V O L U M E 25, NO. 6, J U N E 1 9 5 3 Table 11.
897
Results Obtained on Blood of Typical Patient Treated with Pyrazinamide
Dosage, Grams 0 75 (First day)
Time Sample Taken after Final Dosage, Hours
0 76
Pyrazinoic Acid Found, -,/Ml.
Pyrazinamide Found, y/Ml.
1
42
28
10
4
28
22
IO
1 4
39 44
22 19
10 10
Total Blood Collected, RI1.
(Second day) 2 . 80 (First day) 0.75 (Second day)
In order to determine the recovery of pyrazinoic acid xhen treated in the same manner as the unknowns, recovery determinations mere made on both blood and urine. In the case of blood, 120 micrograms of pyrazinoic acid were added to 1 ml. of dog blood and treated according to the above procedure. The results obtained are given in the following table: Sample No.
-3, 1
Pyrazinoic Acid, y Added Recovered 120 120 120
Recovery, % 83 104 98
100 126 118
In the case of urine, 1.07 mg. of pgrazinoic acid were added to 10 ml. of normal urine and treated according to the procedure The results obtained are given in the following table: Sample No.
Pyraeinoic Acid, Mg. Added Recovered 107 107 107
1.18 1.16 1.13
first study the percentage of pyrazinoic ncid in the urine increased from 62 to 82% in 12 hours and, in the same time, 29% of the original dosage of pyrazinamide had been eliminated. Referring to Table 11, the blood levels of the patient in the first study show 42 micrograms per milliliter of pyrazinoic acid and 28 micrograms per milliliter of pyrazinamide to be present after 1 hour. In practically all rases studied, the concentration of pyrazinoic acid has exceeded that of the amide. In the second study, the blood levels remained fairly constant over the 4-hour period. This is probably related to the fact that the previous day’s dosage v a s much greater than in the first case. Little is known about the nature of the pyrazinamide hydrolysis in the body. It may be of an enzymatic nature. h study was made of gastric juice washings in order to establish the extent of hydrolysis there. The gastric juice mashing before dosage contained no pyrazinamide and had a pH of 6.50. One hour after dosage the washings contained 99.i% of the amide given and only O.3y0of the acid (taking as 100% the total pyrazinamide plus pyrazinoic acid present) and the pH had decreased to 1.63. Two hours after dosage the pyrazinamide level had decreased to 5.4 nig. per ml. but this was still 99.5% of the total amide plus acid present. Thus only negligible hydrolysis took place in the stomach. To test for the extent of hydrolysis in the bladder, 160 mg. of pyrazinamide were added to 100 nil. of normal urine and incubated at 37” C. dfter 20 hours only 6.4y0 of the pyrazinamide has been hydrolyzed. A study of the relationship of dosage to blood level and the therapeutic effect of the drug is contemplatetl
Recovery, % , 110 108 106
In both cases the recoveries obtained are acceptable and show that the reagents used in the precipitation steps remove little or none of the pyrazinoic acid. The results on tx7-o studies of a typical patient are shown in Tables I and 11. ;Iceording to the urine levels obtained the pyrazinamide is hydrolyzed to a large extent in the body. In the
LITERATURE CITED
(1) Kushner, S., Dalalian, J. L., Sanjurjo, J. I,., Bach, F. L., Jr., Safir, S . R., Smith, V. K., Jr., and Williams, 3. H., J Am. Chem. SOC.,74,3617 (1952). ( 2 ) AMalone,L., Schurr, 4.,Lindh, H., llcKenzie, D., Kiser. J. S.. and Williams, J. H., A m . Rev. Tuber., 65, 511 (1952). RECEIVED for review M a y 14, 1952. -4ccepted February 11, 1953. P r e sented before the Division of Biological Chemistry a t the 121st M e e t i n g of the . ~ M E R I C A X CHEMICAL SacIErY, llilxaukee, T i s .
Determination of Sulfite and Sulfate (as Sodium Sulfate) in Sodium Petroleum Sulfonates A n Amperometric Titration B. E. GORDON AND R. S. URNER Research Laboratory, Shell Oil Co., Martinez, Calif.
