246
AAVALY TZCAL EDI TIO-V
solutions were made with fresh ether containing about 2.5 per cent alcohol to give solution7 which should have required 2.50, 1.00, 0.50, 0.25, 0.10, 0.05, and 0.026 cc. of 0.01 A' alkali. I n titrating these solutioiis very closely agreeing values were found in every case. the maximuin error being 0.01 cc. Hence, this ether could not have been acid by itself, and yet it altered slightly the blue color of the indicator. About 10 cc. of 0.01 N sodium acetate solution were placed in each of several cylinders of appropriate size. A drop of bromothymol blue indicator was added to each and a bluish green color produced. Amounts of anesthetic ether ranging from 10 to 100 cc. were added to the different cylinders. The color changes were very nearly alike in all cases whether 100 or 10 cc. of ether were present. Hence, the ether could not have been acid. The shifting of the color must hare been due to the influence upon the indicator of the alcohol and ether taken up by the water. The effect of solvents upon phthaleins has received comment before ( 2 , 5). Small amounts of impurities which might be found in poorly made ether or decomposed ether, such a? acetone, acetaldehyde, or peroxide, were added to ether and no change in acid values was found. Acids in Very Old Ether
I n studying the spoilage of ether, acidity has been found to develop a t a late stage. Relatively large amounts of peroxide, representing the first stage of decomposition, can be formed without the appearance of acid. Usually when aldehyde. or at least substances giving the aldehyde reaction. form, acidity begins to develop, but there has not been found a fixed ratio of aldehyde to acid, or of peroxides to aldehydes such as reported b y King ( 3 ) . I n some cases no peroxide and very little aldehyde hare been found, but considerable acid was present. There was on hand some very old ether which had been exposed to air to favor decomposition. Part of this ether was carefully distilled off in a still similar to that of Peters ( 4 )
Vol. 2, S o . 3
to concentrate the acids. The residue, which still contained alcohol and et'her, was extracted with 5 per cent sodium hydroxide solution, using bromothymol blue as indicator. The aqueous layer was then separated and evaporated. I n this way the sodium salts of the acids present, were obtained. There was a small amount' of an oil which was soluble in alcohol and thereby separated. Crystals then fornied which corresponded to those of sodium acetate. The mother liquor was treated with sulfuric acid and ethyl alcohol. K h e n the mixture was poured upon water, odors were present of acetic acid, ethyl acetate, and other substances, including ethyl formate. Tests with sodium carbonate and potassium permanganate solutions showed a decolorizing of the latter. Silver salts were reduced. Bromine water was not clecolorized. S o precipitate could be obtained by the addition of calcium chloride or acetate mith the subsequent addition of aiinnonia. These tests eliminated the unsaturated acids and those vhich form insoluble calcium salts. They confirmed the presence of formic acid as one of the decomposition products. King (.?) detected formic acid in old ethers by odor alone. Acetic acid has generally been accepted as the final decomposition product, based upon the work of Richardson and Fortey (6). The presence of both these deconiposition products is confirmed, and thus the work of these various investigators is substantiated. Acknowledgment
The writer wishes to acknowledge the assistance and cooperation received from members of the staff of this laboratory in connection with this investigation. Literature Cited (1) Baskerville and Hamor, J. IND.ENG. C H E X . ,3, 306 (1911). ( 2 ) Cohn, Z . angetu?. Chem., 19, 1389 (1906). (3) King, J . Chem. .Coc., 1929, 738. (4) Peters, J. IND. EXG.CHEY.,14, 476 (1922). ( 5 ) P r a t t and Coleman, J . A m . Chem. Soc., 40, 238 (1918). (6) Richardson and Fortey, J. Chem. Soc., 69, 1352 (1896).
Determination of Centralite in Double-Base Smokeless Powders' H. Levenson PICATINNYARSENAL,DOVER, K. J.
