( 3 ) Boos, R. S . , Jones, S. L., Trenner, s.R.,A N A L . CHEM. 28,390 (1956). (4)Bradley, J. E. S., Holloway, R. C., JIcFarlane, A. S.,Bwchen. J. 57, 192 i,19.54) - - - ,. ( 5 ) Buchanan, D. L., J . Biol. Chem. 229, 211 (1957). 16) Buchanan. D. L.. Xakao, A,, J . A m . . ,Chem. SOC.74, 2389 (1952). (7) Christman, I>. R., 13sy, ?rT. E., Hansell, 1’. R., Anderson, R. C., ANAL. (‘IIE\l. 27, 1935 (19%). I
( 8 ) Grosse, A. V., Hindin, S. G., KirshenSaum, A. D., Ibid., 21,386 (1949). (9) Hackspill, L., D’Huart, G., Bull. SOC. c h i n 35, 800 (1924). (10) Kirsten. W.,ANAL.CHEU.25, 1097 (1954). (11) Naughton, 3. J., Frodyma, M. M., Ibid., 22, 711 (1950). (12) Northcote, D. H., Horne, R. W., Bwchem. J . 51, 232 (1952). (13) Parkes, G. D., “Rlellor’s hlodern
Inorganic Chemistry,” p. 431, Longmans, Green, London, 1951. (14) Van Slyke, D. D., Steel, R., Plazin, J., J . Biol. Chem. 192, 769 (1951). (15) Wilzbach, K. E., Sykes, W. Y . , Science 120, 494 (1954).
RECEIVED for review hfarch 2, 1959. Accepted June 8, 1959. Work given partial support by the U. S. Public Health Service.
Spectrophotometric Determination of Primary Nitroparaffins by Coupling with p-Diazobenzenesulfonic Acid ISRAEL R. COHEN and A. P. ALTSHULLER Air Pollution Enaineerina Research, Robert A. Taft Sanitary Enaineerina Center, Public Health Service, U. S. Departmeit o f Hklth, Education, and Welfare, Cinchma< Ohio
-
+ Primary
nitroparaffins have been determined spectrophotometrically by means of their coupling reaction with p-diazobenzenesulfonicacid. Secondary nitroparaffins and 2-nitro-2alkyl-1 -alkanols do not interfere, but 2-nitro-2-alkyl- 1,3-alkenediols react with p-diazobenzenesulfonic acid. Nitromethane can b e determined at 440 mp in the concentration range up to 50 y per ml.;while nitromethane and 1 -nitropropane can be determined at 395 mp up to 80 and 100 y per rnl., respectively.
T
HE present work was stimulated by
the need to identify the nitroparaffins formed in an investigation of the gas phaae reactions of nitrogen oxides with olefins (1). Although much has been published on the analysis of aliphatic nitro compounds (3,4, only a few of the reactions discussed in the literature appear to be specific for primary nitroparah. The procedure of Scott and Treon (67, which employs the pink color developed when primary nitroparaffins are treated with hydrochloric acid and ferric chloride, was not sensitive enough for theconvenient determination of microgram quantities of primary nitroparaffins. From the data given (6), it can be calculated that the specific extinction coefficients in absorbance units per microgram per milliliter-centimeter of optical path length are only about 0.002. The method used by Turba, Haul, and Tjhlen (7) involving the coupling of diazotized sulfanilic acid with the primary nitroparsans appeared to have good sensitivity. These investigators used filter photometry and were able to deter1638
ANALYTICAL CHEMISTRY
*e nitromethane in the presence of higher molecular weight primary nitrop a r a h . They also claimed that the colors formed were stable for the first 15 minutes if the solutions were b u f f e d to p H 6, after which the color in solutions containing the hizher molecular weight n i t r o p a r a 5 s began to fade. This method has been adapted for spectrophotometric use, but i t was found necessary to use a difIerent p H and buffering system. Linear plots have been obtained for nitromethane, nitroethane, and 1-nitropropane. The interferences of Znitropropane, %nitro%rhethyl-l-propanol, and %nitro-% ethy1-ll3-propanediol were investigated. Because the colors faded, the rate of decrease of absorbance with time was studied. The effect of pH on the absorbance variations with time also was investigated for the 1-nitropropane-p diazobenzenesulfonic acid reaction. EXPERIMENTAL DETAILS
Nitro Compounds. The nitroethane, 1-nitropropane, and 2-nitropropane used were redistilled samples of materials obtained from K and K Laboratories, Jamaica, N. Y . Two samples of nitromethane were available. One %-asa Matheson, Coleman and Bell material, boiling point 99-102”. The other was a sample of nitromethane claimed to be of 99.9yopurity provided by Commercial Solvents Corp. The %nitro-Zmethyl-1-propanol and %nitro2-ethyl-l,3-propanediol were presented by Commercial Solvents Corp. The nitromethane, nitroethane, l-nitropropane, and Znitropropane were rtnalyzed for impurities by gas chromatography using a Perkin-Elmer 154C instrument. The column used consisted of 2 meters of 20% &benzyl ether on 40-to .%-mesh firebrick. The chro-
