ANALYTICAL CHEMISTRY
1066 (0.2 to 1.2%) of benzene were added from a microburet to 50 ml. of ether, the solutions shaken with 50 ml. of saturated sodium chloride solution, and the specific gravities measured. The values were found to lie on a reasonably straight line ( A , Figure 1). As certain plant' samples of ether contained amounts of benGene that were below the sensitivity of the method, concentration by distillation was attempted. Solutions consisting of 150 ml. of ether containing added benzene were concentrated to approximately 50 ml. by distillation and then the specific gravities of the residues were measured. The values plotted in B , Figure 1, sho17 that a slight loss of benzene occurs. It is, therefore, advisable for each analyst to distill known solutions in his apparatus, construct his own graph, and use it in calculating the benzene content of samples. Apparatus. The distillation apparatus is similar to that described by Shaefer (W), except that a 2-liter suction flask containing a 100-ml. test tube is used as a receiver for the distillate. Procedure. Measure a 150 nil. sample of the ether into a 500nil. round-bottomed flask. Attach the flask t o a 3-bulb Snyder column, condenser, and receiving flask containing a large test tube marked a t the 100-ml. point. Direct a moderately strong current of compressed air against the lower bulb of the column. Distill 100 ml. of the ether a t the rate of 2 to 3 drops per second and discard it. Cool the flask and transfer the residual ether to a 250-ml. Squibb separatory funnel, add 50 ml. of saturated sodium chloride solution, stopper the funnel, and shake vigorously for 30 seconds. Allow the t'wo layers to separate and discard the aqueous layer. Rash the ether with two more 50-ml. portions of salt solution to remove any alcohol present. Transfer the ether layer to a 50-ml. graduated cylinder, read the volume, and measure the specific gravity a t 20"/20" C. If measured a t a higher temperature, add 0.0011 per 1' C. From a graph prepared after distilling known mixtures of cther and benzene, read the per cent benzene in the distillation residue. Calculate the per cent benzene in the original sample by the following equation: Volume of residue X
yobenzene in residue 150
0.72
0 $72
2 0
,\" 0 7 2 N
t >
2
072
5 u
'Y
072 -0-
w 0.71
0.71
--A--CURVE B-RESIDUES L E F T A F T E R D I S T I L L A T I O N OF KNOWN SOLUTIONS
I
I
0 5
I O
PERCENT
The foregoing procedure was applied to two known solutions of ether and benzene which contained 1% each of water and
I 5
I
I
2.0
2.5
BENZENE
Figure 1. Concentration of Benzene in Ether us. Specific Gravity of Benzene-Ether Solution
alcohol. Typical plant-rectified samples are known to contain small amounts of these substances. The method was also applied to three samples of plant-rectified ether, both as received and after the addition of known amounts of benzene (Table I). ACKNOWLEDGMENT
Most of the experimental work described in this art.icle was carried out a t the Radford Ordnance Works, operated by the Hercules Powder Company.
70 benzene, by volume RESULTS
CURVE A- KNOWN SOLUTIONS WITHOUT D I S T I L L A T I O N
LlTERATURE CITED
(1) Kouba, D.
L.,Kangas, L. R.,and Becker, W. W., ANAL.CHEM.,
20,1063 (1948). (2) Shaefer, W. E., IXD. ENG.CHEM., ANAL.ED.,16,432 (1944).
RECEIVED February 9, 1947.
Determination of Diethyl Phthalate in Smokeless Powder P. G. BUTTS', G. B. PRINE2, D. L. KOUBA, AND W. W. BECKER Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. Diethyl phthalate in solventless type smokeless powder can be determined by digesting a sample with potassium hydroxide and hydrogen peroxide, distilling from the reaction mixture the ethyl alcohol so formed, and determining the ethyl alcohol in the distillate by oxidation with potassium dichromate.
