V O L U M E 2 7 , NO. 4, A P R I L 1 9 5 5 state, or dissolved in physiological saline solution, phosphate buffer solution, or sesame oil. Accordingly, stability studies in these solvents and in the dry state were carried out on iV,N',N"triethylenephosphoramide and N,N',N"-triethylenethiophosphoramide. The analytical procedure for these determinations, except for the solutions in sesame oil, was the same as the proredure already described. (With the phosphate buffer solution it was necessary to run careful blanks to allow for the effect of the buffer in consuming alkali.) For the solution of the thiophosphoramide in sesame oil a modification was used in which (Lath addition of the acid or alkali was accompanied by vigorous -haking. The purpose was to extract the compound from the *?same oil layer into the water layer. But with phosphoramide dissolved in sesame oil, this extraction into the aqueous phase was much too slow. Therefore, boiling thiosulfate solution was added to the sample, followed immediately by a measured volume of boiling standard hydrochloric acid solution. The titration mas then completed a t the boiling point with standard hydrochloric acid and sodium hydroxide solutions. The procedure gave results of relatively poor precision, but served to indicate the stability in a satisfactory manner. Results of these determinations show t h a t the aqueous solutions, both physiological Qalineand phosphate buffer, were unstable. However, the compound in the solid state and in the sesame oil solution showed little, if any, loss in strength over the period studied.
543 ACKNOWLEDGMENT
The authors are greatly indebted to Frederick S. Philipe, Sloan-Kettering Institute for Cancer Research, New York, N. Y., who suggested a t the outset of the study that the thiosulfate titration method used for the nitrogen mustards ( 1 ) might be applied to the assay of the ethylenimines. Philips also obtained some preliminary data which indicated that the reaction of triethylenemelamine with thiosulfate was accompanied by a release of acid. The authors also Tl-ish to thank Erwin Kuh and Doris Seeger for furnishing the samples of the phosphoramides, P. F Dreisbach and C. M. Hofmann for furnishing the other samples, D. S . Kendall for the infrared work, and Z. F. Smith for obtaining some of the results in the stability studies. LITERATURE CITED
(1) Golumbic, C . , Fruton, J.
S.,and Bergmann, XI., J . Ore. Chem., 11,518(1946). ( 2 ) Karnofsky, D. .4.,Burchenal, J. H., Armistead, G. C., Jr., Southam, C . >I., Bernstein, J. L., Craver, L. F., and Rhoads, C. P., Arch. Internal Med., 87, 477 (1951). ( 3 ) Philips. F. S., and Thiersch, J. B., J . Pharmacol. Erptl. Therap., 100,398(1950). (4) Ross, W. C. J., J . Cham. SOC.,1950,2257.
RECEIVEDfor review June 17, 1954. Accepted December 1, 1954, Presented a t the Meeting-in-Miniature of the North Jersey Section, AMERICAN CHEMICAL SOCIETY, Newark, N. J., January 26, 1953.
Volumetric Determination of Nitrocellulose and Nitroguanidine By Transnitration of Salicylic Acid HARRY STALCUP and RICHARD W. WILLIAMS U. S. Naval Powder Factory, lndian Head, Md. This investigation was undertaken because of the need for a direct chemical method for the determination of per cent nitrogen in nitrocellulose for specialized applications where the nitrometer was either inapplicable or inaccurate. Nitrogen in nitrocellulose samples of various levels of nitration and nitramine nitrogen in nitroguanidine were determined volumetrically by the transnitration of salic?-licacid in sulfuric acid solution, the sample being used as the nitrating agent, followed by reduction of the resulting nitrosalicylic acid with standard titanous chloride. Determinations on samples of known nitrogen content showed a standard deviation of 0.02% and were in good agreement with nitrometer values. The method offers a new approach to the determination of nitramine-type ingredients in propellant-powder formulations.
