to form succinonitrile or propionitrile. No attempt waa made to detect these. The methane yield was not affected by adding enough glacial acetic acid to the electrolysis solution to raise the acetic acid concentration to 0.5M. The initial concentration resulting from the acetic acid present in the tetrabutylammonium acetate crystals was 0.07M. I t is not surprising that the measured yield of carbon dioxide is not 100% and that the sum of the yields of methane and ethane is not equal to the carbon dioxide yield, in view of the free-radical reaction mechanism. Simple free radicals, because of their instability, are notoriously nonselective in their attack on neighboring molecules. The literature shows that a number of side reactions could consume the radicals without resulting in the formation of the major products. Such side reactions could lead to the formation of esters (11, 12, 16, 17), diacyl peroxides and peroxy acids (8, 3, 6, IO), olefins (4, II), and alkyl perchlorates (IO).
SIR: The direct exposure technique of Wilzbach (8) for labeling organic compounds with tritium has received considerable attention recently because it is a simple and economical method of obtaining radioactive tracers for application in petroleum chemistry, biochemistry, and other similar fields. Means for accelerating the exchange of tritium for hydrogen have been reported more recently by Lemmon and coworkers (2), Westermark, Lindroth, and Enander (6),Dorfman and Wilzbach (I), and Mottlau (3). These advances have made the general application of tritium-labeled compounds as tracers even more attractive. Olefins, as a class of hydrocarbons, are of considerable interest in petroleum research. However, these compounds have proved difficult to label with tritium by the direct exposure technique! with or without acceleration. This is particularly true of terminally bonded mono-olefins because of saturation of the double bond with tritium, which produces a labeled paraffin rather than substitution of tritium for hydrogen (4,5). The Bureau of Mines has used two techniques with considerable success in preparing tritium-labeled terminally bonded mono-olefins. These techniques 1284
ANALYTICAL CHEMISTRY
ACKNOWLEDGMENT
The chromatographic analyses were performed with the kind assistance of R. G. Rinker and Y. L. Wang. LITERATURE CITED
.
(13) ’ J. ~,Kolthoff. I. hl.. Coetzee. J. F.. Am. Chem. *Soc.79; 870 (1957). (14) Lingane, J. J., ANAL. CHEM. 26, 1021 (1954). (15) Miiller, E., “Methoden der Or-
ganischen
Chemie (Houben-Weyl),”
Auflage 4, Band I, Teil2,828 (1959). (16) Petersen, J., 2. physik. Chem. 33, 99 (1900). ( l i j Salauze, J., Compl. rend. 180, 662 (1925). (18) Shukla, S. N., Walker, 0. J., Trans. Faraday SOC.28, 457 (1932). (19) Weedon, B. C. L., Quart. Revs. 6, 380 (1952). C. D. RUSSELL \ - - - - , -
(1) Clusius, K., Schanzer, W., 2. physik. Chem. 192A, 273 (1943). (2) Denina, E., Ferrero, G., de Paolini, F. S., Gazz. chim. ital. 68, 443 (1938). (3) Fichter, F., Buess, H., Helv. Chim. Acta 18, 445 (1935). (4) Fichter, F., Meyer, R. E., Ibid., 16, 1408 (1933). (5) Fichter, F., Zumbrunn, R., Ibid., 10, 869 (1927). (6) Fuoss, R. M., Cox, N. L., Kraus, C. A., Trans. Faraday Soc. 31,749 (1935). (7) Furlani, C., Morpurgo, G., J. Electroanal. Chem. 1,351 (1960). (8) Geske, D. H., Ibid., 1, 502 (1960). (9) Glasstone, S., Hickling, A., J. Chem. SOC.1936,820. (10) Hallie, G., Rec. trau. chim. 57, 152 (1938). (11) Hopfgartner, K., Maatsh. 32, 523 (1911). (12) Kolbe, H., Ann. Chem. Liebigs 69, 257 (1849).
