Anal. Chem. 1982, 5 4 , 807-809 Monitoring and Support Laboratory, US. Environmental Protection Agency: Cincinnati, OH, 1979; Methods 204.2, 206.2, and 270.2, and Part 4.1.3 of Metals Section. (7) Oehme, M. Anal. Chim. Acta 1979, 107, 67-73. (8) Reamer, D. C.; Veiiion, 6.; Tokousbaiides, P. T. Anal. Chem. 1981, 53, 245-248. (9) Gouiden, P. D.;Anthony, D. H. J. Anal. Chem. 1978, 50, 953-958.
807
(10) Pierce, F. D.; Brown, H. R. Anal. Chem. 1978, 4 8 , 693-695. (11) Giadney, E. S.; Perrin, D. R.; Owens, J. W.; Knab, D. Anal. Chem. 1979, 51, 1557-1569.
RECEIVED for review July 7, 1981. Accepted October 19, 1981.
Spectrophotometric Determination of Aromatic Amines by the Diazotization-Coupling Technique with 8-Amino- 1-hydroxynaphthalene-3,6-disuIfonic Acid and N-( l-Naphthy1)ethyienediamine as the Coupling Agents George Norwitz and Peter N. Keliher" Chemistry Department, Villanova University, Villanova, Pennsylvania 19085
A comprehensive study is made of the application of the diazotizationtoupiing spectrophotometric technique to the determination of diverse aromatic amines, using H-acid (8amino-l-hydroxynaphthaliene-3,6-dlsulfonicacid) and N-( 1naphthyi)ethyienediamine (also called N-( l-naphthaieny1)1,2-ethanediamlne or N-na) as the coupling agents. The methods were tested successfully on halogenated anilines, 2,4-dichioroaniiine,nltroanliines, methyianiiines, aminobenzoic acids, amlnobenzenesulfonic acids, sulfanilamide, and certain other substituted anilines. The methods are not recommended for phenylenediamines and aminophenois, which produce llttle or no color. The aromatic amines containing negative groups tend to couple and produce colors more readily than aromatic amines not containing such groups. The amount of reagent and tlme required for full1 color development is less for aromatic amines containing negative groups, specially for the N-na method. Both methods are about equal in accuracy but the N-na method Is on the average about 1.6 times more sensitive than the H-acid method.
Recently, the authors described methods for the spectrophotometric determination of aniline by the diazotizationcoupling technique, using H-acid (8-amino-l-hydroxynaphthalene-3,6-disulfoinicacid) ( 1 ) and N-(l-naphthyl) ethylenediamine (also called N-(l-naphthenyl)-1,2-ethanediamine or N-na) (2) as the coupling agents. It is the purpose of the present work to report on the application of the methods to the determination of diverse aromatic amines, particularly substituted anilines. No systematic study has previously been made of the application of H-acid and N-na methods to various aromatic amines. A great many of these aromatic amines are of considerable importance in industrial, toxicological, and pharmaceutical aspects (3).