T
H E determination of nitrate nitrogen in nitrocellulose and nitramine nitrogen in nitroguanidine is of importance in the production of gun and propellant powders. A nitrometer is ordinarily used, but because of their low solubility in cold sulfuric acid, some nitrocellulose fractions prepared in this laboratory under various experimental conditions failrd to yield their true nitrogen values in the nitrometer. For this reason a rapid and accurate titration procedure was sought. A procedure has been developed, based in part on the Moore (4)modification of the Forster ( 2 ) salicylsulfonic acid method for nitrate nitrogen, in which the nitrate compound is used as the agent for the nitration of salicylic acid in a sulfuric acid medium. The resulting nitro compound is then reduced with standard titanous chloride by the Knrcht-Hibbert method ( 3 ) . Compounds containing
both nitrate and nitramine nitrogen-such as b-nitroxyethylnitroguanidine-have been analyzed, and nitroguanidine in gun propellant compositions has been determined. The rompound produced in the salicylic acid-nitrate reaction has been identified as 5-nitrosalicylic acid. APPARATUS
Cylinder of carbon dioxide or nitrogen gas. Heat source, Variac-controlled hot plates or heating mantle to fit 250-ml. refluxing flask. Refluxing flask, 250 ml. Soxhlet unit, 20-ml. capacity siphoning cup. Reflux condenser, water-cooled to fit Soxhlet unit. Reflux condenser. water-cooled with ground-glass standardtaper tip. Glass bottle of 2-liter capacity, equipped with an automatic buret for storage and use of the titanous chloride solution. The siphon tube and buret must be connected in such a way that only carbon dioxide or nitrogen gas, supplied from a tank, will be drawn into the reagent bottle as the solution is used. The bottle should be covered with black paint or black paper to exclude light. Refluxing flask, 500-ml. capacity, with a round bottom and two necks. One of the necks should be of ground glass with a standard taper to fit the reflux condenser. REAGENTS
TITANOUS CHLORIDESOLUTION (0.3N). For each liter of titanous chloride solution, 225 ml. of 20% titanium trichloride is mixed with 100 ml. of 38% hydrochloric acid. The mixing operation should take place before diluting, and in these operations the solution should be protected from the air as much as possible by means of carbon dioxide. The solution should then be thoroughly mixed by means of a current of carbon dioxide and stored in reagent bottle. An alternative procedure for making titanous chloride from titanous hydride is as follows:
ANALYTICAL CHEMISTRY
544
T o 22 grams of titanous hydride weighed into a 1-liter Table I. Per Cent Nitrogen Content of Various Compounds Erlenmeyer flask, 200 ml. of Comparison of Salicylic Acid Nitration Method with Nitrometer concentrated hydrochloric acid Salicylic Acid-Titanous Chloride hlethod is added slowly. The mixture XtromTest S o . is heated on a steam bath Compound eter 1 2 3 4 5 .IY. Calcd. Range S.D. (caution, hydrogen evolved) in Sitrocellulose 11.73 11.74 11.77 11.74 1 1 . 7 5 11.75 11.75 ... 0.04 0.02 a hood in an atmosphere of S-itrocellulose 12.60 12.61 1 2 . 0 1 12.00 12.62 12.61 12.61 .., 0.02 0.01 carbon dioxide. After the re13.15 13.17 13.16 13.1f 13.14 13.15 13.16 0.03 0.01 Xi t rocellulose h-itroguanidine 1 3 . 4 1 13.39 13 40 13.39 13.41 13.40 13.40 13:iG 0 . 0 2 0.01 action has subsided, 200 ml. of P-Sitroxyethylhydrochloric acid is added and nitroguanidine ... 14.56 14 51 , ... ... 14 54 14.50 ... ... .Immonium nitrate ... 17.44 17 4fi ... ... 17 45 li.50 ... ... the solution allowed to stand for 1 hour. The solution is then filtered (under carbon diTable 11. Per Cent Nitroguanidine in Nitroguanidine oxide), diluted t o 2 liters, Propellant mixed, and stored as previously described. Water For standardizing titanous chloride solution the following Salicylic Acid XitrationExtractionprocedure is recommended. -4 current of carbon dioxide is Titanous Chloride Reduction ~ ~ ~ passed for 5 minutes through the 500-ml. refluxing flask equipped Replica Uncorrected Corrected" Method with an inlet tube. From a buret 25 ml. of 0.2A%rsolution of 58.78 58 95 59.04 potassium dichromate (reagent grade) is added, followed by 50 58.70 58.87 58.88 58.83 59.00 59.04 ml. of 10% sulfuric acid solution. The titanous chloride solution 5 8 . 