ON THE REACTIONS BETWEEN PHOSPHORUS PENTACHLORIDE AND LACTONES

Abstract

Reactions between PCl₅ and substituted or unsubstituted β-, γ- and ϵ- lactones have been investigated. Although γ- butyrolactone substituted at α- position with an alkyl radical has given phosphorylated products of both cyclic ethers and chlorinated carboxylic acid chlorides along with γ- chlorobutanoic acid chloride, halogen substituted γ-butyrolactone such as α-bromo-γ-butyrolactone yielded α-bromo-γ-chlorobutanoic acid chloride in similar manner with β-propiolactone which gives β-chloropropionic acid chloride. The nature of radicals present at γ-position also affects the reaction products. Methyl or heptyl radicals yielded different products; in the latter case phosphorylated products were not isolated. The reaction pathway of ϵ-caprolactone with PCl₅ is changed by the temperature of the reaction mixture. It reacts at 20–30°C to give α,α-dichlorooxepane and ϵ-chlorohexanoic acid chloride, while a phosphorylated product was observed at 60–70°C. Possible mechanisms of these reactions are discussed.

Key Words:

• Lactones
• phosphorus pentachloride
• phosphonic acids
• phosphonic dichlorides
• chlorocarboxylic acid chlorides