are described below. The first is more efficient but less vemtile, in that it requires a specific starting material which may not be readily available. This method involves the saturation of one olefin bond in a terminally bonded diolefin with tritium. The second method combines the Wilzbach exchange labeling with a simple organic synthesis. APPARATUS
The only special apparatus required, aside from that proposed by Wilzbach or others for the direct exposure labeling procedure, is purification equipment that can separate a terminally bonded mono-olefin from its corresponding diolefin or paraffin. In the bureau laboratories, gas-liquid chromatography was used for this separation. It employed a 12-meter by ‘/l-inch column packed with Chromosorb P impregnated with propylene carbamate in a ratio of 5 to 1 by weight. A series such as n-hexane, 1-hexene, and 1,Shexadiene is readily separated with this apparatus. EXPERIMENTAL PROCEDURES A N D RESULTS
Approximately 0.34 gram of 1,5hexadiene was exposed to a tritium atmosphere of 3.7 curies for 1 hour with a potential of 15 kv. a t 3 ma. An accelerated labeling procedure similar to
FRED C. ANSON
Gates and C r e e Laboratories of Chemistry California Institute of Technology Pasadena, Calif. RECEIVEDfor review April 19, 1961. Accepted June 5 1961. Contribution 2699, Gates and &ellin Laboratories of Chemistry. Work supported b the U. S. Army Research Office under &rant No. DA-ORD-31-12461-G91 and by the National Science Foundation in the form of a fellowship held by CDR.
that described by Lemmon (2) was used. The sample incorporated 52 mc. of the tritium, giving a specific activity of 150 mc. per gram, as assayed by liquid scintillation counting (7). A portion of the exposed material then was processed by gas-liquid chromatography to separate the 1-hexene that had been produced. This 1-hexene had a specific activity of 1500 mc. per gram. None of the other components of the exposed sample was collected, but ionization chamber current measurements of the effluent from the GLC unit indicated that a small quantity of tritiated n-hexane and 1,5-hexadiene also could have been obtained. The yield of 1-hexene as indicated by integrating the area beneath the peaks from a gas-liquid thermal conductivity detector was 0.5%. A second sample of 1,Shexadiene (0.77 gram) was exposed a t room temperature to an atmosphere of tritium gas (4.1 curies) for 8 weeks, by the conventional Wilzbach technique (8). This time interval was selected only for convenience in scheduling laboratory work. A total of 1.29 curies of activity was incorporated into the sample, giving a specific activity of 1680 mc. per gram. This. was separated and purified as before. The material charged to the GLC unit represented 35 mc. of activity. The 1-hexene and 1,5-hexadiene peaks were trapped. The 1-hexene component had a total activity of 1.5 mc.
and t h ~1,Shexadiene had 0.62 mc. The specific activity of the purified I-hexene was 1110 mc. per gram and the specific activity of the 1,5-hexadiene was 35 mc. per gram. The yield of 1-hexene as indicated by thermal conductivity measurements in a gas-liquid chromatograph was 7%. However, the ’very high specific activity of this material compensates for the apparent low-yield. The second technique, consisting of a combination of direct exposure and organic synthesis, was used t o prepare . titrated l-octene. The procedure outlined earlier could have been employed, but 1,7-octadiene was not available for use as a starting material. 1-Bromopentane (n-amyl bromide, 1.57 grams) was exposed to 3.9 curies of tritium gas for 8 weeks. Here, too, the storage interval was chosen only from a standpoint of convenience. At the end of this period, the tritium was removed and the sample was assayed. The total tritium incorporated was 877 mc., giving a specific activity of 559 mc. per
gram. Considerable bromine was evolved during the tritiation and a shorter exposure period to tritium gas may be advisable. The. tritiated 1bromopentane, plus radiation damage products, was reacted with magnesium in ethyl ether to give a labeled Grignard. The resulting Grignard then was coupled with 3-chloropropene (allyl chloride). Finally the solution was hydrolyaed and most of the ether was removed by warming the solution in a water bath. Approximately 0.66 gram of material was recovered with a total activity of 226 mc. This corresponds to a specific activity of 343 mc. per gram. The l-octene was purified through gas - liquid chromatography. The purified l-octene had a specific activity of 9.4 mc. per gram. The yield of I-octene was about 60%. The techniques described have not been applied to many compounds, but the bureau believes they are applicable to this entire class of mono-olefins.
