Liquid-solid nitrogen mixture

Fig. 1.5. Apparatus to produce a mixture of liquid and solid nitrogen.

Fig. 1.5. Apparatus to produce a mixture of liquid and solid nitrogen. 1, Inner container with LN2 2, external container with LN2 connected to a vacuum pump 3, the container 2 is evacuated to 124 mbar and kept at that...

The intermediate (VII) (1.48 g., 2.0 mmoles) is dissolved in methylene chloride (50 ml.), and trityl tetrafluoroborate (660 mg., 2.0 mmoles) is added. The clear yellow solution is allowed to stand for 5 minutes then ether (200 ml.) is added. This precipitates an oily white solid. The mixture is allowed to stand until the supernatant liquid is clear (ca. 1.5 hours). The supernatant is then poured off and the solid clinging to the walls of the flask is washed with ether (three times with 50 ml.). It is then dried in a stream of nitrogen and recrystallized twice by dissolving in methylene chloride (ca. 50 ml.) and precipitating with ether (ca. 200 ml.). This gives the product as a white solid. Yield is 1.07 g. (73%).t Anal. Calcd. for C26H27-AsBClF4Pt C, 42.7 H, 3.7 As, 10.2. Found C, 42.5 H, 3.6 As, 10.0. 

The checker points out that the necessity of taking several portions of fluorine can be eliminated if nitrogen that has previously been chilled to its triple point by pumping on the Dewar flask is used as a coolant. The reactor should first be cooled with regular liquid nitrogen. Then the use of the solid-liquid nitrogen mixture will reduce the vapor pressure of fluorine from 300 to about 20 mm. 

In the case of NO2 the brown color disappears, and its dimer N2O4 condenses out as a colorless solid. The mixture of nitrogen dioxide and monoxide gives a blue liquid on cooling this solidifies to a blue solid (N2O3) on further cool-ing. 

Purification of the desired product is accomplished by sublimation where only the unreacted A1(BHi+)3 and AnCBH ) are volatile. The large difference in volatilities of these compounds permit easy separation. ThCBHit) and PaCBHit) are obtained on a 0° cold finger by heating the solid reaction mixture to 120° and 55°, respectively. Uranium, neptunium, and plutonium borohydrides sublime at room temperature and are collected in a dry ice trap through which the A1(BHi+)3 passes into a liquid nitrogen trap. 

Selenium, dried at 200°C, is spread in a shallow layer in a large-diameter reaction vessel of glass or quartz. The vessel is ice cooled. A fluorine-nitrogen mixture (1 1 ratio) is passed over the solid at a rate of 1 liter/hour. Efficient cooling and careful fluorination are important, since otherwise SeFg is formed. Finally, the liquid product is vacuum distilled. 

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