A QUALITATIVE TEST for OXYGEN in ORGANIC COMPOUNDS C. VERNE BOWEN, Washington and
reffenon College,
JAMES F. BOURLAND,
Washington, Pennsylvania
AND
ED. F. DEGERING
Purdue University, Lafayette, Indiana
A simple, dependable method for the detection of oxygen in organic compounds is presented. The method consists of vapurizing the sample of organic cumpound and passing the vapors through a bed of glowing charcoal, then through barium hydroxide solution. If the com@und is oxygenated, the oxygen will be converted into carbon d i o d e which i s
[email protected] as barium carbonate upon cmning in contact with barium hydrode solution. The test has been tried out on two classes of students, none of whom had any previous experience in organic qualitative analysis. The average score on a series of ten unknowns was eighty per c a t . correct by the one group, and on twenty-smen unknowns the other group scored eighty-fine per cent.
a No. 0 rubber stopper and at the other end with a No. 00 one-hole stopper into which is fitted a delivery tube of 4-mm. tubing. The arm of this tube should be of sufficient length to extend to the bottom of a five-inch test-tube. A loose mass of coarse lumps of wood charcoal is held in place a t a position about five centimeters from the exit end of the tube by two plugs of asbestos
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N THE absence of a satisfactory qualitative test for oxygen in organic compounds it is customary to assume its presence until its absence has been proved by further examination of the chemical and physical properties of the compound under investigation. If the presence or absence of oxygen in a compound were definitely known, the task of identification would be much simplified, as fewer groups would have to be investi~ated. .-. . .. . -~ There is here presented a simple but dependable method for the detection of oxygen. No specialized equipment is required, the apparatus being constructed of material available in any chemical laboratory. The method consists essentially of vaporizing the compound to be investigated, passing the vapors over glowing wood charcoal, and then through a saturated solution of barium hydroxide. Any . oxyzen . - present will be converted by charcoal a t this temperature to carbon dioxide which is precipitated as barium carbonate upon entering the barium hydroxide solution. 0---
APPARATUS Tbe reaction tube for this determination is a 25-cm. length of 16-mm. Pyrex tubing closed a t one end with 'Present address: U. S. Department of Agriculture, Washington. D. C.
fiber. The sample and a scavenging agent are contained in two small combustion boats. For successful operation of this determination it is imperative that all apparatus be clean and absolutely dry. The sample must be free from water, and it is advisable to heat the charcoal before using to expel adsorbed oxygen and water vapor. PROCEDURE
The apparatus is set up as shown in the figure. The bottom of the delivery tube is covered with a halfcentimeter layer of heptane or toluene to prevent entry of air once the test has been started. About one gram of the unknown is placed in one of the combustion boats, and this boat pushed deep into the tube. A second boat is filled with about three milliliters of heptaue or toluene and placed in the tube just behind the
sample. The mouth of the tube is closed tightly with the solution does not indicate the presence of oxygen in the unknown. The cloudiness is generally due to a stopper. A low flame is applied below the boat containing the incomplete purging or to traces of water in the sample. Because some organic chemicals will distill over to hydrocarbon. Its vapors drive the contained air from the tube, thus removing any oxygenated compounds give precipitates in barium hydroxide solution, i t is from the system. When almost all of the scavenging well to acidify the solution with dilute, sulfate-free agent has been volatilized, a second flame is placed hydrochloric acid. Dissolution of the precipitate under the charcoal, raising its temperature to a dull with evolution of tiny bubbles of gas indicates the prered heat. At this point ten milliliters of clear, satu- cipitate to be barium carbonate, while in general the rated barium hydroxide solution is introduced into the organic precipitates will not dissolve in the acidled test-tube. The inert hydrocarbon, which was covering solution. This method of analysis has been tried out with the end of the delivery tube, will float on top of this excellent results in two classes of junior organic chemsolution, protecting i t from contact with the air. istry students, none of whom had had any previous The flame beneath the scavenging agent is now experience in organic qualitative analysis. On a moved to a position below the boat containing the series of ten compounds, the average score was eighty unknown, and sufficientheat applied to insure volatili- per cent. correct for the one group. The other group zation of the sample. As the vapors of the compound in another institution scored eighty-five per cent. pass through the red-hot charcoal, decomposition takes correct on twenty-seven unknowns. The greatest place, any oxygen present being converted to carbon number of mistakes was made on those compounds not dioxide, which is identified as a heavy, flocculent containing oxygen, the presence of a cloudiness or precipitate of barium carbonate. It must here be slight precipitate in the barium hydroxide solution noted that a tiny precipitate or slight cloudiness in misleading the students to some extent.
