Quantitative Determination of Carbon Disulfide In Presence OF Carbon Tetrachloride by Use OF the Dead-Stop End Point RICHARD L. BISHOP AND E. LOUISE WALLACE,
0
F SEVERAL methods for the determination of small amounts of carbon disulfide (1-4,6), none was found fully satisfactory for determining this substance in carbon tetrachloride. A satisfactory method, however, was developed by the adaptation of the iodometric method of Matuseak (S), who has reviewed the pertinent literature. This method involves the formation of a xantliate by the reaction between carbon disulfide and alcoholic potassium hydroxide. The xanthate formed is quantitatively determined by direct titration with 0.001 N iodine using the dead-stop end point.
A',ETIC
@-CzHs
+ KOH + C&OH
+
&d
L
N. Y .
Standard 0.001 N sodium thiosulfate solution for standardizing the iodine waa made up fresh when needed by dilutin the pro er amount of 0.1 N solution to 1 liter with freshly boilei and coogd distilled water. IODINE SOLUTION.A 0.1 N iodine solution was prepared by dissolving 12.7 grams of reagent grade iodine and 20 grams of reagent grade potassium iodide in distilled water to make 1 liter of solution. This stock solution was stored in a dark brown glasssto pered bottle. dandard 0.001 N iodine solution waa made up fresh daily b diluting 10 ml. of the stock 0.1 N iodine solution to 1 liter w i d distilled water. The 0.001 N iodine was then standardized agaipst a measured amount of 0.001 N sodium thiosulfate solution, uang the dead-stop end point at 100 millivolts electrode potential. No attempt waa made to obtain a 0.001 N iodine solution from a carefully measured amount of standard 0.1 N iodine because a slight error develops from the loss of iodine in high dilutiop. ALCOHOLICPOTASSIUX HYDROXIDE. Six grams of reagent grade potassium hydroxide were dissolved in 100 ml. of absolute alcohol. This solution should be prepared fresh each week and stored in a refrigerator in a reagent bottle with a paratbed glass sto per. ACID. Sixty grams of reagent grade glacial acetic acid were diluted to 1liter with distilled water. Ethyl alcohol, 3A specially denatured. Carbon tetrachloride, Eaatman Reagent No. 444 (carbon disulfide-free). Carbon disulfide, reagent grade. Starch indicator. Phenolphthalein indicator.
The iodometric titration of xanthate has been adapted to the determination of 1 to PO0 p.p.m. of carbon disulfide in carbon tetrachloride, b y use of the dead-stop end point. The method is rapid, precise, and accurate, and is especially suited for routine analysis of many samples concurrently b y one analyst.
(2%
Eastman Kodak Company, Rochester,
+ HzO K
GENERAL PROCEDURE
The procedure resulting from the experimental work outlined in this paper and found most satisfactory for routine purposes is as follows:
The original method of Matuszak (9) was tried with little success because it was impossible to obtain a good end point with starch indicator in the presence of a large amount of carbon tetrachloride.
Measure a 26ml. sample of the material to be tested in a raduated cylinder, and pour it into a 250-ml. glass-stoppered%denmeyer flask. (In cases where a preliminary run shows more than 50 p.p.m. of carbon disulfide to be present, it .is best to take a smaller sample.) Add 2 mi. of alcoholic potassium hydroxide to the sample and allow it to stand for 30 minutes with occasional agitation while the xanthate forms. Add one drop of phenolphthalein indicator and make the solu-
APPARATUS
The apparatus for adding the iodine and stirrin the solitions was exactly like that used by Wernimont and Ifopkinson (S), except that an ordinary 50-ml. buret was substituted for the automatic buret. The deadstop apparatus employed was very similar to that described by Wernimont and Hopkinson (7), with the potential between the electrodes set at 100 millivolts. Some trouble was encountered when mercury was used as a contact medium between the short platinum tips and the copper lead wires in the glass tubing of the electrodes. This was eliminated by using a 15-cm. (6-inch) length of platinum wire, so that a solid contact could be made between the platinum and the copper leads. The Serfass electron-ray titrimeter (6) was tried in place of the dead-stop apparatus, but was not sensitive enough to produce a sharp end point when used with 0.001 N reagents.
I2204
REAGENTS
SODIUMTHIOSULFATE SOLUTION.A standard 0.1 N solution waa made by dissolving 25.0 grams of reagent grade sodium thiosulfate pentahydrate in freshly boiled and cooled distilled water to make 1 liter of solution. This solution waa standardized against N.B.S. potassium dichromate and then stored in a glassstoppered bottle. When prepared and stored in this manner the solution did not show a change in strength over a period of several weeks.
0 IO 2030
60
0 I02030
I20
TIME OF REACTION IN MINUTES Figure 1.
Time
60
120
TIME OF REACTION IN MINUTES
of Reaction to Form a Xanthate for Knowns of Carbon Disulfide i n Carbon Tetrachloride
01 mrrrent,p.p.rn.: A, 1.
563
8 , 9.
C, 3.
D , 5.
E, 10. F, PI.
C , 50.
H,100. J , LOO
INDUSTRIAL A N D ENGINEERING CHEMISTRY
564 Table
1.
Anrlysis of Knowns
Sample Amount of 0.001 A', Iodine No. Sample Solution, Net Ml. M1.
Carbon Disulfide Present Found Difference P.p.m. P.p.m. P.p.m.
