Английская Википедия:Fluorination by sulfur tetrafluoride
Fluorination by sulfur tetrafluoride produces organofluorine compounds from oxygen-containing organic functional groups using sulfur tetrafluoride. The reaction has broad scope, and SF4 is an inexpensive reagent. It is however hazardous gas whose handling requires specialized apparatus.[1][2] Thus, for many laboratory scale fluorinations diethylaminosulfur trifluoride ("DAST") is used instead.[3]
Main functional group conversions
Carboxylic acids, amides, esters, and carboxylate salts convert to the trifluoromethyl derivatives, although conditions vary widely:
For carboxlic acids, the first step gives the acyl fluorides, in keeping with the tendency of SF4 to fluorinate acidic hydroxyl groups:
Similarly SF4 converts sulfonic acids to sulfonyl fluorides:
Aldehydes and ketones convert to geminal difluorides:
Alcohols convert to alkyl fluorides, although this conversion works best with acidic alcohols, such as fluorinated alcohols:[4]
Mechanism
The mechanism of fluorination by SF4 is assumed to resemble chlorination by phosphorus pentachloride.[1] Hydrogen fluoride, a useful solvent for these reactions, activates SF4:
Species of the type ROSF3 are often invoked as intermediates. In the case of aldehydes and ketones, SF4 is thought to initially add across the double bond to give R2CFOSF3.[4]
Examples
A solution of sulfur tetrafluoride in hydrogen fluoride converts hydroxy-containing amino acids to the fluoro amino acids:[5]
When vicinal diols are combined with SF4, difluorination occurs with inversion of configuration at only one of the alcohols. This was demonstrated in the synthesis of meso-difluorosuccinate from (L)-tartrate and the synthesis of (D)- and (L)-difluorosuccinate from meso-tartrate.[6]
Carbonyl compounds generally react with SF4 to yield geminal difluorides. Reaction times tend to be on the order of hours and yields are moderate.[7] Fluorination of lactones can provide heterocyclic fluorides, although ring opening has been observed for γ-butyrolactone. The six-membered lactide does not experience ring opening.[8]
Fluorination opens epoxides to give either geminal or vicinal difluorides in most cases. Monoarylepoxides give geminal products with migration of the aryl group. Yields are low for sterically hindered di- and trisubstituted epoxides. Epoxides substituted with an ester group give vicinal difluorides via an alkoxysulfur trifluoride intermediate.[9]
Carboxylic acids react with SF4 to afford trifluoromethyl compounds:[10]
The formation of the trifluoromethyl derivative sometimes competes with formation of tetrafluoroalkyl ethers, which arise from the reaction between difluoromethyl cation and acyl fluoride.[11][12]
Sulfur tetrafluoride can be used to fluorinate polymers efficiently. This often has a profound effect on polymer properties—fluorination of polyvinyl alcohol, for instance, improves its resistance to strong acids and bases.[13]
A prostaglandin bearing a trifluoromethyl group at C-16 is prepared using sulfur tetrafluoride.[14]
Related reagents
For small scale reactions, SF4 can be inconvenient since it is a gas and stainless steel reaction vessels are required. Many transformations require elevated temperatures. The reaction generates hydrogen fluoride. These concerns have led to interest in alternative fluorinating reagents.[1] Selenium tetrafluoride, a liquid at room temperature, behaves similarly to SF4. Diethylaminosulfur trifluoride (DAST) is a derivative of SF4 that is easier to handle, albeit more expensive.[3]
References
- ↑ 1,0 1,1 1,2 Шаблон:March6th
- ↑ Шаблон:Cite book
- ↑ 3,0 3,1 Шаблон:Cite book
- ↑ 4,0 4,1 Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Bell, M.; Hudlicky, M. J. Fluorine Chem. 1980, 15, 191.
- ↑ Mobbs, H. J. Fluorine Chem. 1971, 1, 361.
- ↑ Muratov, N.; Burmakov, I.; Kunshenko, V.; Alekseeva, A.; Yagupol'skii, M. J. Org. Chem. USSR (Engl. Transl.) 1982, 18, 1220.
- ↑ Yagupol'skii, M.; Golikov, I.; Alekseeva, A.; Aleksandrov, M. J. Org. Chem. USSR (Engl. Transl.) 1971, 7, 737.
- ↑ Шаблон:OrgSynth
- ↑ Dmowski, W.; Kolinski, A. Rocz. Chem. 1974, 48, 1697.
- ↑ Dmowski, W.; Kolinski, A. Pol. J. Chem. 1978, 52, 547.
- ↑ Bezsolitsen, P.; Gorbunov, N.; Nazarov, A.; Khardin, P. Vysokomol. Soedin., Ser. A 1972, 14, 950 [C.A., 77, 75710e (1972)].
- ↑ Holland, G. W.; Jernow, J. L.; Rosen, P. U.S. Pat. 4,256,911 (1981) [C.A., 89, 146500x (1978)].
.png){kind=link}
