Iron(III) chloride (FeCl₃)-catalyzed electrophilic aromatic substitution of chlorobenzene with thionyl chloride (SOCl₂) and the accompanying auto-redox in sulfur to give diaryl sulfides (Ar₂S): Comparison to catalysis by aluminum chloride (AlCl₃)

GRAPHICAL ABSTRACT

ABSTRACT

The Lewis acids MCl₃ (M = Fe and Al)-catalyzed electrophilic aromatic (ArH) substitution reactions with thionyl chloride (SOCl₂) have been shown to give diaryl sulfoxide (Ar₂SO) and the reduced diaryl sulfide (Ar₂S). Under various selected conditions, the FeCl₃-catalyzed reactions of chlorobenzene gave substantially much higher percent yields of Ar₂S (Ar = p-ClC₆H₄) than the reactions catalyzed by AlCl₃, showing that FeCl₃ facilitates the reduction in the sulfur center of SOCl₂. A d_π −> p_π^* back bond between Fe(III) and the O˭S group is thought to be responsible for enhancement of the reduction.

KEYWORDS:

• Iron catalysis
• auto-redox, aromatic
• CH substitution
• chlorobenzene
• d_π-p_π^* bonding

Funding

We would like to thank University of Charleston and its Chemistry Program for financial support.