March 15, 1942
ANALYTICAL EDITION
(55) Willntlitter, R.. and Stoll, A,, “Untersuchungen fiber Chlorophyll, Methoden und Ergebnisse”, Berlin, Julius Springer, 1913.
. ,
(56) Wilson. J- . N... J . Am. Chm. Soc.. 62.1588 (1940).
(57) Winterstein, A.,in G. Klein’s, “Handbueh der Pflanzenenalyse”, Vol. IV p. 1403, Wien. J Springer, 1933. (58) Winterstein, A., and Schon, K., 2.physiol. Chem., 230, 146,158 (1934).
(59) Winterstein. A., and Stein, G., Ibid.. 220, 263 (1934). (60) Zerhmeieter, L.,and Cholnoky. L. v., Ann., 516, 30 (1935). (61) Zechmeister, L..and Cholnuky, L. v.. “Die chromatographische Adsorptionsmethode, Grundlagen, Methodik, Anwendungen”,
249
2nd ed., Berlin, J. Springer, 1938; English translation: “Principles and Practice of Chromatography”, London, Chapman and Hall, 1941 (N. Y., John Wiley & Sons). (62) Zechmeister. L.,and Cholnoky, L. v., Monatsh., 68, 68 (1936). (63) Zechmeister, L., Cholnoky, L. v., and Ujhelyi, E., Bull. soc. chim. biol., 18, 1885 (1936). (64) Zechmeister, L.,T6th, G . , and Vajda, Enzymologia, 7, 170 (1939).
e.,
PRESENTED before the Division of Agricultural and Food Chemistry, Symposium on New Analytical Tools for Biologiral and Food Research at the CxEarrcAL SOCIETY, Atlantic City. N . J. 102nd Meeting of the AMERICAN
Sodium Salt of Quinizarin-6-Sulfonic Acid as an Acid-Base Indicator J. H. GREEN, State Agricultural & Mechanical College, Orangeburg, S. C.
T
HE red sodium salts of quinizarin sulfonic acid have been used as dye intermediates by the I. G. Furbenindustrie (S), and for the formation of metallic lakes by Bayer & Co. (1). The author observed that when the sodium salt of quinizarin-Asulfonic acid was treated with acid, the yellow quinizarin-6-sulfonic acid was formed, while treatment with alkali produced a blue-violet coloration As these reactions indicated t h a t the sodium salt of quinizarin-6sulfonic acid might be used as an indicator in acidimetryalkalimetry, this investigation was undertaken. Preparation of Reagents The quinizarin is prepared according to the method of Bigelow and Reynolds (?). To make the sodium salt of quinizarin-6sulfonic acid ( 4 ) quinizarin, boric acid, and 20 per cent fuming sulfuric acid are heated to 90-100’ C. fpr 1.5 hours, .after which 60 per cent fuming sulfuric acid containing mercuric sulfate is added; the temperature is raised to.170-180’ C., and kept constant until the melt becomes soluble in water. The mass iw then poured into water and the quinizarin-6-sulfonic acid is neutralized with sodium carLonate and salted out with sodium chloride. Red cryfitals are obtained, which are purified by recrystallization from alcohol. The sodium salt of quinizarin-6-sulfonic acid is soluble in water and concentrated sulfuric acid. Approximately 0.1 N solutions of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, sodium hydroxide, and sodium carbonate, and a 0.2. N solution of sodium hydroxide were prepared, as was the universal buffer mixture of Prideaux and Ward (5), which gives pH values between 2 and 12. A 0.1 prr cent aqueous solution of the sodium salt of quiniearin-6sulfonic acid is used. Color Ranges and Constants of Indicators This indicator changes from a yellow color under distinctly acid conditions t o pink and finally t o blue-violet as alkali is added. The change from yellow t o pink is sharp, and that from pink to blue-violet is gradual. The color ranges were obtained through the use of a series of buffer solutions, made by titrating the Prideaux and Ward universal buffer solution with 0.2 N sodium hydroxide. All buffer solutions employed in this investigation were checked b y means of a Beckman p H meter, The p H range for the change from yellow t o pink was found to be 7.1 to 9.1, and from pink t o blue-violet 9.1 to 11.5 at 20” c. The ionization constants were determined b y using a Bausch & Lomb hydrogen-ion colorimeter. The pKa for the first hydrogen was found t o be 8.2 and for t h e second hydrogen 10.7 at 20” C.
Titration Acid and base titrations were made b y using t h e appropriate indicator in each case. These were compared with
similar titrations made b y using a 0.1 per cent aqueous solution of the sodium salt of quinizarin-6-sulfonic acid as the indicator, the end point being the color change from yellow t o pink.
Discussion T h e preparation of the indicator required no special apparatus. The cost of preparation of the compound was less than that of phenolphthalein. The author found that in titrating acids with bases, the color change was sharper when using the sodium salt of quinizarin-6-sulfonic acid than when using phenolphthalein. In titrating bases with acids, the sodium salt of quinizarin-6-sulfonic acid gave a sharp color change, whereas phenolphthalein cannot be used so efficiently. This indicator can be used for colorimetric determinations of pH over the range from 7 to 11.5. TABLE I. TITRATIONS OF ACIDS WITH BASES“ Acid-Rase Ratio
Mean Deviation
Acid M1. HC1 29.00
Base, NaOH M1. 27.81
0.960
0.000
28 G6 29,40
27.47 27.91
0.959
0,951
-
0.000 0.001
HNOt 28.32
27.03
1.047
+0.001
27.61 27.47
1.050 1.055
+0.001 0.000
29.77
0.962
$0.001
30.24
0.959
-0.001
28.99 29.00 HCzHaOa 28.66 28.99 HzCzOil 28.66
Indicator
Na salt of quinizarinfi-sulfonic acid Phenolphthalein Methvl oranre
Na salt of quinizarinG-sulfonic acid Phenol hthalein Methyporange N a salt of quinizarin8-sulfonic acid Phenolphthalein
32.43 0.884 -0.001 N a salt of quinizarin6-sulfnnir acid 0.000 Phenolphthalein 28.32 32.02 0.883 a Values are means of several titrations, using volumes between 20 and 40 ml.
The sodium salt of quinizarin-6-sulfonic acid can be used as an indicator in the titration of strong acids with strong bases, and weak acids with strong bases.
Literature Cited (1) Bayer & Co., British Patent 17,743(July 27, 1914). (2) Bigelow and Reynolds, “Organic Syntheses”, Collective Vol. 1, by Gilman. p. 464, New York, John Wiley & Sons, 1932. (3) Farbenindustrie, I. G.,British Patent 308,359 (March 22, 1928). (4) Mildner, Hans, U. S. Patent (to General Aniline Works) 1,879,390 (September 27, 1933); German Patent 492,000 (March 23,
1928). (5) Prideaux and Ward, J . Chcm. SOC.(London), 125, 426.
