1833
V O L U M E 2 7 , NO. 1 1 , N O V E M B E R 1 9 5 5 water is added and the solution is acidified n.ith dilute sulfuric acid. A trap ( 1 ) is attached to the flask and the tertiary thiol fraction is collected by steam distillation and measured. The precipitate is warmed on the filter by blowing a stream of air through a long test tube inserted into the filter to dissociate the ammonium mercaptide to thiol and ammonia. Dissociation is ordinarily complete before room temperature is reached. The regenerated primary and secondary thiol fraction is washed through the filter with pentane and recovered by distilling off the pentane. The receiver for the washings consists of a 15-m1., conical, graduated centrifuge tube sealed to the bottom of a roundbottomed flask. This p m n i t s diqtillation of the pentane and measurement of the residue in the same vessel. In a few instances the ammonium mercaptides have been difficult to dissociate. In this event a small amount of dry ice is placed on the filter, allon-ed to stand a fen- minutes, and washed with pentane. A residue of ammonium carbamate remains. The procedure should be carrizd to conclusion without interruption after the filtration has bzen made to prevent oxidation of the thiols after the ammonia has evaporated and air gains access to the sample under basic conditions. If t'he filtrate residue is diluted with acidified water immediately after the ammonia has evaporated, there is little chance for oxidation. Table I sunimariees the results of tests on a nuniber of binary mixtures of primary or sccondary thiols with a tertiary thiol. A mixture of 0.5 ml. of each component was dissolved in 50 ml. of dimethyl ether and added to 100 ml. (50 ml. for C1+& mixtures) of liquid ammonia. The precipitate was filtered after about 30 minutes' standing in a dry ice bath. The fractions from the precipitate and filtrate were recovered as described above. -411 of the tertiary thiols were commercial; each is a mixture of isomers of unknown structures. The high results for component d in the case of the 1-heptanethiol-tert-heptylmercaptan mixture
are attributable to a substance in the tert-heptylmercaptan which yields a precipitate, but this substance has not yet been identified. A second determination using the filtrate from a blank run on tert-heptylmercaptan gave normal yields of precipitate and filtrate. The fractions were analyzed by infrared spectroscopy to determine the amounts of primary or secondary and tertiary thiols in both the filtrate and precipitate. The absolute accuracy of analysis is thought to be &5%. The availability of pure standards would better this value considerably. CONCLUSIOXS
Primary and secondary alkanethiols may be separated from tertiary alkanethiols as an aid in identification of individual compounds in the mixture. The efficiency of the separation increases with increase in molecular weight for those mixtures on which data are given. On the other hand the mixture of 5-ethyl-2-nonanethiol and tert-dodecylmercaptan can be eeparated only under ideally chosen conditions. The separation failed under the conditions adopted for the method. LITERATURE CITED (1) Hopkine, R.L.. and Smith, H. lI.,ASAI. C H E x . , 26, 20B (1954). (2) Thompson, C. J . , Coleman, H. J.,Rall, H. T , and Smith. H. AI., Ibid.. 27. 175-85 (1955). (3) Williams, F. E., with Gebauer-Fuelnegg. E., J . Am. Chem. Sac.. 53, 352 (1931). R E C E I V Efor D review May 18, 1955.
Accepted August 26. 1955.
Absorption of Organic Vapors by Anhydrous Magnesium Perchlorate A. L. BACARELLA, DAVID F. DEVER, and ERNEST GRUNWALD Chemistry Department, Florida State University, Tallahassee, Fla.
Anhydrous magnesium perchlorate has been used as an absorbent for various organic vapors from mixtures of these with inert gases. For all the polar compounds tested, the absorption was quantitative. No explosions have occurred in 4 years, but adequate safety precautions are recommended.
Table I.
Compound Mrtlianol Ethyl alcohol Acetone 1 ,I-Dioxane Pyridine Acetonitrile Ammonia Kitromethane Chloroform
D
URING the past 4 years, anhydrous magnesium perchlorate has been used as a quantitative absorbing agent for a number of organic vapors. The procedure is completely analogous to that used in the determination of water vapor in air or other permanent gases, and appears to be equally quantitative for all but two of the vapors so far tested. A sample of inert gas containing organic vapor is passed through a Sesbitt absorber containing ea. 50 grams of magnesium perchlorate, and the increase in weight of the absorber is measured. Gas flow rates ranged up to approuimately 2 liters per hour a t 1 atmosphere, n i t h the organic vapor usually present a t its saturation pressure. Some sample data illustrating the quantitative nature of the absorption are shown in Table I. In experiments with methanol, e t h l l alcohol, acetone, and dioxane, air Tvas first bubbled through the liquids and then passed through two Nesbitt absorbers connected in series. In experiments with pyridine, acetonitrile, nitromethane, and chloroform, the second Kesbitt absorber was replaced by a cold trap a t dry-ice temperature. Ammonia was dralvn directly from a commercial cylinder and was not diluted with an inert gas. In this case, the second absorber contained an aqueous solution of bromothymol blue. For dioxane and chloroform, absorption is not quantitative. On the basis of these data, i t is reasonable to suppose that magnesium perchlorate could be a general reagent for the vapors of alcohols, aldehydes, ketones, amines, nitriles, and nitro compounds, or, more generally, polar rather than nonpolar compounds.
Absorption of Organic Vapors by Anhydrous 3Iagnesium Perchlorate at 25" f 2" C. Weight Increase, Granis Absorber A Absorber B 1.3890 - 0 , on02n 0.i180 - 0.0003a 0 4968 -o.OOO6= 2,4497 0.0367& n.oooib 0.00;Ob I . 408 5 .ii4
0 . i7.i 1.osn
n
051
n:0002 0.4418b
Magnesium perchlorate absorber. Cold trap. Aqueous bromothymol blue solution, colored yellow by dissolved CO2. S o color change during experiment. a
b
C
As magnesium perchlorate is k n o m to give explosive mixtures with organic materials ( I ) , i t is significant that the authors have not had a single explosion. The adsorbent was always kept at room temperature, and no attempts were made to regenerate it after use. This, however, should not be taken to imply that there is no explosion hazard under these conditions, and adequate precautions should be taken when this absorbent is used for organic vapors. LITERATURE CITED
(1) Stross, AI. J. and Zimmerman, G., Ind. Eng. Chem.. S e w s Ed., 17, 70 (1939). RECEIVEDfor review April 27, 1955. Accepted August 25, 1955. Work supported in part under Contract Nonr 988 (021, Project N R 055-330, betmeen the Office of S a v a l Research and Florida State University. Reproduction in whole or in part is permitted for a n y purpose of the United States Government.
