Homolytic Aromatic Sulfonation with K 2 S 2 O 5 Promoted by a Combination of Mn(OAc) 3 ·2H 2 O and HFIP.

Herein, we reported a so far unprecedented Mn(OAc) 3 ·2H 2 O-promoted homolytic aromatic sulfonation. The reaction was performed under mild conditions with K 2 S 2 O 5 employed as a green sulfonating reagent. Various arenes were successfully converted into desired sulfonic acids or sulfonates in high efficiency. Preliminary mechanistic studies demonstrated that the present reaction proceeds via a homolytic aromatic substitution-type mechanism involving an SO 3 - radical. The combination of Mn(OAc) 3 ·2H 2 O and HFIP plays a crucial role.