CHaCOOK
+ HClOi
+
KClOi
+ CHaCOOH
Previous difficulties in attempts to standardize the perchloric acid-glacial acetic acid solution were overcome with the substitution of Bureau of Standards acid potassium phthalate for sodium carbonate as the primary standard. The use of crystal violet in place of bromophenol blue and bromocresol purple as the indicator, as suggested by Seaman and Allen (11) eliminated difficulties due to faulty end points. The lower recovery values for dimethyl phthalate may be due to its greater solubility in the aqueous solutions used during the extraction and neutralization operations. Based on a 94% recovery of dimethyl phthalate by
the proposed method (Table I) an empirical factor may be calculated as follows:
0.801 = 0.85 0.94 LITERATURE CITED
(8) Mullaly, RI. A. C., Zbid., 80, 237 (1955). (9) Pristera, F., ANAL. CHEY.25, 844 (1953). 10) Ribaudo, C., Campisi, J., Picatinny Arsenal Project EPO No. EP-13, Rept. 4, PA Serial KO.1742, Jan. 19, 1951. 1 1 ) Seaman. W..Allen, E.. ANAL.CHEM. 23,592 (1951). Shaefer, W. E., Becker, W. W., Ibid., 25, 1226 (1953). Shreve, D. D., Heether, M. P., Ibid., 23, 441 (1951). Thames, F. C., IND.ENG.CHEM., ANAL. ED. 8, 418 (1936). I
Butts, P. G., Prine, G. B., Kouba, D. L., Becker, W. W., ANAL. CHEM.20, 1066 (1948). Dickson, W.,Easterbrook, W. C., Analyst 47; 112 (1922).
'
Goldberg, A . I., IND.ENG.CHEM., ANAL.ED.16,198 (1944). Grodzinski,J., ANAL.CHEM.27, 1765
Whitnack, G. C., Gantz, E. S. C., ANAL.CHEX.25, 553 (1953). Wight, T. W., Naval Ordnance Inspection Laboratory, Caerwent, N.O.I.L. Rept. CR2/48 (May
(1955).
Ka pelmeier, C. P. A., Paint, Oil, $hem. Rev. 99. KO. 12,, 34,, 36 (1937). (6) Kavanagh, F., IND.ENG. CHEM., ANAL.ED.8, 397 (1936). ( 7 ) Lamond, J., Analyst 73, 674 (1948).
,
1948).
RECEIVED for review October 30, 1956. Accepted May 3,1957.
Reduct io n of NitrogIy ce rin by Cata Iy tic Hy d roge no Iys is in Analysis of Propellants for DioctyI Phthalate HARRY STALCUP, MAE I. FAUTH, JAMES 0. WATTS', and RICHARD W. WILLIAMS* U. S. Naval Powder Factory, Indian Head, Md.
b Spectrophotometric, gravimetric, and polarographic procedures are described for the determination of dioctyl phthalate in propellants. The interference caused by nitroglycerin is removed by catalytic hydrogenolysis, using platinum oxide or palladium black. When 2-nitrodiphenylarnine is determined ethyl alcohol is the extraction solvent and the absorption at 425 mk in an unreduced aliquot of the extract from the propellant is measured. For the determination of dioctyl phthalate by a spectrophotometric procedure, the interference due to 2-nitrodiphenylamine is removed by catalytic reduction. The reduced sample is passed through Amberlite IR-120. The phthalate is measured If a determination at 276 mp. of 2-nitrodiphenylamine is not required, the propellant is extracted with a pentane-methylene chloride azeotrope, and the extract subjected to catalytic hydrogenolysis. In the spectrophotometric and the gravimetric methods the phthalate is precipitated as the dipotassium salt by alkali saponification. The polarographic determination of phthalate is made directly from the filtered extract after catalytic hydrogenolysis.