EXPERIMENTAL SECTION Apparatus and Reagents. A Bausch and Lomb Model 70 spectrophotometer (l-cm cell) and Hewlett-Packard Model 845OA recording spectrophotometer (l-cm cell) were used. The chemicals used were ACS reagent grade except the aromatic amines and H-acid. The aromatic amines were Eastman Kodak reagent chemicals. The H-acid (available only in the technical grade) was purified as described previously (I). 0003-2700J82/0354-0807$01.25/0
Standard Aromatic Amine Solution No. 1 (1 mL = 5.00 mg of the Aromatic Amine). For the aminobenzenesulfonic acids (orthanilic, metanilic, and sulfanilic acids), dissolve 0.5000 g in hot water, cool, and dilute to 100 mI, in a volumetric flask with water. For the remaining aromatic amines, dissolve 0.5000 g in ethanol (heating and then cooling to room temperature, if necessary) and dilute to 100 mL in a volumetric flask with ethanol. Standard Aromatic Amine Solution No. 2 ( 1 mL = 0.50 mg of the Aromatic Amine). Dilute a 10-mL aliquot of standard aromatic amine solution no. 1 to 100 mL in a volumetric flask with water. Prepare fresh every 3 days. Standard Aromatic Amine Solution No. 3 ( 1 mL = 0.010 mg of the Aromatic Amine). Dilute a 10-mL aliquot of standard aromatic amine solution no. 2 to 500 mL in a volumetric flask with water. Prepare fresh daily. N o k Disposable polyethylene gloves (Fisher) should be worn in handling the concentrated aromatic amine solutions (standard aromatic amine solutions no. 1and 2), since many of the aromatic amines are toxic or carcinogenic. Sodium Nitrite Solution ( 1 % )and Sulfamic Acid Solution (3%). Prepare fresh every 3 weeks. H-Acid Reagent (0.75%). Prepare fresh every 3 days from purified H-acid and store in a brown bottle. N-na Reagent (0.(75%).Prepare fresh every 4 days and store in a brown bottle. €I-Acid Method (fur the Analysis of the 24 Aromatic Amines Listed in Table I). Prepare a calibration curve by transferring portions of standard aromatic amine solution no. 3 (1mL = 0.010 mg of the aromatic amine) to 100-mL volumetric flasks. Select the portions in accordance with the sensitivity of the color for the individual aromatic amine (see Table I). The maximum absorbance should be about 0.7. Dilute to about 75 mL with water, add 2.0 mL of 0.3 N hydrochloric acid and 2.0 mL of sodium nitrite solution ( l % ) ,swirl, and allow to stand 5 min. Add 2.0 mL of sulfamic acid solution (3%), swirl, wash down the sides and neck of the flask with water, and allow to stand 10 min. Add 10.0 mL of sodium bicarbonate solution (6%), swirl, add 2.0 mL of H-acid reagent (0.75%), and swirl again. Dilute to the mark, mix well, and store in the dark. Measure the absorbance against water in the interval 15-45 min at the wavelength indicated in Table I. Deduct the blank and plot absorbance against milligrams of aromatic amine per 100 mIA.For the analysis of an actual sample, transfer an appropriate aliquot to a 100-mL volumetric flask, dilute to about 75 mL, and proceed as described in the preparation of the calibration curve. N-na Method (for the Analysis of the 24 Aromatic Amines Listed in Table I). Prepare a calibration curve by transferring portions of standard aromatic amine solution no. 3 to 50-mL 0 1982 American Chemical Society
808
ANALYTICAL CHEMISTRY, VOL. 54, NO. 4, APRIL 1982
Table I. Spectrophotometric Determination of Aromatic Amines by the H-acid and N-na Methods H-acid N-na
A (0.20
nm
A (0.05 mg/50 mL)
