ANALYTICAL CHEMISTRY
900 amides. The latter gave positive tests in Procedure B. whereas the former did not. The single exception found is o-iodobenzamide, where again the slower rate may be due to the large iodo group in close proximity to the amide carbon, thereby decreasing its positivity. It seems anomalous that dicyandianiide and diethyl cyanamide gave positive tests in Procedure B, but m-ere negative in Procedure C. This phenomenon is probably due to the greater instability of the resulting aniidoximes as the solution becomes progressively alkaline. The approximate order of the rates of hydroxylaminolysis can be summarized in the following series: A 1. Acylated aniline with electronegative groups in 0- and ppositions, greater than R 1. Nitriles with,basic groups 2. Unsubstituted amides 3. Ai-alkyl substituted amides greatey than
c,
1. Unsubstituted nitriles 2. N-aryl alkyl amides
greater than L)
1. lY-aryl aryl amides
The variation in the rate of this reaction with proteins may or may not be meaningful because of the purity of the samples used. If crystalline or highly purified samples were to give the same results, this reaction might be useful in pointing up structural differences in certain amide linkages of proteins. Finally, these results show that a n appreciation of such factors as temperature, reaction time, stability of reaction product, and p H may make the difference betn-een a positive and a negative qualitative analytical result. ACKVOWLEDG.MENT
Most of the compounds tested mere from commercial sources. The authors acknowledge with thanks gifts of experimental samples from the American Cyanamid Co., Armour Chemical Corp , hlonsanto Chemical Co., and Rohm & Haas Co. The egg albumin sample was kindly furnished by Harry D‘agreich, Chemistry Department, City College. LITERATURE CITED
(1) Buckles, R. E., and Thelen, J. C., ANAL.CHEM., 22,676 (1950). (2) Davidson, D., J. Chem. Edzccation, 17,81 (1940). 13) Feigl, Fritz, “Laboratory Manual of Spot Tests.” p. 186, Xem
York, Academic Press, 1943.
A41thoughonly a few of the less common derivatives of carboxylic acids were tried, the indications are that the test may be used to detect amidines, hydrazides, and possibly other derivatives. It appears to be general for ureas and guanidines.
(4) Nordmann, E., Ber., 17,2746 (1884). (5) Sidgwick, N;V., “Organic Chemistry of Nitrogen,” p. 198. S e r r Tork. Oxford University Press, 1937. KECEIVED for review June 17, 1951.
lccepted November 8, 1953
Microdetermination of Azide by a Kjeldahl Procedure LEONARD P. PEPKOWITZ’ University of California, Los Alamos Scientijic Laboratory, Los Alarnos, iV. iV. ELATIVELY few methods for the determination of the azide
€3 group have been reported and to the writer’s knoa ledge no
micromethod has been proposed. Methods based on the gravimetric determination of silver azide ( 6 ) , titration with iodine ( 2 ) , titration with silver nitrate ( 3 , 6), titration of the excess silver nitrate ( 9 ) , titration with nitrous acid (8), titration with permanganate (IO), and liberation of free nitrogen by the decomposition of azide with ceric ammonium nitrate ( I ) have been published. The described method is based on Kjeldahl-type procedure and has the advantage of being a micromethod so that only small quantities of explosive materials need be handled. The method is simple and accurate and should be applicable to the semimicro and macro scale as well. The method is based on the observation ( I f ) that hydrazoic acid in the presence of a reducing agent liberates one third of the azide nitrogen as ammonia and the remaining two thirds as free nitrogen. The reaction is quantitative and in spite of the poor factor offers a satisfactory microprocedure because of the accuracy with which ammonia can be determined by the Kjeldahl technique. R E4GERTS
Concentrated sulfuric acid, nitrogen-free. Selenium oxychloride, 12 grams per liter of concentrated sulfuric acid. Sodium thiosulfate, :337,. Perchloric acid, 3594, dillited from the 80 to 72% reagent grade with distilled water. Boric acid, 2y0. Mixed indicator, 5 parts of 0.1 Jf bromocresol green and 1 part of 0.1 Mmethyl red (4). Standard hvdrochloric acid, 0.05 1 Present address, Knolls Atoiiiic Power Laboratory, General Electric Co., Scheneotady, N. Y .
