Solublllty of Mercury
Vltrasound in the Undergraduate Lab To the Editor:
To the Editor:
Recently a numher of reports ( I ) have appeared on the an~lication of ultrasound t o organic synthesis. Our early .. studies (21,which werr inspired by ubservationi hy others ( 3 , 11,runcerned Wurtz-like couplings of alkyl and aryl halides in the. oresenre of lithium metal and ulrrasound. Yanv of the ~-~~ reports appearing in the last few years have concerned the activation of metals in heterogeneous reactions. Several recent publications have concerned the utilization of ultrasound in "nonmetal" heterogeneous reactions, however. In the course of our studies we have noted ultrasound promoted rate enhancements in a numher of heterogeneous reactions. I would like to share two applications of ultrasound in undergraduate organic chemistry experiments with your readers. 1) Initiation of Grignard Reactions. Grignard reactions are notoriously temperamental and may be difficult to initiate. We have found that these troublesome reactions may he initiated bv immersing the reaction flask in a common laboratory ul&asouic cleaning bath and sonicating for 1 or 2 min. Generally the addition of an iodine crystal is also helpful. Further reaction proceeds without further sonication. In one class I found i t necessary to emphasise that ultrasound is not usually deemed necessary to initiate Grignard reactions. Luche and Damiano have reported (3)on the utility of ultrasound in preparing organolithium and organomagnesium compounds. 2) Baeyer Test. The Baeyer test is commonly used for identifying alkenes and alkynes. However, since most hydrocarbons are insoluble in water, the mixture must be shaken vigorously to ensure reaction. The solution may still not completely loose its purple coloration and the test may appear inconclusive to a beginning student. We have found that ultrasound sienificantlv promotes this reaction. A 5% solution of cycloheiene in d&ke (1 ml) gave an incomplete reaction when shaken viaorouslv with 1% potassium permanganate solution (1mi). However if the test tube isimmersed in an ultrasonic cleaning bath and sonicated for 30 s, reaction is romplete. All the purple n h r is lost and a dark hrown suspensmn of manganesr dioxide is ohser\~ed.Phnse tmn-ter reagents have also I)wn used (5) in thr l3neyer test toadvantage. Howcwrr the addition uf a furrher rrayent may confuse a student. Ultrasound may he perceived as a physical effect, although its mode of action is unclear (6). Many more applications of ultrasound to the promotion of heterogeneous organic chemical reactions are likely to he reported in the next few years. Some of these may find a place as undergraduate chemistry laboratory experiments.
I have read with interest the letter of H. H. Sisler [61,566 (1984)) commenting on the solubility of mercury in water discussed earlier by V. Kumar and B. Tate [59,971 (1982)l. Sisler makes a good point, concerning the efficacy of making generalized statements about soluhility to beginning students of chemistry. Unfortunately the soluhility of mercury in water quoted is in error by a factor of 100. The Cotton and Wilkinson value quoted was taken from I. Sanemasa [Bull. Chem. Soc. Jpn., 1975,48,1795 (1975)l who gave his value as 63.9 pg 1-I which g 1-I at 298.15 K, and I should like to correct is 6.39 X the record on this point. We recently completed a compilation of all solubility of mercury values in water, aqueous solutions, hydrocarbons, alcohols. and other oreauic solvents from the literature. Over 15 papers report values of the soluhility of mercury in water. Our evaluation of the available literature values " eives as tentative solubility values (g Hg per 1kg of water)
~~~
.~
~~~
~~
~
2.7 X 10-5
273
platm
6.1 X
298
48.1 X 10-5 373 1
24
15
773 500
773 1000
Thus one can see the effect of temperature and pressure. The solubility of mercury in water increases with temDerature and decreases with increases in pressure. The solubility can be expressed as Henry's constant which goes through a maximum value at a temperature of about 460 K. The solubility of 24 g Hg per 1kg of water a t 733 K and 500 atm total pressure is from V.I. Sorokin [Dohl. Ahad. Nauh SSSR, 213, 852 (1973)]. The complete results of our evaluation of the soluhility of mercury in water and aqueous electrolyte solutions should appear in J. Phys. Chem. Ref. Data within the year. H. Lawrence Clever
Solubility Research 8 InformationProject Emory University Atlanta, GA 30322
Double Balloons To the Editor:
Timothy D. Lash
The double balloon method for long term protection of sensitive materials, described by Robert Duty [6], 261 (1984)] should not be used to protect against carhon dioxide or other gases which have high soluhility in (i.e., high diffusion rates through) rubber. I recall a demonstration which has been long used to illustrate the high diffusion rate of carhon dioxide through balloons. A halloon filled with nitrogen is placed in a helljar filled with carhon dioxide, and a second balloon filled with carbon dioxide is placed into a second identical belljar filled with nitrogen. After a few hours or up to a day, the second (carbon dioxide-filled) balloon has collapsed, while the first (nitrogen-filled balloon in the carbon dioxide atmosphere) has spontaneously become larger. Eugene McLaren
Norihern State College Aberdeen. SD 57401
State University of New York at Albany Albany. NY 12222
Literature Cited (I) Luche, J.-L.,La Recherche, 14, 1276 (1983): Susliek, K. S., and Schubert, P.F..J. Amer Cham. Soc., 105.6042 (1983). (2) (a) Lash, T. %and Barry, D., J. CHEM.EDUC.,~~,~~ (1984): (h) Trumb0.D.W., and Lash. T. D., Proc. S. D. Acod. Sci, 62. 193 (1983l; (4 Lash, T. D., 7th Rocky MauntainRegianal ACS Meefing,Albuqucrque.Now Merim, June6. 1984.Abstrsd
720
solubility T/K
Journal of Chemical Education
