Silicon tetrafluoride, reaction

Silicon tetrafluoride is a colourless gas, b.p. 203 K, the molecule having, like the tetrahalides of carbon, a tetrahedral covalent structure. It reacts with water to form hydrated silica (silica gel, see p. 186) and hexafluorosilicic acid, the latter product being obtained by a reaction between the hydrogen fluoride produced and excess silicon tetrafluoride ... 

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

It is recognised that vitreous enamel possesses good acid resistance, but an exception occurs with hydrofluoric acid. This is due to the relative ease of reaction between this acid and the silica (which is the largest constituent in the frit) to form silicon tetrafluoride. This reaction is made use of in some de-enamelling plants. 

H.13 Hydrofluoric acid is used to etch grooves in glass because it reacts with the silica, Si02(s), in glass. The products of the reaction are aqueous silicon tetrafluoride and water. Write a balanced equation for the reaction. 

Sodium beryllium fluoride (Na2BeF4) is water-soluble and sodium aluminum fluoride (Na,AlF6) is water-insoluble. A part of the silicon volatilizes off as silicon tetrafluoride (SiF4), while the other part remains in the residue as silicon dioxide (Si02). Fluorination of silicon is unnecessary and it would be economical to recover all of it as silica. This is accomplished by using soda ash, i.e., sodium carbonate (Na2C03) in the reaction mixture ... 

Sir Humphry Davy attempted to isolate this unidentified element through electrolysis—but failed. It was not until 1824 that Jons Jakob Berzehus (1779—1848), who had earlier discovered cerium, osmium, and iridium, became the first person to separate the element silicon from its compound molecule and then identify it as a new element. Berzehus did this by a two-step process that basically involved heating potassium metal chips with a form of silica (SiF = silicon tetrafluoride) and then separating the resulting mixture of potassium fluoride and silica (SiF + 4K —> 4KF + Si). Today, commercial production of sihcon features a chemical reaction (reduction) between sand (SiO ) and carbon at temperatures over 2,200°C (SiO + 2C + heat— 2CO + Si). 

Hydrogen fluoride may be made from silicon tetrafluoride produced from phosphate rocks. A major step in the process involves reaction of sflicon tetrafluoride with recycled ammonium fluoride solution ... 

An alternative route of manufacture is from silicon tetrafluoride that is generated in large quantities as a by-product of the production of phosphate fertilizers. The reaction is... 

Aliphatic, aromatic, and alicyclic alkenes have been converted into the corresponding bromo fluorides 2 by reaction with l,3-dibromo-5,5-dimethylhydantoin (DBH) and silicon tetrafluoride in 1,4-dioxane at room temperature in a highly regio-, stereo- and chemoselective manner.9... 

Reaction of silicon tetrafluoride with phenylmagnesium bromide at 0 C in diethyl ether provides fluorotriphenylsilane and fluorodiphenylsilane in 59.5 and 5% yield, respectively.3 Chloro(cy-clohexyl)(l-naphthyl)silane is converted into (cyclohexyl)fluoro(l-naphthyl)silane by reaction with a reagent which is prepared by bubbling silicon tetrafluoride through a mixture of tet-rahydrofuran and water.12... 

Methylmagnesium fluoride is obtained in 100% yield by the reaction of dimethylmag-nesium with silicon tetrafluoride in tetrahydrofuran at room temperature.13... 

Silicon Fluoride or Silicon Tetrafluoride. See in Vol 6, F146-R to F147-L, and G100-L under the history of NG manufacture where the use of SiF4 to separate the liq phases and recover the NG is Silicon Nitride. Si3N4 mw 140.31 grey-white amorph powd mp 1900 (sublimes) d 3.44g/cc. Sol in HF acid, Prepn is by reaction of powd Si and nitrogen in an electric furnace (Refs 1,37 ... 

Tetraalkylsilanes also undergo redistribution reactions with silicon tetrafluoride (128) when heated in an autoclave at 300° to 400° C. Phenyl groups (225) redistribute readily with chlorine atoms on silicon when the... 

Nonmetal Halides. Vigorous or explosive reactions occur with phosphorus tribromide on addition of drops of water,20 phosphorus trichloride, phosphorus pentachloride,21 diselenium dichloride,22 sulfur dichloride, boron tribromide, sulfur dibromide,17 seleninyl bromide,23 phosphoryl chloride, sulfinyl fluoride, silicon tetrachloride, and silicon tetrafluoride.24... 

