Results of the analysis of samples of trialkylaluminums and diethylaluminum hydride are shown in Table IV. Samples 1 and 2 were prepared from known mixtures of AlEts and EtAIH. The purity of each was determined to be "+% by gas evolution, mass spectrometric analysis of the gas, and infrared analysis. The
&Me3 was analyzed in the same manner and the purity was found to be 9€.3%.
(4) Keumann, '8. P., Angew. Chem. 69,
730 (5) Vaillant, M., Chim. Anal. 39, 413 (1957).
LITERATURE CITED
(1) Bonitz, E., Chem. Ber. 88,742 (1955). (2) Farina, M., Donltti, M., Ragazaini, M., Ann. chim. (Rome)48,501 (1958). (3) Henderson, S. R., Snyder, L. J., ANAL.CHEM.31,2113 (1959).
RECEIVED for review August 29, 1960. Resubmitted April 21, 1961. Accepted June 29, 1961. Division of Analytical Chemistry, 138th Meeting, ACS, New York, N. Y., September 1960.
Spectrophotometric Determination of Naphthylamines HANS 0.SPAUSCHUS Major Appliance Laboratories, General Electric Co., Louisville, Ky.
When naphthylamines, or nitrogensubstituted derivatives thereof, are dissolved in certain halogenated solvents and exposed to ultraviolet irradiation, colors rapidly develop. The Beer-Lambert law is obeyed for concentrations in the range of 10 to 100 p.p.m. Irradiated solutions of N-phenyl-1 -naphthylamine in chloroform absorb at 640 mp. Color intensity varies with concentration according to the least-squares equation, 68.9 X p.p.m. of amine = 16.9 absorbance. The average standard deviation of the data points from their estimated value according to the correlation line is 0.022 absorbance unit. Other naphthylamines such as 1 N-phenyl-2-, N-methyl-1 and N,N-dimethyl-1-naphthylamine also react with halogenated solvents under the influence of ultraviolet light. These photo-induced reactions should prove generally useful as a basis for both qualitative and quantitative determinations. To determine naphthylamine-type additives in mineral oils, a known excess of chloroform is added to the oil, and color is formed by ultraviolet irradiation of the solution. Thus N-phenyl- 1 -naphthylamine, an oxidation inhibitor for lubricating oils, can be determined simply and rapidly in both new and used oils.
+
-,
D
-,
commercial applications and some reported physiological effects of 1- and 2-naphthylamines and their nitrogen-substituted derivatives have created a demand for methods of detecting and determining these compounds. Numerous spot test procedures (7, 8, 10) and color reactions with specific reagents (8, 4, 5 ) have been reported. For quantitative determination, primary naphthylamines have been diazotized and coupled and the absorption spectra of the resulting azo dyes measured (1, 3, 6). Analytical methods in which the naphthylamines IVERSE
1334
*
ANALYTICAL CHEMISTRY
produce a color with a diazonium salt have also been reported (9, 13, 14). Methods employing the diazo reaction are complicated and precautions must be exercised to ensure complete conversions. Liebhafsky and Bronk (12) reported that a reaction between N-phenyl-1naphthylamine and Nessler's reagent produced an intense color with an absorption maximum below 400 mp. Unfortunately, the color continues to develop for a t least 16 hours, seriously impairing the utility of this reaction as a basis for an analytical method. The present investigation was pursued when it was observed that naphthylamines, dissolved in certain halogenated solvents and esposed t o ultraviolet radiation, yield colored solutions suitable for spectrophotometric study. Results for solutions of N-phenyl-1-naphthylamine in chloroform established that color intensity is proportional to the concentration of amine. Other naphthylamines, including 1-naphthylamine, N-phenyl-2-naphthylamine, N-methyl-1-naphthylamine,and N,Ndimethyl 1 - naphthylamine, all yield colors when dissolved in selected halogenated solvents and exposed to ultraviolet radiation. Substituted naphthylamines are frequently used as additives for petroleum oils. The present method has been applied to the direct determination of N-phenyl-1-naphthylamine in mineral
-
Oil * EXPERIMENTAL
Reagents and Apparatus.
