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 The gas - liquid chromatography. 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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