Selenium tetrafluoride

We also developed a number of other useful new fluorinating reagents. They ineluded a convenient in situ form of sulfur tetrafluoride in pyridinium polyhydrogen fluoride, selenium tetrafluoride, and ey-anurie fluoride. We introdueed uranium hexafluoride (UFg), depleted from the U-235 isotope, which is an abundant by-product of enrichment plants, as an effective fluorinating agent. 

The tetrafluoride is prepared by interaction of chlorine trifluoride and selenium in selenium tetrafluoride as solvent. The crude tetrafluoride must be substantially free from excess chlorine trifluoride to avoid danger during subsequent distillation at 106°C/1 bar. 

The tetrafluorides of selenium and tellurium are similar to SF4 both structurally (in the gaseous molecules) and in terms of reactivity, ffowever, the bonding in condensed phases is different and leads to several types of structures. Selenium tetrafluoride can be prepared by combining the elements, but it can also be obtained by the reaction of Se02 with SF4 at high temperature. The tellurium compound can be prepared by the reaction of SeF4 and Te02 at 80 °C. 

Fluorination with Selenium Tetrafluoride and Its Pyridine Complex... 

The preparation of selenium tetrafluoride in normal glass apparatus has been reported by the reaction of selenium metal with chlorine trifluoride and selenium tetrafluoride as the solvent.81 Caution chlorine trifluoride (C1F3) is extremely reactive and must be handled with care, avoiding organic compounds and moisture. 

Selenium tetrafluoride is a liquid (bp 106 C) which is soluble in halogenated solvents enabling reactions to be carried out at atmospheric pressure. It is has been reported to fluorinate alcohols to their corresponding fluorides, carbonyl compounds to gem-difluorides, e.g. 1—2, and carboxylic acids to acid fluorides. 

Although alcohols can be fluorinated directly with selenium tetrafluoride, yields can be disappointing because of rearrangement/polymerization due to the presence of hydrogen fluoride produced during the reaction. Higher yields have been obtained when the reaction is performed in the presence of 1 equivalent of pyridine, which forms a 1 1 donor-acceptor complex with selenium tetrafluoride. The reaction proceeds in two distinct steps first is the reaction of the alcohol with the complex to form an alkoxyselenium trifluoride, the second is the thermal decomposition to the alkyl fluoride. 

For example, treatment of benzyl alcohol with selenium tetrafluoride-pyridine quantitatively yields benzyl fluoride.81... 

Potassium hexafluorovanadate(IV) can be prepared from [VF4] and KF in selenium tetrafluoride(III)416 or by fluorination of K2VF5 for example. K+, Rb+ and Cs+ salts obey the Curie-Weiss law with high values of 6. [VF4] reacts with py and NH3 forming [VF4L], probably fluorine-bridged polymers.416... 

Selenium hexafluoride, SeFg, the only clearly defined hexahalide, is formed by reaction of fluorine with molten selenium, It is more reactive than the corresponding sulfur compound, SFs, undergoing slow hydrolysis. Selenium forms tetrahalides with fluorine, chlorine, and bromine, and dihalides with chlorine and bromine. However, other halides can be found in complexes, e.g,. treatment of the pyridine complex of SeF/i in ether solution with HBr yields (py)2SeBrc Selenium tetrafluoride also forms complexes with metal fluorides, giving MSeF complexes with the alkali metals. 

Methylselenol CHaSeH.. . . Selenium hexafluoride SeFe-Selenium tetrafluoride SeF, Selenyl fluoride SeOFj. 

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