Swarts fluorination

A newer field of application of Swarts fluorination in carbohydrate chemistry is the synthesis of glycosyl fluorides from the corresponding bromides [46] (Scheme 2.16.). 

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. 

Antimony tnfluoride is a mild fluorinating reagent. However, it is much mote effective ia the Swarts reactions where its effectiveness as a fluorinating reagent is dramatically iacteased by addition of CI2, Bt2, or SbCl to the reaction mixture (2). Antimony tnfluotide can be used for the replacement of chlorine or bromine ia halocatbons, hydtohalocatbons, and nonmetal and metal haUdes. Typical reactions can be summarized as follows ... 

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. 

Our resolution to this dilemma has been to work out a compact procedure based upon the fluorinating agent SbF3 catalyzed by SbCl5 using acetonitrile as a solvent (i.e., the Swarts reaction).6... 

Also active at this time was Swarts, already the leader in research on aliphatic fluorine chemistry (see Section 1.4.2.1.). Polysubstituted aryl fluorides (N02, NH2, OH, alkoxy and Cl derivatives) were produced, interrelated with, and complementary to, Holleman s results. Rinkes carried out sequences leading to products bearing various functions (NHOH, NHNH2, NO, and -N = N-). 

It was recognized in the 1930s that Swarts work on (trifluoromethyl)benzene opened the way to the synthesis of many side-chain-fluorinated arenes. Aryl trichloromethyl groups were found to be readily converted to trifluoromethyl groups by anhydrous hydrogen fluoride, and systematic work in the area was initiated. This included commercial investigations, and patents were filed on potential uses of both side chain and nuclear fluorinated arenes. 

Swarts made a vast contribution to organo-fluorine chemistry. It is unlikely that its impact will ever be equaled hy that from any other individual s work, within their respective contexts. 

Chlorine atoms in (trichloromethyl)benzenes which have fluoro, chloro, dichloromethyl, chloroformyl, cyano, isocyanato, jV-phthalimino or methyl substituents in the ring are substituted by fluorine using antimony(III) fluoride (Swarts reaction).3 4 2-(Trifluoromethyl)phen-yl isocyanate, 4-chloro-2-(trifluoromethyl)phenyl isocyanate, 2,4- and 2,5-bis(trifluoro-methyl)phenyl isocyanate, and 2,4-bis(trifluoromethyl)-l,5-phenylenc diisocyanate can be obtained in this way.5... 

SWARTS REACTION. Fluorination of organic polyhalides with antimony trifluoride (or zinc and mercury fluorides) in the presence of a trace of a pentavalent antimony salt. 

Fluorination of sulfuryl halides by halogen exchange is apparently a very difficult process to force to completion even at temperatures as high as 300° the usually effective Swarts reagent takes sulfuryl chloride only to the chloride... 

It has been observed that a definite threshold temperature exists below which the Swarts reaction will not proceed. The best results are obtained if the desired product is removed as fast as it is formed. More highly fluorinated products may be obtained if the reaction products are refluxed in the reactor. 

Hydrogen fluoride is used in the Swarts reaction on a commercial scale to regenerate the antimony (III) fluoride. The compound to be fluorinated and anhydrous hydrogen... 

Since fluorine is the most electronegative element, the abundant fluorides are natural tools for fluorination. As a matter of fact chemists had already started employing nucleophilic displacements using fluorides during the 19th century, as evident from Swart s work where AgF was used for the synthesis of methyl fluoroacetate from the corresponding iodo derivative (equation l)7. 

The chemistry of fluorine and its compounds has long lagged behind the chemistry of the other three halogens. While hydrochloric acid was well known in antiquity, hydrogen fluoride was first described by Scheele only in 1771, and fluorine was first prepared by H. Moissan in 1886. Organic fluorine compounds were studied systematically by F. Swarts only at the end of the last century, and the first industrial application of fluorine compounds came from the discovery of fluorinated refrigerants by A. L. Henne and T. Midgley around 1930. 

Arsenic trifluoride and especially SbF3 (called the Swarts reagent) are very useful reagents for fluorination of various nonmetallic substrates, as indicated by the following conversions ... 

The fluorination of an aromatic trichloroinethyl group is also achieved with antimony(III) fluoride in molar ratios ranging from antimony(III) fluoride/(trichloromcthyl)benzene 5 1 to 2 1 129 135 jjjjj chemistry (the Swarts reaction) has been extended to substituted aromatics, with some examples given by the formation of 7, 8, 9 and lO. - ... 

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