(RO)2SO. Carboxylic acids convert to trifluoromethyl derivatives. For example, treatment of heptanoic acid with SF4 at 100–130 °C produces 1,1,1-trifluoroheptane. Hexafluoro-2-butyne can be similarly produced from acetylenedicarboxylic acid. The coproducts from these fluorinations, including unreacted SF4 together with SOF2 and SO2, are toxic but can be neutralized by their treatment with aqueous KOH. The use of SF4 is being superseded in recent years by the more conveniently handled diethylaminosulfur trifluoride, Et2NSF3, "DAST", where Et = CH3CH2. This reagent is prepared from SF4: SF4 + Me3SiNEt2 → Et2NSF3 + Me3SiF Other reactions Sulfur chloride pentafluoride (), a useful source of the SF5 group, is prepared from SF4. Hydrolysis of SF4 gives sulfur dioxide: SF4 + 2 H2O → SO2 + 4 HF This reaction proceeds via the intermediacy of thionyl fluoride, which usually does not interfere with the use of SF4 as a reagent. Toxicity reacts inside the lungs with moisture, generating sulfur dioxide and hydrogen fluoride: SF4 + 2 H2O → SO2 + 4 HF References Sulfur fluorides Fluorinating agents Hypervalent molecules ja:フッ化硫黄#四フッ化硫黄