Sodium hydroxide, 30%. Ceric sulfate, sat.urated aqueous solution. PROCEDURE
Keigh 5 to 10 mg. of sample on a 3.5 X 4.5mm. piece of cigarette paper and introduce the sample together with the paper into a clean dry 18 X 150 mm. rimless test tube. Add 3 drops of 33% sodium thiosulfate and mix thoroughly t o wet the sample. Then add 1 ml. of concentrated sulfuric acid and 0.5 ml. of the selenium oxychloride solution. Mix well by swirling the solution and proceed with the digestion as described by Pepkowitz and Shive ( 7 ) . DIGESTION.Heat the solution moderately with a microburner for a minute or two to determine whether the sample will froth excessively. Following the subsidence of the frothing, if it occurs, boil the sulfuric acid solution vigorously for 10 to 15 minutes. This period depends on the length of time necessary for the material to go int.0 solution, clear, and pass from the black stage through the muddy brown stage and finally t o a clear ruby wine color. In this final st,age a colorless liquid condenses on the walls of the test t.ube and t,he evolut,ion of white fumes is materially decreased. Cool the digest t o room temperature and add 2 drops of 35% perchloric acid directly to the digest in order to minimize the loss of perchloric acid by volatilization from the sides of the test tube during the subsequent heating. Gently heat below the boiling point until the digest clears and becomes colorless. Cool t,he solution and dilute with a few milliliters of distilled water. Determine the ammonia in the digest by the usual microdistillation procedure using 2% boric acid as the absorbing solution. Titrate the ammonium borate with 0.05 S hydrochloric acid using the bromocresol green-methyl red indicator (4). In some lead azide preparations a proteinaceous material, usually gelatin, is added t o limit the size of the crystals in order t o prevent spontaneous detonation. This protein nitrogen will be included wit,h the azide nitrogen by the described procedure. To correct for the nonazide nitrogen, weigh 10 mg. of the sample in a microplatinum boat, as cigarette paper is an effective reducing agent,, and carefully slide the boat to the bottom of the digestion test tube. Add 1 nil. of R saturated aqueous solution of
901
V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2
-
.-
Table I.
Recovery of Azide from Sodium Azide
Sample, XI g.
Azide Sitrogen, Mg. Found
Taken
3.47
3.37 3 70 3.97 4.1.5 4.22 5.10 5.31 5.72
.5,2l .3.72
6.17
6,43
2.53 1.90
8 22 8 85 9 18
3.62
-0.08 +0.01
3.98
-0.0.5 -0.0:
4.10 4.21 5.15 5.25 5 60 6.04 6.12
t0.O.J -0.00
-0.1% +0.05 +0.02 A v . zt0.06 Standard de\.iation 0.07
5.99
G.10
9.44
Error +0.10
Table 11. Analysis of Lead Azide Sample, hlg. 12 9 14.8 15.0 15 1 16 0 17 0 21 1
-
Calculated 3 54 4.06 4.11 4 22 4.39 4 66
5 711
Azide Xitrogen, N g . Found 3 38 4 04
Deviation +0.04 -0.02
tO.O1
4 1” 4 20 4 .4:3
-0.02
t0.04
. 7.3
-0.07 -0.14 Av. z t 0 . 0 3 Standard deriat,ion 0.07
2.0:
ceric suliate. Mix well to decompose the azide and evaporate to dryness on a water bath or in an electric oven a t 110” C Cool and proceed as above eliminating the addition of the thiosulfate. As only one third of the azide nitrogen is recovered, the per cent azide can be calculated from the following equation
yo azide
= 1200 .Ir
G - :>
where S = norinality of t.he standard acid, 1’ = ml. of acid used for total nitrogen, v = ml. of acid used for protein nitrogen, S = mmple weight for total nitrogen, and s = sample weight for protein nitrogen.