N-
Phenyl-1-, N-phenyl-2-, and N-methyl1-naphthylamines, Eastman Grade, were obtained from the Eastman Kodak Co. High purity 1-naphthylamine, reagent grade N,N-dimethyl1-naphthylamine, and indicator grade diphenylamine were obtained from the Fisher Scientific Co. All amines were used as received. The chloroform was Mallinckrodt analytical
reagent grade containing 0.75% ethyl alcohol as preservative. The alcohol was removed from the chloroform for some of the experiments by shaking a quantity of chloroform three times with a small volume (5%) of concentrated sulfuric acid, washing four times with an equal volume of distilled water, drying over anhydrous potassium carbonate, and distilling through a small column. The fraction boiling a t 60.3" to 60.4" C. a t 747.1 mm. of Hg was stored in a tightly sealed amber bottle. Other solvents used in the experiments included Transistar grade carbon tetrachloride (Mallinckrodt) ; bromoform (Eastman White Label, stabilized with diphenylamine) ; absolute methanol (analytical reagent grade, Mallinckrodt) ; 1,2-dichloroethane (purified, Fisher Scientific Co.) ; and trichloroethylene (b.p. 86-87 " C., Matheson, Coleman and Bell). Solutions were prepared by weighing the components on an analytical balance, and the concentration is expressed in parts per million by weight. A Blak-Ray Model X4 ultraviolet lamp provided radiation of 3660-A. wave length. This lamp was placed across the open top of a small box, 7 cm. deep. Solutions were irradiated in fused silica absorption cells of IO-mm. light path by placing the cells in the bottom of the box directly under the center of the lamp. Absorption studies in the visible region were made with the Cary recording spectrophotometer, Model 14M, a t scanning speeds of 10 and 50 A. per second. Procedure. A solution of naphthylamine in chloroform was transferred to one of a pair of matched 10-mm. cells. The second cell was filled with the pure solvent, the cells were placed in the sample compartment of the Cary spectrophotometer, and the differential spectrum was recorded from 550 to 700 mp. No absorption peaks were observed and the background absorbance changed a maximum of only 0.02 absorbance unit over the range scanned. The cell containing the solution was irradiated by the ultraviolet lamp for 1 minute. The cell was in-
n
I
0.8 -
0.7
2 Mln.
U.V.
2 Hr. Interval -4
-
b Figure 2. Complex formation and stability
0.6 W
2 0 Hr. I n t e r v a l In R e f r i g e r a l o r
W
1.0
0
* 0.5 -
4
m
m
0.4 -
v)
m
-
0.3
-
Y
0.2
0
I
U.V.
