Synthesis of 2-(perfluoroalkyl)ethyl potassium sulfates based on perfluorinated Grignard reagents

Abstract

The first example of nucleophilic substitution with perfluoroalkyl Grignard reagents on the sp 3 carbon centre is described. Thus, a series of organometals R F-MgBr, prepared from perfluorinated alkyl iodides R F-I with R F = C 4F 9, C 6F 13, C 8F 17, C 10F 21 and C 12F 25, reacted with 1,3,2-dioxathiolane-2,2-dioxide to afford the corresponding 2-(perfluoroalkyl)ethyl magnesium sulfates, which were isolated after metathesis to the corresponding potassium salts. In the model reaction, perfluorohexylmagnesium iodide was reacted with methyl triflate yielding polyfluorinated alkane. The attempts to extend the reaction to 1,3,2-dioxathiane-2,2-dioxide were unsuccessful due to its inferior reactivity and only reduced polyfluoroalkane and the product of coupling were detected in the reaction mixture. Polyfluorinated sulfates are easily hydrolyzed with hydrochloric or triflic acid to the corresponding alcohols, which is an alternative to standard transformation of perfluoroalkyl iodides to 2-(perfluoroalkyl)ethanols. Quantum-chemical calculations of the PES of the reaction with both sulfur-containing heterocycles found that the failure of the reaction with 1,3,2-dioxathiane-2,2-dioxide is caused by higher activation energy of the process.