Pentafluoride

Difluoroamidosulfur pentafluoride is a colorless liquid that boils at —7.5 0.50°C. It can be stored in stainless steel at room temperature. Its infrared spectrum shows major bands at 885, 913, and 945 cm.-1. The purity may be checked by molecular weight (179) and elemental analysis (N, 7.82 S, 17.9). 

1-DIFLUOROUREA SOLUTIONS AND DIFLUORO-AMINE—EXTRA-HAZARDOUS MATERIALS 

Submitted by C. O. PARKER and J. P. FREEMANt Cheeked by WILLIAM GRAHAM and MAX LUSTIGt 

Difluoroamine (fluorimide) was discovered by Kennedy and Colburn as a by-product accompanying tetrafluorohydrazine in the reduction of NF3 by arsenic1 and arsine. It was found to be a product of hydrolysis of fluorinated urea80 and was detected in trace amounts among the products of fluorination of ammonia.8 Reactions to be considered for preparative purposes include the following (1) reduction of tetrafluorohydrazine,4 (2) hydrolysis of difluorourea, (3) protonation of trityldifluoroamine, (4) hydrolysis of difluorosulfamide,7 and (5) hydrolysis of isopropyl difluorocarbamate.8 

Trityldifluoroamine and isopropyl difluorocarbamate are reported to be stable reagents which permit the generation of difluoroamine directly with a minimum of preliminary effort. Tetrafluorohydrazine also can be converted to difluoroamine with ordinary laboratory equipment. If these difluoroamino compounds are not available or if expense is a factor to be considered, the straightforward fluorination of urea or sulfamide in water followed by hydrolysis in situ permits the preparation of usable quantities of difluoroamine in a simple manner. 

Submitted by KAREL LUTAR, ANDREJ SMALC, and BORIS 2EMVA Checked by SCOTT A. KINKEADf 

Chlorine pentafluoride was first synthesized by fluorination of chlorine trifluoride with fluorine under pressure of 250 bar at 360°C. Later on this method was modified, for example, by use of alkali metal tetrafluorochlortttes instead of chlorine trifluoride. It has also been found that nickelfll) fluoride catalyzes the reaction between chlorine trifluoride and fluorine.  

The reaction is carried out in a 150-mL heavy-wall Monel pressure vessel rated to 350 bar, equipped with an 0.25-in. NPT opening and corresponding adapter with a Monel high-pressure valve with PTFE stem packing, rated to 700 bar. About 2 g of pulverized anhydrous nickel(II) fluoride is put into the vessel. The vessel is prefluorinated once or twice with about 500 mbar of fluorine and subsequently once or twice with about 500 mbar of chlorine trifluoride for an hour under occasional heating up to 300-400°C. Into the seasoned reaction vessel, cooled to - I96°C, about 40 mmol of chlorine trifluoride and about 400 mmol of fluorine are condensed. 

The reaction vessel is then removed from the liquid-nitrogen bath and placed into a cold electric furnace with an aluminum block. The aluminum block is then heated to 200°C for 3 h. Subsequently, the reaction vessel is cooled with liquid oxygen to — 183°C and excess fluorine is distilled off into another container, cooled to - 196°C. The rest of the fluorine is pumped dff through a soda-lime trap. Chlorine pentafluoride is removed from the reactor 

Chlorine pentafluoride at room temperature is a colorless gas that condenses to a colorless liquid (bp — 14°C) and freezes to a white solid (mp — 103°C). It appears to be less corrosive to metals than chlorine trifluoride and can be stored in nickel, Monel, or stainless steel containers. It is extremely reactive toward water. 

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Phosphorus pentafluoride PF will readily accept an electron pair from a fluoride ion F to form the stable hexafluorophosphate(V) anion PF C. This ion is isoelectronic with SF. and neither SF nor PF show any notable tendency to accept further electron pairs, though there is some evidence for the existence of an SF ion. 

Arsenic forms only the pentafluoride AsFj, a colourless liquid, b.p. 326 K. This resembles phosphorus pentafluoride. 

My work on long-lived (persistent) carbocations dates back to the late 1950s at Dow and resulted in the first direct observation of alkyl cations. Subsequently, a wide spectrum of carbocations as long-lived species was studied using antimony pentafluoride as an extremely strong Lewis acid and later using other highly acidic (superacidic) systems. 

Perchloric acid (HCIO4 Ho —13.0), fluorosulfuric acid (HSO3F Ho — 15.1), and trifluoromethanesulfonic acid (CF3SO3H Ho —14.1) are considered to be superacids, as is truly anhydrous hydrogen fluoride. Complexing with Lewis acidic metal fluorides of higher valence, such as antimony, tantalum, or niobium pentafluoride, greatly enhances the acidity of all these acids. 

In a generalized sense, acids are electron pair acceptors. They include both protic (Bronsted) acids and Lewis acids such as AlCb and BF3 that have an electron-deficient central metal atom. Consequently, there is a priori no difference between Bronsted (protic) and Lewis acids. In extending the concept of superacidity to Lewis acid halides, those stronger than anhydrous aluminum chloride (the most commonly used Friedel-Crafts acid) are considered super Lewis acids. These superacidic Lewis acids include such higher-valence fluorides as antimony, arsenic, tantalum, niobium, and bismuth pentafluorides. Superacidity encompasses both very strong Bronsted and Lewis acids and their conjugate acid systems. 

In eontrast, dialkylhalonium salts sueh as dimethylbromonium and dimethyliodonium fluoroantimonate, whieh we prepared from excess alkyl halides with antimony pentafluoride or fluoroantimonie acid and isolated as stable salts (the less-stable chloronium salts were obtained only in solution), are very effective alkylating agents for heteroatom eompounds (Nu = R2O, R2S, R3N, R3P, ete.) and for C-alkylation (arenes, alkenes). 

Iodine Acetaldehyde, acetylene, aluminum, ammonia (aqueous or anhydrous), antimony, bromine pentafluoride, carbides, cesium oxide, chlorine, ethanol, fluorine, formamide, lithium, magnesium, phosphorus, pyridine, silver azide, sulfur trioxide... 

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