Modified Determination of Unsaturation in Olefins by Titration with Ozone SIR: Boer and Kooyman (1) showed that unsaturation in olefinic compounds can be quantitatively determined by titration with ozone. Modifications of their procedure have been used in several laboratories ( 3 , 4 ) ,and Maggiolo and Tumolo ( 4 ) improved the procedure considerably by using commercial equipment. The basic principle of the quantitative determination is measurement of the time required to titrate an olefin with a known concentration of ozone. An ozone stream is passed into a solution containing a known quantity of the olefin sample, and the time required to liberate iodine from a potassium iodide solution, which is placed behind the vessel containing the olefin, is recorded. The amount of iodine liberated is determined by titration with sodium thiosulfate, and the amount of ozone consumed by the olefin sample is then calculated. The following conditions are prerequisite. First, the olefin must react quantitatively with ozone. This requirement depends on the nature of the olefin and is beyond the control of the investigator. Second, the end point of the titration must be instantly recognizable. With most olefins, the end point can be recognized without difficulty. With slow-reacting olefins, however, the end point can be obscured. Third, the concentration of ozone must be maintained constant. To accomplish this, the flow of air is regulated by precision flowmeters and valves and constant voltage is maintained in the ozone generator. Constant voltage is necessary because a line variation greater than 1% adversely affects the generation of ozone. A drawback of the method is that commercial ozonators are very expensive. Laboratory-produced equip-
Table
Olefin n-Octene-lc n-Octene- 1d n-Octene- 1d n-Decene-1 n-Dodecene-1 n-Tetradecene-1 n-Hexadecene-1
I.
ment is cheaper, but voltage control is difficult and frequent checks of ozone production rate are required during a series of analyses. The authors have devised a new method. It obviates the problems of ozone control and end point detection without sacrifice of accuracy. The ozone stream produced in the ozonator is divided into two equal streams. One stream is passed through the olefin sample and then into a potassium iodide solution. The other stream is passed directly into a potassium iodide solution. The amount of ozone consumed by the olefin is calculated from the difference in the titration of both potassium iodide solutions. EXPERIMENTAL
Apparatus. The ozone stream was produced by a noncommercial ozonator, a t a rate of approximately 3.4 mg. per minute, and introduced into the apparatus shown in Figure 1. In the apparatus, the ozone stream is divided by into two equal streams, ill and the use of two precision valves, Vl and V 2 (Ideal, No. 2512A, Ideal-Aerosmith, Cheyenne, Wyo.). The flow rate of A I and A z is controlled by two calibrated precision flowmeters, F1 and Fz (Precision Bore Flowmeter Tube KO. 08F1/16-20-4/36 55 19008, Fischer and Porter Co., Warminster, Pa.). Stream d l is first passed into vessel C, containing the olefin sample dissolved in 18 ml. of chloroform, and then into vessel D,,containing 50 ml. of 2y0 neutral aqueous potassium iodide solution. Stream .42 is first passed through an empty vessel, E. The volume of vessel E is equal to the volume above the liquid in vessel C. Then stream A2 is passed into vessel D2, a180 containing 50 ml. of 2% neutral potassium iodide solution. The total gas volume above the liquids in lines A 1 and A 2 is approximately the same.
Olefin Added, Found, mg. mg. 53 32 55 74 82 100 115
12 50 77 89 16 30 20
53 32 54 73 81
18 32 67 82 45 93 69 111 39
Ozone valuea Theory, Found, grams grams 42 42 42 34 28 24 21
86 86 86 29 57 49 43
43 43 42 34 28 24 20
02 04
44 14 61 34 93
Amount of ozone (in grams) consumed by 100 grams of olefin. Alean values of eight replicate experiments. 99.73qc research grade, Phillips Petroleum Co. d 9gL& development chemicals, Gulf Oil Corp.
0
mg. 03
=
[(ml.D, - nil.D,) 2.41
-F
where ml.D, and ml.D, is the volume of thiosulfate solution used to titrate the contents of vessels D2 and D1, respectively, and F is an empirical correction factor, explained below, which was 0.25 mg. of O8 under our experimental conditions.
Determination of Unsaturation of Olefins with Ozone
a b
2508
Procedure. A 5-mmole sample of the olefin is weighed into a 50-ml. volumetric flask and chloroform is added to the mark. h 5-ml. aliquot containing 0.5 mmole is pipetted into vessel C and diluted with chloroform to a total volume of 18 ml. The vessel is connected to the apparatus (Figure 1) and is cooled to -30' 2' C. by immersion in a Dewar flask containing acetone and chips of carbon dioxide. Vessels D1and D2, each containing 50 ml. of 2% neutral aqueous potassium iodide solution, are placed in the apparatus. The ozone stream (approximately 50 ml. per minute) is turned on by using the main valve, V.M. Valves 8, and V 2are preset, thus avoiding major adjustments during an experiment. Iodine is immediately liberated in vessel D2. Ozonization is terminated when a yellow color is visible in vessel D1. The termination of the ozone stream is not critical. The contents of D1 and Dzare acidified uith 15 ml. of dilute sulfuric acid, and the iodine is titrated with 0.1,V sodium thiosulfate solution by using a starch indicator. From the difference in the titration of the contents of D,and D,, the ozone consumption is calculated as follows.
