High specific surface area metal fluorides as catalysts for the fluorination of 2-chloropyridine by HF

The catalytic fluorination of 2-chloropyridine into 2-fluoropyridine by Cl/F exchange in presence of HF and a metal fluoride as catalyst was investigated. Crystallized metal fluorides (BaF2, MgF2, CaF2, ZnF2, LaF3 and CeF3) with significant specific surface area between 65 and 125 m2 g−1 were prepared by thermal decomposition of corresponding metal trifluoroacetates at 350 °C under nitrogen. These solids were stable under fluorination operating conditions involved in the formation of 2-fluoropyridine. An important gain in activity for the catalytic fluorination of 2-chloropyridine was obtained with these metal fluorides compared to corresponding oxides used as catalyst. BaF2 and MgF2 were the most active catalysts for the fluorination of 2-chloropyridine. The higher activities are in relation with the weak or moderate strength of Lewis acidity of the active sites, measured by CO adsorption followed by IR spectroscopy.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (188 K)Download as PowerPoint slideHighlights► Heterogeneous catalytic process with HF gas used to prepare 2-fluoropyridine. ► High specific surface area metal fluorides used as catalyst. ► Thermal decomposition of metal trifluoroacetates synthesis used to prepare metal fluoride catalysts. ► Fluorination of 2-chloropyridine involving unsatured metals as active sites with a weak or moderate Lewis acidity.