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Thionyl chloride is an inorganic compound with the chemical formula SOCl 2.It is a moderately volatile, colourless liquid with an unpleasant acrid odour.Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes (50,000 short tons) per year being produced during the early 1990s, [5] but is occasionally also used as a solvent.
It occurs in compounds such as thionyl fluoride, SOF 2. Thionyl chloride , SOCl 2 , is a common reagent used in organic synthesis to convert carboxylic acids to acyl chlorides . In organic chemistry , the thionyl group is known as a sulfoxide group or sulfinyl group, and has the general structure RS(=O)R'.
It can also be produced from a range of methylphosphonates (e.g. dimethyl methylphosphonate) via chlorination with thionyl chloride. Various amines catalyse this process. [4] With hydrogen fluoride or sodium fluoride, it can be used to produce methylphosphonyl difluoride. With alcohols, it converts to the dialkoxide: [5]
A typical representative organic reaction displaying this mechanism is the chlorination of alcohols with thionyl chloride, or the decomposition of alkyl chloroformates, the main feature is retention of stereochemical configuration. Some examples for this reaction were reported by Edward S. Lewis and Charles E. Boozer in 1952. [2]
Key applications of thionyl chloride also include the pharmaceutical, pesticide, dye, and organic synthesis industries, among others. Thionyl chloride's versatile nature allows it to serve as an acylation agent and a dehydrating agent in various chemical reactions, making it indispensable in the synthesis of specialty chemicals, dyes, and reagents.
Aside from the widely used reactions described above, phosgene is also used to produce acyl chlorides from carboxylic acids: R−C(=O)−OH + COCl 2 → R−C(=O)−Cl + HCl + CO 2. For this application, thionyl chloride is commonly used instead of phosgene.
A convenient laboratory method is refluxing arsenic(III) oxide with thionyl chloride: [9] 2 As 2 O 3 + 3 SOCl 2 → 2 AsCl 3 + 3 SO 2. Arsenic trichloride can also be prepared by the reaction of hydrochloric acid and arsenic(III) sulfide. As 2 S 3 + 6 HCl → 2 AsCl 3 + 3 H 2 S
Alkenes react with hydrogen chloride (HCl) to give alkyl chlorides. For example, the industrial production of chloroethane proceeds by the reaction of ethylene with HCl: H 2 C=CH 2 + HCl → CH 3 CH 2 Cl. In oxychlorination, hydrogen chloride instead of the more expensive chlorine is used for the same purpose: CH 2 =CH 2 + 2 HCl + 1 ⁄ 2 O 2 ...