matograph was operated a t a flow rate of 200 ml. per minute and the air bath wm maintained at 77”. The nitromethane from Commercial Solvents was found to contain about 0.03% nitroethane, 0.05% Znitropropane, 0.5% water, and 0.03% of an unknown impurity. Consequently, aside from water, the other impurities totaled only 0.1%. The Matheson, Coleman and Bell nitromethane had 1.1% nitroethane, 1.7% Znitropropane, and 0.3% water as impurities. The l-nitropropane had as impurities about 0.1% nitroethane, 1.3% %nitropropane, about 0.3% of what probably is a nitrobutane, and 0.1% water. The >nitropropane contained 3.7y0 nitroethane and 2.0% 1-nitropropane as impurities. These percentages are area determinations calculated by multiplying the peak heights by the half widths. Area percentages are assumed to be equal approximstely to weight percentages (2, 5). However, no correction for varying thermal conductivities was made. APPARATUS
Most of the qualitative and many of the quantitative data were obtained with a Cary Model 11 spectrophotometer. Some of the data were obtained using the Beckman Model B spectrophotometer. Soluti6ns for reaction of p-diazobenzenesulfonic acid with nitroparaffins: I. Dilute 1.1 gramsof KNOlto 100 ml. with water. 11. Mix 7.2 grams of sulfanilic acid (purest grade) and 18 ml. of HCl (sp. gr. 1.19) and dilute to 1 liter with water. 111. Dilute 30 grams of KOH to 1 liter with water. IV. Dilute 10.4 grams of NaHzPOl.2He0 to 1 liter with water.
1.25
I
i
I
l
OF HlTfiOMilHbNE
/
0
I
I
I
'.
--.
400 450 WAVE LENGTH, Mu
350
I
, 500
Figure 1. Absorption curves for coupling products of nitromethane and 1 -nitropropane with p-diazobenzenesulfonic acid at pH 4.3 2.40
I
I
1
I
I
I
I
1
I eo
I
I
40
60
I
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I
80
loo
IPO
140
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' 180
TINE. IN Y I I U I L S
Figure 2. Variation in absorbance with time of product in coupling reaction of 1-nitropropane with p-diazobenzenesulfonic acids in solutions at pH 4.3 and 6.3
I
4 Figure 3. Beer's law curves for coupling products between nitroparaffins and p-diazobenzenesulfonic acid
40
50
60
70
EO
90
00
WT. OF NITROPARAFFIN. IN 7
V. Dilute 17.88 grams of Na*HPO,.7HzO to 1 liter with water. V. Dilute 17.88 grams of NazHPO,.7H~0 to 1liter with water. VI. Add 4 volumes of IV to 1 volume
of V to prepare phosphate-buffer mixture. VII. Dissolve the nitroparaffin in 10% methanol. PROCEDURE
To react the pdiazobenzenesulfonic acid with nitroparaffins, pipet 1 ml. of sample and 1 ml. of blank (10% methanol in water) into two separate Erlenmeyer flasks (about 25 ml.). Add to each 1.4 ml. of solution VI and 0.6 ml. of solution 111. Add to each solution, with vigorous shaking, 5 ml. of a solution formed by mixing equal quantities of I and 11. Read absorbance at 4-40 mp for nitromethane, and 395 mrr for higher nitroparaffins, within 1or 2 minutes after mixing for the higher nitroparaffins. Calibration curve readings can also be made at up to 10 minutes after mixing without appreciable loss of sensitivity due to fading. RESULTS AND DISCUSSION
The buffer used by Turba, Haul, and Uhlen (7), on which they reported a p H of 6, repeatedly gave a solution with a pH of around 3. The colors formed in the reaction began to fade immediately and the position of the absorption maximum and the intensities could not be reproduced for the reactions of either ni-
troethane or l-nitropropane with pdiazobenzenesulfonic acid, despite repeated attempts to do so. The position and magnitude of the absorption maxima for nitromethane could be fairly well reproduced. After attempts to obtain reproducible results a i a number of p H values with phosphate-type buffers, a phosphatebuffered solution of pH 4.3 was selected. The absorption maximum under these conditions for the nitromethane pdiazobenzenesulfonic acid reaction was located at 440 mp. The corresponding reactions using nitroethane and 1-nitropropane resulted in a product absorbing a t 395 mp. The products of these coupling reactions would seem to be a 1nitroformaldehyde psulfophenylhydrazone, 1-nitroacetaldehyde psulfophenylhydrazone, and l-nitropropionaldehyde psulfophenylhydraeone. 2-Nitropropane also gave a product with weak absorption a t 395 nip, probably due to impurities. Absorption curves for nitromethane and 1-nitropropane are shown in Figure 1. The optical absorbance a t 440 mp of the product of the nitromethane-p diazobenzenesulfonic acid coupling reaction was constant for about 10 minutes. Between 10 and 20 minutes the absorbance decreased about 5%. The optical absorbance at 395 mp for what are presumed to be 1-nitroacetaldehyde p