T
investigation was undertaken to improve the gravimetric method for the determination of phthalates in propellants (10). In the original method, the nitroglycerin in the acetic HIS
1482
ANALYTICAL CHEMISTRY
acid extract or in the dried methylene chloride extract, acidified with dilute acetic acid, was reduced with zinc dust. After extraction and filtration, the phthalate was saponified with alcoholic potassium hydroxide and precipitated by the Kappelmeier (1) technique as the dipotassium salt. Kuhn (2) found that nitrate esters could be effectively reduced by catalytic hydrogenolysis. This fact was utilized in the development of the present method. The determination of phthalate esters in propellant formulations by spectrophotometric measurements has been reported by several investigators ( 3 , l O ) . Schroeder and coivorkers (4-8) included 2-nitrodiphenylamine as well as some of the phthalate esters in their extensive studies of the absorption characteristic of propellant ingredients. Schemes based on preliminary chromatographic separations for the spectrophotometric analysis of phthalates in propellants are described in their papers. Additional work on such methods is indicated (11, 19). The use of spectrophotometric methods in the analysis of phthalates is described by Shreve and Heether (9). Investigators a t Picatinny Arsenal (3) determined phthalates spectrophotometrically in propellants by a procedure in which nitroglycerin and nitroaromatic compounds were reduced with titanous chloride. After a series of extraction operations before and after alkali saponification the phthalate was
finally determined spectrophotometrically. Previous work by Watts and Stalcup ( I d ) , based on the earlier work of Kuhn ( 2 ) with amyl nitrate, demonstrated that the interference of nitroglycerin in the determination of phthalate esters in the double-base propellants could be eliminated by catalytic hydrogenolysis of the ester. I n more recent investigations, it was found that the phthalate in propellants which contain 2-nitrodiphenylamine could be determined directly by spectrophotometric measurement, provided that the interference from the reduction products of 2-nitrodiphenylamine could be removed. This is accomplished by passing the alcohol extract containing the phthalate and the reduced products through the cation exchange resin Amberlite IR-120. 2 - Nitrodiphenylamine is determined spectrophotometrically on an unreduced aliquot of the alcohol extract. When the determination of 2-nitrodiphenylamine in the same sample is not desired, a smaller amount of sample may be used and after suitable extraction and hydrogenolysis procedures, the phthalate may be separated by precipitation as dipotassium phthalate. The phthalate content may then be determined by spectrophotometric, polarographic, or gravimetric methods. Present addres8, American Instrument
Go., Silver Spring, Md.
2 Present address, Bureau of Ordnance, Washington, D. C.
APPARATUS
Cylinder of hydrogen gas. Parr low pressure hydrogenation apparatus, shaker type. Beckman Model DR recording spectrophotometer with matched silica cells or equivalent. Extraction thimble, glass with fritted bottoms of medium coarse porosity. Volumetric flasks, 250-ml. and 100ml. Iodine flasks, 250-ml. Soxhlet extraction assembly, preferably one having a siphoning chamber of 40- to 50-ml. capacity. Refluxing flask, no larger than 250-ml. capacity with standard-tapered neck to fit Soxhlet tube. Glass column, 3 em. in diameter and a t least 25 cm. long, fitted with 29/26 ground-glass joint. Volunietric flask, 1-liter capacity. Filter paper, Whatman No. 40. Heat source, steam bath and a Variaccontrolled hot plate. Lipless glass beakers for half-cells, or cap-type weighing bottles with 45/12 joint. Polarograph, Sargent Model XXI is recommended. Capillary with a drop rate of 5 or 6 seconds per drop. Saturated calomel reference electrode. Constant temperature bath, 30" =k 0.1OC.