8 5 59.02 5 8.65 is used for the titration, 3 drops of a 0.5% aqueous solution of 58.89 59. O l i 58.98 sodium diphenylbenzidine sulfonate being added near the end .I\ 58.81 58.98 58.92 point. The indicator color change is from a distinct light blue Range 0.34 0.19 0.19 to bright green. Diphenylamine (0.5%) in strong sulfuric acid 0.07 SD 0 Oi 0.16 may be used instead of sodium diphenylbenzidine. The color a Corrected for nitration of 13.41Y0 (99.63uc theoretical); obtained by change at the end point is from blue to sea green. dividing uncorrected yalues by 99.63. FERRIC AmxosInr SULFATESOLUTIOX (0 151%~).For each liter of ferric ammonium sulfate solution 75 grams of hydrated ferric ammonium sulfate [Fen(SO~)~.(i\H4)aS04.24H20] is mixed with 25 ml. of 95% sulfuric acid. The mixing should be done b y means of a current of carbon dioxide. The solution is standis added, and the excess titanous chloride is titrated with 0.15N ardized as follows: The air in a two-necked refluxing flask is ferric ammonium sulfate solution t o the red end point. A blank displaced with carbon dioxide. A solution of 40 to 45 ml. of is run on the reagents, only the sample being omit,ted, and any ferric ammonium sulfate is accurately measured into the flask significant correction applied. and 25 ml. of 1 to 1 hydrochloric acid solution and 50 ml. of Calculations. water are added. The solution is titrated with the 0 . 3 s titanous chloride until near the end point; then 5 ml. of 20'% ammonium 111. of TiC1, used X iV of TIC13 X 0.002335 X 100 thiocyanate solution is added. The titration is continued until Grams of sample the red color just disappears. Temperature and buret corper cent of nitramine or nitrate nitrogen rections are applied to the observed readings, and the normdity of the ferric ammonium sulfate solution is calculated. where 0.00235 = gram of nitrogen equivalent to 1 nil. of normal Aill.\ron.rc-M T ~ ~ o c ~ a l r(20%). a ~ E Twenty grams of amtit,anous chloride monium thiocyanate (c.P.) is dissolved in 100 ml. of distilled water. 111. of TiCly used X A' of TiClr X 0.01735 X 100 ACETIC ACID (70%). Seven hundred milliliters of glacial Grams of sampk acetic acid is mixed a i t h 300 ml. of distilled water. per cent nitroguanidine SULFURIC-S.4LICYLIC-AkCETIC A C I D bfIXTURE. One part by volume of glacial acetic acid is mixed with 9 parts by volume of where 0.01735 = gram of nit,roguanidine equivalent to 1 ml. of concentrated sulfuric acid; then 100 grams of dry salicylic acid normal titanous chloride. is dissolved in 1000 ml. of the mixture. Smaller samples of nitroguanidine may be used with corSULFURIC-SALICYLIC ACID MIXTURE. Twelve grams of dry respondingly smaller volumes of titanous chloride. salicylic acid is dissolved in 1000 ml. of concentrated sulfuric Volumetric Procedure for Determination of Nitroguanidine acid. in Propellant Compositions. A 0.5-gram sample (ground in a DRYCARBOX TETRACHLORIDE. Kiley mill to 20-mesh part,icle size) is weighed accurately into a small paper extraction thimble. A plug of glass wool is inserted into the t,himble and the latter is dropped into a small Soxhlet PROCEDURE extraction t'ube having a siphoning-cup capacity of approxiDetermination of Nitrogen in Nitroguanidine or Nitrocellulose. mately 20 ml. The sample is extracted for 3 hours with dry A 0.30 f 0.05-gram sample is weighed accurately into a glass carbon tetrachloride under a water-cooled condenser. A heating mantle or ot,her Variac-controlled heat source is adjust.ed so that weighing bottle of 20- to 25-ml. capacity. Ten milliliters of the sulfuric-salicylic-acetic acid mixture is added. The solution is the solvent vapors will condense in an almost continuous stream then stirred carefully unt,il dissolved and allowed to st,and for above the sample. about 20 minutes. After extraction the paper thimble is removed and both the thimble and Soxhlet tube are dried thoroughly. The thimble is Nitrocellulose samples above 