700
600
WAV.E
Figure 1. phenyl 1 complex
500 700 600 LENGTH,mp
Absorption spectra of
500
N-
- - naphthylamine -chloroform
verted several times to produce uniform color distribution, then returned to the sample compartment of the spectrophotometer, and a second differential spectrum recorded. This procedure was repeated, alternating irradiation and absorption measurements. Typical absorption spectra are shown in Figure 1. As color developed in the solution, the absorption peak increased in intensity, reaching a maximum after 5 to 10 minutes of total radiation time. This time interval increases with increasing concentration of naphthylamine. RESULTS AND DISCUSSION
The color of a naphthylamine complex can serve as a basis for a quantitative analytical method, provided the complex is sufficiently stable to permit accurate absorption measurements and the color intensity is proportional to the concentration of the naphthylamine. These factors were studied with solutions of N-phenyl-1-naphthylamine in chloroform. Complex Stability. Results of differential absorption measurements of a solution of 121 p.p.m. of N phenyl-1-naphthylamine in inhibited chloroform are given in Figure 2. Color develops rapidly during the first few minutes of ultraviolet irradiation and then changes very slowly, as illustrated by the relatively flat maxima in the curve between 5 and 10 minutes. Irradiation beyond the time required to develop the maximum color enhances the breakdown of the complex above the rate a t which it decomposes in storage. Lowering the temperature of the solution appears to inhibit the rate of decomposition, a8 shown by the relatively small drop in
IO
I5
I R R A D I A T I O N
T I M E ,
5
absorbance which occurred during 20hour storage of the solution in a refrigerator. The possibility that the incident radiation in the spectrophotometer was contributing to the decomposition of the complex was also considered. To study this factor another solution was prepared and the complex formed by &minute ultraviolet irradiation. This solution was placed in the spectrophotometer, the wave length fixed a t 450 mp, and the sample irradiated for 2 minutes with the chart "on" so as to detect any effect on absorbance. The changes in absorbance were less than 0.01 unit. The experiment was repeated a t 50-mp intervals up to 800 mp with the same results. The complex is not decomposed appreciably by the visible radiation used for the absorbance measurements. In all experiments a small shift in the absorption maximum toward longer wave length was observed as ultraviolet irradiation times were increased. In a total of 10-minute irradiation, the absorption peak shifted from 638 to 644 mp for a solution of N-phenyl-lnaphthylamine in chloroform. The magnitude of this shift is less than the spectral band width of commercial spectrophotometers. Consequently the errors introduced in absorbance meas-
Table I.
uv
20 MIN.
urements a t fixed wave length are negligible. Absorbance
vs.
Concentration.
Solutions containing 20.0, 33.3, 50.0, 75.0, 100.0, and 117.6 p.p.m. of N phenyl-1-naphthylamine in chloroform were prepared from a 1000p.p.rn. stock solution by dilution with chloroform. The intensities of the 640mp absorption peak for increasing irradiation times are given in Table I. When the maximum absorption for each solution is plotted against the concentration of amine, a straight line is obtained, showing that the solution obeys the Beer-Lambert law. The least-squares line, P.p.m. = 16.9 f 68.9 X absorbance
was calculated from the concentrations and maximum absorbance values given in Table I. The average standard deviation of the data points from their estimated value according to the correlation line is 0.22 absorbance unit. A sample was also prepared with about 10 p.p.m. of amine. On irradiation with ultraviolet, no noticeable color developed nor could be detected by the spectrophotometer. Thus the lower limit a t which the method is applicable is between 10 and 20 p.p.m. of amine. The upper limit was not established, but it was determined that
Absorbance of N-Phenyl-1-naphthylamine Solutions of Various Concentrations
Amine, P.P.M.
Time, Min .
20.0
33.3
1 2 3 4 5 6 7 8 9 10
0.032 0.065a 0.061 0.048
0.157 0.217 0.2265 0.215
50.0
75.0
100.0
117,6
0.239 0.392 0,441 0.450" 0.436
0.346 0.606 0.755 0.825 0.856 0.866" 0.859
0.418 0 736 0.961 1.097 1.163 1.193 1.207O 1.195
0.470 0.841 1.090 1.251 1.361 1.414 1,4540 1.350 1.335 1.323
Absorbance, 640 MM
~
Maximum absorbance valuee.