0
NE of the constituents added to certain types of solventless smokeless powder is diethyl phthalate. During World War 11, a rapid and accurate method was needed for its determination. Before the war the only available direct procedure was the Thames oxidation method ( 2 ) which, essentially, consists in digesting a 5.0-gram sample with 40% (1 to 1) nitric acid, whereby the nitrocellulose is hydrolyzed to a water-soluble form and the phthalic ester is converted to phthalic acid. After 1 Present address, Department of Chemistry, Purdue University, Lafayette. Ind. 4 Present address, Columbia Powder Company, Tacoma, Wash.
oxidation of the oxalic acid (formed by oxidation of the cellulose) with potassium permanganate, lead acetate is added in order t o precipitate lead phthalate. This precipitate is filtered, dissolved in nitric acid, and treated with sulfuric acid. The resulting precipitate of lead sulfate is filtered, dried, and weighed, and the percentage of diethyl phthalate is calculated. When Smith and Strempfer (I) used lead acetate as a precipitating agent, they obtained high results, which they attributed to contamination of the precipitate with varying amounts of basic lead acetate. When lead acetate was added to known amounts of phthalic acid, the analytical values obtained for phthalic acid were 3Iy'
1067
V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 Table I.
Recovery of Phthalate by Thames Method on Known Samples
Phthalate Sample Phthalic acid Potassium acid phthalate
Calcd. from Weight of Lead Phthalate No. of Range of * detns. results, % 4
124.9-123 9
4
126.0-126.5
Calcd. from Weight of Lead Sulfate No. of Range of detns. results, 7% 4
130.9-131 9
.... ..
Table 11. Analysis of Known Mixtures of Diethyl Phthalate and Diethyl PhthalateFree Powder Diethyl Phthalate Added
Diethyl Phthalate Found Uncorrected Corrected
Difference
%
%
7%
%
2.91
3.23 3.62 3.23
2.91 3.30 2.91
0.00 0.00 -. 0 . 0 4
3.30
2.95
too high, which confirmed the results of Smith and Strempfer. However, when a sample of powder containing a known amount of diethyl phthalate was analyzed, using lead acetate, results were only about 10% too high. Evidently a considerable loss of diethyl phthalate must take place during the nitric acid and permanganate oxidations. Because the Thames method required 2 to 3 days, it was not a witable control method. A survey of the literature yielded no promising method for the determination of the phthalate radical in the presence of nitroglycerin and nitrocellulose. However, it appeared that the diethyl phthalate might be saponified with alkali, and the resulting ethyl alcohol isolated and determined. A procedure, called the distillation method, embodying this principle was worked out. Briefly, a sample of the powder is digested with 307, potassium hydroxide, whereby the nitrocellulose and nitroglycerin are decomposed, and the diethyl phthalate is saponified to yield equivalent amounts of potassium phthalate and ethyl alcohol. After addition of hydrogen perovide to oxidize aldehydes present, the alcohol is removed by distillation and determined by oxidation a i t h potasqium dichromate. THAMES METHOD
The Thames oxidation method was first applied to known phthalate samples with the results shown in Table I. The recoveries were calculated from the weight of both lead phthalate and lead sulfate. Very high results were obtained, presumably due to the presence of basic lead acetate in the precipitates. A special pilot plant lot of smokeless powder which contained 2.96% diethyl phthalate was prepared and quadruplicate analyses were made by the oxidation method. Values of 3.24 to 3.29u' diethyl phthalate, representing recoveries of 110 to Ill7', were found Results are about 10% high. DISTILL4TION METHOD
The distillation method, including refluxing, was first tested on a known solution of alcohol. I t was found necessary to install a thistle-tube water trap in the top of the condenser, to avoid loss of alcohol vapors during refluxing. On six runs, an average value of 99.8y0 recovery was obtained. The method was then applied to a sample of diethyl phthalate, with an average recovery of 99.5%. The method was next applied to known nlixtures of diethyl phthalate, nitroglycerin, ethyl centralite, and nitrocellulose. The results obtained at first were much too high. I t was thought that volatile aldehydes resulting from the decomposition of the nitrocellulose and nitroglycerin were distilling over and consuming potassium dichromate. An excess of hydrogen peroxide was added, therefore, to the saponification mixture for the purpose of oxidizing these aldehydes to their corresponding acids, which would then be retained in the alkaline qolution. The distillate
