same concentration as the crotonaldehyde. DISCUSSION
CHexylresorcinol appears to be the first colorimetric reagent with even fair specificity towards crotonaldehyde. Other unsaturated aldehydes if present in about equal amounts will interfere appreciably. However, the method has good selectivity when the crotonaldehyde is to be determined in the presence of saturated aldehydes or ketones, saturated or unsaturated alcohols, esters, acids, or phenols. The absorption peaks are only about onetenth the intensity of the acrolein product band a t 605 mp. Consequently, the method for crotonaldehyde is much less sensitive than the method described elsewhere for acrolein. The serious interference of nitrogen
dioxide with the determination of crotonaldehyde is unfortunate. This interference prevents the crotonaldehyde in combustion sourcea producing appreciable quantities of nitrogen oxides. This is in contrast to the successful application of the general method to acrolein in combustion sources (2). The difference in applicability is the result of the presence of the crotonaldehyde product bands in the ultraviolet rather than in the visible, and of their lower intensities. LITERATURE CITED
(1) Alekseev. S. V., Sintet Kauchuk 10, \
,
13-16 (19g6). ‘ Cohen. I. R.. Altshuller. A. P.. ANAL.
(2)
Annual MeetinControl Association, Cincinnati, Ohio, May 22-26, 1960. (4) Kyryacos, G., Menapace, H. R.,
Boord, C. E., ANAL. CHEM.31, 222 (1959). (5) M,acNevin, W. M., Urone, P. F., Omletanski, M: L. B., Dunton, M. L., Fifth Symposium (International) on Combustion, pp. 402-5, Reinhold, New York, 1955. (6) Malmbere. E. W.. Smith. M. L.. Bigler, J. E:, Bobbitt, J. A., ‘Ibid., pp: 389-91. (’ 17 ) Mold, J. D., MacRae, M. T., Tobacco 144, 24 (1957). (8) Snell, F. D., Snell, C. T., “Colorimetric Methods of Analysis.” Vol. 11, pp. 61-70, Van Nostranh, New York; 19x7..
(9) Wahl, R., Tabak-Forsch Wiss. Bed. Suddeut. Tabakztg. 22, 61 (1957). (10) Wearn. R. B., Murray, W. M., Jr., ’ Ramsey, ’M. P.,’ Chandier, N., ~ N A L ; CHEM.20,922 (1948). RECEIVED for review January 9, 1961. Accepted June 5, 1961. Work performed at the Laboratory of Engineering and Physical Sciences, Division of Air Pollution, U. S. Department of Health, Education, and Welfare, Public Health Service, Cincinnati 26, Ohio.
Spot Test Detection and Spectrophotometric Determination of AzuIene Derivatives with 4-Dimethylaminobenzaldehyde EUGENE SAWICKI, THOMAS W. STANLEY, and WALTER C. ELBERT Division of Air Pollofion, Robert A. Tuft Sanitary Engineering Center, Cincinnati 26, Ohio
b The detection and determination of azulenes with 4-dimethylaminobenzaldehyde have been investigated, One microgramof azulene, guaiazulene, or 2,4,6-trimethylazulene can be detected on a spot plate. These azulene compounds can be determined spectrophotometrically at 6 2 0 or 6 4 2 mp (for guaiazulene). Their molar absorptivities range around 90,000. The chromogenes formed in the procedure obey Beer’s law from 0.1 to 4 pg. of azulene compound per ml. of final solution. Spectrophotometrically it was possible to detect 1 part of the azulene compound in 5 million parts of test solution.
T
HE PRESENCE in
the air of American communities of a fairly large number of polycyclic aromatic hydrocarbons has been unequivocally demonstrated with the help of ultraviolet-visible absorption spectrophotometry, spectrophotofluorometry, and various general color tests (9-21). In addition, some highly selective color tests have been described for the detection of anthracene ( I ) , pyrene (If?), and fluorene (8),including derivatives of each, and for polycyclic compounds containing a cyclopentadiene ring (13).