T
HE usefulness of petroleum sulfonates as industrial deter-
gents, solubilizers, emulsifiers, and lubricating oil additives has resulted in a marked increase in their production. The usual method of manufacture consists of sulfonation of a spray or lubricating oil stock with oleum and neutralization of the sour oil with caustic, followed by purification and concentration. One of the factors affecting subsequent processing of a batch of sulfonates is the concentration of inorganic salts present, notably sodium sulfite and sulfate. It is, therefore, of considerable value to a processing group to obtain data regarding the inorganic content of both crude and concentrated sulfonates a t various stages in the manufacturing procedure with a minimum of elapsed time. In this paper the term “crude sulfonates” refers to the oilsulfonate phase following neutralization, and “concentrated sulfonates” refers to the purified article of commerce from which most of the oil and inorganic salts have been removed.
The inorganic content of sulfonates is regarded by sonic consumers as an indication of purity, and many specify a masimum allowable inorganic salt concentration. The reasons for this are varied, one of them being interference with further processing through the formation of deleterious insoluble sulfates and sulfites. A rapid, relatively simple method of determining the inorganic salt content of petroleum sulfonates would, therefore, be useful to both producers and consumers of these materials. One method based upon an extraction technique hai evolved over the past few years and with minor modifications has been generally accepted (1). Because this method involves wveral estractions, an oxidation, and finally a gravimetric determination of the precipitate, an elapsed time of 5 to 7 hours is common. The widespread use and ready applicability of the amperometric titration technique (3, 4) made it particularly attractive as a
ANALYTICAL CHEMISTRY
898
The ASTM procedure for determination of inorganic salts in sodium petroleum sulfonates is tedious, requiring 5 to 8 hours per analysis. A simple, rapid method involving an amperometric titration with lead ion has been developed for determination of inorganic salts, principally sodium sulfite and sulfate, in petroleum sulfonates. Results are comparable in accuracy to those obtained with the AST3I procedure. Elapsed time for the analysis is about 1 hour for the average single sample, although as many as four samples can be run in 90 minutes. The method greatly facilitates determination of inorganics in petroleum sulfonates, supplementing tedious existing methods.
possible method of attack upon the problem of reducing the time required for determining inorganics in sulfonates. EXPEKIiMENTAL WORK
Sulfate determination is one of the more attractive applications of amperomettic titrations because of the rapid stoichiometric reaction of lead and sulfate. Barium, although a more sensitive reagent for sulfate, suffers from the disadvantage that stoichiometric combination is obtained only after aging of the precipitate. The actual determination of the inorganics in thiq report is confined solely to the use of a solution of lead nitrate a" titrant iifter some experimentation, a unit was designed which proved to be most convenient for the work involved (Figure 1). The use of a water bath was found desirable to minimize changeq in ambient temperature during a titration. The bath is simple to arrange, as it uses a slip stream from the exit water of a waterjacketed polarographic cell (2). The simple automatic siphon keeps the water a t a constant level and returns the eucess to the constant temperature bath. The saturated calomel electrode (SCE)deqcribed by Lingane (6) showed no change of potential compared to a Beckman saturated raloniel electrode after 3 months' use. The nitrogen inlet tube permits the effluent nitrogen to evcape during Qcrubbing,while preventing the entrance of air during current-measuring periods. The pipet shown extends below the surface of the solution. This dipping tip can be used only if the last 3 cni. of the buret is a capillary of small bore, ca. 0.5 mm. in inside diameter, to prevent interdiffusion of titrant and titration medium. Sufficient turbulence is provided by the nitlogen stream to niiu the solution between additions of lead.
Sodium sulfate in water, 1mg. per ml., made from C.P. salt. Methyl red indicator solution. Isopropyl alcohol, 99% purity. hgar-potassium chloride. Add 3 grams of U.S.P. agar-agar to 100 ml. of saturated potassium chloride solution. Heat in a water bath until agar dissolves. PROCEDURE
Mix the sulfonate by heating, if necessary, and shaking until homogeneity is ensured. Accurately weigh 5 grams into a 50-ml. volumetric flask and dissolve in benzene to make 50 ml. Pipet a 1-ml. aliquot into the centrifuge test tube and add 5 ml. of amyl alcohol and 2 ml. of 0.1 Ar ammonium perchlorate. Shake thoroughly and centrifuge until a clear lower phase results-ea. 10 minutes.
