Higher-Valent States Oxides and Oxoacids

In our experience, the mechanisms of cyclooctachalcogen ring formation are perceived as a bit more difficult than nucleophilic breakdown of the same rings. They are certainly quite challenging exercises in arrow pushing. We hope you ll get more comfortable with practice  

The two common oxides of sulfur, SO2 and SO3, are typical acidic oxides they react with water to yield sulfiirous acid (H2SO3) and sulfuric acid (H2SO4), respectively  

A by-product of fossil fuel combustion, SO2 is a major pollutant, and the above two reactions, which take place in cloud droplets, play a key role in the processes leading to acid rain. 

Sulfur trioxide is a strong Lewis acid and reacts with Lewis bases (indicated below as L) such as pyridine and triphenylphosphine to give stable adducts  

Sulfur trioxide reacts with anhydrous HF and HCl to yield the corresponding halo-sulfonic acids, XSO3H  

---