synthetic chemistry, two classes of chlorination are usually of interest: oxidative chlorinations and substitutive chlorinations. Oxidative chlorinations entail the transfer of Cl2 from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl5 can be used for both processes. Upon treatment with PCl5, carboxylic acids convert to the corresponding acyl chloride. The following mechanism has been proposed: It also converts alcohols to alkyl chlorides. Thionyl chloride is more commonly used in the laboratory because the resultant sulfur dioxide is more easily separated from the organic products than is POCl3. PCl5 reacts with a tertiary amides, such as dimethylformamide (DMF), to give dimethylchloromethyleneammonium chloride, which is called the Vilsmeier reagent, [(CH3)2N=CClH]Cl. More typically, a related salt is generated from the reaction of DMF and POCl3. Such reagents are useful in the preparation of derivatives of benzaldehyde by formylation and for the conversion of C−OH groups into C−Cl groups. It is especially renowned for the conversion of C=O groups to CCl2 groups. For example, benzophenone and phosphorus pentachloride react to give the diphenyldichloromethane: (C6H5)2CO + PCl5 → (C6H5)2CCl2 + POCl3 The electrophilic character of PCl5 is highlighted by its reaction with styrene to give, after hydrolysis, phosphonic acid derivatives. Comparison with related reagents Both PCl3 and PCl5 convert R3COH groups to the chloride R3CCl. The pentachloride is however a source of chlorine in many reactions. It chlorinates allylic and benzylic CH bonds. PCl5 bears a greater resemblance to SO2Cl2, also a source of Cl2. For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl5 since the gaseous SO2 by-product is readily separated. Chlorination of inorganic compounds As for the reactions with organic compounds, the use of PCl5 has been superseded by SO2Cl2. The reaction of phosphorus pentoxide and PCl5 produces POCl3 : 6 PCl5 + P4O10 → 10 POCl3 PCl5 chlorinates nitrogen dioxide to form unstable nitryl chloride: PCl5 + 2 NO2 → PCl3 + 2 NO2Cl 2 NO2Cl → 2 NO2 + Cl2 PCl5 is a precursor for lithium hexafluorophosphate, LiPF6. Lithium hexafluorophosphate is a commonly employed salt in electrolytes in lithium ion batteries. is produced by the reaction of with lithium fluoride, with lithium chloride as a side product: PCl5 + 6 LiF → LiPF6 + 5 LiCl Safety PCl5 is a dangerous substance as it reacts violently with water. It is also corrosive when in contact with skin