VOL. 33, NO. 10, SEPTEMBER 1961
1335
pale yellow color after 12-minute irradiation time. With methanol, a nonhalogenated solvent, the solution remained essentially colorless. The complex which is formed apparently has very limited solubility in carbon tetrachloride, as shown by the formation of a solid phase during irradiation. The other solutions remained clear during the irradiation experiments. A solution of l-naphthylamine in bromoform produced a striking array of colors during irradiation. Since this bromoform was stabilized with diphenylamine, the solvent without 1-naphthylamine was also irradiated as a blank. In this experiment an orange to red color was produced, showing that the stabilizer itself was capable of reacting with the solvent. Solutions of bromoform with and without 1-naphthylamine produced different colors in the early stages of irradiation. For longer radiation periods both solutions became red, probably because of the dominating effect of the relatively high concentration of diphenylamine stabilizer. Solutions of 1-naphthylamine in chloroform with and without ethyl alcohol stabilizer gave different colors on irradiation. A small quantity of ethyl alcohol was added to the unstabilized solution after 12-minute irradiation time. A further short irradiation period produced the same color pre-
the Beer-Lambert law was obeyed to 117.6 p.p.m., the highest measurable concentration in a 10-mm. cell. Complexes of Various Naphthylamines in Chloroform. Chloroform solutions of five naphthylamines and diphenylamine were irradiated in 10mm. fused silica absorption cells and inspected for color formation. The results are given in Table 11. Colored complexes were formed with all naphthylamine-chloroform solutions but not with diphenylamine. The color and color intensity are influenced by the nature of the substituted groups and their position on the naphthalene nucleus. The N, N-dimethyl-l-naphthylamine solution produced only a weak color a t 157 p.p.m. in chloroform, but a deep co!or resulted when the concentration was increased to 340 p.p.m. These colors provide a simple and rapid qualitative method for detecting and distinguishing between different naphthylamines. Complexes of 1-Naphthylamine in Various Solvents. Solutions of 1naphthylamine in different solvents were irradiated with ultraviolet light for various time intervals and the colors noted. The results are recorded in Table 111. Complexes of intense color were formed in all halogenated solvents except trichloroethylene. The solution of l-naphthylamine in this solvent produced only a
Table
It.
Complexes of Various Naphthylamines in Stabilized Chloroform
N-Phenyl-1- N-Phenyl-2Amine 1-Naphthyl- naphthylnaphthylW Time, amine, amme, nmine, Min. 114P.P.M. 77P.P.M. 107 P.P.M. C vp violet p violet Violct Violet Violet
0 1
3 5 8 12
viously observed for the stabilized chloroform solution. These solutions were not studied spectrophotometrically. Determination of N-Phenyl-1naphthylamine in Mineral Oil. A colorimetric method for determining AT-phenyl-1-naphthylamine in new and used oils, based on reaction with diazotiaed p-nitroaniline, has been described by Levine and BIarshall (11). Experiments with the irradiation method described in this paper revealed that it is readily adapted for determining naphthylamines and N-substituted naphthylamines in mineral oils. The oil is diluted with a known excess of chloroform, and the intensity of the color formed by ultraviolet irradiation is measured spectrophotometrically. This method obviates the use of an unstable reagent such as diazotized p-nitroaniline and is applicable over a wider range of concentrations than those reported by Levine and Marshall. Six solutions were prepared by adding chloroform to oil samples containing known amounts of N-phenyl-l-naphthylamine. The mineral oil-N-phenyl1-naphthylamine solutions contained no other additive. The analytical results given in Table IV show that the ratio of chloroform to oil is not critical in the range 80 to 95 weight % chloroform. The same procedure has been utilized
C
N-Methyl-1naphthylamine, 163 P.P.M.
C
C
p blue Blue d blue d blue Green
p yellow Yellow
green Green-blue d green-blue d blue vd blue
Yellow
d yellow d yellow
N,N-Dimethyl-lnaphthylamine Diphenylamine 157p.p.m. 340p.p.m. 105 p.p.m. 426p.p.m. C C C C C Violet C C vp violet Blue C C vp violet d blue C C vp violet C C vd blue vp yellow vp violet vd blue C
C = colorlees; vp = very pale; vd = very deep. Table 111.
