Thiodiglycol, or bis(2-hydroxyethyl)sulfide (also known as 2,2-thiodiethanol or TDE), is a viscous, clear to pale-yellow liquid used as a solvent. Its chemical formula is C4H10O2S, or HOCH2CH2SCH2CH2OH. It is miscible with water, acetone, alcohols, and chloroform.