Thionyl tetrafluoride

A storage cylinder containing thionyl fluoride is attached to the manifold of the vacuum line by means of a ball joint, and the thionyl fluoride is allowed to expand into one of the calibrated storage bulbs. After 0.021 mole of thionyl fluoride is collected in the bulb, the excess in the manifold is recondensed into the storage vessel with liquid nitrogen. The measured volume of thionyl fluoride is condensed into the shielded 300-ml. Monel pressure reactor, which is attached to the vacuum line at F. The reactor is then closed and kept at —196°. 

The vacuum line is isolated from the forepump, and a liquid-nitrogen bath is put around trap D. The fluorine metering system is partially evacuated with the water aspirator, as discussed above. Then the vacuum line is completely evacuated with the forepump. Fluorine is allowed to expand slowly into the metal system by means of the needle valve 3. As the pressure increases above atmospheric, some fluorine is allowed to bleed into the vacuum line and storage bulbs until a pressure of 650-700 mm. is reached. First needle valve 1 on the metal system and then the fluorine control valve 3 are quickly closed. (Some fluorine may escape from the blowout manometer during this operation.) Approximately a 10% excess of fluorine (0.023 mole in this case) is condensed into the metal pressure reactor containing the thionyl fluoride. The amount of fluorine used is measured by the pressure drop in a calibrated volume in the pressure range of approximately 700-400 mm., since fluorine has a vapor pressure of approximately 400 mm. at —196°. 

The reactor is closed with the extension rod, and the Dewar flask is lowered. After the reactor has stood for at least 30 hotirs at ambient temperature, it is cooled to —196°. Liquid-nitrogen cold baths are also placed on trap D and on the U-tube trap E 

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Fig. 6,11 Molecular structures of (a) sulfur tetrafluoride (b) thionyl tetrafluoride ...

Thionyl tetrafluoride and pentafluorosulfur hypofluorite can be prepared by the fluorination of thionyl fluoride. The product distribution obtained upon fluorination appears to be dependent not only upon the reaction conditions, but on whether a source of fluoride ion is present. Fluorination of thionyl fluoride over a hot platinum gauze or in a Monel pressure reactor produces thionyl tetrafluoride, whereas fluorination in the presence of cesium fluoride or a silver fluoride catalyst jdelds pentafluorosulfur hypofluorite. The role of the fluoride ion in the fluorination has not been conclusively established however, the avail-... 

Although thionyl tetrafluoride and pentafluorosulfur hypofluorite can be prepared by fluorination in a flow reactor, the procedures described here are performed in a static system. This method offers several advantages. The metal equipment needed is commercially available, and the ability to closely control the stoichiometry of the reactions results in the formation of the products in high purity. However, the amount of material that can be prepared in one run is limited. Thionyl tetrafluoride may also be prepared in good yield by the oxidation of sulfur tetrafluoride. This method is also easy to carry out if the requisite high-pressure equipment is available. 

The procedures for the preparation of thionyl tetrafluoride and pentafluorosulfur hypofluorite are essentially the same, with one important difference the use of a catalyst. The apparatus employed in the preparations consists of several Monel pressure vessels (which have been prefluorinated at 150-200 ), a standard glass vacuum line equipped with several large calibrated storage bulbs (1- or 2-1.), a partial fractionation train, and several ball-joint connections on the main manifold. All the joints and stopcocks on the vacuum line are lubricated with Kel-F-90t grease, and all mercury manometers are covered with Kel-F-10 oil,t which has been well outgassed. The vacuum line is connected to a fluorine metering system and a water... 

Thionyl tetrafluoride is a gas (m.p. —99.6°, b.p. —49°) which is hydrolyzed by water to sulfuryl fluoride and hydrogen fluoride. It may be handled in glass provided the system is dry, and it is readily identified by its infrared spectrum, which contains strong bands at 1383, 928, and 821 cm. . ... 

A study of the reaction of fluorine with SO2 has shown that at temperatures up to 500 °C the reaction rapidly gives sulphuryl fluoride. If the quantity of fluorine is large enough, then SFe is formed, but only slowly, and via the formation of thionyl fluoride, thionyl tetrafluoride, and pentafluorosulphur hypo-fluorite. The fluorination of SO2 by Xep2, in the presence of compounds of the type MX (M = NMe4, Cs, or K X = F or Cl), has been studied. A variety of products were observed (Table 2) and reaction mechanisms were proposed in which the Xep2 functions as a weak Lewis acid. 

Moissan and Lebeau (1902) mixed fluorine and thionyl fluoride at room temperature and obtained a new product. From the change in pressure during the reaction they considered the product to have the formula SOF4. They did not definitely identify the substance (217). The substance was prepared and studied in the laboratory of O. Ruff in 1937 but the work was not published until after World War II. The reaction of Fa with SOF2 took place in the presence of platinum at about 150° (165, 17A). Thionyl tetrafluoride has also been produced from SOF2 and F2 in a copper tube reactor packed with a fluorinated copper, AgF2 catalyst (78). 

Thionyl tetrafluoride is a colorless gas which reacts with water rapidly forming S02F2, HF, H+, and S02F. With NaOH solution it gives F and SCbF-. It reacts slowly with mercury at room temperature to give mercurous fluoride and thionyl fluoride (78, 165). The density and vapor pres-... 

The mass spectrum is known (78) and there is only one nmr line for fluorine in the nmr spectrum of thionyl tetrafluoride at room temperature (79). This probably means that there is a rapid exchange of fluorine atoms within the molecule. 

In 1955 Dudley, working with Cady and Eggers, obtained pentafluorosulfur hypofluorite by the reaction of fluorine, in excess, with thionyl fluoride, or sulfur dioxide, at 200° in the presence of copper coated with fluorides of silver (78). It is probable that thionyl tetrafluoride is an intermediate in the process and that it combines with fluorine to give FjSOF. ... 

Thionyl tetrafluoride is stored under pressure in steel cylinders or in glass ampoules cooled with Dry Ice or liquid nitrogen. 

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