Nitryl hexafluoroarsenate

Submitted by MICHAEL J. MORAN, JOANN MILLIKEN,t and RONALD A. DE MARCOf Checked by SCOTT A. KINKEADI 

The recent interest in nitryl hexafluoroarsenate, [N02][AsFJ, as an oxidizing agent has emphasized the need for a simple, one-step, high-yield synthesis of fliis compound. Previous syntheses have involved the initial preparation of NOjF and subsequent reaction with AsF, the use of HF with HNO3, ClNOj, or nitrate esters the reaction of NOj, BrFj, and S2Of the use of PNOj or metathetical reactions from other [AsF ] salts. These reactions generally are conducted in metal cylinders or quartz vessels. The method reported here involves the direct reaction of NO2, Fj, and AsFj in a Pyrex vessel and provides a pure product. 

Fluorine [Matheson] is pretreated to remove HF and SiF4 impurities and is handled in a passivated copper vacuum line designed for fluorine use. Approximately I g of NaF and four stainless steel balls are placed in a 200-mL high-pressure stainless steel Hoke cylinder [Koch Associates] and a high-pressure stainless steel needle valve [Koch Associates] is attached to the cylinder. The cylinder is evacuated on the copper line and cooled to — 196°. A total of 50 mmol of fluorine is carefully condensed into the cylinder. The cylinder valve is closed. The cylinder is allowed to warm slowly to ambient temperature in an empty, precooled Dewar flask (- 196°). It is removed from the vacuum line, shaken to loosen and spread the NaF, placed on its side for 2 days, and shaken periodically. The cylinder is reattached to the vacuum line, and the space between the valves (interspace) is evacuated. A stainless steel infrared cell (8.0 cm) with AgCl windows is attached to the vacuum line and evacuated. A high-pressure infrared spectrum (2 atm) indicates that traces of CF4 are present, but HF and SiF4 are absent.  

The arsenic pentafluoride [Ozark-Mahoning] and NO2 [Matheson] must be carefully purified by trap-to-trap fractional condensation on a standard Pyrex vacuum line (10 torr) equipped with Teflon/glass valves. To purify the AsF, the less volatile impurities (HF and AsFj) are condensed at - 95° (toluene/liquid nitrogen), the AsFj is condensed at - 126° (methylcyclohexane/liquid nitrogen), and the more volatile SiF4 is condensed at - 196°.t The NOj is purified by collecting the NOj in a bath at -78° (acetone/Dry Ice) and passing the more volatile NO into a bath at — 196°. The trap-to-trap distillations are repeated at least three times in each case. The removal of all traces of NO is important. We believe that traces of NO form side products, most likely NOF, that contaminate the product.]  

A Pyrex reaction vessel with a volume of approximately 390 mL is constructed from a 350-mL round-bottomed Pyrex flask with a 29/42 standard taper male joint connected to the neck, and a Teflon/glass stopcock that has a 29/42 standard taper outer joint. The standard taper joints are lubricated with Fluorolube grease 

---

Nitryl hexafluoroarsenate is a white crystalline solid that is stable at room temperature and sensitive to moisture. The product is identified and its purity established (extraneous peaks are not observed) by infrared spectra (Nujol and... 

---