APPARATUS
A Sargent ;\lode1 S S I polarograph or similar current-voltage instrument is used. The amperometric cell shown in Figure 1is thermostated if necessary. Prepare the saturated calomel electrode by drawing melted agar-potassium chloride through the sintered disk up to the bend in the tubing. Withdraw the tube and allow it to cool until the agar gels. Add mercury, calomel, and saturated potassium chloride solution with potassium chloride crystals to 1 em. above the junction of the bridge to the cell. Excess solid potassium chloride solution should be present a t all times. The dropping mercury cathode is made from marine barometer tubing 0.03 to 0.05 mm. in inside diameter. The semimicroburet is of 5-ml. capacity, reading to 0.01 ml. The lower 3 cm. of the buret is made of 0.5-nim. capillary tubing. The microburet, Gilmont type made by Emil Greiner Co., is of 1-ml. capacity dispensing in increments of 0.001 ml. The microcentrifuge, E. H. Sargent Co., is capable of holding four 13 X 100 mm. test tubes, 9-ml. capacity. A 1-ml. tuberculin hypodermic syringe is used, with 8-cm. needle cut square at tip. REAGENTS
Amyl alcohol and benzene, C.P. Perchloric acid, 0.1 in 60% isopropyl alcohol. Ammonium perchlorate, 0.1 N in water, made from C.P. salt. Lead nitrate in 60% isopropyl alcohol made from C.P. salt. (1) 23.3261 mg. per ml., of which 1 ml. = 10 mg. of sodium sulfate (concentrated lead). (2) 11.6631 mg. per ml., of which 1 ml. = 5 mg. of sodium sulfate (medium lead). (3) 2.3326 mg. per ml., of which 1 ml. = 1 mg. of sodium sulfate (dilute lead).
Figure 1.
imperometric Cell
Lying the hypodermic syringe. transfer the clear aqueous layer to the amperometric cell and add sufficient water to make 4 ml. Usually 2.35 ml. of water is required. Add 6 ml. of isopropyl alcohol, mix, and add 2 drops of methyl red. Add 0.1 -V perchloric acid from the Gilmont microburet until a persistent pink color is obtained. If, because of color in the aqueous phase, the transition point is difficult to see, prepare a comparison sample and experiment u ith it until confident that the solution is slightly acid. Use this as a comparison for the sample to be run. A pH meter may be used if desired. Fill the buret with the dilute lead solution if a sample of less than 0.8% inorganic content is being run, or with the concentrated lead solution if a sample containing more than 0.8% inorganics is to be analyzed. This applies to sulfonates of equivalent weight about 430 or higher. If sulfonates of lower equivalent weight are to be analyzed-Le., equivalent weight ca. 375-use the medium lead for all samples. Place the components of the cell in position and scrub the solution for 10 to 15 minutes with nitrogen which has previously passed through a solution of 60%
899
V O L U M E 25, NO. 6, J U N E 1 9 5 3 Table I.
-4mperometric Titration of Sodium Sulfate with Lead
NanSOa -4dded, hlg.
1.20
Titration Medium 80% isopropyl alcohol 0.04 -11NaXOa
SazSOa
Found, LIE. 1.21
70% Hz0
12.00 1.20 0.120
1,20 0.120 12.00 12.00 12.00
40% isopropyl alcohol 0 . 0 4 .M NaN03 11.78 0% He0 50% isopropyl alcohol 0 . 0 5 .ll " 2 1 0 4 1.15 50% Hz0 50% isopropyl alcohol 0 . 0 5 .II HClO4 Erratic current 50% Hg0 60% isopropyl alcohol 0 . 0 5 .If HClOi 1.18 40% HzO 60% isopropyl alcohol 0 . 0 5 .If HClOi 0.121 40% Ha0 60% isopropyl alcohol 0 . 0 4 .TI SaNOa 11.90 40% HzO 60% isopropyl alcohol 0 4 .If S a x 0 1 17.80 40% HzO 60% isopropyl alcohol 0 . 8 dl NaSOa Erratic current 40% Hz0
isopropyl alcohol in water. Set the e.m.f. a t -0.80-volt sensitivity to give good increases in current with the solution used (for concentrated lead, S = 0.1 pa. per mm., for medium lead, S = 0.04 pa. per mm., for dilute lead, S = 0.01 pa. per mm.), and use no damping. After scrubbing, adjust the pen position to a low value and titrate with increments of 0.1 ml. of lead nitrate, moving the chart one major division (3.45 em.) after each recording. Scrub for 2 minutes between increments and use the peak value of the current to plot milliliters of lead nitrate against corrected current values. Draw a line through the points and extrapolate back to the base line. This point of interception is the equivalence point and establishes the volume of lead used. Calculations. Correction of Current Values. Corrected current value = observed
total volume initial volume of soln. (10 ml.)
