As a strong Lewis acid, BCl3 i forms adducts with tertiary amines, phosphines, ethers, thioethers, and halide ions.[4] Adduct formation is often accompanied by an increase in B-Cl bond length. BCl3 · S(CH3)2 (CAS# 5523-19-3) is often employed as a conveniently handled source of BCl3 because this solid (m.p. 88-90 °C) releases BCl3: