Sulfur tetrafluoride groups

With alcohols, mixtures of alkyl fluorides and alkyl ethers are obtained (100). Alcohols beating electron-withdrawiag groups can be converted to the corresponding fluorides ia high yield (101). Sulfur tetrafluoride replaces the carboayl oxygea with fluorine (100,102). 

Highly fluorinated tertiary alcohols usually give olefins on iluormation with sulfur tetrafluoride [759/, but in certain cases, replacement of the hydroxyl group with fluorine occurs under mild conditions Hexafluoro-2-arylpropan-2-ols react with sulfur tetrafluoride at low temperatures to give high yields of heptafluoro-isopropylarenes [766] (equation 77), and similarly, 3,8 dihydroxy 9,9,9,10,10,10-hexafluoro-p-menthane affords 3,8,9,9,9,10,10,10-octafluoromenthane [766] (equation 78)... 

Treatment of a- or P hydroxyacids with sulfur tetrafluoride leads to conver Sion of the carboxylic group into the tiifluoromethyl group, but the hydroxyl group undergoes either fluorination, fluorosulfination, esterification, or dehydration to form esters, ethers, or alkenes The ratio of the products depends on P substitution [209, 210] (equations 103 and 104)... 

Furan-2-carboxylic acid reacts with sulfur tetrafluoride at 0 °C to give 2-furoyl fluoride, but attempts at further fluorination results in resin formation [222] A second carboxylic group and/or electron withdrawing substiments, such as the nitro or tnfluoromethyl group, stabilize the furan ring Thus, turandicar-... 

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)... 

A series of reactions with gases have been selected for the rapid quantification of many of the major products from the oxidation of polyolefins. Infrared spectroscopy is used to measure absorptions after gas treatments. The gases used and the groups quantified include phosgene to convert alcohols and hydroperoxides to chloroformates, diazomethane to convert acids and peracids to their respective methyl esters, sulfur tetrafluoride to convert acids to acid fluorides and nitric oxide to convert alcohols and hydroperoxides to nitrites and nitrates respectively. 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

Sulfur tetrafluoride provides an inexpensive method for selectively converting a carbonyl to a difluoromethyl group. However, the reactions involving sulfur tetrafluoride, in general, require pressure equipment constructed of fluorine-resistant material such as Hastelloy-C bombs.8 Phenylsulfur trifluoride may be used to advantage for the same reaction, where small amounts are involved, since the reaction may be run at atmospheric pressure in glass, polyethylene, or metal containers. 

The sulfur tetrafluoride molecule has a distorted trigonal bipyramid structure with point group C 2V. The four fluorine atoms occupy four corners of the bipyramid around the central sulfur atom the fifth position is occupied by a lone pair of electrons.4... 

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. 

The result of the reaction of sulfur tetrafluoride with alcohols strongly depends on the structure of the alcohol. Simple aliphatic alcohols, such as methanol, ethanol and propan-2-ol, give alkyl ethers as the main product with only small amounts of fluoroalkanes.41 42 Yields of fluorinated products increase with increasing acidity of the hydroxy group and, in general, the reaction is only synthetically useful with alcohols equally or more acidic than tropolone (p K, = 6.42). 

Secondary and tertiary alcohols substituted with perhalogenated groups, such as 2,2,2-trifluoro-l-(pentafluorophcnyl)cthanol, 2-chloro-2.2-difluoro-l-(pentafluorophenyl)elhanol49 0 and l,l,l,3.3,3-hexafluoro-2-phcnylpropan-2-ols, 1-52 react with sulfur tetrafluoride in a conventional way to give products of the replacement of the hydroxy group by fluorine, la, lb and 2, respectively. 

Increasing the number of hydroxy groups in the substrate results in a sharp decrease in the yield of fluorinated compounds due to resinification and carbonization. This may be avoided by conducting the reactions at low temperatures in anhydrous hydrogen fluoride. Thus, the reaction of sulfur tetrafluoride with propane-1.2,3-triol (glycerol) at — 40 C gives 3-fluoro-propane-l,2-diyl sulfite (5) in high yield.60... 

Likewise, unprotected polyhydroxy compounds can be successfully fluorinated to give the products resulting from substitution of the hydroxy groups by fluorine, wn-o-lnositol reacts with sulfur tetrafluoride and anhydrous hydrogen fluoride at ambient temperature to give a moderate yield of the cyclic sulfite ester of tw/o. cfo-5,6-difluoro-7-oxabicyclo[2.2.1 heptane-e.w,e.vo-2,3-diol (6) and, alter hydrolysis, the free difluoro diol 7.61... 

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... 