for the method presented here. .Is hy thip method sulfate and sulfite are included in a single determination, it was essential for purposes of comparison that only these anions be precipitated in the amperometric titration. The results of work with sodium sulfite, sodium carbonate, and sodium silicate are presented in Table 11. Sodium nitrate, 0.05 X,was the supporting electrolyte. Evidently a t a yH of 6 (methyl red) the bisulfite anion is stable, the bicarbonate anion is sufficiently dissociated to carbon dioxide so that it i s lost by repeated nitrogen scrubbing, and ionization of silicic acid is suppressed, thereby removing it as a possible interference. Even though the bisulfite anion is formed by the neutralization, the precipitate must be lead sulfite rather than lead bisulfite, Pb(HSOI)?; else the recovered sodium sulfite would he only half of the added amount. The reaction therefore 1s :
SO,-- -t H + = HSO8- (neutralization) PbT+
+ HS03-
=
PbSOs
+ €I+ (amperometric titration)
This is also supported by the observation that the solution became more acid a8 the titration proceeded. It is evident that prior neutralization to a methyl red end point is desirable in this titration, to avoid interference from hydroxide, carbonate, and silicate, and to avoid loss of sulfite (as sulfur dioxide) in strongly acidic sulfonates. Oxidation of the bisulfite to bisulfate during the manipulation would result in t'he same increase in acidity during amperometric titration. STUDIES WITH SULFOXATES
In situ Analyses. The in situ approach is the most attractive in any analysis, because manipulative errors are a t a minimum and uncertainties regarding degree of isolation of the desired component are absent. A study was therefore made of several solvent s p t e m s for both crude and concentrated sulfonates.
Per Cent Sodium Sulfate.
where V = volume of lead used a t equivalence point T = titer of lead, mg. of sodium sulfate per ml. W = sample weight, mg., in I-ml. aliquot TITRATIONS OF PURE REAGENTS
To study the effect of different supporting electrolytes and titration media, a series of known amounts of sodium sulfate was amperometrically titrated under different conditions. The purpose was to determine whether coprecipitation phenomena such as reported by Kolthoff and Pan ( 6 ) would be a source of trouble in the analysis. The lead nitrate used as titrant was diqwlved in a solvent similar to the titration medium. The results in Table I support the findings of Kolthoff ( 6 ) , that with alcohol concentrations above 30% supporting electrolytes of the alkali salts of 0.1 -Ifor greater will interfere with the determination. Dilute perchloric acid does not interfere with the precipitation of lead sulfate in 60% isopropyl alcohol, thus offering the possibility of using this acid as supporting electrolyte in media which will not dissolve the usual salts. Because considerable sulfite is formed during the sulfonation, owing to reduction of sulfur trioxide, the amperometric titration of this anion was studied. I n addition, the effect of hydrouide, carbonate, and silicate in the titration was studied; these are possible inorganic contaminants introduced with the sodium hydroxide used to neutralize sulfonic acids. A slightly modified -4STiht method ( 1 ) was used as a referee procedure. I n this technique ammonium carbonate has been substituted for sodium carbonate as the desalting agent. The total elapsed time for a determination is 5 to 7 hours, a. compared to 45 to 60 minutes
Table 11. -4mperometric Titration of Sodium Sulfite, Sodium Carbonate, and Sodium Silicate in Unneutralized and Neutralized Media Salt NazSOz
XazC01 KaaSiOa
dmount hdded, M g . 1 10
1.00 1.14 NaPSOP 1.10 a I n 0 . 0 5 Y HC10,.
Amount Found, M g , Neutralized to Unneutralized methyl red 1.11 1.12 0.01 1 02 0.00 1.10 1.12 None
Isopropyl alcohol-water, methyl Cellosolve-water, ethyl Cellosolve-water, and isopropyl alcohol-benzene-water were tried using a typical petroleum sulfonate of 460 equivalent weight, 0.47% inorganics (by the ASTM method), and containing 60% by weight sodium sulfonates, the remainder being mainly oil. ,411 runs were unsuccessful because of phase separation, interference with capillary performance, or the formation of insoluble lead sulfonates which increased the results several fold. Solubility tests with these lead sulfonates showed them to be soluble in 60% isopropyl alcohol-water, but this medium did not completely dissolve the sulfonate-oil mixture. This approach was therefore abandoned. Extractive Methods. -4small scale continuous liquid-liquid extractor was constructed and a benzene solution of the sulfonate mentioned above was extracted with water. The separation was poor, owing to the strong emulsifying characteristics of the sulfonates. The emulsion gradually built up a t the interface until it flowed over into the aqueous phase. Batch extraction of the sulfonate was therefore investigated (Table 111). Ten grams of the concentrate were dissolved in 100 ml. of benzene and I-ml.
