Xenon fluorinating agents

Silver difluoride [7783-95-1], AgF2, is a black crystalline powder. It has been classified as a hard fluorinating agent (3) which Hberates iodine from KI solutions and o2one from dilute aqueous acid solutions on heating. It spontaneously oxidizes xenon gas to Xe(II) in anhydrous hydrogen fluoride solutions (20). 

Eused-ring polycycHc fluoroaromatics can be made from the corresponding amino fused-ring polycycHc or from preformed fluoroaromatics, eg, 4-fluorophenyl-acetonitrile [459-22-3] (275). Direct fluorination techniques have been successfully appHed to polycycHc ring systems such as naphthalene, anthracene, benzanthracenes, phenanthrene, pyrene, fluorene, and quinoHnes with a variety of fluorinating agents xenon fluorides (10), acetyl hypofluorite (276), cesium fluoroxysulfate (277), and electrochemical fluorination (278,279). 

Stable noble-gas compounds have no industrial uses as of this writing but are frequently utilized in laboratories as fluorinating and oxidizing agents. Xenon difluoride and xenon tetrafluoride are relatively mild oxidative fluorinating agents and have been used for the preparation of phosphoms, sulfur, tellurium. 

Electropositive fluorinating agents are categorized in distinct classes as (1) fluoroxy reagents, in which the fluorine is bound to an oxygen atom (for reviews, see references 1,2,3, 4, 5, and 6) (2) fluoraza reagents, in which the fluorine atom IS bound to the nitrogen atom of either an amide or ammonium ion structure (for a partial review, see reference 6), (3) xenon difluoride, in which the fluorine atoms are bound to xenon (for reviews, see references 5, 7, 8, and 114) and (4) perchloryl Iluoride, in which the fluorine atom is bound to the chlorine atom of the perchloryl function (for a review, see reference 9). 

The xenon fluorides are used as powerful fluorinating agents (reagents for attaching fluorine atoms to other substances). The tetrafluoride will even fluori-nate platinum metal ... 

Xenon difluoride has proved to be an effective fluorinating agent for surface fluorination of polymers. 

Safety precautions applicable to direct liquid phase fluorination of aromatic compounds are discussed [1]. Attention is drawn to the hazards attached to the use of many newer fluorinating agents [2], In a study of fluorination reactions of hafnium and zirconium oxides by the fluoroxidisers xenon difluoride, chlorine trifluoride and bromine trifluoride, reactivity decreased in the order given [3],... 

Very few are known, all may be seen as derived from FKr+. All are thermodynamically unstable and energetic fluorinating agents. Listed are Fluorohydrocyanokrypton hexafluoroarsenate, 0367 Fluorokrypton hexafluoroarsenate, 0096 Krypton difluoride, 4313 See also xenon compounds... 

Various fluorine compounds, such as xenon(II) fluoride, act under certain conditions (irradiation, gas-phase reaction) as radical fluorinating agents. Electrochemical fluorinations (see Section 7.) carried out in hydrogen fluoride containing systems (ref 7, pp73-76) are further examples of radical-type reactions. 

Among the noble gas fluorides, the binary fluorides of xenon have received the most attention as fluorinating agents. Krypton fluorides seem to be more exotic novelties than real reagents. 

On the other hand, oxidizing fluorinating agents like silver difluoride, xenon difluoride, or bromine trifluoride replace one chlorine group and then cleave the sulfur-nitrogen bond [5(5]. 

Xenon difluoride is a convenient electrophilic fluorinating agent, since it can be stored for long periods in a dry atmosphere and it is quite versatile. Its price per reactive fluorine, however, is high and this somewhat limits its popularity. 

The reaction of a citronellic enolate—a potential precursor to a 5-hexenyl-type radical clock—with various fluorinating agents leads exclusively to the corresponding a-fluorinated ester derivatives. The complete absence of cyclic fluorinated products is proof that the fluorination does not occur via radical intermediates, while the formation of a cyclic product in the reaction with xenon difluoride is an indication that electron transfer is a competitive process which does not give a fluorinated product31 (Scheme 9). 

Fluorination with elemental fluorine diluted 1 20 with nitrogen was used to prepare pentafluorophenyl tellurium trifluoride from bis[pentafluorophenyl] ditellurium at — 60° with fluorotrichloromethane as the reaction medium. The yield in this reaction was 80% 4-Methoxyphenyl tellurium trifluoride was obtained by electrochemical oxidation of the diaryl ditellurium in 0.5 M hydrofluoric acid at platinum electrodes2. Bisfpentafluoroethyl] ditellurium and chlorine fluoride (1 6) reacted at — 78° to give pentafluoroethyl tellurium trifluoride, a white solid melting at 95°3. The same compound was obtained with xenon difluoride as the fluorinating agent and melted at 143°4. 

In chemical behavior similar to that of interhalogens, the xenon fluorides act as fluorinating agents in a wide variety of reactions. Xenon difluoride is a milder reagent than is the tetrafluoride or the hexafluoride. It readily reacts with olefins to add fluorine ... 

The role of the silver salt is not completely understood. No evidence for a single electron transfer mechanism has been found. Although extremely reactive electrophilic fluorinating agents, such as xenon fluoride triflate (FXeOTf) or trifluoromcthanesulfonyloxy fluoride (TfOF), may be generated from the combination of xenon difluoride and silver(l) triflate, the reaction appears to proceed following initial interaction of the alkcnc with the silver ion. ... 

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