[CONTRIBUTION FROM
THE DIVISIONOF AGRICULTURAL BIOCHEMISTRY, UNIVERSITY OF MIWNESOTA]
STTDIES IK OZONOLYSIS. I. ACTION OF OZOYE ON SOLVENTS USED IK OZOKIZ,4TIOS1 FRED L. GREENWOOD
Received A p r i l 30, 2945
From the very beginning (1) of the study of ozonolysis it has been rather well recognized that the solvents commonly used for this reaction are attacked more or less by ozone. The literature contains many qualitative and contradictory statements regarding the action of ozone on numerous solvents. In only one case (2) could any quantitative information be found. Some jnvestigations (3,4,5,6)have been reported, in which a quantitative determination of the ozone decomposed by the solvent must have been carried out, but no pertinent data were given. Solvents, in addition to effecting a loss of ozone available for reaction with the unsaturated compound, also exert an influence on the yields of products obtained in ozonolysjs reactions (5, 7, 8, 9, 10, 11). The solvent has also been reported (12, 13) as having an influence on the amount of polymeric ozonide formed during ozonization. Then, too, there have been instances where, because of explosion, some ozonides could not be prepared in certain solvents. In carrying out ozonizations it would often be advantageous to know approximately the amount of ozone actually absorbed by the unsaturated compound. Such a determination would be greatly simplified by a solvent which would be unaffected by ozone. The present paper summarizes the results of a search for such a solvent. The solvents studied in this investigation were various halogenated hydrocarbons, n-pentane, acetic acid, ethyl acetate, methanol, ethanol, and water. These solvents were studied, as nearly as possible under the same experimental conditions, in an apparatus which permitted the determination of the concentration of ozone in the gas both before and after passing through the solvent. In nearly every case the amount of ozone in the gas issuing from the reaction flask achieved a relatively constant value after ozone had been led through the solvent for half an hour, or less. The behavior of several of the solvents during ozonization is shown in Figure 1. The other solvents studied gave curves of the same general type as those shown in Figure 1. The percentage of unreacted ozone passing through each solvent, after it had achieved a relatively constant value, and the time required to reach this constant value are indicated in Table I. The halogenated hydrocarbons studied mere methylene chloride, chloroform, carbon tetrachloride, ethyl chloride, n-propyl chloride, ethyl bromide, monofluorotrichloromethane (Freon l l ) , and 1,1,2-trifluoro-l , 2 ,2-trichloroethane (Freon 113). With the exception of carbon tetrachloride, ethyl chloride, and Freon 11, halogen was liberated from the organic halides when they were subjected to a continuous stream of ozone. After ozonization, carbon tetrachloride, 1
Paper No. 2231. Scientific Journal Series, Minn. Agri. Expt. Sta., St. Paul, Minnesota.
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ACTION OF OZONE ON SOLVENTS
ethyl chloride, and Freon 11 gave a very faint iodine color with aqueous potassium iodide. This color may have been due to peroxidic compounds or t o incompletely i-
FIG. 1. TYPICAL BEHAVIOR OF SOLVENTS ON OZONIZATION TABLE I AMOUNTOF UNREACTED OZONE PASSING THROUGH SOLVENTS AFTER THE UNREACTED OZONE HAD ACHIEVED A RELATIVELY CONSTANT VALUE. GASFLOW: 11.4 L./RR. SOLVENT
TEMPERATWE OF SOLVENT D W I N G OZONIZATION,
'c
CH,C& . . . . . . . . . . . . . . . -18 t o -21 CHCl,. . . . . . . . . . . . . . . . -13 t o -16 cc14.. . . . . . . . . . . . . . . . . -15 to -19 CFC13. . . . . . . . . . . . . . . . -32 to -36 CFzClCFClr . . . . . . . . . . - 16.5 t o - 19 CzHsC1. . . . . . . . . . . . . . . -38 t o -42 n-CsHrCI.. . . . . . . . . . . . -15 t o -16.5 C:HjBr.. . . . . . . . . . . . . . -17.5 t o -19 n-CjH12... . . . . . . . . . . . . -13.5 to -17 CH 3 C00H . . . . . . . . . . . . 25 CH3COOC2H6. . . . . . . . . -14 t o -19 CH,OH. . . . . . . . . . . . . . . -12.5 t o -15.5
ZONCENTBATION OF OZONE LED INTO SOLVENT, PER CENT BY VOLUME
PER CENT UNBEACTED OZONE PASSING THROUGH SOLVENT
TIM23 FOB UNREACTED OZONE TO BEACH A CONSTANT VALUE, HBS.