Table I gives the recoveries from the purified sodium azide and indicates the accuracy of the method. With 5- to IO-mg. samples the average deviation from the theoretical quantities of azide was 1 0 . 0 6 mg. with a standard deviation of 0.07 mg. The data in Table I1 were obtained with a sample of lead azide containing a proteinaceous material as a stabilizing agent. Because of the large molecular weight of lead azide, slightly larger sample weights were used in order to obtain amounts of nitrogen equivalent to the data in Table I. -4s the sample was not pure lead azide, the data in column 2 v ere calculated from the mean per cent azide and the data in Table I1 are therefore indicative of the precision of the method. An average deviation of izO.05 mg. and a standard deviation for precision of 0.07 were obtained, n-hich are practically identical with the error statistics for sodium azide. It is essential to add the thiosulfate first, so that K reducing agent is present when the hydrazoic acid is liberated. Experinirats in which the thiosulfate was added after the sulfuric acid invariably gave l o a results. The digestion step is imperative, whether carbonaceous material is present or not. Experiments in which the sample of sodium azide was weighed in platinum boats and no heat applied resulted in the recovery of less than 1% of the theoretical amounts of nitrogen. Since the perchloric acid digestion is so short ( - 20 minutes), the use of cigarette paper, which acts as an additional reducing agent during the digestion step, is advocated. L I T E R A T U R E CITED
(1) Copemail, D. A., J . S. African Chem. Insf., 10, 18 (1927). (2) Feigl, F., and Chargav, E., 2. anal. Chem., 74,376 (1928). (3) Haul, R., and Uhlen, G., Ibid., 129,21 (1949). (4)
Ma, T. S., and Zuazaga, G., IND.ENQ.CHEM.,. ~ N A L . ED., 14, 280 11942).
( 5 ) Marqueyrol: M.,and Loriette, P., Bull. soc. chim. France (4), 23, 401 (1918). (6) Yioskovich, S. SI.. Bey. Inst. phusik. Chem. A k a d . Wiss. Ukr. S.S.R., 6, 179 (1936). ( 7 ) Pepkowitz, L. P., and Shim, J. W., IND.ENG.CHEM.,ANAL.ED., ~~
DISCUSSION
Sodiunl azide was used to test the method.
14,914 (1942).
Eastman technical grade sodium azide was purified by recrystallization. The sodium azide was dissolved to make a saturated solution and filtered through Whatman S o . 42 filter paper. The filtrate was diluted with an equal volume of 95% ethyl alcohol and the sodium azide was precipitated by adding an excess of diethvl ether. After an hour, the salt was filtered through Whatman h o 42 filter paper on a Biichner funnel and dried for 1 hour a t 110” C. Only one recrystallization was used, because repeated recr~-stalliaationsresulted iii decomposition of the azide.
(8) Reith, J. F., and Boun-man, J. H. -i., Pharm. Weekblad, 67, 473 (1930). ( 9 ) Thiele, J., Ber., 41, 2681 (1908). (10) Van der lleulen, J. H., Rec. trar. chim., 67, 600 11948). (11) Yost, D. AT., and Russell, H., “Systematic Inorganic Chemistry,” S e w York, Prentice-Hall, 1946. R E C E I I - bfor . ~ yeview June 2 q , 1951. Accepted October 8, i 9 2 , Bnsed on work perforrued a t Los .\lamas Scientific Laboratory of the University of California under Government Contract W-7405-eng-36.
Determination of Elementary (Red) Phosphorus by Potassium Bromate
’
G. S. DESIIMLKH AND B. R. SANT Department of Chemistry, Benares Hindu Gnicersity, Benares, India
l H E use of potassium iodate in the volumetric determination
of elementary phosphorus has been investigated by Biiehrer and Schupp (1). This method is based on the oxidation and subsequent conversion of phosphorus into phosphoric acid. Iodine liberated during the process or/and the unreacted iodate after the completion of the reaction is estimated iodometrically and the amount of phosphorus is calculated from the following reaction mechanism:
6P i 6KI03
+ 3HzSOa + 6H20 --+ GI-IJ’04
+ 31, + 31
