Described herein is a direct approach to symmetrical thioethers from either aromatic carboxylic acids or aromatic aldehydes with elemental sulfur (S-8) by using a reducing system combined with InI3 and 1,1,3,3-tetramethyldisiloxane (TMDS). This sulfidation does not require functionalized sulfur reagents, such as sulfides, disulfides, or metal sulfides, and it simultaneously forms two carbon-sulfur bonds in a single catalytic system.