1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 2.5 2.5 2.5 2.5
reddish purple reddish purple reddish purple reddish purple reddish purple reddish purple reddish purple reddish purple purplish red reddish purple violet reddish purple violet reddish purple
540 544 556 540 546 556 5 54 544 536 546 570 5 56 566 5 50
0.450 0.499 0.446 0.295 0.462 0.295 0.547 0.358 0.402 0.469 0.311 0.290 0.308 0.345
0.504 0.328
2.5 1.0
reddish purple reddish purple
542 542
0.40 7
524
0.374
1.0
reddish purple
544
0.289
cherry red
5 26
0.519
1.0
reddish purple
542
0.335
cherry red cherry red cherry red cherry red purplish red cherry red
528 528 5 26 518 536 5 27
0.41 8 0.327 0.450 0.270 0.413 0.769
1.0 1.0 1.0 2.5 2.5 2.5
reddish purple reddish purple reddish purple pink violet reddish purple
540 550 530 506 568 554
0.395 0.277 0.307 0.335 0.297 0.584
mg/ mLof 1 0 0 m L ) reagent
aromatic amine
color
2-chloroaniline 3-chloroaniline 4-chloroaniline 2,4-dichloroaniline 3-bromoaniline 4-bromoaniline 4-fluoroaniline 2-nitroaniline 3-nitroaniline 4-nitroaniline 2-meth ylaniline 3-methylaniline 4-methylaniline 2-aminobenzoic acid (anthranilic acid) 3-aminobenzoic acid 2-aminobenzenesulfonic acid (orthanilic acid) 3-aminobenzenesulfonic acid (metanilic acid) 4-aminobenzenesulfonic acid (sulfanilic acid) sulfanilamide 3-aminoacetanilide 4-nitro-2-aminotoluene
cherry red cherry red cherry red cherry red cherry red cherry red cherry red purplish red cherry red purplish red purplish red cherry red cherry red cherry red
534 526 530 536 526 530 528 542 520 534 548 528 534 528
0.560 0.579 0.563 0.386 0.545 0.418 0.717 0.441 0.455 0.670 0.289 0.515 0.479 0.262
cherry red cherry red
526 526
cherry red
2-chloro-6-methylaniline 5-chloro-2-methoxyaniline
aniline
.III.x~
color
Amax,
nm
Am,,
0.268
____--
_ _ _ I I
Table 11. Effect of Sodium Bicarbonate Concentration on the Determination of Various Aromatic Amines by the H-Acid Method
a
aromatic amine
1.o
2-nitroanlined 2-aminobenzoic acidd sulfanilimided anilinee
0.40 0.21 0.32
pH 6.0.
* pH 7.2.
pH 7.8.
absorbance readings for mL of 6% sodium bicarbonate solution 2.0a 5.0 10.0b 20.0 6 g NaHCO,C
0.00
0.20 mg/100 mL.
0.43 0.25 0.42 0.27 e
0.43 0.27 0.42 0.37
0.43 0.27 0.42 0.39
0.40 0.27 0.42 0.40
0.35 0.27 0.42 0.44
0.10 mg/100 mL.
volumetric flasks. Select the portions in accordance with the sensitivity of the color for the individual aromatic amine (see Table I). The maximum absorbance should be about 0.7. Dilute to about 35 mL with water, add 3.0 mL of 1 N hydrochloric acid and 1.0 mL of sodium nitrite solution (l%), swirl, and allow to stand 5 min. Add 1.0 mL of sulfamic acid solution (3%), swirl, wash down the neck and sides of the flask with water, and allow to stand 10 min. Add 1.0 or 2.5 mL of N-na reagent (0.75%), as indicated in Table I. Dilute to the mark, shake, and remove the stoppers (to allow the escape of nitrogen gas). Allow to stand 10 min for the development of the color if 1.0 mL of the N-na reagent was used and 90 min if 2.5 mL of the N-na reagent was used. Measure the absorbance against water at the wavelength indicated in Table I. Deduct the blank and plot absorbance against milligrams of the aromatic amine per 50 mL. For the analysis of a sample, transfer an appropriate aliquot to a 50-mL volumetric flask, dilute to about 35 mL, and proceed as described in the preparation of the calibration curve. Note: Clean all glassware, including cells, frequently with concentrated hydrochloric acid.