suliophenylhydrazone and l-nitropropionaldehyde psulfophenylhydrasone started decreasing immediately with a 10% decrease in intensity in the first 10 minutes after the reaction stnrted. Because the initial coupling reaction is rapid, the color is essentially a t maximum intensity within 30 or 45 seconds after the components are mixed. Consequently, it is desirable to measure the absorbance either immediately n f k r mixing reactant or a t a short fixed i n t w val after miring for example. 5 or 1G minutes. The changes in absorbances with trmc for the reaction of 1-nitropropane with pdiazobenzenesulfonic acid a t pH 4.3 and 6.3 are shown in Figure 2. The absorbance of the solution buffered a t p H 6.3 goes through a minimum a t about 10 minutes. After this it increasrs steadily, finally flattening off after about 3 hours a t an absorbance somewhat higher than that obtained initially for solutions a t a pH of 4.3. The optical behavior of these solutions is very sensitive to pH in the 6 to 8 region. The gradual rise in absorbance Kith time a t pH 6.3 using the phosphate buffering system offers an alternative procedure, if a reaction period of several hours is convenient. Absorbance IIS. concentration curves for the reaction of pdiazobenzenesulfonic acid with nitromethane a t 440 mp and with nitroethane and 1-nitropropane a t 395 mfi are given in Figure 3. Beer's law is followed up to about 50 y per ml. of nitrometilane, 80 y per ml. of nitroethane, and 100 7 per ml. of 1-nitropropane. Practically all of the experimental data are within 5% of the curves shown in Figurn 3. The experimental data have VOL. 31, NO. 10, OCTOBER 1959
1639
been corrected for the impurities present, in each nitroparaffin. These corrections amount to an increase of 0.5% for the data obtained using nitromethane, 401, for nitroethane, and 1.7% for l-nitropropane. However, when the observed absorbances for 2-nitropropane are corrected for impurities, they are reduced to only 20% of their original values. After correction, the absorption of the product of the 2-nitropropane and p diazobcnzcne sulfonic acid a t 395 mp is only 1 or 2Oj, of the absorbances a t 395 mp for the rcactions involving nitroethane and 1-pitropropane. Even this small amount of absorbance may be due to too small a correction for impurities, as the alpha carbon in a secondary nitroparaffin should not be capable of coupling t o form a hydrazone. In terms of specific extinction coefficients in absorbance units per microgram per milliliter for a 1-cin. optical path length, the following values are obtained for the product of the reaction of p-tiiazobenzenesclfonic acid with nitro-
methane, 0.042; with nitroethane, 0.023; with 1-nitropropane, 0.016; and with 2nitropropane, 0.0003. The corresponding molar absorption coefficients are 9.0 X lo3 for 1-nitroformaldehyde p sulfophenylhydrazone, and 3.9 X lo3 for 1-nitropropionaldehyde psulfopheny lhydrazone. It was not possible to resolve the product peaks when a mixture of 75 y of 1-nitropropane and 30.6 of nitromethane reacted with diazotized sulfanilic acid. Instead, a broad absorption maximum a t about 412 mp mas observed. However, it would seem possible to determine nitromethane in the presence of smaller quantities of higher nitroparaffins. A solution containing 100 y of 2-nitro2-methyl-1-propanol did not seem to react with pdiazobenzenesulfonic acid to produce any appreciable absorption in the region above 350 mp. However. 100 y of 2-nitro-2-ethyl-1, 3-propanediol had an absorbance of 1.05 at an absorption maximum near 390 mp. Consequently, it appears that the 2-nitro-2-
alkyl-] ,3-alkanediols would interiere appreciably if present in a sample with 1nitroparaffins. ACKNOWLEDGMENT
The authors thank Clarence Clemons for obtaining the gas chromatographic data on the nitroparaffins, which permitted them to calculate the amount of impurity in each nitroparaffin. LITERATURE CITED
(1) Altshuller, A. P., Cohen, I., I d . Eng. Chem. 51, 776 (1959). (2) Browning, L. C., Watts, J. O., ANAL. CHEM.29, 24 (1957). (3) Hass, H. B., Riley, E. F., Chem. Revs. 32, 373 (1943). (4) Jones, L. R., Riddick, J. A , , ANAL. CHEM.24, 1533 (1952). (5) Rosie, D. M., Grob, R. L., Zbid., 29, 1263 (1957). (6) Scott, E. W., Treon, J., IND.ENG. CHEM.,ANAL.ED.12, 189 (1940). (7) Turba, F., Haul, R., Uhlen, G., Angew. Chem. 61, 74 (1949).