13% in nitrogen content must then reinserted into the Soxhlet tube. A 250-ml. refluxing flask first be dissolved in 10 ml. of concentrated sulfuric (room temperature) and left in contact with the acid for a period no longer containing 40 ml. of 70% acetic acid is attached to the Soxhlet than 20 minutes. Then 10 ml. of the sulfuric-salicylic-acetic tube and the sample extracted for 2.5 hours. The heat source acid solution is added with stirring and the mixture is allowed should be adjusted so that a siphoning cycle is obtained in 6 to stand for an additional 10 minutes. minutes or less. After the extraction the siphoning cup is allowed The contents of the weighing bottle are transferred to a 500nearly to fill (15 to 20 ml.) and the heat is then turned off, The ml. two-necked refluxing flask attached to a carbon dioxide tank refluxing flask containing the nitroguanidine and lead acetate and washed in with 40 to 50 ml. of distilled water. After the air in 20 t o 25 ml. of acetic acid is detached and cooled in an ice in the flask has been replaced with carbon dioxide, 75 ml. of bath. A cold solution containing 85 ml. of the sulfuric-salicylic standard 0 . 3 5 t,itanous chloride solution is added. A420 to acid mixture is introduced into the flask and the contents are 25'3& excess of reagent is sufficient. The flask is attached to a thoroughly mixed. The solution is permitted to stand 15 to 30 minutes, then it is diluted with 150 ml. of water, and transferred water-cooled reflux condenser and the contents are boiled for 1 minute. Then the heat is removed and while the flask is still to a 500-ml. round-bottomed two-necked refluxing flask. Carbon attached to the condenser, it is cooled to room temperature by dioxide is bubbled through the solution for 5 minutes and 75 ml. of 0.3.2' titanous chloride (or a calculated 25y0 excess) is added. means of a container of cool running water. It may be necessary to increase t,he flow of carbon dioxide before cooling to The flask is attached to a water-cooled condenser, the carbon dioxide flow is continued, and the contents are boiled for 2 or 3 prevent air from entering the reaction chamber and oxidizing the titanous chloride. The flask is Temoved from the condenser, minutes. The heat source is removed and while the flask is 1 ml. of a saturated solution of ammonium thiocyanate indicator still attached to the condenser, it is cooled to room temperature, , ,
.
~
.
i
V O L U M E 27, NO. 4, A P R I L 1 9 5 5
545
by means of a vessel of cold running water. The flask is detached from the condenser, 5 ml. of a 20% solution of ammonium thiocyanate indicator is added, and the excess of titanous chloride titrated with 0.15N ferric ammonium sulfate t o the red-brown end point. A blank is run on the reagents for the presence of reducible impurities, and any significant corrections are applied. Calculations.
bIl. of TiCl, corisuined X S of Tic13 X 0.01i35 X 100 Grams of saniple per cent nitroguanidine DI SCUSSIO\
The described method was originallj- designed for “specialtv” applications-i.e., for samples of nitrocellulose either too small or too insoluble in cold sulfuric acid to be readily determined b\the nitrometer. Homever, standard lots of nitrocellulose and nitroguanidine iyere used in comparing the accuracy and precision of the new method with the nitrometer Thc rewlts given in Table I on three lots of nitrocellulose and one lot of nitroguanidine show a mavimum range of 0.04% and a standard deviation no greater than 0.02% in anv case. E x cellent agreement with the nitrometer was also obtained. Duplicate determinations on ammonium nitrate and p-nitrovyethylnitroguanidine indicate further applicahilitj- of the method. A practical application of the method is demonstrated by the results shoim in Table I1 on a typical nitroguanidine propellant. -4range of 0.1970 and a standard deviation of 0.07yo indirate a more satisfactory degree of precision for powder analysis than that obtainable by a water extraction-gravimetric method.
Table IIJ.
\-olumetric Determination of Nitrocellulose of 12.60% Nitration by Salicylic Acid-Nitration Method Test h-0. 1
Refluxinga Time, Min.