RESULTS AND DISCUSSION Solubility of Aromatic Amines. For preparation of the calibration curves, it is necessary that the aromatic amines be soluble in water or ethanol and that the compound not precipitate when the aliquots from the ethanol solutions are diluted with water. The aminobenzenesulfonic acids (orthanilic, metanilic, and sulfanilic acids) dissolved in water but
not ethanol. The remaining compounds listed in Table I dissolved in ethanol, but not water. The methods are not applicable to dinitroanilines or trichloroanilines. These compounds have a slight solubility in ethanol, but much of the dissolved material precipitates on diluting with water. Study of Conditions for Developing the Colors by the H-Acid Method. The procedure for the different aromatic amines by the H-acid method is the same as previously described for aniline (I), insofar as acidity for diazotization, amount of nitrite, time for diazotization, and the use of sulfamic acid to destroy the excess nitrite is concerned. The effect of the amount of sodium bicarbonate to be added prior to the addition of the H-acid was investigated for three typical aromatic amines (2-nitroaniline, 2-aminobenzoic acid, and sulfanilimide). The results, in conjunction with the data obtained for aniline, show that each aromatic amine has its own plateau region for sodium bicarbonate for optimum color development (Table 11). Ten milliliters of the sodium bicarbonate solution (6%) lies in the plateau region for all the aromatic amines tested and was selected as the amount to be used. Subsequent work showed that this amount of sodium bicarbonate was satisfactory for all the aromatic amines to which the H-acid method was applicable. The amount of H-acid reagent (2.0 mL of 0.75% solution) and the time for color development (15-45 min) used for aniline (I)were found t o be satisfactory for the diverse aromatic amines.
ANALYTICAL CHEMISTRY, VOL. 54, NO. 4, APRIL 1982
809
Table 111, Effect of Hydrochloric Acid Concentration on the Determination of Various Aromatic Amines by the N-na Method absorbance readings mL of concentrated HCl
mL of 1 N HCl I___
aromatic aminea
0.10
0.50
1.0
2.0
5.0
10.0
20.0
5.0
2-nitroaniline b 2-aminobenzoic acidC sulfanilamide aniline
0.33 0.30 0.35 0.53
0.35 0.30 0.37
0.37 0.35 0.38 0.57
0.37 0.35 0.38 0.57
0.37 0.35 0.38 0.57
0.37 0.33 0.38 0.54
0.38 0.27 0.38 0.40
0.10 0.38
0.55
10.0
0.38
1.0 mL of N-na reagent was used and the absorbance measured after 1 0 min. a 0.050 mg/50 mL. reagent was used and the absorbance measured after 90 min.
Study of Conditions for Developing the Colors by the N-na Method. The procedure for the different aromatic amines by the N-na method is the same as previously described for aniline ( Z ) , insofar as amount of nitrite, time for diazotization, temperature for diazotization, and the use of sulfamic acid to destroy the excess nitrite is concerned. With the N-na method, acidity has a dual role in diazotization and coupling. The effect of acidity was investigated, using the three aromatic amines previously examined for the H-acid method. The results, in conjunction with the results obtained for aniline, show that each aromatic amine has its own plateau region for acidity (Table 111). Three milliliters lies in the plateau region for all the aromatic amines tested and was selected as the amount to be used. This amount of acid was found to give satisfactorJy results for all the aromatic amines to which the N-na method was applicable. As with aniline, 2.5 mI, of N-na reagent (0.75%)and a standing period of about 90 min were necessary for full development of the color for 2-methylaniline, 3-methylaniline, 4-methylaniline, and 5chloro-2-methoxyaniline.For the remaining aromatic amines, only 1.0 mL of the N-na reagent and a standing period of 10 min were necessary. Spectrophotometric Studies. Spectrophotometric curves were run for on all the compounds to which the H-acid and N-na methods were applicable. The type of color, wavelength of maximum absorption (A,=), and the absorbance for 0.20 mg/100 mL for the H-acid method and 0.05 mg/50 mL for the N-na method are shlown in Table I. The colors for the H-acid method and N-na method are generally cherry red and reddish purple, respectively, but there are many exceptions. for the H-acid and N-na methods for the The spread of A,, different aromatic amines was 30 and 64 