black added. It is essential that catalyst particles adhering to the walls of the bottle be washed down with 95% alcohol to prevent possible flashing during the air evacuation step. The bottle is mounted on a Parr shaker and the contents are flushed five times with hydrogen. The hydrogen pressure is adjusted to 30 pounds per square inch and the reduction continued for 1 hour. The pressure is released and the solution filtered through No. 40 filter paper directly into the column containing the prepared cation exchange resin. The pressure bottle and filter paper are washed thoroughly with 95y0 alcohol and the washings passed through the column. The bulk sample, together with the wash solutions from the bottle and column, is collected in a 250-ml. volumetric flask and sufficient alcohol added so that the total volume is 250 ml. Additional alcohol is run through the column and a small portion collected in a beaker for use as a blank, because a slight amount of resin may be dissolved. PREPARATION OF COLUMN.Standard columns of 3-cm. diameter, fitted with 29/26 ground-glass joints, are filled to a height of 20 cm. with the resins selected for use. Each column containing the resin is washed thoroughly with 95% alcohol, first a t room temperature and finally with hot alcohol. The absorbance of the effluent is measured with the spectrophotometer to determine if any substances which absorb in the ultraviolet region are being washed out of the column. When the absorbance of the effluent is negligible, the column is ready for use.
Values for the blank usually run from -0.008 to +0.025 in absorbance. A correction must be made for the absorbance of the solvent cell and the solution cell relative to one another.
where D is the absorbance and V is the final volume of the eluate in millimeters, The factor 28.78 is the ratio of the concentration of the phthalate in milligrams per 100 ml. to the absorbance. DETERNINATION O F %NITRODIPHENA 50-ml. aliquot representing 1.5 grams of sample of the unreduced alcohol extract is transferred to a 100ml. volumetric flask and diluted to volume with 95% alcohol. Absorbance measurements are taken a t 425 mp.
YLAJIINE.
,
% 2-nitrodiphenylamine = D
X 3.35 X V Mg. of sample
The factor 3.35 is the ratio of the concentration of the 2-nitrodiphenylamine in milligrams per 100 ml., to the absorbance. This value may vary somewhat with different lots of 2-nitrodiphenylamine and is determined experimentally. All absorption spectra were measured with a recording Beckman ;\lode1 DR specREAGENTS trophotometer. Matched silica cells Isopropyl alcohol, reagent grade. and a hydrogen light source were used Methylene chloride, reagent grade. for all absorption measurements. The Pentane, reagent grade. solvent used was 95% alcohol. Tetrabutyl ammonium hydroxide, Procedure for Determination of 0.1M. Dioctyl Phthalate. SPECTROPHOTOPotassium hydroxide, 0.5N solution, METRIC. A 1-gram sample of the dissolved in anhydrous isopropyl alcoAbsorbance curves on the column powder, either microtomed or ground hol. effluent are run before and after each t o 20-mesh particle size in a Wiley Platinum oxide, Fisher Scientific CO. sample is passed through. The colmill, is placed in a glass extraction Benzene, reagent grade. umns are conditioned for use after two thimble, having a fritted-glass bottom Hydrochloric acid, concentrated, 0.1N of coarse porosity. The thimble should or three reduced samples are run and and 0.0500N. be of sufficient size to fit upright in the they can be used 30 to 40 additional Nitroglycerin and 2-nitrodiphenylSoxhlet extraction tube. Sixty-five amine for preparing standard curve. times. milliliters of pentane-methylene chloPotassium acid phthalate, primary To determine whether 2-nitrodiphenride (2 to 1 ratio by volume) are added standard grade. ylamine could be separated from dito a refluxing flask no larger than 250Ethyl alcohol, 957& octyl phthalate, weighed samples of ml. capacity. The extraction unit is Palladium black, Fisher Scientific Co. each compound were dissolved in 95% assembled and the sample extracted for Amberlite IR-120, analytical grade, alcohol and aliquots run through pre4 hours over a steam bath. The flask Fisher Scientific Co. pared columns containing