Silica is present in the mineral as an impurity, and it reacts with hydrofluoric acid to yield silicon tetrafluoride, which can be converted to fluorosifi-cic acid, an important source of fluorine. More than half of the phosphoric acid that is produced by the reaction of phosphates with sulfuric acid is converted directly to sodium or ammonium phosphates to be used as fertilizer thus, purity is not a concern. 

There appears to be only one really satisfactory method for preparing pure germanium(IV) fluoride. This method involves the thermal decomposition of barium hexafluoro-germanate1 in a quartz or Vycor tube, a method analogous to that described for the preparation of silicon tetrafluoride (synthesis 47). Germanium(IV) fluoride has also been produced by the fluorination of germanium(IV) chloride with antimony (III) fluoride 2 however, it is necessary to distill fractionally the mixture of chlorofluorides resulting from the reaction. 

Mix 0.5 gram of the precipitated silica with 1 gram of powdered calcium fluoride. Place the mixture in a test tube, moisten it with 36 N H2S04, and warm it gently under the hood. Dip a stirring rod in water and lower it, with a drop adhering, into the gas in the test tube. Note the precipitate that forms in the drop of water. Write equations for all the reactions, and state what rather unusual properties are shown by this experiment to be possessed by hydrofluoric acid and by silicon tetrafluoride. 

A slight modification of the above description is necessary if this reaction is to be used for the synthesis of other alkylfluoro-phosphoranes (CH3CH2PF4, CH2=CHPF4, n-CH3CH2CH2PF4). Because all other tetraalkylstannanes are not transferable in a vacuum system at 25°, they can be syringed into the reaction bulb before attachment to the vacuum lines. Care to use dry samples and equipment must be observed, however, since the presence of even small amounts of water will lead to formation of phosphoryl fluoride and silicon tetrafluoride. 

Quite often additional trifluorosilane can be obtained by simply returning the unreacted silane to the reaction vessel and allowing additional reaction time. A single reaction period yields about 1.5 g. (65% based on HSiCl3 employed) of product having an observed molecular weight of 86.9 (calcd. 86.1) and an infrared spectrum consistent with pure trifluorosilane.11 However, on some occasions the product is contaminated with silicon tetra-fluoride due to a reaction of the antimony compounds with the trifluorosilane. The silicon tetrafluoride impurity does not interfere with the preparation of tetracarbonyl(trifluorosilyl)cobalt. 

Apply the microcosmic bead test If a skeleton bead is obtained, silica or a silicate is indicated. A negative result does not definitely prove that silica or a silicate is absent, as a skeleton is not always formed. The silicon tetrafluoride test should then be employed (Section IV.26, reaction 6). 

The appearance of silicon tetrafluoride during an investigation of organic fluorine compounds in glass equipment is generally understood to imply the transient formation of hydrogen fluoride this interpretation should be applied here. An interesting point, not yet fully understood, is the appearance of nitroalkane and carbinol only in the reaction of trityl-difluoramine with excess acid. 

The failure of difluoramine to appear among the final products is not particularly surprising. In the presence of nitric acid and/or nitrogen oxides, it might easily be oxidized and may well constitute the source of the silicon tetrafluoride. The formation of a carbonium ion from trityl-difluoramine would be favored by resonance stabilization. In the tert-butyl case, on the other hand, this driving force is not present and formation of the ion would be expected to occur less readily. In addition, both the tert-butyl carbonium ion and the difluorammonium ion from which it is derived would be more subject to a variety of side reactions than the corresponding trityl species. 

There are two fluorination reactions with ester substrates reported in the literature which consist of only a single example each. One is the formation of fluoroethene from acetoxyethene and lithium fluoride in the presence of palladium acetate. The other is formation of fluoro-ethane from ethyl orthoformate with silicon tetrafluoride. - ... 

Silicon tetrafluoride reacts with pure silicon at low pressure in a flow system at 1200 °C to yield a transient species, SiF2, which can be condensed to yield a fluorosilane polymer, (SiF2) . Sihcon difluoride has a half-life of about 150 s in glass at low pressure in the gas phase. The chemistry of SiF2 shows many different reactions and has been reviewed. When condensed at —196 °C, a red-yellow deposit is formed,... 

---