These tests have also been applied to the detection of these compounds in the air. The presence of the dicyclic hydrocarbon azulene in tobacco smoke (2, 3) and in town air (3) has been reported. However, sensitive analytical methods were needed that could be of value in the unequivocal detection and determination of this hydrocarbon in the air. The presence in solution of fairly large amounts of azulene or a n alkyl derivative of azulene can be detected by the weak violet to blue color of these compounds. Azulene can be readily characterized by its many ultravioletvisible absorption bands in a polar solvent and by the three diverse types of spectra obtained in polar, nonpolar and acidic solvents (Figure 1). Although azulene can be determined directly (6), the method lacks sensitivity. A much more sensitive test for azulenic compounds, consisting of the reaction of azulene with 4 N , N dimethylaminobenzaldehyde in acid solution to give a blue dye, has been described (6, 14). The method has been developed into a colorimetric procedure for the determination of azulene-forming materials in the yarrow plant ( 7 ) . This method of determining azulene has been investigated
more fully in this paper and applied to spectrophotometric use. The blue chromogen, I, formed in the method has the following structure
(4):
The pure dye, analogous to I, obtained from guaiazulene (1,Cdimethyl7-isopropylazulene) absorbs a t a wave length maximum of 647 mp with a molar absorptivity of 99,000 in acetic acid (4). These data compare favorably with the results obtained in the determination of 1,4-dimethyl-7-isopropylazulene or guaiazulene, for which the wave length maximum and molar absorptivity in alcohol-acetic acid are 642 mp and 94,000, respectively. EXPERIMENTAL
Reagents. 4-N,N-Dimethylaminobenzaldehyde (Matheson, Coleman and Bell) was crystallized from hexane t o give colorless plates, m.p. 74’ t o 75’ C. A 1% solution was made up in acetic acid. Azulene and its deVOL. 33, NO. 9, AUGUST 1961
0
1183
DISCUSSION
Figure 1.
Ultraviolet (left) and visible (right) absorption spectra of azulene
---
.. .
-Pentane, Ethyl alcohol, 95% Hydrochloric acid, concd. Concn. of azulene in pentane and ethyl alcohol: Right. 5 X 10-5M left. 2 3 0 to 2 9 0 rnp, 3 X 10-5M 2 9 0 to 400 rnp, 4 X 10-4M Concn. in “3, 5 X 10 -5M
rivatives were obtained from the bldrich Chemical Co. and were sufficiently pure for the problem. Procedures. SPOT PLATE.T o 1 drop of the alcoholic test solution add 1 drop of the dimethylaminobenzaldehyde reagent solution and allow the mixture t o stand for 2 minutes Then add 1 drop of concentrated hydrochloric acid followed by 1 drop of water. I n the presence of a 1Table I. Spectrophotometric Determinationof Azulene Compounds
Compound Azulene 4,6,&Trimethylazulene Guaiaeulene
e1.0
ex ,A,
620
620
642
10-8 86 93 94
or 3-unsubstituted azulene, a blue color is obtained. All three azulene compounds gave an identification limit of 1 pg. The blank is colorless to pale yellow. SPECTROPHOTOMETRIC. To 5 ml. of the alcoholic test solution, add 5 ml. of the 1% acetic acid solution of 4-dimethylaminobenzaldehyde followed by 0.1 ml. of a solution containing 50 mg. of trichloroacetic acid in 15 ml. of concentrated hydrochloric acid. Fifteen minutes after the addition of the acid, obtain the absorbance values at the wave length maximum of the chromogen (Table I). For azulene the intensity reached a maximum and remained stable for 17 to 32 minutes after addition of acid; for 4,6,8-trimethylazulene and guaiazulene the corresponding stability times were 10 to 14 and 4 to 10 minutes, respectively (Figure 2).
I:..
1
i
... ......(..................................................................................................
I
1 IO
I
20
I
30 MINUTES
i
40
Figure 2. Change in absorbance with time, following addition of acid mixture, in following determinations
- Azulene at A,,
. . .. .