the following is removed and the contents are evaporated to dryness on the stea.m bath resins: EXPERIMENTAL under a gentle stream of dry air. The Name Type of Resin residue is transferred to a Parr preswre Procedure for Determination of bottle with several portions of anhyAmberlite IRC-50 Carboxylic acid Dioctyl Phthalate and &NitrodiphenNuclear sulfonicacid drous isopropyl alcohol totaling 40 to ylamine in Same Sample. PREPA- Amberlite IR-112 Amberlite IR-120 Kuclear sulfonic acid 50 ml. Approximately 0.2 gram of platiRATIONOF SAMPLE.A7.5-gramsample Amberlite M E 3 Cation and anion num oxide catallst is added. Catalyst of the powder is ground to 20-mesh exchange resin particles adhering to the walls of the particle size in a Wiley mill and placed bottle must be washed down with isoin an extraction thimble provided with In each case recovery of the 2-nitropropyl alcohol t o prevent possible a coarse fritted-glass bottom. The diphenylamine from the effluent was flashing during the air evacuation step. thimble is placed in a Soxhlet tube and quantitative. Similarly dioctyl phthalThe bottle is mounted on a Parr shaker extracted with 100 ml. of 957" . - alcohol for ate was observed to pass through coland the contents are flushed three times 6 hours. umns containing these resins. with hydrogen. The hydrogen pressure The samole is cooled and filtered is adjusted to 30 pounds per square inch through Nd. 40 Whatman paper into DETERMINATION OF DIOCTYL PHTHAL- and hydrogenolysis of the nitrate ester a 250-ml. volumetric flask, to remove effected during a 20-minute period of ATE. The column is prepared preany insoluble inorganic salts that may shaking or, for powders containing 2viously by washing with 95% alcohol be present. Sufficient alcohol is added nitrodiphenylamine, until the orange until the absorbance of the washings to the flask so that the total volume is color of this compound disappears. is negligible or reaches a constant value. 250 ml. A 50-ml. aliquot is transThe pressure is released, and the resiAbsorption of the blank, sample, and ferred to a Parr pressure bottle and due filtered with mild suction through tailings is measured a t 276 mp. approximately 0.30 gram of palladium VOL. 29, NO. 10, OCTOBER 1957
1483
a glass filter funnel into a 250-ml. iodine flask. The fritted bottom of the filter funnel should be of medium porosity and covered with a glass-fiber filter paper cut to fit. The residue and bottle are washed with three IO-ml. portions of isopropyl alcohol. Rapid flow of air through the filter funnel after passage of all the liquid mixture should be avoided because of the possible fire hazard involved. The contents of the flask are adjusted to 100 ml. with isopropyl alcohol, and evaporated a t low heat on a hot plate to a volume of 50 ml. Twentyfive milliters of 0.55 solution of potassium hydroxide in absolute isopropyl alcohol are added to the hot contents of the flask. A short air condenser is inserted in the neck of the flask, which is heated gently on the hot plate for 20 t o 25 minutes. This operation removes residual ammonia and expedites precipitation of the potassium phthalate. Twenty-five milliliters of benzene are added to the flask contents and the precipitate transferred with suction t o a fritted-glass crucible of medium porosity. The precipitate is washed with several portions of isopropyl alcoholbenzene solution (2 to 1 ratio by volume) followed by an additional washing with isopropyl alcohol t o remove the benzene. The contents of the crucible are dissolved in water and transferred to a 250-ml. volumetric flask by means of a Bell jar suction apparatus. Five milliliters of concentrated hydrochloric acid are added to the flask, and the contents are diluted to volume with water and thoroughly mixed. The ultraviolet spectrum of the flask contents is obtained by means of a Beckman Model DR automatic recording spectrophotometer. Silica absorption cells of 10-mm. light path length are used. The absorbance reading is taken a t the absorption maximum occurring a t 276 mp. The phthalate content of the powder is determined from a standard curve based on the spectrum of potassium acid phthalate. Hydrochloric acid, 0.1N, is used in the reference cell. A correction