cc4
CHBrp
Complexes of 1 -Naphthylamine in Various Solvents
CHBrp 100
C
0
P green
1
p green-cl p green-cl
3 6 8 12
WEEt1
C
p orange
Orange Red-orange Red-orange Red
Solvent CHC1,’ CHCla’ ClH&-CH&l 1-Naphthylamine, P.P.M. 100 100 100
c
Blue d hlrre vd blue d violet d red
C
Green Green Green-yellow Green-yellow Blue-violetd
Green-yellow -v cl Bromoform stabilized with diphenylamine. * Chloroform with ethyl alcohol st,abilizer removed. Chloroform stabilized with 0.75y0 EtOH. d One drop ethyl alcohol added after l&min. irradiation. C = colorless; vp = very pale; vd = very deep; cl = cloudy 20
1336
0
ANALYTICAL CHEMISTRY
p green
C p violet Violet
Blue-violet Blue-violet Blue-violet
C
p green p green
Yellow Yellow Yellow Yellow
Cl&=CClH
CHSOH
100
127
C C C vp yellos vp yellow p yellow
C C
C C vp yellow vp yellow
to determine N-phenyl-] -naphthylamine in used oils. The method is successful even with highly discolored (dark brown) oils, since the color intensity is greatly reduced by dilution with chloroform. The lower limit of detection for dark oils is about 20 p.p.m. of naphthylamine.
Table IV. Determination of N-Phenyl1 -naphthylamine in Mineral Oils
Wbi1% 5.44
Naphthylamine, P.P.M. Theoretical Found 54.4
54.2
LITERATURE CITED
(1) Allan, Z. J., Muzik, F., Chem. liaty
47,380 (1953). 4. (2) J., Ann. chim. (Rome) 44, . . Bertetti, J.. , 4 . 313 (1954). ' (3) Butt, L. T., Stafford, N., J . Appl. Chem. 6, 525 (1956). (4) Deal, A. J. A., A,, Trans. Inst. Rubber h d . 23, 148 (1947).
(5) Engelbertz, P., Babel, E., Zentr. Arhei1,med. u. Arbeitsschutz 3, 161 (1053). (6) English, F. L., ANAL.CHEM.19, 457 (1947).
(7) Feigl, F., Costa Neto, Cl., Silva, E., Ibid., 27. 1319 (1055). (8) Hanot; C., Bull.. soc. chim. Belges 66, 76 (1957). (9) Koide, T.. Kubota, T., Furuhnshi, M., Sato, T., J . SOC.Rubber Ind. Japan 22, 108 (1949). (10) Lamhert, J. L., Cntes, V. E., ANAL. CHEM.29,508 (1957). (11) Levine, W. S., Marshall, W. A., Ibid., 27, 1019 (1955). (12) Liebhafsky H. A., Bronk, L. B., Ibid., 20,588 (1948). (13) Vaskevich, L). N., Sergeeva, 1 Gigiena i Sanil. 21, No. 3, 41 (1956). (14) Zijp, J. W. H., Elec. tzau. chim. 'I 313 (1957).
RECEIVEDfor review March 17 1961. Acrepted June 8, 1961. Divi6on of Analytical Chemistrv, 130th Meeting, ACS, S t . Louis. Mo., hfnrch 1961.
An a Iysi s of Tu ngste n-Tant a Ium- Rhe nium AI Ioys JAMES F. REED Westinghouse Research laboratories, Pittsburgh 35, Pa.
b In the analysis of alloys of tungsten, tantalum, and rhenium, acid hydrolysis is used to separate tantalum and tungsten from rhenium. Tantalum and tungsten oxides are dissolved b y fusion with potassium carbonate and extraction with water. Tantalum is separated as the insoluble magnesium tantalate and weighed as the oxide after extraction of the magnesium salts with acid. The tungsten is precipitated from the acidified filtrate with cinchonine. Rhenium is precipitated in either dilute acid or alkaline solution as tetraphenylarsonium perrhenate. Tungstates, nitrates, and cinchonine do not interfere, but tantalum does. Small amounts of rhenium are separated from large amounts of tantalum b y hydrogen sulfide.
