A. D. Broadbent University of Adelaide Adelaide, southAustralia
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A Practical Method of RemovingOxygen from Inert Gases
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supply of oxygen-free inert gas is essential for investigating solutions of compounds which are sensitive to aerobic oxidation. Several methods of removing oxygen from nitrogen have been reviewed by Clark,' who concludes that passage of the gas over copper wire a t high temperature is the most efficient procedure. The author does not dispute this, but wishes to draw attention to a simple and most efficient alternative method. Oxygen may be effectively removed from nitrogen and other inert gases using BTS-Catalyst,? a multipurpose gas purification catalyst manufactured by Badische Anilm- und Soda-Fabrik.3 It consists of a carrier, containing a finely dispersed copper compound, and suitable activating agents. For removal of oxygen the catalyst is initially prepared by heating a t 12C140°C in a stream of hydrogen. Copper metal, in an active form, is produced by reduction, and the catalyst assumes a black appearance. It absorbs oxygen in an exothermic reaction to give copper oxides. The activity of the catalyst can be repeatedly restored by reduction with hydrogen. To purify nitrogen for potentiometric and kinetic investigations of 2-hydroxy-9,lO-anthrahydroquinones, molecules which are extremely sensitive to aerobic oxidation, the author has used the apparatus shown in Figure 1. This consists of pyrex tubing, three-way vacuum stopcocks and a Dreschsel bottle, with a fine sintered glass bubbler, joined together to form a single all-glass unit. The gas supply tube was subsequently fused to the inlet tube of the cell containing the solution. For preparation and regeneration of the catalyst the tube was wrapped with electric heating tape. The unit could be clamped to a single stave, which is attached to the cylinder trolley. Purified gas could therefore be available in any laboratory. The Drechsel bottle can be omitted if the reauirement is for completely' dry gas. The solution in it is essentially the same as that commonly known as Fieser's s ~ l u t i o n but, , ~ in place of sodium 9,lO-anthraquiFigure 1. Diagram of the unit used t o remove oxygen from nitmgen.
none-2-sulphonate contains only a trace of 2-hydroxy9,lO-anthraquinone. The catalyst removes oxygen extremely effectivelya t room temperature, even at high flow rates. The efficiency is illustrated in Figure 2. This shows the rate of oxidation of 2-hydroxy-9,lO-anthrahydroquinone under various conditions using the purification unit described. The diagram gives the oxidation rates observed on bubbling nitrogen (0.2% oxygen) a t a rate M 2of 150 ml min-I through a solution of 1.0 X hydroxy-9,lO-anthraquinonein 1.0 M aqueous sodium hydroxide, partly reduced by addition of alkaline sodium dithonite solution. The gas previously was passed through unreduced BTS-Catalyst and water (curve A), unreduced catalyst and the reducingsolution (curveB),
Figure 2.
Roter of oxidation of 2-hydroxy-9,lO-anthrohydrequinone
bee k x t ) .
and reduced BTS-Catalyst and the reducing solution (curve C). The points representing extent of reduction are the mean of potentiometrically and polarographically determined values. In poteutiometric investigations potential drifts caused by oxygen never exceeded 0.1 mv hr-l, even when the hydroquinone concentration was only 4.0 X lo-= M. The author's results on the use of this catalyst over several years, and with differing grades of nitrogen, have proved its value as a method for removing oxygen. Its simplicity and efficiency make it a highly recommendable procedure. 1 CLARK, W. M., c'Oxidation-hductionPotentials of Orgmic Systems," Williams & Wilkins, Baltimore, 1960, p. 301. S C ~ T ZM., E , Angew. Chem.,70,697(1958). 8 Information concerning prices, availability and ordering can be obtained from the American agents: BASF Colors and Chemicalls Inc., 845 3rd Avenue, New York, N. Y., 10022. 4 V O G EA. ~ I., "A Text-Book of Practical Organic Chemistry" (3rd ed.), Longmans, London, 1956, p. 186.
Volume 44, Number 3, March 1967
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