2
3 4 5 I
8 9
10 11 12 13 a
1 1 1
Sitrocellulose,
G
0.1720 n 26.z 0.3258 0.2184 0.2776 0.2810 0.2858 0.3296 0.2547 0.4099 0.3387 0.3043 0.3919
12.60 12.69 ~. 12.64 12.71 12.60 12.68 12.63 12.64 12.63 12.61 12.62 12.61 12,61 ~~
tion permissible t o ensure a minimum solubility of the nitrocellulose during the extraction of nitroguanidine and other compounds from the powder. During this investigation 85 ml. of concentrated sulfuric acid containing 1 gram of salicylic acid was found to be the minimum quantity that could be added to 25 ml. of 70% acetic acid containing nitroguanidine in solution and still effect quantitative nitration. IDE>TIFICATION OF NITRO COhIPOUND
Conflicting statements appear in the literature regarding the identity of the nitro compound formed from the action of nitrates on salicylic acid in sulfuric acid medium. I n his extensive Fork on the estimation of nitrates in fertilizers by the Forster method (a),AIoore ( 4 ) suggested the following reaction:
OH /
2c,H,
‘OOOH Salicylic acid
\
SO,
Nitrophenol The nitro compound was reduced to the corresponding amine with sodium thiosulfate and the nitrogen then determined by the Kjeldahl method. Dickinson ( 1 ) stated that the salicylic acid is converted to 5-nitrosalicylic acid and submitted evidence t o show that aminosalicylic acid is the derivative produced upon reduction of the nitro compound with sodium thiosulfate. The identity of the nitro compound produced is only of academic interest because its final measurement, whether based on the modified Kjeldahl or the method described here, depends only on the presence of a nitro group. However, because of the
Table IV.
Reflux time begins when first drop falls from condenser.
Commercial nitroguanidine used in powder manufacture usually ranges bettc-een 13.30 and 13.43% in nitration values as compared with the theoretical value of 13.46%. Therefore, for a n accurate determination of the nitroguanidine content of a powder, the nitration value of the nitroguanidine should be known. Table I11 ? h o w experimental results obtained on a sample of nitrocellulose of 12.6070 nitration. The refluxing period becomes a critical factor if continued beyond 2 minutes. I n Table IV, nitrocellulose of 13 15% nitration gave unreliable results when the procedure for the lower nitrations was used. However, when the sample was first dissolved in 10 ml. of purr sulfuric acid for a contact period of 20 to 30 minutes and then the sulfuric-salicylic-acetic acid reagent added for a n additional contact time of 10 to 15 minutes, results agreed closely with the nitrometer values. S o serious difficulty was encountered with the nitroguanidine determination. However, in order t o make the procedure applicable to a determination of the nitroguanidine in a gun propellant, further investigation was necessary. Seventy per cent acetic acid has been found t o be the strongest concentra-
+ 2 ~ a ~ 0+3H ~ S O+ ~
Test h-0. 1 2 3
10 11 12 13
Sitrogen i n Nitrocellulose of 13.15% Nitration (Determined with two methods) Salicylic Acid-Stration lIetliod Original llodified Contact Contact Time, Min. time in salicylicSulfuricsulfuric salicylicmix!ure, >-, Sulfuric acetic min. % acid mixture 10 12.24 15 10 10 12.03 13 15 13.17 1.5 20 10 1.5 13,14 20 10 13 20 12.87 15 13.16 15 20 15 15 13,Ol 20 20 13.28 20 1.5 23 13.41 20 30 15 20 BO 13.40 :1 13.62 90 10 30 13 82 120 20 35 3.5 13,86 ... ..
N,
%
13.17 13.16 13.14 13.16 13.15 13.16 13.21 13,26 13.16 12.82 12.87 12.47
Table 1.. Analysis of Synthesized Nitro Compound XOy by
Compound Synthesized nitro compound, found 5-Nitrosalicylic acid, calcd. 3-Nitrosalicylic acid, calcd. 3-Nitrosalicylic acid (anhydrous), calcd. o-Xitrophenol, calcd.
Salicylic acid (alkali titration)
Carbon
Hydrogen
TiCls reduction
45.79 45.91 41.80
2.76 2.75 3.50
25.12 22.88
75.68 75.43 08.66
45.91 51.80
2.75 3.62
25.12 10.07
75.43
25.19
...