900
ANALYTICAL CHEMISTRY
aliquots of this were used as test samples. Solvents for the organic phase included benzene, amyl alcohol, and butyl alcohol and solutes for the aqueous phase included sodium nitrate, perchloric acid, ammonium nitrate, and ammonium perchlorate.
Table 111. Recovery of Inorganics (as Sodium Sulfate) from Sodium Sulfonates NazS04 by ASTRI iMethod, 7 0 Wt. 0.47 0.47
Organic Solvent, 6 311. Benzene Benzene
0.47
Amyl alcohol Benzene
0.47
Amyl alcohol Benzene
0.47
~
0.47
Amyl alcohol Benzene
0.47
Amyl alcohol Benzene
~
~
~
NagSOI by Amperometric Method, yo wt.
Aqueous Solvent, 2 311. Water 0 . 5 N SaSOs
:$)
%g} yi3i ~
0.14
0.12
o , 5 iv N a ? i ~ 3 0
0.26
0 ,j N ~ ~ 1 0 ,
0.31
.v
~2 . 0 o HCIOI h o
l
0.12
E%} 0.1
NH,SO~
0.43
%g} 0.1N
"4~l~,b
0.46
Second extraction of organic phase yielded 0.1% NarSO4. Second extraction of organic phase yielded 0.01% NarSO4.
The data presented in Table I11 are of particular interest for several rea5ons. One would expect best extraction of the inorganics to be in the benzene-xater system because of the low polarity of benzene. Instead, this is the poorest. It is possible, therefore, that a loose complex between the inorganics and sulfonates exists which is favored in benzene and is destroyed when the polarity of the medium is increased. The effect of amyl and butyl alcohols in increasing the recovery of sulfate substantiates this hypothesis. Furthermore, the use of an electrolyte of high polarity which would partition itself between the two phases should increase the yield by overcoming the sulfate-sulfonate attraction. Such is actually the case with perchloric acid, ammonium nitrate, and ammonium perchlorate. Perchloric acid results are low, presumably because of the loss of sulfite (see Table 11). Ammonium nitrate was less suitable than ammonium perchlorate as a solute because considerably larger ewesses of lead nitrate were required to precipitate the lead sulfate and obtain a useful titration curve. Presumably, this is due to the greater solvent action of nitric acid (from dissociation of ammonium nitrate) over perchloric acid on lead sulfate. Ammonium perchlorate is the best solute tried, and it was used in the analysis of a series of sulfonates of widely different salt and sulfonate contents 1% hich had been previpusly analyzed by the modified ASTM gravimetric method. The data in Table IV are representative of those from a large number of analyses of petroleum sulfonates in the equivalent weight range of 430 and above, made from lubricating oils. The method appears to be reliable for these, the most common type of petroleum sulfonates. Extension to Sulfonates of Low Equivalent Weight. Occasionally it is necessary to determine the inorganic content of sulfonates of low equivalent weight, in the range 350 to 400. These sulfonates are generally characterized by a somewhat higher solubility than the product of higher equivalent weight. m7hen the method was applied to these, results were not .;atisfactory for the products low in inorganics, always being lower than would be expected from ASTM values. However, good checks were obtained on samples containing more thdn 0.7070 inorganics. The cawe was finally traced to the fact that a dilute lead solution (1 i d . = 1 nig. of sodium sulfate) was being used for the titration of the samples low in inorganics. S o precipitate appeared during the titration when a reasonable excess of titrant was added in contmst to sulfonates of higher equivalent
