V O L U M E 2 1 , NO. 1 2 , D E C E M B E R 1 9 4 9
1529 Table I.
Analysis of Indene in Synthetic Samples
Approximate Composition of Diluent
toi&ne, ;On naphthalene 32% toluene, 0 % styrene, 63% benzsm 71% toluene, 26% Tetralin 73% toluene, 27% cyclohesene Y3c$ toluene, 7% fluorene
-96%
Figure 2.
2.58 1.89 4.26 1.96
0.7
1.2 1.1 0.2
2.61
1.87 4.27 1.99 2.19
2.14
70
Error,
1. 5
2.3
pared and analyzed by the recommended procedure. There were included in some of the samples various hydrocarbons which it was thought might interfere with the analysis. The results from these tests are given in Table I; excellent results were obtained in each case. The only hydrocarbons which have been encountered which interfere with the procedure are cyclopentadiene and some of the methyl derivatives of indene. The presence of the former in a sample is indicated by the development of a yellow color within 3 minutes after adding the reagents and a t room temperature. The methyl derivatives give a color which is nearly identical with the color formed with indene, and the proposed method has been used also for the analysis of these compounds in certain mixturrq.
Itate of Color Development at Boiling Temperature
tained by t liis n i t s t hot1 will Ijc slightly greater than that obtained by heating the solutions. Analysis of Samples. Weigh out samples and dilute with benzene or petroleum ether to such,a volume that the concentration of indene is between 0.2 and 2 my. per ml. Take 5-ml. aliquots and treat in exactly the same way as the standards. A reagent blank Ghould be run with each series of samples. Reference to the calibration curve gives the milligrams of indene in the aliquot.
Indene, % Present Found J . 69 3,73
1.4 .
I
I
I
,
1.2
j
I
,
Y
1
DISCUSSION
The color obtained upon mixing benzaldehyde with indene in the presence of alkali is an intense yellon. which has an absorption maximum in the ultraviolet region of the spectrum. However, the quantitative nieasurements described herein were made a t 420 mp because i t was desired to have a method that would be adaptable to the use of visual photometers or colorimeters. The rate of color development is relatively s l o ~at room temperatures. For example, in the presence oi’ 0.3% potassium hydroxide a t least 8 hours are required t o reach the maximum color, and 24 hours are required t o reach the same color with 0.15y0potassium hydroxide (Figure 11. Higher concentrations of alkali give more rapid reactions: however, theseare to be avoided because excessive values for the blank are obtained as :I result of side reactions of t,he benzaldehyde. The reaction rate can be markedly increased by raising the temperat,ure. Thus a t 40” C. 2 hours are required for maximum color, while a t reflux temperatures full color is obtained in less than 10 minutes when the alkali concentration is 0.3%. This is illustrated in Figure 2. The color produced by the reaction was found to follow Beer’s law. However, the slope of the straight line relating optical density and concentration Tvas somewhat less when t,he color was developed a t the boiling temperatures of the solutions than when the reaction was carried on a t room temperatures (Figure 3). From the standpoint of accuracy and reproducibility, the two methods of color developnient are equally satisfact,ory and both have been used for analyses. The stability of the color was found to be excellent, particularly if the escess potassium hydroxide was neutralized with a little acetic acid after the reaction was complete. For example, solutions measured immediat,ely after color development and after 7 2 hours showed no change in optical density. I n order to test, the proposed method of analysis, a series of synthetic samples containing knom-n quantities of indene was pre-
CONC. INDENE -mg. / 50d. Figure 3 .
Calibration Curves for Indene Analysis LITERATURE CITED
(1) Hammick. D. L.. and Lanerish. D.. J. Chem. SOC..1937. 79T-801. ( 2 ) Mighill, T. H., Am. Gas. 154, 33 (1941). (3) Thiele, J., Ber., 33, 3395 (1900).
i,
(4) Uhrig, K., Lynch, E., and Becker, H. C., IXD. ENG. CHEM., . ~ N A L . ED., 18, 550 (1946). R E C E I V EJDu l y 2 5 , 1940
Correction In the article on “Determination of Cottonseed Oil on Tin Plate” [Donelson, J. G., and Keish, R . A., ANAL.CHEY.,21, 1102 (1949)], Figure 2 on page 1104 was printed upside down. The numbers on the horizontal axis should have been 10, 20, 30, 40, 50, and not 10, 20, 40, 60,80 as printed.