5.5 5.7 5.5 4.5 4.7 5.1 5.2 4.6 5.2 4.9 5.1 5.1 5.0 5.1
96" 9@ 95 94 93a 100 92O 89" 71 98 85 27 38 99
0.42 .42 1.92 0.75 .58 .75 .42 * 22 .50 .25 .42
.08 .08 2.00
Values possibly somewhat high. Halogen was liberated during ozonization and some could easily have been entrained from the solvent into the aqueous potassium iodide used for analysis.
removed, dissolved ozone. In the case of ethyl bromide so much bromine was liberated that the solvent acquired a marked reddish brown color. ?%-Propyl
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FRED L. GREENWOOD
chloride, as ordinarily prepared, contains some material, not an unsaturate, which actually absorbs ozone. This was noted in an experiment in which no unreacted ozone whatever emerged from the alkyl chloride until about an hour after ozone was first led into the solvent. Very careful fractionation of the chloride gave a product which did not exhibit this behavior. After being subjected to the action of ozone, methylene chloride and chloroform had a strong phosgene odor and Freon 113 had a slight phosgene odor. Chloroform has been used often as a solvent for ozonization reactions. This seems rather odd in view of a report by Harries (1) that chloroform with ozone gave rise to phosgene, and that the ozonide prepared in this solvent generally contained traces of chlorine. He (14) later stated that the attack of chloroform by ozone was so considerable that it could scarcely be used as a solvent. Of the other solvents studied, n-pentane, acetic acid, ethyl acetate, methanol, ethanol, and water, only water did not liberate iodine when a sample of the solvent, after ozonization, was shaken with aqueous potassium iodide. Acetic acid, however, gave rise to only a very faint iodine color. This liberation of iodine indicated that peroxidic compounds had been formed in these solvents during ozonization. The n-pentane, after ozonization, had a sharp, disagreeable odor. Saturated hydrocarbons and alcohols are known to undergo considerable attack by ozone (1, 6, 14). Paillard and Briner (15) studied the action of ozone on acetic acid and came to the conclusion that the acid was only slightly attacked. EXPERIMENTAL
Solvents. The solvents were prepared or purified as indicated below, and unless otherwise stated, they were distilled through a total condensation Fenske column packed with single turn, one-eighth inch helices. The portion of the column packed with helices was 1.5 x 70 cm. Just before use the solvents were tested for free halogen with aqueous silver nitrate, for peroxidic compounds with aqueous potassium iodide, and for unsaturates with dilute bromine-carbon tetrachloride. I n every case negative results were obtained. The carbon tetrachloride was purified according to Fieser (16) and dried over phosphorus pentoxide. The material boiled a t 76"/733 mm. Chloroform was purified according to Fieser (16). The solvent used for ozonization boiled a t 60.9/732 mm. E t h y l bromide was prepared according t o Kamm and Marvel (17) ; b.p. 38.6"/746 mm. The ethyl chloride was an Eastman Kodak product, and was reported t o boil at 12.513'. Before use, this material was filtered through a layer of phosphorus pentoxide which was supported by a fine sintered-glass funnel. Methylene chloride was obtained from Eastman Kodak and distilled through the Fenske column; b.p. 39.9"/736 mm. The monoJEuorotrichEoromethu~e(Freon 11) was obtained from Kinetic Chemicals, Inc. and reportedly boiled a t 23.8-24.2'. This solvent was dried in the same manner as the ethyl chloride. The propyl chloride first used was an Eastman Kodak product, which was purified in the usual way and distilled through the Fenske column; b.p. 46-46.5"/733 mm. When subjected t o ozonization this material actually absorbed ozone for about a n hour. The chloride was then prepared according to Whaley and Copenhrtver (18) and carefully fractionated. A large forerun was discarded and the material used for ozonization boiled at 47"/747 mm.
