New hydrofluoropolyethers: I. Synthesis and reaction pathway evaluation

A novel family of hydrofluoropolyethers (HFPEs) was obtained with 60-80% selectivity by hydrogenation of perfluoropolyether acyl chlorides with Pt/CaF₂. These compounds are characterized by a macromeric fluorinated body end-capped, on one or both sides, by a (1,1-difluoro)ethoxy group. A reaction pathway for the reduction was proposed consistently with the observed yields and side products. The hemiacetal originated by reaction of the aldehyde (first product of reduction) with the corresponding alcohol was postulated to be the key precursor leading to the HFPE. The metal appears to play a fundamental role promoting the hydrogenolysis of this unexpected intermediate. Exhaustive reduction of the alcohol, generally recognized as the path affording hydrocarbons in the hydrogenation of acyl chlorides, was excluded by products analysis and by specific experiments.