HE dialkyldiphenylureas, known as centralites, are
T
used as stabilizers (anti-acid compounds) in the manufacture of some double-base powders made from nitrocellulose and nitroglycerin. The analysis of such powders has hitherto presented considerable difficulty inasmuch as there was available no direct method of determining the centralite present with known limits of accuracy. Such a method has now been developed and the procedure used is recorded in this paper. Previous Methods
The initial step in the analysis of a double-base powder containing centralite consists of extracting with absolute ether, the nitroglycerin and centralite being dissolved and the nitrocellulose left as a residue. The ether is evaporated from t h e solution and the relative concentrations of nitroglycerin and centralite in this residue are determined. As but small quantities of centralite are used, previous Published by permission of the Chief of 1 Received February 18, 1930. Ordnance, U. S War Department.
workers have attempted to determine the nitroglycerin and find the centralite by difference. Cope and Rarab ( I ) have shown that the nitron method is not applicable to the accurate determination of nitroglycerin. The use of the nitrometer for this purpose is open to two serious objections: The nitrogen content of the nitroglycerin must be assumed to be within an arbitrary range, and the nitric acid liberated reacts with the centralite and a low result for nitroglycerin is obtained. Giua and Gastalla (2') state that, on treatment with fuming nitric, diethyldiphenylurea is nitrated to 2, 4, 2", 4"-tetranitrodiethyldiphenylurea, m. p. 176-177" C., and note that the nitrometer gives low results because of the action on the centralite of nitrous vapors resulting from the decomposition of the nitroglycerin by sulfuric acid. They recommend the determination of the total nitrogen in the mixture by the Dumas method and the calculation of the relative proportion of the components from this and the nitrogen content of each, but here too an assumption of a nitrogen content of 18.5 per cent for the nitroglycerin is made. I n practice, the
I S D C S T R I A L A S D E S G I S E E R I X G CHEMISTRY
July 15, 1930
247
value of this may be from 18.3 to 18.45 per cent and a difference of 0.1 per cent in this will cause an error of 1.3 per cent in the centralite content calculated. Lecorche and Jovinet ( 3 ) describe a direct method of determining centralite in such mixtures. This involves saponification of the nitroglycerin, formation of sulfone of the centralite, steam distillation of the ethyl aniline formed from the sulfone b y the addition of sodium hydroxide, formation of ethylaniline hydrochloride with a n excess of standard hydrochloric acid, and back-titration of the excess acid. This method is complicated and tedious and is open to question in regards to accuracy. as it is to be expected that some tetranitrodiethyldiphenylurea would be formed when sulfuric acid is added to form a sulfone. The tetranitro compound xould not be carried over by the steam distillation and so would be 1o.t. The methods suggested to date appear, therefore, to be inaccurate or too difficult for general use.
flask is quickly stoppered, the contents are mixed by gentle shaking, and exactly 30 seconds from the time of addition of the acid 10 cc. of a 15 per cent solution of potassium iodide are added. The iodine liberated is immediately titrated with 0.1 N sodium thiosulfate solution, freshly prepared starch solution being used as the indicator. The disappearance of the blue color is taken as the end point. The nitroglycerin present is calculated by difference. The bromide-bromate solution is prepared by dissolving 5.568 grams of potassium bromate and 30 grams of potassium bromide in water and diluting to 1 liter. This solution is standardized by placing 50 cc. of ethanol and 25 cc. of the solution in a 250-cc. glass-stoppered Erlenmeyer flask, cooling to 20" C., adding 5 cc. of concentrated hydrochloric acid, and, after 30 seconds, titrating with 0.1 N thiosulfate as above. The number of cubic centimeters of thiosulfate required in the standardization minus the number required for the sample represents the bromine combined with the centralite. 1 CC. 0.1 N Na&03 = 0.0067044 gram oc (X.C2H6.C&6)2 (cc. 0.1 N Na2SnOs by diff.)(0.0067044) = per cent tenwt. sample tralite in sample
Nitrometer Method
LIMITSOF dccun.hcY--Using carefully prepared mixtures of nitroglycerin and centralite of known composition, determinations of the centralite were made by the method given above. I n some cases check determinations were made by another chemist. The results are given below.
I t was considered advisable to determine the error involved in the determination of nitroglycerin in the presence of centralite by means of the du Pont form of the Lunge nitrometer. A mixture containing 95.25 per cent of nitroglycerin (18.24 per cent nitrogen) and 4.75 per cent of centralite (ni. p. 72.5' C.) was made u p and analyzed by the nitrometer. Although good check results were obtained, the 9.47 per cent of centralite indicated to be present by this method represents an error of alinost 100 per cent. The reaction was then carried out in a beaker with larger quantities of nitroglycerin, centralite, sulfuric acid, and mercury. From the resulting mixture of reaction products tetranitrodiethyldiphenylurea was isolated and identified. The conclusions of Giua and Gastalla were thus confirmed.
