Oxygen with sulfur tetrafluoride

The reaction ot tormamides with sulfur tetrafluoride in the presence of potassium fluoride leads to replacement of both carbonyl oxygen and hydrogen with fluorine. The formyl group is directly converted into the trifluoromethyl group A-(trifluoromethyl)amines are formed in near quantitative yields [233] (equation 121)... 

Dodecafluoro(2,3-dimethylbutane-2,3-diol) reacts with sulfur tetrafluoride in an unconventional way instead of replacement of the hydroxy groups by fluorine, the substitution of four fluorine atoms in the sulfur tetrafluoride molecule by oxygen occurs to give a good yield of perfluorinated spiro-A4-sulfane 8.62... 

Perfluorinated tertiary amides and cyclic imides react cleanly with sulfur tetrafluoride/ hydrogen fluoride at elevated temperatures by replacing the carbonyl oxygen atom by fluorines to give good yields of tertiary perfluoroamines, e.g. formation of 13 and 14.178... 

Nitriles are resistant to reaction with sulfur tetrafluoride under the conditions generally used for fluorination of oxygen functions. Acetonitrile, which is used as the solvent in the laboratory synthesis of sulfur tetrafluoride (see Section 8.1.2.), is particularly resistant and no reaction occurs up to 260"C, at which temperature extensive decomposition takes place and 1,1,2-tri-fluoroethyliminosulfur difluoride is formed in low yield,202... 

The hypofluorite, fluorine fluorosulfate (12), reacts explosively with sulfur tetrafluoride at liquid nitrogen temperature to afford a low yield of pentafluorosulfur fluorosulfate (13), together with sulfuryl fluoride, sulfur hexafluoride and oxygen.217... 

Oxygen functionalities bonded to a metalloid are replaced by fluorine when reacted with sulfur tetrafluoride. Triphenylphosphane oxide, phenylarsenic acid,219 and triphcnylantimony oxide and its bis(trifluoroacetoxy) derivative222 can be converted by sulfur tetrafluoride into the corresponding organophosphorus, organoarsenic and organoantimony fluorides 16,20 and 21. 

Deep fluormation using the La-Mar technique was carried out on polymers such as polyethylene and polypropylene [/ ], on polyethers [19, 20, 21], and on polyesters subsequently treated with sulfur tetrafluoride [22] Deep fluorinations carried out under conditions producing limited fragmentation produced oligomeric perlluoropolyethers from powdered polyethylene oxide [23] Deep fluorinations carried out in the limited presence of molecular oxygen result m the conversion of... 

The esters of aliphatic a- and /J-hydroxy carboxylic acids react with sulfur tetrafluoride to form mixtures of the corresponding esters of fluorocarboxylic acids and alkoxycarbonyl fluoro-sulfites. If there are electron-withdrawing substituents, such as trifluoromethyl groups, in the a-position the carbonyl oxygen is substituted by two fluorine atoms without substitution of the hydroxy group. ... 

Substitution of hydrogen atoms instead of the carbonyl oxygen has been observed in the reaetion of anthrone with sulfur tetrafluoride-hydrogen fluoride. 

Carboxylic esters, usually methyl or ethyl esters, can be converted into trifluoromethyl compounds by reaction with sulfur tetrafluoride in the presence of an excess of hydrogen fluoride. In comparison to carboxylic acids more vigorous conditions are needed." Substitution of the ester group carbonyl oxygen is observed with fluoroalkyP or phenyl esters " of polyfluorocarboxylic acids, fluorine-containing a-oxo esters,fluorine-containing a- and j -hydroxy esters, " and furancarboxylic esters. ... 

Sulfur tetrafluoride [7783-60-0] SF, replaces halogen in haloalkanes, haloalkenes, and aryl chlorides, but is only effective (even at elevated temperatures) in the presence of a Lewis acid catalyst. The reagent is most often used in the replacement of carbonyl oxygen with fluorine (15,16). Aldehydes and ketones react readily, particularly if no alpha-hydrogen atoms are present (eg, benzal fluoride [455-31-2] from benzaldehyde), but acids, esters, acid chlorides, and anhydrides are very sluggish. However, these reactions can be catalyzed by Lewis acids (HP, BF, etc). 

The most general and useful application of sulfur tetrafluoride is replacement of carbonyl oxygen and hydroxy groups by fluorine. The reaction has broad scope and is effective with all carbonyl and hydroxy compounds. Alcohols are converted into monofluoro derivatives 1, aldehydes, ketones and quinones into gew-difluoro compounds 2 and 3, and carboxylic acids, acid anhydrides, acid halides and amides into trifluoromethyl compounds 4. 

In most cases, the reaction of sulfur tetrafluoride with oxygen functions requires the presence of catalytic to molar amounts of hydrogen fluoride or Lewis acid type fluorides. Standard quality sulfur tetrafluoride, unless special precautions are taken, is unavoidably contaminated by trace amounts of hydrogen fluoride. The existence of ionic species SF3+ and HF2 in the SF4/HF system has been documented by spectral and conductometric investigations34 and there is evidence from vapor-pressure measurements of retardation of the reaction by coordination of hydrogen fluorine on the carbonyl oxygen.35... 

Esters of carboxylic acids are resistant toward sulfur tetrafluoride up to 300 °C. However, in the presence of an excess of hydrogen fluoride, they react like the acids to give trifluoromethyl compounds [187,235] In contrast, esters of highly fluorinated acids or alcohols react with sulfur tetrafluonde in a hydrogen fluoride solution under mild conditions without cleavage of the ester bond and give products of the replacement of carbonyl oxygen by fluorine a,a-difluoroethers [235, 236, 237, 238] (equations 124 and 125). 

A fluoride of composition SF4 is formed when fluorine diluted with nitrogen is passed over a film of sulfur at — 75°C in the absence of oxygen and moisture. Write the Lewis structure of sulfur tetrafluoride. 

Sulfur tetrafluoride converts carboxylic acids, in the first reaction step, into the acyl fluorides, and in the second step into trifluoromethyl compounds. By selecting suitable reaction conditions, the acyl fluorides can be isolated. " Thus. /> ra-substituted benzoic acids react at 20 C to yield the acyl fluorides almost exclusively." Substitution of the carbonyl oxygen requires higher reaction temperatures. Similar findings have been made with a series of different cyclohcxanedicarboxylic acids. ... 

Sulfur, unlike oxygen, has the capacity to expand its valence shell beyond the normal octet of electrons to form hypervalent compounds such as sulfur tetrafluoride (SF4) with 10 electrons in the outermost shell and sulfur hexafluoride (SF6) containing 12 electrons in the valence shell.63,7 The chemistry of hypervalent sulfur started in 1873 with the discovery of the unstable compound sulfur tetrachloride (SCI4). The existence of hypervalent sulfur compounds is an important feature of the chemistry of sulfur and the precise nature of the bonding in these molecules has remained a puzzling problem. 

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