Сообщение
comby1 » Ср фев 14, 2007 1:43 am
Из книги Purification of Laboratory Chemicals для аргона и азота:
Argon [7440-37-1] M 39.95, b -185.6°. Rendered oxygen-free by passage over reduced copper at 450°,
or by bubbling through alkaline pyrogallol and H2SO4, then dried with CaSO4, Mg(ClO4)2, or Linde 5A
molecular sieves. Other purification steps include passage through Ascarite (asbestos impregnated with sodium
hydroxide), through finely divided uranium at about 800° and through a -78° cold trap.
Alternatively the gas is passed over CuO pellets at 300° to remove hydrogen and hydrocarbons, over Ca chips at
600° to remove oxygen and, finally, over titanium chips at 700° to remove nitrogen. Also purified by freezepump-
thaw cycles and by passage over sputtered sodium [Arnold and Smith J Chem Soc, Faraday Trans 2 77
861 1981].
Nitrogen [7727-37-9] M 28.0, b -195.8°. Cylinder N2 can be freed from oxygen by passage through
Fieser's soln [which comprises 2g sodium anthraquinone-2-sulfonate and 15g sodium hydrosulfite dissolved in
10OmL of 20% KOH [Fieser, J Am Chem Soc 46 2639 1924} followed by scrubbing with saturated lead acetate
soln (to remove any H2S generated by the Fieser soln), cone H2SO4 (to remove moisture), then soda-lime (to
remove any H2SO4 and CO2). Alternatively, after passage through Fieser's solution, N2 can be dried by
washing with a soln of the metal ketyl from benzophenone and Na wire in absolute diethyl ether. [If ether
vapour in N2 is undesirable, the ketyl from liquid Na-K alloy under xylene can be used.]
Another method for removing O2 is to pass the nitrogen through a long tightly packed column of Cu turnings,
the surface of which is constantly renewed by scrubbing it with ammonia (sg 0.880) soln. The gas is then
passed through a column packed with glass beads moistened with cone H2SO4 (to remove ammonia), through a
column of packed KOH pellets (to remove H2SO4 and to dry the N2), and finally through a glass trap packed
with chemically clean glass wool immersed in liquid N2. Nitrogen has also been purified by passage over Cu
wool at 723oK and Cu(II) oxide [prepared by heating Cu(NO3)2.6H2O at 903oK for 24h] and then into a cold
trap at 770K.
A typical dry purification method consists of a mercury bubbler (as trap), followed by a small column of silver
and gold turnings to remove any mercury vapour, towers containing anhydrous CaS04, dry molecular sieves or
Mg(ClO4)2, a tube filled with fine Cu turnings and heated to 400° by an electric furnace, a tower containing
soda-lime, and finally a plug of glass wool as filter. Variations include tubes of silica gel, traps containing
activated charcoal cooled in a Dry-ice bath, copper on Kieselguhr heated to 250°, and Cu and Fe filings at 400°.
