F) with 2 mol equivalent of S03 to produce the 2 1 species (a pyrosulfonic acid) is instantaneously fast and highly exothermic. The follow-up reaction to the desired product is fast and again exothermic. 

RC6H5 + 2S03 -> 2RC6H4S020S03H (fast) pyrosulfonic acid... 

The reaction is highly exothermic with a AH of -170 kJ/gmol. Due to the slow second reaction aging is required to convert the formed pyrosulfonic acid with alkylate to the desired end product LAS (Table 2). There are two main side reactions anhydride formation and sulfone formation. 

Premature stabilization. Not all pyrosulfonic acid may be converted in LABS A (slow reaction). Then... 

Koeberg-Telder and Cerfontain (1975) also examined the nmr behavior of both CH3S03H and p-BrC6H4S03H in fuming sulfuric acid. They felt that the changes observed in the nmr spectra were best accounted for by a combination of protonation of the sulfonic acid to RS03HJ (161) and reaction of the sulfonic acid with sulfur trioxide to form the pyrosulfonic acid RS03S03H (162). 

The sulfonation of toluene proceeds via a complex scheme of elemental reactions with numerous side and consecutive reactions. Toluene sulfonic acid and sulfur trioxide can read in a consecutive process to give toluene pyrosulfonic acid, which can undergo further reactions [315,316]. Reaction of this acid with another molecule of toluene yields two molecules toluene sulfonic acid or ditolyl sulfone. In addition, toluene sulfonic anhydride may be formed via readion of toluene pyrosulfonic acid with toluene sulfonic acid. 

Aromatic Sulfonation. Reaction of an arene (ArH) with SO3 leads to sulfonation with formation of arenesulfonic acids (ArSOsH). Mechanistically two different stages can be recognized, viz. primary and secondary sulfonation. In the primary stage, arenepyrosulfonic acids (ArS206H) are formed. A pyrosulfonic acid is a mixed anhydride, liable to disproportionate... 

We have discussed reaction mechanism and kinetics of sulfonation of benzene (B) with SO3 (A) in aprotic media [3] and have concluded that the reaction proceeds according to Van de Vusse kinetics (1-3), with kj (25°C) >9.4 m /kmol s and z = >4. Pyrosulfonic acid (I) and Ar S3O9H d ) are both unstable and react with benzene to give the desired product benzenesulfonic acid (P) and the unwanted product diphenyl sulfone (X), respectively... 

Table II. Estimated values for ges-liquid interface pyrosulfonic acid concentration rise (Cjj- C ),surface temperature rise (T.-T) and reaction rata constant (k2D ) in stirred cell reactor sulfonation experiments.

The influence of pyrosulfonic acid concentration on viscosity is neither known nor measurable because of the instability of this intermediate [3]. We measured the viscosity of a reaction mixture at 23.5°C as a function of benzenesulfonic acid concentration. The relationship obtained... 

---