ACTION OF OZONE ON SOLVENTS
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1 ,1,d-TrifEuoro-l,d,d-trichloroethane (Freon 113) was obtained from Kinetic Chemicals, Inc. and was reported as boiling a t 47.2-47.4'. This solvent was dried as the ethyl chloride. The acetic acid was the Grasseli-du Pont glacial acetic acid, 99.5% acetic acid minimum. The ethanol was an absolute grade of the solvent which was dried according t o Smith (19); b.p. 78.5'/736 rnm. The ethyl acetate was analytical grade material which was dried over phosphorus pentoxide and distilled; b.p. 76.8"/740 mm. The methanol was synthetic material, dried with magnesium and distilled; b.p. 64.5'/ 740 mm. The n-pentane was the pure grade of the hydrocarbon produced by the Phillips Petroleum Company. The material was dried over phosphorus pentoxide and distilled; b.p. 36O/ 742 mm. The water was distilled water. Procedure. The conventional laboratory ozonizer was modified so that, in any one experiment, the concentration of ozone in the ozonized oxygen could be maintained constant a i t h i n 0.1% ozone by volume (20). I n the different experiments, however, the absolute ozone concentration varied from 4.5% t o 5.7% by volume. The ozonization apparatus was so designed that the stream of ozonized oxygen could be directed by means of a three-way stopcock into an analytical flask or into the reaction flask. Attached to the reaction flask Nas a trap which, in turn, was attached to an analytical flask. To avoid decomposition of ozone when dispersing i t into the solvent, a tube which had several small holes in the end had to be used. A sintered-glass plate, made of 80-mesh Pyrex glass, was first used. This plate, a t first, did not decompose ozone, but after a time i t was observed that the plate was decomposing ozone. The amount of decomposition was not constant but decreased as ozone continued to be passed through the plate. Even after seven hours the plate was still decomposing some ozone. I n every experiment 140 ml. of solvent was used. During ozonization the solvents were cooled t o the temperatures indicated in Table I. The trap attached t o the reaction flask was cooled with dry ice-ethanol, when possible; otherwise, i t was cooled as much as possible without causing solidification of the solvent entrained into the trap. To be certain the ozonizer was producing a constant concentration of ozone, it was operated several hours before leading ozone into the solvent. Also, during ozonization, the stream of ozone was diverted from the reaction flask several times t o check the ozone concentration. The gas, after passing through the solvent, was analyzed for ozone at various intervals of time, using the method described by Smith (21). After the ozonization was completed, the solvent was kept at the temperature maintained during the ozonization and nitrogen bubbled through the solvent until the issuing gas no longer colored potassium iodide paper. The remaining solvent was then tested for peroxidic compounds with aqueous potassium iodide, and, in the case of the organic halides, for free halogen with aqueous silver nitrate. SUMMARY
From the standpoint of resistance to attack by ozone, water, acetic acid, ethyl chloride, carbon tetrachloride, and monofluorotrichloromethane are satisfactory solvents for the ozonization of unsaturated compounds. The choice among these solvents would be dependent upon the solubility of the unsaturate and on the method selected for the decomposition of the ozonide. On ozonization, free halogen was liberated from the other halogenated compounds studied, and the other solvents gave rise to peroxidic compounds. SAINTPAUL, MI".
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L. GREENWOOD
REFERENCES HARRIES, Ann., 343,340 (1905). BRINER,EGGER, A N D PAILLARD, Helv. Chim. Acta, 7,1018 (1924). BRUSAND PEYRESBLANQUES, COmpt. rend., 190,501,685 (1930). NOLLER,CARSON, MARTIN,AND HAWKINS, J . A m . Chem. SOC.,68, 24 (1936). LONGAND FIESER, J . A m . Chem. SOC.,62,2670 (1940). FISCHER, Ann., 476,233 (1930). BRIKERAND FRANK, Helv. Chim. Acta, 21, 1297 (1938). DORLAND AND HIBBERT, Can. J . Res., 18B, 30 (1940). ALLENAND PINGERT,J . Am. Chem. SOC., 64, 1365 (1942). HENNEAND PERILSTEIN, J . Am. Chem. SOC.,66,2183 (1943). MARVEL AND XICHOLS, J . Org. Chem., 6, 296 (1941). FISCHER, DULL,AND ERTEL, Ber., 66, 1467 (1932). KAWAMURA, J . Chem. SOC.Japan, 62,259 (1941); Chem. Abstr., 37,4372 (1943). HARRIES, Ann., 374, 288 (1910). PAILLARD AND BRINER, Heh. Chim. Acta, 26, 1528 (1942). FIESER, “Experiments in Organic Chemistry”, 2nd Edition, Heath, New York, 1941, p. 365. (17) KAMMAND MARVEL,“Organic Syntheses”, Coll. Vol. I, 1st Edition, John Wileg, New York,1932, P. 23. (18) WHALEY AND COPENHAVER, J . Am. Chem. SOC., BO, 2497 (1938). (19) SMITH,J . Chem. SOC.,1288 (1927). (20) GREENWOOD, Ind. Eng. Chem., Anal. Ed., 17, 446 (1945). (21) SMITH,J . Am. Chem. Soc., 47, 1844 (1925). (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