weight and comparable inorganic content. Evidence of this effect is shown in Table V. On the basis of Table V it appeared reasonable to use a lead solution of "medium" strength ( I ml. = 5 mg. of sodium sulfate) for all titrations of these sulfonates of lower equivalent weight. The results with the most concentrated lead solutions are high, probably because of the solubility effect of large excesses of lead on the slightly soluble lead sulfonates. Where high results were encountered the precipitate was usually yellow to brown in color rather than the characteristic white color of lead sulfate. For these reasons, it is advisable to check the first analysis of low equivalent weight sulfonates of unknown solubility characteristics against a referee method to determine the optimum titrant concentration. Data regarding analyses of several sulfonates support the use of medium strength titrant (Table VI). The results are generally satisfactory, although samples 7 4 and 10.4 show wider disagreement than is desirable. A possible explanation is presented below. DISCUSSION
The method has been applied to a large number of samples with generally acceptable results. It is believed to be more reliable for the high equivalent weight sulfonates than for the lower. I n the analysis of low equivalent weight sulfonates whose sodium salts have appreciable solubility in aqueous solution, the titrant was chosen on an empirical basis, as a stoichiometric relation between the apparent sulfate content and concentration of titrant does not hold for different concentrations of titrant. Evidently excess lead has two conflicting effects upon the formation of an insoluble lead precipitate. The first (a desirable effect) is the suppression of the solubility of lead sulfate in the presence of strong detergents such as the water-soluble sulfonates in the extract. The second (an undesirable effect) is the suppression of the solubility of the slightly soluble lead sulfonates. The use of lead nitrate of medium strength was based upon the assumption that the lead sulfate (and sulfite) was more insoluble than the lead sulfonates and that therefore
Table IV. Comparison of Methods for Determining Inorganics (as Sodium Sulfate) i n Lubricating Oil Sulfonates KarSOI,
Sample Designation Concentrate 1 Concentrate 2 Concentrate 3 Concentrate 4 Concentrate 5 Sulfonate A Crude la Crude 2O Crude 3 O
Amperometric 0.44, 0 . 4 6 0.37. 0.39 0.46, 0.47 0.36, 0.33 0.38, 0.37 4.33,4.22 2.63, 2.61 5.10, 4 . 9 5 5.73, 6 . 0 8
% Weight Gravimetric 0.46 0.38 0.47 0.33 0.39 4.23 2.57 5.10 5.90
a Samples high in inorganics showed considerable precipitation on solution in benzene. For these, immediate withdrawal of I-ml. aliquots following benzene dilution was mandatory because a solid cake usually formed a t the bottom of the flask after a short period.
Table V. Effect of Strength of Titrant on Recovery of Inorganics from Transformer Oil Sulfonates (0.30% sodium sulfate b y ASTM method) Concn of P b + + Eq. A i d l 0 . 1 MI. Pb+'a, X g . NaoQO4/Ml. NazSOI Found, % Wt. Mm. 20 1 0.0 2 0.08 30 5 0.30,0.31, 0.31 41 0.39, 0 . 7 0 42 8 42 10 0.41. 0 . 6 0 a This term represents the increase in wave height In mm. for each 0.1 ml. of P b + + added, well past the equivalence point. Adjustment to equivalent sensitivities and allowance for volume changes have been made. The value for Aid/O.l ml. P b of dilute lead for a solution free of sulfonates is 41 mm. a t S = 0.01 I.' a. per mm. + +
V O L U M E 25, NO. 6, J U N E 1 9 5 3 Table YI. .4nalysisof Lower iMolecular Weight Sulfonates NazSO4, % Weight Sample Designation Amperometrio Gravimetric (ASTM) 1A 0.31 0.30 2.64 2A 2.54 1.20 3A 1.21 0.70 0.72 4A 1.84 5A 1.86 1.12 1.16 6A 1.44 7A 1.72 0.37 0.35 8A 5.23 7.34 9A” 0.25 0.31 10.4 a Sample contained a n unusually large proportion of water-soluble sulfonates. On extraction of this material with 0.1 N NH4C104, most of the sulfonates entered the aqueous phase.