Aliphatic a-hydroxy ketones react with sulfur tetrafluoride, generally to provide trifluoroal-kanes. However, under carefully chosen conditions the carbonyl group in hydroxy ketones remains intact while the hydroxy group undergoes selective substitution by fluorine. Thus, 5-hydroxyoctan-4-one reacts with sulfur tetrafluoride (20°C, 3 h) to give a 1 1 mixture of 5-fluorooctan-4-one(l b) and 2-oxo-l-propylpentyl fluorosulfite.63 a-Fluoro ketones 1 are formed in high yield and as the sole product when diethyl ether is used as solvent.64... 

Reaction of esters of hydroxyalkanoic acids with sulfur tetrafluoride, unless forcing conditions arc applied, generally results in selective replacement of the hydroxy group by fluorine to give almost equimolar mixtures of fluoroalkanoates 3 and alkoxycarbonylalkyl fluorosulfites 4 in high total yield.65... 

Sulfur tetrafluoride undergoes addition across the carbonyl groups of glyoxal to form 1,2-difluoroethane-l,2-diol orthosulfite 13 the reaction occurs at room temperature in the presence of a hydrogen fluoride scavanger, such as sodium fluoride.75... 

All aromatic aldehydes and heterocyclic aldehydes substituted with strong electron-withdrawing groups react cleanly with sulfur tetrafluoride at elevated temperatures, preferably in the presence of hydrogen fluoride, to give good yields of the respective difluoromethyl derivatives typical examples are given by the formation of 15. 

The low reactivity of the conjugated steroidal 3-oxo group towards the sulfur tetrafluoride/ hydrogen fluoride reagent is illustrated by the reaction of 5a-androst-1 -enc-3,11,17-trione which gives the 17,17-difluoro steroid 6 (66%) and the 3,3,17,17-tetrafluoro steroid 7 in only 7% yield.72... 

In 5o -fluoro-6,17-dioxo steroids and 5a-fluoro-6,20-dioxo steroids the 6-oxo group is preferentially fluorinated by sulfur tetrafluoride. For example, treatment of 3/ -acetoxy-5a-fluoropreg-... 

Only a few qui nones react with sulfur tetrafluoride in the normal way by replacing each carbonyl group by two fluorine atoms. The examples are 9,10-anthraquinone (l),41 phenanthrene-9,10-quinone (2),100 and acenaphthoquinone and its substituted derivatives 3.101102 The reactions proceed at 150-300 C, preferably in the presence of anhydrous hydrogen fluoride. 

The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

Adamantanecarboxylic acids with a carboxylic group at a bridgehead position, e.g. adaman-tane-1-carboxylic acid (8),111 react with sulfur tetrafluoride in the conventional way giving high yields of the corresponding trifluoromethyl-substituted adamantanes. l-(Trifluoromethyl)-adamantane (9) can also be formed in one step from adamantane by treatment with a mixture of sulfur tetrafluoride, hydrogen fluoride and formic acid the latter serves as a source of carbon monoxide. The reaction is believed to proceed via carbonylation of an intermediate carbocat-... 

Adamantane-2-carboxylic acid, in which the carboxy group is at a secondary carbon atom, on treatment with sulfur tetrafluoride gives a product with fluorine atoms at bridgehead positions, 5,7-difluoro-2-(trifluoromethyl)adamantane (10), in over 90% yield (see Section 8.2.10.).87... 

Aliphatic amino acids are converted into (trifluoromethyl)amines 12 by treatment with sulfur tetrafluoride in hydrogen fluoride. Hydrogen fluoride simultaneously protects the amino group by protonation and serves as a catalyst.113 The reactions proceed with retention of configuration. Yields of (trifluoromethyl)amines from a-amino acids vary from very low to approximately 40% and are limited by the formation of dioxopiperazines.113... 

The type of products formed in reactions of /(-hydroxy acids with sulfur tetrafluoride depends on the substituents on the carbon alom adjacent to the hydroxy group. Acids such as 3-hy-droxypropanoic acid (21) and 3-hydroxybutanoic acid (22) give, in addition to 1,1,1,3-tetra-fluoroalkanes, mainly dimeric products, i.e. fluorinated esters or ethers, together with small amounts of unsaturated acid fluorides. In contrast, n7C -4,4,4-trifluoro-3-hydroxybutanoic acid (23), depending on the reaction conditions, affords 3,3,3-trifluoro-l-(lrifluoromethyl)propyl fluorosulfite or a mixture of 1,1,1.2,4,4,4-hcptafluorobutanc and l,l,1.4.4,4-hcxafluorobut-2-ene.116... 

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