LITERATURE CITED
(1) Dorfman, L. M., Wikbach, K. E., J . Phys. Chem.63,799(1959). (2) L e m o n , R. M., Tolbert, B. M., Strohmeier. Walter, Whittemore. I. M., Science 129, 1740 (i959). (3) Mottlau, A.Y., J . Phys. Chem. 64,931 (1960). (4) Nystrom, R. F., Sunko, D. E., Atomlight (issued by New England Nuclear Corp.), January 1959. (5) Rosenblum, Charles, Nwkonica 17, No. 12, 80 (1959). (6) Westemark, Torbjom, Lindroth, Hans, Enander, Bengt, Intern. J . A p l . Radiation and Isotopes 7 , 331 (1960f (7) Whisman, M. L., Eccleston, B. H., Armstrong, F. E., ANAL. CEEM. 32, 484 (1960). (8) Wilzbach, K. E., J . Am. Chem. Soc. 79, 1013 (1957). MABVINL. WEISBUN Bartleaville Petroleum Research Center U. S. Bureau of Minea Bartleaville, Okla. WORKsupported in part by the Department of the Army, Ordnance Project TB5-0010G.
Absorption of Carbon Dioxide by Solutions of 2-Amino-2-(hydroxymethy1)-1,%propa nediol SIR: Tris(hydroxymethy1)aminomethane [2-amino-2-(hydroxymethyl)l,3-propanediol J is finding extensive ‘use, both as a primary acidimetric standard and as a buffer for pH control in the physiological range p H 7 to 8. It, therefore, seems desirable to correct an erroneous impression that solutions of this base do not absorb carbon dioxide from the air. The negative logarithm of the dissociation constant of the cation acid (BH+) conjugate to tris(hydroxymethy1)aminomethane (B) is 8.076 a t 25’ C. (1). Solutions of the base at concentrations of 0.01M or higher, therefore, have pH values in excess of 10. At this level of alkalinity, reaction with atmospheric carbon dioxide, a1though slow, is inescapable. Nevertheless, it has been stated that “Tris(hydroxymethy1)aminomethane and solutions of this salt (sic) do not adsorb (sic) carbon dioxide from the air” (2). In a later paper it is stated that “it is readily soluble in water, and such solutions are stable on storage for weeks because they do not absorb carbon dioxide” (3). The absorption of carbon dioxide by “tris” solutions was demonstrated as follows: Ordinary laboratory air and carbon dioxide-free air were drawn alternately through solutions of the base, and the changes of pH were observed by means of a glass-electrode pH meter. The results of two experiments are shown
in Figure 1. The upper curve was obtained when a stream of laboratory air was passed through a 0.02M solution of “tris” at the rate of about 220 ml. per minute. The data for the lower curve were obtained with a 0.01M solution of the base. After 20 minutes had elapsed (point a), the stream of air was diverted through a tube of Ascarite. At point b, the passage of untreated laboratory air was resumed, and a t point c the stream was once more diverted through the tube of Ascarite. In a blank experiment, the pH of carbon dioxide-free water fell to a constant value of 6.2 upon the passage of laboratory air.
Tris(hydroxymethy1)aminomethane is obtainable commercially in pure form. It is not appreciably hygroscopic and
can be weighed readily. Solutions of the free base, if required, should be guarded from contamination with atmospheric carbon dioxide and should be replaced at frequent intervals. LITERATURE CITED
(1) Bates, R. G., Pinching, G. D., J . Research Natl. Bur. Standards 43, 519 (1949). (2) F o p m , J. H., Markunas, P. C., Riddick. J. A., ANAL. CEEM. 23, 491 (1951).‘ (3) Whitehead, T. H.,J . Chem. Edw. 36,297(1959). ROQEBG. BATES HANNAH B. HETZER National Bureau of Standard Washington 25, D.C.
Figure 1. Effect of laboratory air on the pH of solutions of tris(hydroxyrnethy1)aminomethane Carbon dioxide-free air passed through 0.01M solution between points a and b and after point c
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