RECEIVED for review January 21, 1959. Accepted June 8, 1959.
Spectrographic Analysis of Molybdenum Metal Powder RUDOLPH DYCK and THOMAS J. VELEKER Chemical and Metallurgical Division, Sylvania Electric Products Inc., Towanda, Pa.
b The following elements in molybdenum metal powder are determined spectrographically: aluminum, barium, calcium, chromium, copper, iron, potassium, magnesium, manganese, sodium, nickel, lead, silicon, tin, strontium, and tungsten. Samples are buffered with graphite mixtures containing the internal standard. A high voltage alternating current arc i s used for all the elements except the alkalies and tungsten, for which direct current is used. The combined effect of graphite buffering and high voltage alternating current excitation produces an extremely refractory matrix during arcing, depressing molybdenum and enhancing the medium volatility elements. Tungsten is enhanced by buffering with zinc oxide. The method is far superior to wet chemical analysis in simplicity, speed, and sensitivity. It is reasonably accurate and has been applied to the control of molybdenum purity.
T
currrnt need for heat-resistant materials is creating much interest in molybdenum, not only as an alloying constituent, but also as a metal in its own right. It is a highly refractory metal that is now finding many applications in aircraft and missile technology. It is widely used for electrodes, filament HE
1640
ANALYTICAL CHEMISTRY
wire, filament supports, and high temperature heating elements. There are several major problems associated with molybdenum fabrication, such as protection from catastrophic oxidation, its relatively high ductileto-brittle transition temperature, and its microstructure after fabrication (3). The two latter problems are greatly influenced by the impurity level in the molybdenum. For example, surprisingly small additions of various impurities make sintered molybdenum rods unworkable (6). Certain impurities that have relatively high vapor pressures cause blistering on the surface of rods during sintering. Although the role of many trace impurities is not fully understood ( 5 ) , there is ample evidence that the estimation of trace elements is of paramount importance in the processing of molybdenum. Chemical determination of 16 trace elements in a matrix such as molybdenum would be difficult t o perform routinely, from the standpoint of the time and analytical skill required. The emission spectrograph is ideal for such a comprehensive analysis; however, there are problems inherent in the spectrochemical analysis of molybdenum. Molybdenum, like other refractory metals, emits an extremely complex
spectrum as well as an intense continuum under ordinary arc excitation. This results in line interferences and an unfavorable line to background ratio, and thus poses a serious problem for the spectrographer. A technique must be sought that will depress the matrix spectrum without depressing the spectra of the impurity elements. A technique in which this is accomplished is presented here. There is an analogy between this technique and a method reported by the authors for the spectrochemical analysis of tungsten ( 2 ) . The molybdenum metal powder is mixed intimately with high purity graphite (except for the tungsten determination) and arced using high voltage alternating current. For the tungsten and alkali determination, direct current is used. Excitation parameters are so selected that molybdenum carbide is formed in situ as soon as the arc is initiated. This results in a marked depression of the molybdenum spectrum while the more volatile impurity elements are enhanced. The metal powder matrix is particularly advantageous in the case of molybdenum, because the trioxide is extremely volatile and will result in poor spectral sensitivities for most elements, even if the trioxide is diluted with graphite. Other advantages in analyzing the metal powder are its greater density, and the