CENTRALITE MIXTURE P e r cent 0 45
IS
1 73 4 61
---CEKTRAI.ITE FOVSD---I I1 4v P e r cent P e r cent P e r cent 0 44 0 45 0 45 0 45n 0 45 0 45= 1 75 1 81 1 68 1 81a 1 83 1 84a
4 37 4 42a 6 25 6 10 10 7 8 10 66 4 3 10 43 08 88 34 88 29 a Determination b y co-worker.
4 4 6 10 42 88
45
60" 11 73
94 29
4 41 4 51 6 11 10 i o 4 3 01
88 29
DEVIATIOK P e r cent 0 0 0 0 0 02 0 08 0 20 0 10 0 14 0 08 0 09 0 06
Precipitation .Method
Conclusion
I t was noted that when a n alcoholic solution of nitroglycerin and centralite was saponified and diluted with water the centralite was precipitated. This was not found to be applicable as the basis of a gravimetric method. K h e n the precipitate from a known quantity of a mixture containing 5.0 per cent of centralite was caught on a Gooch crucible, washed, dried. and weighed, a centralite content of 2.4 per cent was calculated.
The deviations found may be considered as of the usual order of experimental error. The results indicate that the method may be expected to give result's which are slightly low. It, will be noted that a definitely short time is allowed to intervene between the addition of hydrochloric acid and nitration. The reaction bet,ween bromine and alcohol is dependent, upon time, temperature, and relative concentrations, and it is necessary to standardize the first two; bromine reacting wit,h alcohol not being determined as excess and so causing a high result for centralite to be obtained. =ifter the application of this method t'o the determination of centralite had been developed b y the writer, an abstract of a paper published some time before appeared ( 4 ) . As this paper appeared in a journal which has not been found available and no details are given in the abstracts, it' was considered advisable to proceed with the publication of this paper. The priority of Turek in developing t h e method, however, is recognized.
Volumetric Bromination Method
A volumetric method of determining diphenylamine in certain types of smokeless powders b y bromination with an excess of standardized bromide-bromate solution in the presence of hydrochloric acid was thought to offer possibilities with respect to the determination of centralite. The reactions involved would be:
+
+
+
+ +
KBr03 5KBr 6HCl+ 6KC1 3Br2 3H20 O c = ( K ; . C P HC6H6)2 ~ 2Br2 +2HBr oc = (X CzHs C6H4Br)z Brz 2KI -+- 2KBr f I 2 I2 2NazS203+2iTaI Na&06
++
+
+
(1)
(2) (3) (4)
Acknowledgment
From these reactions 1 cc. 0.1 -2' Sa2S203 = 0.0067044 gram diethyldiphenylurea. On trial, this method was found to give accurate results and the following procedure was developed:
The writer desires to acknowledge the assistance of C. S. Davis, assistant chemist', in making the check determinations recorded and that of Wm. H. Rinkenbach, chief chemist, in criticizing and preparing this paper.
An accurately weighed 5-gram sample of the ground powder is extracted with absolute ether for about 24 hours. The ether extract is evaporated t o constant weight, any residual solvent in the powder being removed simultaneously. The liquid residue is transferred to a 250-cc. glass-stoppered Erlenmeyer 5ask with 50 cc. of ethanol. Exactly 25 cc of a standardized bromidebromate solution are added, the mixture is cooled to 20" C , and 5 cc. of concentrated hydrochloric acid are added. The
Literature Cited (1) Cope and Barab, J . A m . C h e m . S o c . , 39, 504 (1917). (2) Giua and Gastalld, A l f i accad. sci. Torino, 60, 7 3 (1925); .4rmy Ordnance, '7, 447 (1927). ( 3 ) Lecorche a n d Jovinet, M l m . poudres, 23, No. 1, 69 (1925). (4) Turek, Chemicky Obaor, 1, 295; C h e m . Z e n l r . , 1927, XI, 999; C. A . , 22, 4819 (1928).