was made cloudy by some ethyl centralite that steam-distilled over. The distillate was saturated with sodium sulfate to salt out the centralite, then filtered. Blank determinations in which the reagents and samples of a powder containing no diethyl phthalate were used showed 0.32% apparent diethyl phthalate. A breakdown to account for this rather large blank showed that most of it was due to oxidizable impurities in the inorganic reagents. In subsequent work, using different lots of reagents, the blank dropped to 0.12%. Known mixtures of diethyl phthalate and diethyl phthalatefree powder were analyzed with the results shown in Table 11. Considering the magnitude of the blank correction (-0.32%), the close agreement .between the amounts of diethyl phthalate present and found must have been fortuitous. A special pilot plant sample of powder containing 2.9670 diethyl phthalate was analyzed by the foregoing procedure and found to contain 2.92y0 of this material. Procedure. Weigh a finely divided 10-gram sample of the powder into a 500-ml. Erlenmeyer flask and add a few particles of Carborundum and 100 ml. of 30% potassium hydroxide. Attach the flask to a reflux condenser which is fitted with a bent thistle tube containing 10 ml. of water to serve as a trap. Reflux on a hot plate for 1 hour. Remove the flask, allow it to cool, remove the thistle tube, and pour 25 ml. of 3% hydrogen peroxide through the condenser. Replace the thistle tube and reflux for an additional hour. After the flask has cooled, pour 100 ml. of water through tho thistle tube, so that its content,s are washed into the flask. Quickly connect the flask to a condenser, with adapter, arranged for downward distillation. Use a 250-ml. volumetric flask with a mark at the 229-ml. level as a receiver, and immerse in a bath of ice water. Adjust the adapter so that it dips into 29 ml. of water in the flask. Slowly distill until the solution reaches the 225-m1. mark. At the end of the distillation, disconnect the flask a t once and wash the adapter with a small amount of water. .4dd 65 grams of sodium sulfate and place in a water bath maintained a t 25 C. ix the contents of the flask from time to time until the sodium lfate is completely dissolved. Dilute the distillate to 250 ml., mix, and filter it through a rapid paper into a second 250-ml. flask. By means of a pipet, transfer a 50-ml. aliquot to a 2501ml. iodine flask, and add 25.00 ml. of 0.2 N potassium dichromate solution and 25 ml. of 40yo sulfuric acid solution. Place a moistened glass stopper loosely in the flask and heat the flask on the steam bath for 75 minutes. Remove t,he flask, cool it, and add 25 ml. of 10%) potassium iodide solution. Titrate the liberated iodine with 0.1 sodium thiosulfate using starch indicator. One milliliter of 1 aV potassium dichromate solution is equivalent to 0.02779 gram of diethyl phthalate. A blank determination should be made, preferably on a mixture of nitrocellulose, nitroglycerin, and ethyl centralite which approsimates the composition of the powder being analyzed, and the correction so obtained should be applied. Analysis of Samples. The foregoing procedure was applied by five analysts to the determination of diethyl phthalate in a sample of regular-production solventless smokeless powder with the results shown in Table 111. O
Table 111. Analysis of a Solventless-Type Powder Formulated to Contain 3.00Yo Diethyl Phthalate Diethyl Phthalate Found,
%
hnalys t A B
3.12, 3.14, 3 . 1 8 3.13, 3.14 3.06 7 , 3 . 1 46
C
D E Ar.
3.08, 3.10 3.12
ACKNOWLEDGMENT
Most of the experimental work described in this article was carried out a t the Sunflower Ordnance Works, operated by the Hercules Powder Company. LITERATURE CITED
(1) Smith, S. B., and Strempfer, J. F., IND. ENG.CHEM.,ANAL.ED., 16, 416 (1944). (2) Thames, F. C., Ibid., 8, 418 (1936).
RECEIVED February
9, 1947.