is applied for a difference of the sample and reference cell a t 276-mp wave length. A water-cooled hydrogen lamp is used as the light source. To prepare the standard curve, an accurately weighed sample (approximately 0.5 gram) of potassium acid phthalate is introduced into a 250-ml. volumetric flask and dissolved in distilled water. Five milliliters of concentrated hydrochloric acid are added and the contents diluted to volume with water. Aliquot portions (8, 9, 10, 11, and 12 ml.) of the stock solution are removed and diluted to 250 ml. with 0.1N hydrochloric acid. Absorbance readings are taken on the spectrophotometer, and a graph is constructed, using the absorbance values as the ordinates and the milligrams of phthalate per 100 ml. of solution, as the abscissas. A straight line passing through these points and the origin should result. GRAVIMETRIC.This procedure is identical to the spectrophotometric method with the following exceptions. 1484
ANALYTICAL CHEMISTRY
Five-gram powder samples are used in place of 1-gram samples. The washed dipotassium phthalate precipitate from the alcoholic alkali saponification is dried 1 hour a t 225' to 250' C., cooled in a desiccator 1 hour, and weighed. The precipitate, which may contain a small amount of potassium carbonate, is dissolved in 50 ml. of distilled water of p H 7 , and the solution
Table I. Reduction of Actual Propellant Containing Dioctyl Phthalate, 2-Nitrodiphenylamine, and Nitroglycerin, and Determination of C/D for Dioctyl Phthalate"
Catalyst, Gram
D 0.683 0.685 0.689 0.683 0.690 0,688 0 690 0 691 0 693
0.200 0.225 0.250 0.275 0.300 0.350 0 350 0 400 0 500
C/Db 28.99 28.91 28.74 28.99 28.70 28.78 28 70 28 65 28 78 Av. 28.78
H, pressure, 30 lb./sq. inch, reduction time, 1 hour. * G = 19.80 mg. per 100 ml., established by gravimetric method for phthalates in propellants ( 1 1 ) . Table II. Catalytic Reduction of Synthetic Propellant Containing Nitroglycerin, 2-Nitrodiphenylamine, and Dioctyl Phthalate and Determination of C/D for Dioctyl Phthalate"
Catalyst, Gram (Pd black) 0 10
o io
0 10 0 10 0 10 0.15 0.15 0.15 0.15 0.20 0.40 a
C/Db 29 04 28 82 28 88 28 80 29 08 Bv. 28.92 29.56 29.30 29.25 29.43 29.34 29.47 Av. 29.39
H, pressure, 30 lb./sq. inch, reduction
titrated with 0.0500N hydrochloric acid to the phenolphthalein end point. Milliliters of acid times normality times 0.1382 = grams of potassium carbonate. The weight of dipotassium phthalate is corrected by subtracting the weight of potassium carbonate found. % dioctyl phthalate = Wt. of potassium phthalate corrected X 1.61 X 100 wt. of sample POLAROGRAPHIC. The procedure is the same as that described for the spectrophotometric method to the completion of the ammonia-elimination stage. The volume of the ammonia-free isopropyl alcohol extract is adjusted to 100 ml. with isopropyl alcohol. A 10ml. aliquot of the sample solution is placed in a 25-ml. volumetric flask and 2 ml. of an aqueous solution of the 0.lil.i tetrabutyl ammonium hydroxide are added. The sample is diluted to volume with 50y0 isopropyl alcohol and polarographed a t an initial potential of -1.5 volts with a saturated calomel reference electrode. The polarogram is recorded a t a sensitivity of 0.02 pa. per mm. The wave height is referred to a standard graph constructed previously for dioctyl phthalate. A blank solution for the preparation of the standard graph is made by dissolving 0.25 gram of nitroglycerin and 0.0170 gram of 2-nitrodiphenylamine in 40 ml. of isopropyl alcohol and subjecting the mixture to the catalytic hydrogenolysis procedure as described above. After hydrogenolysis and removal of the ammonia, the blank sample is placed in a volumetric flask and diluted to 100 ml. in the isopropyl alcohol. Ten-milliliter aliquots of the blank solution are transferred to each of five 100-ml. volumetric flasks. To all but one of the flasks, a known amount of dioctyl phthalate ester in isopropyl alcohol (10 ml.) is added. Two milliliters of 0.liM aqueous tetrabutyl ammonium hydroxide are added to the five flasks and the contents diluted to volume with isopropyl alcohol. The samples are polarographed exactly as described for the powder sample. The wave height is plotted against the weight of phthalate.