A
these laboratories the alloy tungsten-tantalum-rhenium as well as the binary allnys tungsten-tantalum, tungsten-rhenium, and tantalum-rhenium were studied. The analytical methods required are described here. Since the literature revealed no method for the separation of the ternary system, conditions were established lor the simultaneous precipitation of tungsten and tantalum from rhenium by the combined action of cinchonine and acid hydrolysis. For small amounts of rhenium in the presence of tantalum the Geilmann and Lange (1) sulfide precipitation was modified to eliminate the pressure vessel. By complexing tantalum with fluoride its hydrolysis and precipitation under the Geilmann conditions were eliminated. T
The determination of rhenium was completed with the tetraphenylarsonium chloride method of Willard and Smith (6) as modified by Smith and Long (4). The interference, reported by Willard and Smith (6),of small amounts of nitrate was not a problem. Cinchonine and hydrogen peroxide also do not interfere. This method was preferred, because of its fewer interferences, to the nitron method (2). The method of Powell, Schoeller, and Jahn (9) for the separation of tantalum from tungsten as magnesium tantalate was modified to eliminate the ammonium salts and the tannin and yielded satisfactory results. EXPERIMENTAL
Reagents. Cinchonine, 10 grams dissolved in 90 ml. of hydrochloric acid ( 6 N ) . Tctraphenylarsonium chloride, 1% in water. Tctraphenylarsonium pcrrhenate, saturated solution in water for washing
(4).
Procedure for Ternary Alloys. HIGH RHENIUM. A . Dissolve about 0.2 gram of sample in 20 ml. of 6 N hydrochloric acid plus 5 ml. of hydrogen peroxide (30%). Dilute t o 100 nil. and add 10 ml. of cinchonine solution and 5 ml. of nitric acid. Boil until the peroxide is decomposed and set aside overnight a t room tempcrature. Filter through No. 42 Whatman paper. Save ::i tiltrate which contains the rhenium. B . Ignite the paper containing tantalum and tungsten in a platinum crucible until the paper is burned away. Add 5 grams of anhydrous potassium carbonate and fuse until clear. Cool and dissolve the melt in 50 ml. of cold
water. Rinse the crurible, and add 10 ml. of magnesium rhloride solution (10%). Stir and hcat to about 90" C. Let cool for 30 minutes, and filter the magnesium tantalate precipitate on No. 40 Whatman paper. Wash with 1% potassium carbonate solution. C. Acidify the filtrate with hydrochloric acid and add a 10-nil. excess. Boil out the carbon dioxide and add 5 ml. of nitric acid and 10 ml. of cinchonine solution. Allow to remain overnight a t room temperature. Filter through No. 42 U'hatmun paper and ignite to WOs i.n an electric muffle a t 800" C. D. Treat the paper and precipitate of magnesium tantalate with hydrochloric acid ( 1 N ) . Neutralize with ammonia to reprecipitate the tantalum. Filter and ignite over a Meeker-type burner until the paper is gone. Add hydrochloric acid (RN) to the tantalum oxidc to extract the remaining magnesium salts. Depant the clear liquid and ignite the residue to TazOs. E . The rhenium is in the filtrate from the acid hydrolysis of tantalum and tungstcn. Partially neutralize with ammonia, but leave cnough free acid to keep the cinchonine dissolved. Heat and add a 50% excess of tetraphenylarsonium chloride. Allow to remain overnight a t room tempcrature. Filter through a weighed fritted-porcelain crucible. Wash the precipitate with saturated tetraphenylarsonium perrhenate solution. Dry a t 110" C. and wcigh as (CaH&AsRe04. LOW RHENIUMALLOTS. F . If the weight of the rhenium is less than 10 mg. and tantalum is present, the rhenium is best separated as the sulfide. Dissolve the sample with 2 ml. of hydrofluoric acid plus a few drops of nitric arid in a platinum crucible. Heat to drive out nitrogen oxides. Transfer to a borosilicate glass or Teflon beaker conVOL. 33, NO. 10, SEPTEMBER 1961
* 1337