ANALYTICAL CHEMISTRY
Error _ _ Difference, Rel. gram
70
+O. 16 +O 18
0.4 0.4 1.0 0.4 0.1 0.6 2.3
-0.42 -0.15 +0.04 -0.15 -0.50
Figure 1 . Apparatus for determination of unsaturation in olefins by titration with ozone
RESULTS A N D DISCUSSION
The results of a series of determinations of unsaturated olefins are shown in Table I. The conventional analytical procedure requires an ozone stream of constant concentration and an exact knowledge of the ozone concentration. In contrast, in our procedure, changes in the ozone concentration during the determination do not affect the results and it is not necessary to know the exact ozone concentration, Other advantages are that no warming-up time is required for the ozonator and that detection of the end point is not critical. An olefin can be ozonized a t temperatures ranging from room temperature to the temperature of an acetone-dry ice mixture. With the conventional method, most investigators (1, 3, 4)use temperatures below -20' C. At room temperature the solubility of ozone in
chloroform should be negligible. However, because of the risk of degradative reactions of certain olefins and of the solvent, we chose a temperature of -30" C. This temperature was maintained within +2' C. A solubility factor of 0.25 mg. of ozone was established and was used in all the calculations. This value for solubility of ozone of that in chloroform is about given by Boer and Sixma ( 2 ) a t -30' C. for a saturated solution of ozone in chloroform under equilibrium conditions. It can be expected that a much lower solubility figure would be obtained under the flow conditions prevailing in our experiments. Of the three solvents tested, chloroform gave the best results. The use of carbon tetrachloride poses some limitations because of its comparatively high melting point, -23' C. Ethyl acetate gave the least satisfactory results and gave low ozone values on the average.
ACKNOWLEDGMENT
The authors thank the Gulf Oil Corp. for olefin samples. LITERATURE CITED
(1) Boer, H., Kooyman, E. C., Anal. Chzm. Acta 5 , 550 (1951). (, 2.) Boer, H., Sixma, F. L. J., Rec. Trav. Chim. 70, 997 (1951). (3) Kharasch, M. S., Sosnovsky, G., Yang, N. C., J . Am. Chem. SOC. 81, ,5819 il959'i. __ -. ( 4 ) Maggiolo, A., Tumolo, A. L., J . Am. 0 2 1 Chemist's SOC. 38, 279 (1961). KLAUSF. GUENTHER GEORGE SOSKOVSKY ROBERT BRUNIER' IIT Research Institute Chicago, Ill. and Department of Chemistry Illinois Institute of Technology Chicago, Ill. 1 Present address, World Health Organization, Palais des Nations, Geneva, Switzerland. \ - - - - I
Determination of Potassium Ozonide SIR: There is considerable interest in the unfamiliar oxidation state compounds of the alkali metal ozonide type for air revitalization materials-e.g., potassium ozonide, K+03- ( 5 , 7 ) . The synthesis of potassium ozonide is relatively straight-forward. The passage of a dilute ozone-oxygen gas stream through a bed of dry, powdered potassium superoxide or hydroxide will yield potassium ozonide. The ozonide can be separated from the unreacted superoxide or hydroxide by extraction from the reaction mixture with liquid ammonia (1, 2 , 6, 9). To analyze the recovered product, it is important that the analytical method chosen be able to distinguish between the ozonide and possible superoxide impurity. Such a distinction is necessary regardless of the starting material used in the synthesis reaction since potassium ozonide is unstable with respect to potassium superoxide. In addition, because of the similarity in the chemistry of alkali metal ozonides and superoxides, analytical procedures based on the determination of the total amount of oxygen evolved upon reaction of the ozonide with water, dilute acids, or permanganate solutions, can lead to erroneous results as to the actual amount of ozonide in the sample. A distinction cannot be made, using such reagents, between the potassium superoxide and the potassium ozonide content. Although the chemistry of potassium superoxide and potassium ozonide is
Train and N p ,Gas Cylinder
Figure 1. Apparatus for thermogravimetric analysis of alkali metal ozonides
Tube
similar, there is considerable difference in the thermal stability characteristics of these compounds. Potassium superoxide is quite thermally stable. A dissociation pressure of only 0.1 mm. of Hg at 300" C. is observed for the decomposition of potassium superoxide to the peroxide and oxygen ( S , 4 ) : On the other hand, potassium ozonide decomposes at applicable rates at room temperature and above. The decomposition proceeds in the following manner:
+
KOz(s) '/zOz(g) (2) At 50 to 60" C., the decomposition reaction is complete within 30 minutes KO3(s)
(8, 6). Hence, a t slightly elevated temperatures, Reaction 2 proceeds a t a
sufficiently rapid rate to form the basis of a convenient analytical method for the determination of ozonide content in these samples. In these studies, the potassium ozonide samples were kept in tightly capped glass vials, placed in polyethylene bags charged with ,iscarite, and stored in a refrigerator at -30" C. All transferals were carried out in a dry box. Determination of the ozonide content in the samples studied was made by measuring the change in weight resulting from the thermal decomposition of the ozonide sample to potassium superoxide. EXPERIMENTAL
The apparatus designed for the thermogravimetric analysis of alkali metal ozonides is shown in Figure 1. A tared vial is charged with the ozonide sample VOL. 36, NO. 13, DECEMBER 1964
e
2509