10.36 mg.
Table 111. Determination of Dioctyl Phthalate in Propellant by Proposed Spectrophotometric Method"
Dioctyl Phthalate, %
( D X 28.78 X 250) 1500 1 0.683 3.28 2 0.690 3 31 3 0.688 3.30 4 0.685 3.29 5 0.689 3.30 6 0.693 3.32 Av. 3 . 3 0 Range, 0.04%; standard dev., 0.02.
Sample Run
a
D
DISCUSSION
In the analysis of a propellant containing nitroglycerin, the reduction of the nitrate groups to free nitrogen is desirable. Kuhn ( 2 ) found that palladium on calcium carbonate reduced amyl nitrate a t room temperature and a pressure of 1500 pounds per square inch, in accordance with the following equation: 2 RONOz 5H2 + 2 ROH IXz 4Hz0 However, in experiments using a pressure of 30 pounds per square inch, the present authors found this catalyst ineffective for the reduction of nitroglycerin.
+
+
+
Platinum oxide was 1e.s desirable as a catalyst than palladiuni black, because of its greater activity which causes it to attack the benzene ring. The amount of palladium oxide used in relation to sample size was critical. TVhen this tolerance limit was exceeded, the phthalate component was reduced, the amount of the reduction increasing n-ith the amount of catalyst used, although not linearly. When palladium black was used as the catalyst, no reduction of phthalate in propellant extract mas observed in the range between 0.2 and 0.5 gram of catalyst (Table I). Platinum oxide and palladium black were equally effective for the reduction of nitroglycerin. TThen suitable precautions are observed to prevent ring hydrogenation. platinum may be used. However, the reduction is carried beyond elementary nitrogen to ammonia. Ammonia and water formed from the reaction interfered with phthalate recovery values. This necessitated their removal by boiling. before precipitation of potassium phthalate by alkali saponification. This indicates that side reactions between ammonia and unreacted nitrate groups may occur. Kuhn observed that nitrate ions, unlike nitrate esters, do not react in the catalyzed hydrogenolysis reaction. He ascribed this fact to their greater resonance stabilization. Apparently the nitrate reaction products do not interfere with phthalate recovery by the proposed methods. Approximately 60% of the theoretical amount of glycerol, as determined by the periodate oxidation method, is formed from nitroglycerin during the reduction. Kuhn's experiments at high pressures and high temperatures indicated that carboxylic esters are also susceptible to hvdrogenolysis. However, under the test conditions described, no reaction was observed for dioctyl phthalate, and only a slight (1.5 to 2.0%) reduction occurred for triacetin. Dioctyl phthalate in 95% alcohol solution showed a n absorption maximum of 276 mp. T h e n the alcohol extract of a propellant containing both dioctyl phthalate and 2-nitrodiphenylamine mas reduced with hydrogen, the position of this maximum remained constant. S:imples containing only dioctyl phthalate showed maximum absorption a t this wave length before and after treatment with hydrogen and palladium black. However, the reduction product of 2-nitrodiphenylamine had a maximum in the vicinity of 275 mp. The intensity of its absorbance was about ten times greater than that of the phthalate. Since the percentage of phthalate present in some propellants is of the same order of magnitude as that of 2-nitrodiphenylamine. it is obvious that the
Table IV. Determination of 2-Nitrodiphenylamine by Spectrophotometric Method"
Sample 1 2 3
2-Sitrodiphenylamine, yo 1.67 1.69
