Unexpected effect of alkoxides on the reactivity of sodium borohydrid in the reduction of perfluoropolyether carboxylic esters

The reduction of perfluoropolyether carboxylic esters to the corresponding alcohols with sodium borohydride in ethanol has been investigated. This reaction does not follow the expected stoichiometry but a large excess (>60% molar) of reducing agent is required for a complete conversion of the ester; this excess parallels the massive built up of hydrogen observed during the reaction.Interestingly, the addition of catalytic amount of sodium ethoxide strongly influences the course of the reaction, so that both the excess of reducing agent and the evolution of hydrogen during the reaction are strongly reduced. These experimental evidences suggest that different mechanisms are active depending on the selected experimental conditions, so indicating that the considered reduction can follow different pathways.