Swarts catalyst

Although the first technical plants for CFC manufacturing used the Swarts catalyst exclusively, heterogeneously catalysed processes are competitive in the situations described above. Metal(III) oxides, especially chromia and alumina, are frequently used as solid catalysts. Moreover, they have often been used mixed with traces of other, usually metal(II), oxides, to prepare catalysts that have perceived advantages. 

Organic fluorine compounds were first prepared in the latter part of the nineteenth century. Pioneer work by the Belgian chemist, F. Swarts, led to observations that antimony(Ill) fluoride reacts with organic compounds having activated carbon—chlorine bonds to form the corresponding carbon—fluorine bonds. Preparation of fluorinated compounds was faciUtated by fluorinations with antimony(Ill) fluoride containing antimony(V) haUdes as a reaction catalyst. 

The generally accepted mechanism of the Swarts reaction assumes the formation of an antimony (V) halofluoride. The following reactions are postulated in connection with the catalysts mentioned above ... 

The pioneering work in this field was performed by F. Swarts starting from 1892. Treatment of different haloalkanes with HF in the presence of Lewis acids such as SbFs, SbFs, AgF, HgF2, and AIF3 yielded mixtures of partially and fully fluori-nated alkanes, depending on the exact reaction conditions (Scheme 2.14). Stoichiometric amounts of the Lewis catalysts themselves can also serve as the fluoride source [41]. 

The main synthetic route to CFC, HCFC and Halons is the Swarts fluorination. Technically this is often achieved by reaction of a chlorinated or brominated precursor with anhydrous hydrofluoric acid in the presence of a solid Lewis acid catalyst, for example chromia. Other important reactions are Lewis acid-catalyzed halogen isomerization and hydrogenolysis of chlorine or bromine. 

Generally speaking, liquid-phase fluorination catalysts are located in groups 4 (Ti [2], etc.), 5 (Nb, Ta [3], etc.), 6 (Mo, etc.), 14 (Sn [4], etc.) and 15 (Bi, As, Sb [5], etc.) columns of the Periodic Table of the chemical elements. Among all these compounds, SbClj and more specifically the Sb(V)Cl F entities which were first synthesized by Swarts in 1895 [6], are the most active catalysts. From a mechanistic point of view, Sb(V)Cl Fj, in the presence of HF form superacidic species such as SbCl F +i H. Cl/F exchange reaction can be concerted or can proceed via a carbocation followed by addition of F [7], while the addition of HF to a double bond could proceed via two types of attack, nucleophilic (F ) or electrophilic (H ) [8]. 

Moshkalyov SA, Moreau ALD, Guttierrez HR, Cotta MA, Swart JW. Carbon nanotubes growth by chemical vapor deposition using thin film nickel catalyst. Materials Science and Engineering B-Solid State Materials for Advanced Technology 2004 112 147-53. http //dx.doi.Org/10.1016/j.mseb.2004.05.038. 

There is more than one method. Midgley seems to have used the reaction of CCI4 with SbFj (the Swarts reaction), producing CF2CI2 with some CFCI3. Using a suitable catalyst, HF can react... 

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