1.72 4 1.71 5 1.67 Av. 1.69 Range, 0.05~o;standard dev., 0.02. Table V. Dioctyl Phthalate in Propellant Test Sample, Comparison of Three Methods
Replicates 1
I
2 3 4 5 h v . , for un-
dried samples Moisture, loss after 96 hours in desiccator Av., for dry samples Range Man-hours for single detn. Total lapsed time Operating time
Spectrophoto- Gravi- Polarometric, metric, metric, 0C/O % 3 51 3 39 3 40 3 31 3 42 3 42 3 43 3 49 3 42 3 71 3 45 3 39 3 57 :J 45 3 42 3 51
3 44
3 41
0 30
0 30
0 30
3 52
3 45
0.40
0 10
3.42 0 03
6.5
8.5
6 5
0.4
0 6
0.5
percentage ratio of the two components is unfavorable in such cases for measurement of the total absorption and then correcting for the absorption of the amine. No other ingredient appeared to interfere with the phthalate measurement a t a wave length of 275 mp, The alcohol extract from a synthetic mixture containing nitroglycerin, dioctyl phthalate, and 2-nitrodiphenylamine was treated in accordance with the proposed procedure, to determine the spectrophotometric factor C / D . This is defined as the concentration C, in milligrams per 100 ml., divided by the absorbance, D. Absorbance is the log (&/I), where I,, is the intensity of the incident light and I that of the transmitted light. Table I1 shows that when more than 0.1 gram of palladium black catalyst is used for the reduction the value of C / D is increased from a n average of 28.92 to 29.39. I n the actual propellant samples the C / D values show no significant variation for a range of catalyst weights between 0.20 and 0.50 gram (Table I). The reason for this anomaly was not found. The phthalate value in a known sample was found to be 3.3001, by a gravimetric method ( 1 1 ) . The value of C
for a 1.5-gram powder sample \\as established as 19.80 mg. per 100 ml. The average value for C / D was 28.78 as shown in Table I. The C / D value of 28.78 obtained for the actual propellant sample compared reasonably well with the C / D value of 28.92 found as the average for the synthetic sample reduced with 0.10 gram of catalyst. Table 111shows phthalate determinations made on propellant samples employing the C / D value of 28.78. Table IV indicates that the spectrophotometric method for 2-nitrodiphenylamine is applicable without modification. The reduced sample passed through a column composed of the IRC-50 carboxylic acid resin but was retained on a strong acid resin such as the nuclear sulfonic acid type found in IR-120 or MB-3. When the filtered extract obtained after catalytic hydrogenolysis was passed through the resin Amberlite IR-120, the interfering amine was completely removed. Table V shows the agreement obtained by the three methods (under second procedure), indicating that catalytic hydrogenolysis of nitrate esters is a convenient and satisfactory method for their reduction, prior to determination of other propellant ingredients such as phthalate esters. Although data are given only for dioctyl phthalate, it is expected that these methods could be applied to the other phthalate esters which occur in propellant formulations. LITERATURE CITED
(1) Kappelmeier, C. P. A., Paint, Oil, Chem. Reu. 99, Xo. 12, 20, 22, 24
(1937). (2) Kuhn, L. P., J . Ani. Chem. SOC.68, 1761 (1946). ( 3 ) Picatinny iirsenal, Rept. No. HI-1688 (August 1954). (.4.) Schroeder. IT. il.. '4nn. N . Y . Acad. Sci. 49,204 (1948). (5) Schroeder, \I-.h.,Keilin, B., Lemmon, R. >I.) Ind. Eng. Chem. 43, 939 (1951). (6) Schroeder, K. A , Malmberg, E. IT., Fong, L. L., Trueblood, K. N., Landerl, J. I)., Hoerger, E., Ibid., 41,2818(1949). (7) Schroeder, W. A , Wilcox, P. E., Trueblood, I
