Swarts process

Although many syntheses of chlorofluorocarbons and hydrochlorofluorocarbons have been published, those actually used in manufacturing processes are limited. By far the most important is the original Swarts reaction [5]. 

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... 

Because annual growth bands of sufficient size to permit chemical analysis form in corals, considerable effort has gone into the study of incorporation of trace components in these organisms. Experimental studies, such as those by Smith et al. (1979), have contributed substantially to the reliability of the use of the Sr content of corals as a paleothermometer, and the efforts of other researchers (e.g., Buddemeier et al., 1981 Swart and Hubbard, 1982 Shen and Boyle, 1988) have yielded insight into the processes controlling a variety of minor components in corals. 

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. 

A Swarts reaction and related processes (halogen exchange using HF)... 

It is more likely, however, that four-centre reactions occur since the metal fluorides can be used either alone or in catalytic amounts in the presence of anhydrous hydrogen fluoride. This latter process was developed by Swarts and it now usually bears his name (Figure 2.5). 

For many years chlorofluorocarbons (CFCs) were manufactured in huge quantities by Swarts-type processes but, after the introduction of the Montreal Protocol legislation, these compounds were superseded by non-ozone depleting HFCs (see Chapter 1). Fortunately, much of the chemistry developed for the manufacture of the CFCs can be adapted for the production of HFCs [7, 12-15]. 

Numerically small values of AC for solvolysis are also consistent with reaction via a bimolecular transition state which requires a decreasing contribution from structure (9) as the temperature is raised but the stdphonates, again, provide no evidence supporting this view. Concurrent Sifl and Sif2 processes for reaction with the same nucleophile have been reported for other substitutions (Casapieri and Swart, 1961 Kohnstam et al., 1959, 1962) but there is no guarantee that similar considerations will apply to solvol3rtic reactions. 

Since the simplest F-l,3-dithietane (38) cannot be prepared by dimerization of thiocarbonyl fluoride, probably due to propensity of the latter to polymerize, a different synthetic approach is employed for its synthesis. Two-step process includes photocyclodimerization of Cl2C=S and Swarts-type fluorination of the dimer by antimony trifluoride to give 38 (Scheme 2.20). Compound 38 can be a source of very pure thiocarbonyl fluoride, when pyrolyzed at 500°C." ... 

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