1184
---
and 4,6,8-trirnethylazulene, both 2.475 X 1O-’M 6 2 0 rnp Guaiazulene, 1.24 X 10-SM at A,, 6 4 2 rng
ANALYTICAL CHEMISTRY
Variables in the standard procedure were investigated. The possibility of substituting other aldehydes for 4-dimethylaminobenzaldehyde was first explored. 1-Forniylpyrene and 3-nitro4-dimeth~-laminobenzaldeliyde\I ei e unsatisfactory, while 4-diethylaminobenzaldehyde worked well in the standard procedure, giving a wave length masimum of 635 mp and a molar absorptivity of approsimately 75,000 with 4,6,8-trimethylazulene. Increasing the percentage of the dimethylaminobenzaldehyde in the reagent solution gradually increased the absorbance till a maximum value was reached a t concentrations of 1 to 3y0 (Figure 3). At the higher concentrations of 2 to 3%, the color intensities took longer to reach a masimum and the intensities mere lower for guaiazulene and 2,4,6-trimethylazulene. However, azulene gave better results with higher concentrations of 4-dimethylaniinobenzaldehyde. For example, with a 2.5% concentration, a molar absorptivity of 90,000 was obtained for azulene at about 24 to 34 minutes after addition of acid. Thirty-two hours later the molar absorptivity had dropped to 84,000. So, for the determination of azulene this particular modification could be used. In the standard procedure, when 0.1 ml. of a liquid solution of trichloroacetic acid containing a trace of water was used as the acid, the colors took longer to develop and were more stable. With 0.1 ml. of concentrated hydrochloric acid, maximum intensities were reached almost immediately and then started to fade. Consequently, a mixture of the two acids was found which gave maximum stability. Volumes of 0.1 to 1 ml. of the acid mixture used in the standard procedure gave practically identical molar absorptivities. However, a slightly higher absorbance was obtained with the 0.1-ml. volume. Beer’s law was obeyed for all three azulene compounds from about 0.1 to 4 pg. per ml. of final solution as shown for two of them (Figure 4). Spectrophotometrically it was possible to detect l part of the azulene compound in 5 million parts of test solution. The spectrophotometric method for the detection and determination of azulene in a mixture is approximately 300 times as sensitive as the direct method for the analysis of an azulene. Note in this respect that the most intense bands of azulene in the visible a t 581 and 633 mp have molar absorptivities of 320 (Figure 1). The following compounds reacted in the standard procedure gave negligible absorption a t 620 mp: phenol, anisole, N,Ndimethylaniline, naphthalene, 1naphthol, 1-methoxynaphthalene, 1-
0.5
i
___
1
I
I
I 1
0.5 1.0 1.5 2 .o X 4-DIMETHYLAMINOBENZALDEHYDE IN REAGENT
Figure 3. Effect of change in concentration of 4-dimethylaminobenzaldehyde in reagent on absorbance at Amax 6 2 0 mp in determination of azulene, 2.475 10-6M
x
pg/ml FINAL SOLUTION
Figure 4.
Concentration-absorbance curves obtained at
A,,,,, 620 mp in standard procedure
--- Azulene
-4,6,8-Trimethylazulene quantities, and they could be easily differentiated. m
LITERATURE CITED
‘0 x 0
40
( 1 ) Hauser, T. R.. Chemist Amlust 48. 86 (195oj. (2) Johnstone, R. A. W., Plimmer, J. H., Chem. Revs. 59, 885 (1959).
20
Figure 5. Visible absorption spectra obtained in determination of l -naphthylamine, indole, and azulene in standard procedure
naphthylamine, anthracene, pyrene, and benzo [alpyrene. Carbazole and indole were possible interferences, but they gave molar absorptivities of approximately 100 and 400, respectively, a t 620 mp. Pyrrole, indole, and 1naphthylamine reacted readily with the reagent. The absorption spectra of the chromogens thus obtained from indole and 1-naphthylamine are compared with the spectrum of the azulene dye
in Figure 5. Pyrrole, reacted in the standard procedure, gave a dye absorbing a t 548 mh with a molar absorptivity of 42,000. Apparently a Schiff base is formed with 1-naphthylamine. Pyrroles and indoles would be the main possible interferences in the detection or determination of an azulene. However, these dyes absorb a t shorter wave lengths, so that they would cause little interference unless present in large
(3) Kennaway, E., Lindsey, A. J., Llrzt. Med. Bull. 14, 124 (1958). (4) Kirbv. E. C.. Reid. D. H.. J. Chem. Boc. 1660.494. ’ ( 5 ) Koch, K.,Deut. Apotheker Ztg. 55, i58 (1940). ( 6 ) Muller, A., J. prakt. Chem. 151, 233 (1938). ( 7 ) Muller, K. H., Hoverlagen, H., Deut. Apotheksr Ztg. 100, 309 (1960). ( 8 ) Sawicki, E., Elbert, W., Chemist Analyst 48, 68 (1959). (9) Sawicki, E., Elbert, W., Stanley T. W.,Hauser, T. R., Fox, F. T., ANAL.CHEM.32,810 (1960). (10) Sawicki, E., Elbert, W.,Stanley, T. W.. Hauser. T. R.. Fox. F. T.. Intern.’J. A i r Pollution 2, 273 (1960). ( 1 1 ) Sawicki, E., Hauser, T. R., Stanley, T. W., Ibid., 2,253 (1960). (12) Sawioki, E., Stanley, T. W.,Chemist Analyst 49, 77 (1960). (13) Sawicki, E., Stanley, T. W.,Koe, J., ANAL.CHEM.32, 816 (1960). (14) Stahl, E., Deut. Apotheker Ztg. 93. 197 (1953). Received for review December 15, 1960. Accepted May 10, 1961. Work done at the Laboratory of En
gineering and Physical Sciences, whid is affiliated with the Public Health Service U. S. Department of Health, Educatior and Welfare. VOL 33, NO. 9, AUGUST 1961
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