## 2 Syntheses of \(\alpha\),\(\omega\)-Dialkoxyfluoropolyethers
### 2.3. Preparation of DA-FPEs by DAF-PFPE Alkylation
#### 2.3.2 Catalytic Alkylation of Perfluoro(mono)acyl Fluorides and DAF-PFPE  
A classical example of catalytic alkylation is the alkylation of perfluoroacyl fluorides performed by employing SbF\({}_{5}\) as acid catalyst in anhydrous medium that reacts with alkyl fluoride to produce HFE (Figure 7). The first step in this pathway is the reaction of SbF\({}_{5}\) with alkyl fluoride forming high valence metal SbF\({}_{6}^{-}\). The extra F ion from SbF\({}_{6}^{-}\) attacks the carbonyl group of acyl fluorides forming  
Figure 6: **(a)** Reaction between DAF-PFPEs and fluorovinyl alkyl ethers; **(b)** Byproduct converted into hexafluoropropane; **(c)** Synthetic route for alkylating agent -fluorovinyl alkyl ethers. alkoxides. Subsequently, the nucleophilic addition to _in situ_ generated alkoxides produces the PFPE with alkoxy-group endings. In this reaction, work-up with a large amount of partially reacted metal fluoride is avoided; however, the drawback of this method is that the active acid catalyst may promote undesired isomerization or decomposition reactions and consequently deliver low or erratic yields [27]. DA-PFPEs can be also successfully obtained via a novel synthetic route that consists in the reaction of DAF-PFPEs with alkyl fluoroformate (Figure 8) in the presence of a source of fluorine ions, generally metal fluoride (MF); the reaction can be regarded as catalytic alkylation of _in situ_ generated PFPE dialkoxides. This fluoride-catalyzed fluoroformates alkylating reaction gives DA-PFPEs in good yield and CO\({}_{2}\) is the only by-product. Due to the big differences of boiling points among alkyl fluoroformates, DAF-PFPE and DA-PFPEs, un-reacted alkylating reagents can be easily restored through a standard distillation. Alkyl fluoroformate can be methyl, ethyl as well as allyl fluoroformates. The great variety of fluoroformate alkylating reagents improves the utility of this straightforward alkylating reaction. Examples of several successfully employed fluoroformates, which reacted with high boiling point linear DAF-PFPE with good selectivity and yield are reported in Table 1[28, 29]. This catalytic alkoxides alkylation followed two supposed pathways (Figure 9): (a) A nucleophilic addition of the perfluoroalkoxide to alkyl fluoroformate directly forming the DA-FPE and CO\({}_{2}\); or (b) through the carbonate intermediate, R\({}_{\textrm{F}}\)CFOC(O)OR\({}_{\textrm{H}}\), followed by a second nucleophilic substitution to generate the corresponding products [28]. According to both pathways, the rearrangement of the fluoroformate group can release fluorides and replenish the perfluoro-alkyloxy-anions formation by reacting with a new acylfluoride. Therefore, alkyl fluoroformates can be applied not only as alkylating agents but also as an alternative fluorine ion source for the alkoxide formation. \begin{table}
\begin{tabular}{c c c c c} \hline
**Acylifluoride** & **Fluoroformate** & **HFE** & **Conv.\%** & **Sel.\%** \\ \hline z-DAF \({}^{a}\) & CH\({}_{3}\)OC(O)F & CH\({}_{3}\)O-(Z-PFPE)-OCH\({}_{3}\) & 90 & 100 \\ z-DAF \({}^{a}\) & CH\({}_{5}\)CH\({}_{2}\)OC(O)F & CH\({}_{3}\)CH\({}_{2}\)O-(Z-PFPE)-OCH\({}_{2}\)CH\({}_{3}\) & 96 & 100 \\ z-DAF \({}^{a}\) & CH\({}_{2}\)=CHCH\({}_{2}\)O(O)F & CH\({}_{2}\)=CHCH\({}_{2}\)O-(Z-PFPE)-OCH\({}_{2}\)CH=CH\({}_{2}\) & 90 & 100 \\ \hline \multicolumn{5}{c}{\({}^{a}\) linear DAF-PFPE: FC(O)CF\({}_{2}\)O-(CF\({}_{2}\)C\({}_{2}\)O)\({}_{\textrm{H}}\)(CF\({}_{2}\)O)\({}_{\textrm{m}}\)-CF\({}_{2}\)(O)F (AMW 620 amu).} \\ \end{tabular}
\end{table} 
Table 1: Preparation of selected DA-PPFEs through perfluoropolyether acylfluorides alkylation. Figure 8: Reaction between DAF-PFPEs and alkyl fluoroformate with metal fluoride as source fluorine ions. Figure 7: Alkylation of acylfluorides with SbF\({}_{5}\) as acid catalyst. The alkyl fluoroformates are not commercially available and their synthesis comprises the reaction of carbonyl difluoride with alcohols at a low temperature in the presence of anhydrous sodium fluoride.