there should be a certain “area” of excess lead concentration wherein the desirable reaction was promoted while the undesirable one waq avoided. The fair agreement between the two methods for these sulfonates of low equivalent weight a t a certain concentration of titrant may be due to the fact that the gravimetric and amperometric methods are subject to the same general errors: the insolubility of lead sulfonates in the amperometric method and the insolubility of barium sulfonates in the ASTM gravimetric method. The observation that, where deviations occur, the am-
901
perometric method is usually higher indicate? that lead ip the greater malefactor. The use of concentrations of titrant different from those recommended would probably lead to gram deviations from the ASTM method when low equivalent weight sulfonates are analyzed, but not with the heaver sulfonates. This anomaly is due, in the authors’ opinion, to the chemistry of the different types of sulfonates and is not a general weaknws of the amperometric method. ACKNOWLEDG.MENT
The authors gratefully acknowledge the aid of R. C. Eiffert, who was concerned with the initial phases of this investigation, and W. H. Bruce, who assisted in the experimental work. LITERATURE CITED
(1)Am. Soc. Testing Materials, Conimittee D-2, Designation 85546T (1949). (2) Burdett, R. A., and Gordon, B. E., Ax.4~.CHEM.,19,843 (1947). (3) Heyrovskp, J., and Berezicky, S., Collection Czechoslou. Chem. Communs., 1,19 (1929). ( 4 ) Kolthoff, I., and Lingane, J. J., ”Polarography,” New York, In. terscience Publishers, 1941. (5) Kolthoff, I., and Pan, J. D., J . Am. Chsm. Soc.. 62, 3332 (1940). (6)Lingane, J. J., IND. ENG.CHEM.,ANAL.ED.,16,147 (1944). RECEIVED for review July 23, 1951.
dccepted l i a r c h 4, 1953.
Detection and Estimation of Impurities in Hexogen Chromatographic Methods EARL W. MALMBERG’, KENNETH N. TRUEBLOODS AND THOMAS D. WAUGH3 California Znstitute of Technology,Pasadena, Calif.
B a e a u ~the ptesenm of nitfamine impurities in the high explosive hexogen (hexahydro-1,3,5-trinitro-striazine) may affect its properties, a systematic procedure has been developed for their detection and estimation. The chromatographic properties and copreupitation characteristics of hexogen and a series of polynitramines of closely related structure have been investigated and a scheme for the concentration, isolation, detection, and approximate estimation of as little as a few parts per million of the different substances in hexogen has been de-
T
H E study of the mechanism of formation of the high explosive hexogen (hexahydro-1,3,5-trinitro-s-triazine) in the nitrolysis of hexamethylenetetramine has resulted in the discovery of a number of compounds of related structure which are possible intermediates and side products in the reaction ( 1 , ‘7, 15). The presence of some of these compounds even in small quantities in commercial production lots of hexogen may produce undesirable effects. The present report describes the development of a procedure for the detection and estimation of these and other possible contaminants in samples of hexogen. The nitramines which %-ere studied may be conveniently classified according to structure as follon-s. An identifying Roman numeral is given for each substance, together with the ab1 Present address, Department of Chemistry, Ohio State University, Columbus, Ohio. 1 Present address, Department of Chemistry, University of California, Loa Angeles 24, Calif. I Present address, Arapahoe Chemicals, Inc., Boulder, Colo.
vised and tested. Accurate quantitative methods have been developed for the determination of hexogen and of octahydro-1,3,5,7-tetranitro-l,3,5,7-tetrazocine by chromatographic-spectrophotometrictechniques. Certain correlations between the structures of the different nitramines and their chromatographic and other properties are discussed. The general approach that has been used in this work shorld also be applicable to other mixtures of mmpounds which are closely related to each other in structure.
breviation by which the compound has sometimes been designated in both the classified and open literature. Compounds Containing a Six-Membered Ring I. Hexahydro-1,3,5-trinitro-s-triaeine(hexogen or R D X ) 11. l-Acetylhexahydro-3,5-dinitro-s-triazine(TAX) 111. Tetrahydro-3,5-dinitro-1,3,5,2H-oxadiazine (CyOx) Compounds Containing a n Eight-Membered Ring IV. Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(HMX) V. l-Acetyloctahydro-3,5,7-trinitro-1,3,5,7-tetrazocine (SEX) One Bicyclic Compound VI. 3,7-Dinitro-1,3,5,7-tetrazabicyclo[3,3,1] nonane (DPT or DNPT) Open-Chain Compounds VII. 2,4,6-Trinitro-2,4,6-triazaheptane-1,7-diol diacetate (BSX) VIII. 2.4.6.8-Tetranitro-2.4.6.8-tetrazanonane-l.9-diol diace, , , ’ tate (AcAn) IX. 2(or 4)-acetyl-4(or 2), 6,8-trinitro-2,4,6,&tetrazanonane1,9-diol diacetate (H-16) X. 2,4,6-Trinitr0-2,4,6-triazaheptane-l,’?-diol dinitrate (ATX)