546
ANALYTICAL CHEMISTRY
con&king opinions expressed, an effort wm made to identify the nitro compound produced. Salicylic acid in sulfuric acid solution was added to an excess of sodium nitrate. The resulting solution wa8 then poured over cracked ice and the insoluble nitro compound filtered off, washed, recrystdlieed twice, and dried a t 125" C. No carbon dioxide generation was observed during the reaction, an indication that the carboxyl group w&8not displaced. Nitrogen was determined by the titanous chloride reduction method of Knecht and Hibbert (5). Table V shows a comparison of the actual analysis of the synthesized nitro compound with the calculttted analysis of ortho-nitropheuol and the 3-nitro and 5-nitro isomers of nitrostLIieylie acid. Melting points for these compounds are as follows: Compound Synthesised nitro compound 5-Nitrosalicylic acid 3-Nitrosdioylio acid o-Nitrophenol
identity of the nitration products formed from the sodium nitrate-salicylic acid resotion in sulfuric acid indicate the following reactions: HaNC(=NH)NHNOz Nitroguanidine
+ CsH,(OH)CO( Salicylic acid
OaNCeHa(0H)COOH
+ [H2NC(=NH)NH,]rH3S04
Nitrosalicylic acid
(2)
Guanidine sulfate
O,NCaHI(OH)COO€I
+ 6TiCla + 6HC1-
Melting Points, 0 c . 185-192 228-230
123-125; 44-45
14EG149 (anhydrous)
DicknLouLL,
-..
nlvnY.
~ n f i ~ m SY, . .
,,,
IL~Y+I
Fiirster. 0.. C h m . Ztg., 13,229 (1889): 14, 1674 (1890). Knecht. E., and Hibbert, E., "New Reduotion Methods in Volumetrio Analysis,"Longmans, Green. and Co.. New York.
This comparison further substantiates the conclusion that the nitro compound formed is essentially 5-nitrosalicylic acid with a small amount of the &nitro isomer. No attempt was made to identify the nitrogusnidine-salicylic acid reaction products. However, conclusions based on the
1925.
Moore, H. C., J . I d . Eng. Chem.. 12, 669 (1920).
RECEIVED for review October
1, 1964.
Aocepted December 10, 1954.
Analvtical - Distillation in Miniatuire Columns Equipment and Operation J. C. WINTERS and R. A. DINERSTEIN Research Department, Standard O i l Co. (Ind.), Whiting, b
Miniature distillation columnsgiveel;cellentseparations of 15- to 50-ml. samples equal to those obtainable with proportionally larger samples on maem high-efficiency laboratory c o l u m n s . Controls and accessories adapted to the needs of the smaller columns are necessary to obtain such performance. A m o n g these are a closely controlled power s u p p l y for the distilling flaskheater, a receiver system that avoids mixing of fractions and allows accurate measurement of distillate volumes, and a vacuum system designed for leak-free operation. Spinning-band columns =re especially useful for vacuum distillation.
T H E qeed, f0.r fractional distillatim of amall quantities of organic liquids has increased with the trend in research toward small scale experiments. Modern autoclaves (5, 4 ) and new separation techniques give samples of 15 to 50 ml. that need further separation for analysis. Microanalytical methods such as spectroscopy can analyze minute quantities. Tbup, miniature distillation is an essential step between p r e p a r a tion and final analysis in small scale research. Effective miniature distillation requires more than just scaling down large columns. Although efficient columns have been designed for distilling small samples ( 1 , 6, 7), less has been done in developing techniques for scaled-down operation. On the smaller scale, control of throughput and reflux ratio must he more precise; B fluctuation RS little as 0.1 volt io the power to the distilling flask heater e m upset column operation. Losses of sample must be avoided; distillate volumes must be read accurately and entrainment of vapors during vacuum operation must he eliminated. Contamination of fractions must be mini-
Figure 1.
Installation of miniature distilling units
mieed; a aiogle drop of distillate can represent 10% contamina, tion in a succeeding fraction if it is held on the walls of the receiver system. Improved distilling units and controls would make miniature distillation a more practical technique. A fractionation installation has been designed and built that meets the needs of the s m d l scale. The present paper describe8 the equipment and method of operation; a future paper will report testing and evaluation of ithe columna. T A N 0 OPERATION ,:A" -c.+.I.,:..
.xi":^*..r^ A:"L:?,:""
units, four on each side of the central instrument section. Three types of columns are used: spinning band, Hyper-Cal, and con-