1.1 0.58 1.0 25 2.2 1.16 2.0 25 xn 3.2 1.68 25 5.3 2.78 5.0 25 10.0 10.1 25 5.29 24.6 12.89 25.0 25 49.0 10.27 50.0 10 20.63 100.0 98.4 10 20.65 200.0 196.0 6 Speoifio gravity of samples at 20°/4" C. 1.6937
-
fO. 1 +0.2 +0.2 +0.3 +o. 1 -0.4 -1.0 -1.6
-4.0
tion slightly acid by the addition of dilute acetic acid from a buret until 3 or 4 dro s in excess are indicated. Immediately add 50 ml. of ethyl alcotol (3A specially denatured) connect the flask to the titration apparatus, and titrate to a dead-stop end point with 0.001 N iodine solution. Similarly treat a blank containing all the reagents and omitting the sample. At the start of the titration the galvanometer will show no reading. As the end point is a proached the galvanometer will show a temporsry deflection of aiout 3 scale divisions aa each drop of iodine reagent is added. At the true end oint one drop of reagent cauws a permanent galvanometer deflection of 3 to 5 scale divisions. However, greater speed in the titrat@ may be obtained without loss in accuracy by choosing a point at 10 or 15 on the galvanometer scale as the final end point and titrating to this same point with the blank and all the samples. CALCULATION. 1 ml. of 0.001 N iodine = 76 micrograms of carbon disulfide. EXPERIMENTAL RESULTS
The first series of experiments was made to find the time required to complete the reaction of the carbon disulfide with the alcoholic potassium hydroxide, and to determine the stability of the xanthate formed. Knowns of from 1 to 200 p.p.m. of carbon disulfide were used for this experiment. Figure 1shows that any Length of time from 30 minutes to 2 hours may be allowed for this
Vol. 17, No. 9
reaction. However, the 30-minute point was chosen for a routine procedure to speed up the analysis. A second series of experiments was carried out to determine the precision and accuracy of the method when applied to carbon tetrachloride containing various amounts of carbon disulfide (Table I). The samples were pre ared by carefully weighing known quantities of carbon disulfife in a weighed 100-ml. glass-sto pered volumetric flask containing about 25 ml. of carbon disulficfe-free carbon tetrachloride. The mixture was then diluted to the mark at 20" C. Ali uots of this first 100-ml. mixture were measured from a jacketel buret at 20" C. and further diluted with carbon tetrachloride to obtain the desired knowns. SUMMARY
The method described in this paper was found to be very practical and rapid, giving a relatively high degree of precision and accuracy. It was especially useful in routine work where a large number of samples, with approximately the same amount of carbon disulfide impurity, had to be analyzed in a short time. ACKNOWLEDGMENT
The authors are indebted to F. J. Hopkinson of the Induvtrial Laboratory for many helpful suggestions and for the equipment used in this work. LITERATURE CITED
(1) Dept. Sci. Ind. Research (Brit.), Leaflet 6 (1939). (2) Huff, J. Am. Chem. SOC.,48,81-7(1926). (3) Mstusaak, M.P.,IND.ENG.CHEM.,ANAL.ED.,4,98(1932). (4) Moskowitz, Siegel, and Burke, N . Y. State I d . Bull., 19, 8:i (1940). (5) Serfass, E. J., IND.ENG.CHEM.,ANAL.ED.,12, 536-9 (1940). (6) Viles, J . I d . Hug. TozieOl., 22, 188 (1940). (7) Wernimont, G.,and Hopkinson, F. J., IND. ENQ.CHEM.,ANAL. ED., 12, 308-10 (1940). (8)Ibid., 15, 273 (1943).
Analysis of Cyclopropane-Propylene Mixtures by Selective Hydrogenation E. S. CORNER'
AND
R. N. PEASE, Frick
Chemical Laboratory, Princeton University, Princeton,
N. 1.
A new method, presented for the analyaia of cyclopropanepropylene mixtures b y selective hydrogenation, consiats in passing the mixture with hydrogen over a nickel-kieselguhr catalyst partially poisoned with mercury to hydrogenate the olefin, then over a nonpoisoned catalyst to hydrogenate the cyclopropane. Accu-
racies of *0.5 numerical % are obtained. The presence of inert components auch as gaaeous paraffina does not interfere with the analysis and hence a real advantage is realized over other methods cc. N.T.P.) may deacribad in the literature. Small samplea ("1 be analyzed with good accuracy.
A
tion occurred only at temperatures above 80" C. while propylene was easily hydrogenated a t room temperatures. Accordingly, hydrogenation studies were undertaken in an attempt to apply this reported differential effect to a scheme of analysis. Preliminary experiments were carried out using a nickel catalyst supported on kieselguhr. Results showed that this catalyst after reduction in hydrogen completely reduced cyclopropane to propane in a few passes over the catalyst a t temperatures as low as 0" C. Consequently, a reduction of the activity by partial poisoning was attempted. It was found that the introduction of a few drops of mercury sufficiently deactivated the catalyst so that reduction of propylene waa complete after a few pesses while cyclopropane was unchanged a t temperatures up to 200" C. The poisoning technique ia described below. A nonpoisoned catalyst was used for the hydrogenation of cyclopropane, Presumably the differences in activity of the Willstatter and Bruce catalyst and the one employed by the authors are attribut-
SEARCH of the literature reveals no method for the direct determination of cyclopropane. Several methods for the analysis of binary mixtures of propylene and cyclopropane have been proposed, the most widely used of which is based upon absorption of the propylene in a 3% aqueous potassium permanganate solution (I, t , 4 ) . Cyclopropane is found by difference after correcting for solubility effects. However, in the presence of saturated hydrocarbons or other inert gasas, no analysis is possible. A new method, based upon selective hydrogenation, provides a direct analysis for cyclopropane. In addition, mall gas volumes (-1 cc. a t normal temperature and p m u r e ) may be analyzed. Willstlitter and Bruce (b) studied the hydrogenation of cyclopropane over a nickel catalyst and found that appreciable reacI Praent ddreu, Elso Laborstorica, Standard Oil DePdopmsnt Co.. Elirabrtb, N. J.
