Sulfur tetrafluoride, with

Polyhalodiethyl ethers are also formed in the reaction of sulfur tetrafluoride with perhaloacetaldehydes in the case of chloral, a chlorine-fluorine rearrangement occurs [I7Q] (equations 82 and 83). 

Trimethylacetaldehyde reacts with sulfur tetrafluoride with a skeletal rearrangement 2,3-difluoro-2-methylbutane is formed in high yield as the only fluo-roalkane along with bis(l-fluoro-2,2-dimethylpropyl) ether [169] (equation 85)... 

These reactions differ from those of sulfur tetrafluoride with carbonyl compounds in that a formal oxidation-reduction of the sulfur atoms m the thiocarbonyl compound and sulfur tetrafluoride molecule occurs, resulting in the formation of free sulfur and the complete utilization of the fluorine atoms in sulfur tetrafluoride. 

Hydroxymethyl)furan, Triethylamine Jenzen, A. F. et al., J. Fluorine Chem., 1988, 38, 205-208 Reaction of sulfur tetrafluoride with 2-hydroxymethylfuran in presence of triethylamine at —50°C is explosive in absence of a solvent. 

A number of tabular surveys and reviews on the reactions of sulfur tetrafluoride with organic compounds have been published since I960.10-29 33... 

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... 

Support for the participation of fluorocarbenium ions 2 in the above mechanism is provided by trapping with aromatic hydrocarbons in the reaction of sulfur tetrafluoride with haloacetic acids, c.g. formation of 4,36 and haloacetones.37... 

This mechanism, reaction of sulfur tetrafluoride with carbonyl compounds, is also supported by rearrangements observed on reaction with aliphatic aldehydes.38... 

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). 

Rearrangements arc common in reactions of sulfur tetrafluoride with acetylenic and allylic alcohols. Highly acidic acetylenic alcohols derived from hexafluoroacetone and other haloacetones react readily at ambient temperature to give fluorinated allenes 10 as the sole... 

Rearranged fluoroalkenes are also the sole products of the reaction of sulfur tetrafluoride with tertiary allylic alcohols. For example, 1,1,l-trifluoro-2-(trifluoromethyl)but-3-en-2-ol gives exclusively 1,1,1,4-tetrafluoro-2-(trifluoromethyl)but-2-ene (12).57... 

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... 

Trichloroacetaldehyde (chloral) reacts with sulfur tetrafluoride with a Cl-F shift. At 150 C... 

An F-H rearrangement occurs in the reaction of sulfur tetrafluoride with protoadamantan-4-one, to give 1,2-difluoroadamantane (10) in high yield.87... 

The reaction of sulfur tetrafluoride with carboxylic acids (aliphatic, aromatic, and heterocyclic) is of particular importance as the most general and simplest route to trifluorotnethyl derivatives. The reaction proceeds in two steps, the first step gives acyl or aroyl fluorides 1, and then catalysis in the second step by hydrogen fluoride released in the first step results in the tri-fluoromethyl derivatives 2.41... 

The reaction of sulfur tetrafluoride with 4-oxocarboxylic acids proceeds via cyclic lactones to give pentafluoroalkanes as the final product. The intermediate lactones may be isolated from reactions conducted under sufficiently mild conditions, e.g. formation of 27 via lactone 26.117... 

Ring closure is a common feature of the reaction of sulfur tetrafluoride with cyclopropane-, cyclobutane- and cyclopentanepolycarboxylic acids. This tendency seems to be enhanced by steric crowding. Thus, m,tricarboxylic acid gives a 1 1 mixture of cyclic ether 13 and cis,trims-], 2,3-tris(trifluoromethyl)cyclopropane, whereas cyclopropane-... 

Formation of a six-membered ring by cyclization of a,y-carboxylic acid groups is also observed in the reaction of sulfur tetrafluoride with (1 / , S)-( + )-camphoric acid besides 1,2,2-trimethyl-3-(trifluoromethyl)cyclopentanecarbonyl fluoride (20) and camphoroyl difluoride (21). the bicyclic tetrafluoro ether, 2,2,4,4-tetrafluoro-l,8,8-trimethyl-3-oxabicyclo[3.2.1]octane (22). is formed. The ratio of products strongly depends on the reaction conditions.250... 

Similar to other ot-oxo acids, 2-oxopentanedioic acid reacts with sulfur tetrafluoride with elimination of carbon monoxide cyclization is, however, the main reaction pathway. 2,2.5,5-Tetrafluorotetrahydrofuran (26) is formed as the major product together with 1,1,1,4,4,4-hexa-fluorobutane.117... 

Similarly, salts of carboxylic acids are converted into carboxylic acid fluorides, e.g. 4,41 or trifluoromethyl derivatives, e.g. 5,113 by treatment with sulfur tetrafluoride, with or without hydrogen fluoride in the latter case a sufficiently large excess of hydrogen fluoride is required. 

Reactions of sulfur tetrafluoride with organic compounds proceeding with substitution of hydrogen by fluorine are considered anomalous, but there are increasing numbers of reports describing such reactions. The classic example is anthracen-9(10//)-onc which on treatment with sulfur tetrafluoride and hydrogen fluoride, instead of the expected 9,9-difluoro-9,10-di-... 

Diaryldifluorotellurium compounds, e.g. 19, are formed in high yield by reaction of sulfur tetrafluoride with either diaryl tellurides or diaryl ditellurides.221... 

The reaction of sulfur tetrafluoride with tetraisocyanatosilane affords fluorocarbonyliminosul-fur difluoride (29)229 and with bis(trimethylsilyl)carbodiimide230 a mixture of cyanoiminosul-fur difluoride and fluorotrimethylsilane is formed. 

Exercise 16-31 Work out reasonable mechanisms for the reactions of phosphorus pentachloride and sulfur tetrafluoride with carbonyl groups. Both phosphorus and sulfur can accommodate five or more) bonded atoms, and the structure of phosphorus pentachloride in the solid state is [PCI4 ] [PCl60]. 

Reaction of sulfur tetrafluoride with 2-hydroxymethylfuran in presence of triethylamine at —50°C is explosive in absence of a solvent. 

Reactions of sulfur tetrafluoride with glycols usually proceed slightly differently. Yagupolskii and coworkers investigated reactions with 1,2-, 1,3- and 1,4-diols and found that in most cases only one of the hydroxyls was substituted, since a cyclic intermediate was formed and it reacted with a fluoride anion to give fluoroalcohols. The regioselectivity is usually governed by electronic factors (equation 63)117. 

Various hydroxy esters have been fluorinated in excellent yield with sulfur tetrafluoride. with hydrogen fluoride present in the reaction mixture. Dimethyl (-F )-l-tart rate on reaction with sulfur tetrafluoride,-hydrogen fluoride gives dimethyl / )c.vn-2,3-difluorosuccinate (3) in 96% yield. ... 

As discussed above, simple alcohols are not usually fluorinated with sulfur tetrafluoride with good results. For example, the attempted synthesis of 2-(fluoromethyl)furan and l-fluoro-2-phenylethanc from (2-furyl)mcthanol and 2-phcnylethanol at — 50 C in the presence of triethylamine or pyridine as a hydrogen fluoride scavenger gives the desired products in yields of only 20 and 35%, respectively.- ... 

Diethylaminosulfur trifluoride gives results similar to those of the reaction of sulfur tetrafluoride with epoxides, but mixtures of geminal diduorides. vicinal difluorides and bis(2-lluoroalkyl) ethers are obtained in low to moderate yield, depending on the structure of the epoxide." ... 

---