nm, respectively. The N-na method i s on the average about 1.6 times as sensitive as the H-acid method on the basis of the absorbance obtained for 1 mg of the aromatic amine per milliiter. Essentially the same absorbance readings are obtained by using the recording spectrophotometer and the Model 70 spectrophotometer. The calibration curves for all the compounds listed in Table I followed Beer's law. The accuracy and precision of the H-acid and N-na methods were about equal and were about the same as the accuracy and precision previously obtained for aniline. Ease of Coupling. The recommended methods were successfully adapted to the determination of 2-chloraniline, 3-chloraniline, 4-chloraniline, 2,4-dichloroaniline, 3-bromoaniline, 4-bromoaniline, 4-fluoroaniline, 2-nitroaniline, 3nitroaniline, 4-nitroaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, %-aminobenzoicacid (anthranilic acid), 3aminobenzoic acid, 2-aminobenzenesulfonic acid (orthanilic acid), 3-aminobenzenesulfonic acid (metanilic acid), 4aminobenzenesulfonic acid (sulfanilic acid), sulfanilimide, 3-aminoacetanilide, 4-rratro-2-aminotoluene, 2-chloro-6and aniline. The methylaniline, 5-chloro-2-methoxyaniline, methods are not recommended for phenylenediamines and aminophenob, which gentrrally produce little or no color. The reason that colors are produced with some aromatic amines
15.0
25.0
0.37
0.21
0.30
0.12
2.5 mL of N-na
but not with others is primarily related to the ease of coupling (although other factors may be involved). As has been indicated by Zollinger (41,the mechanics of the coupling reaction involves attack of the electronegative or nucleophilic center of the coupling component by the positively charged polarized diazonium radical (ArN2+).The yield in the coupling reaction depends upon the electrochemical character of the diazonium group (as determined by the inductive and resonance effects of the nuclear substituents), on the electronegativity of the site in the coupling component at which the attachment of the diazonium group takes place, and the pH of the reaction mixture. Aromatic amines containing negative substituenb (particularly, NOz, halogens, S03H, and SOzNHz)tend to couple readly, since they cause positive polarization of the nitrogen atom, which withdraws electrons from the ring and increases the positive charge on the diazonum ion. There is no quantitative data available on the relative coupling rates of diazotized amine with H-acid or N-na. However, it was noted by Zollinger ( 4 ) that the relative rates of coupling of certain para-substituted diazotized anilines with phenol as the coupling component (in an alkaline medium) were as follows: NOz, 1300; SOf, 13; Br, 13; H, 1; CH,, 0.4; CH30,0.1. The amount of reagent and the time required for full color development in both the H-acid and the N-na methods was found to be less for aromatic amines containing negative substituents than aromatic amines not containing such groups. This phenomenon is quite marked for the N-na method. It was also apparent with the H-acid method, but the color developed fully for all the compounds, using 2.0 mL of the H-acid reagent and standing time of 15 min. Consideration was given to the possibility that the failure of the methods when applied to some aromatic amines might be due to unsatisfactory conditions for diazotizing these compounds. However, cooling in ice during the diazotization, use of longer diazotization times, and the use of sodium bromide as a catalyst did not produce better color development. Heating during the color development was also not helpful. The methods described in this paper are probably applicable to many other aromatic amines besides those listed. The methods are not applicable to secondary or tertiary aromatic amines, since such amines are not diazotizable.
ACKNOWLEDGMENT We thank the Hewlett-Packard Co. for the loan of the Model 8450A Spectrophotometer and Jay Levine of the company for his useful suggestions. LITERATURE CITED (1) Norwltz, G.; Keliher, P. N. Anal. Chern. 1981, 5 3 , 56-60. (2) Norwitz, G.; Keliher, P. N. Anal. Chem. 1981, 53, 1238-1240. (3) "Kirk-Othmer Encyclopedia of Chemical Technology", 3rd ed.; Wiley: New York, 1978; Vol 2, pp 309-354. (4) Zolllnger, H. "Diazo and Azo Chemistry", Interscience: New York, 1961; pp 41 1-420.
RECEIVED for review October 16, 1981. Accepted January 18, 1982.
