An Improved Kurt Meyer Titration S. R. COOPER
AND
R. P. BARNES
How-ard University, Washington, D. C.
methyl alcohol. The resulting solution was cooled to -5' c. and an excess of an approximately 0.1 V . solution of bromine in absolute methyl alcohol n-as added. The solution was mixed added. The well, and a slight excess of diisobutylene consumed in adding the bromine and absorbing the excess of it was about 15 seconds. Then 5 ml. of a 10 per cent aqueous solution of potassium iodide were added and the mixture was warmed to 30" C. by dipping the flask in hot n-ater while swirling its contents around. The solution \vas alloIved to stand 5 to 10 minutes and was titrated ivith an approximately 0.1 N solution of sodium thiosulfate until the color had become a light yellow. Then 250 ml. of Water and ml. of a 0.6 Per cent Potato starch solution, which had been filtered, were added and the titration was continued to the disappearance of the blue color. Some titrations were made without using water and starch.
EYER (1) proposed the direct titratio11 of the enolic form of a tautomeric compo,ln~m+h an a~coholicbramine solution, and also an indirect bromine t'itration method. I n the indirect method the compound was dissolved in 96 per cent, alcohol and cooled to 10' C., and an excess of an alcoholic bromine solution was added, This excess was remored by adding a small amount of sodium thiosulfate solution. Then a potassium iodide solution was added, and the liberated iodine was titrated m$,h a solution of sodillm thiosulfate. Later ?Ifeyer and Kappelmeier ( 2 )proposed the use of 2-naphtho1, in place of sodium thiosulfate, to absorb the excess bromine. The authors have had some experience with this indirect titration method and have attempted t o improve upon its accuracy. 2-Kaphthol and its alcoholic solutions are usually colored brown, even after the compound has been carefully purified. This makes it difficult, in many cases, to ascertain the point a t which all the excess bromine has been removed, and also causes an error when the alcoholic solution containing free iodine is titrated with sodium thiosulfate until the yellow color due to iodine has been removed. This condition can be remedied by using a compound such as diisobutylene which will absorb bromine by forming a colorless bromide, but will not react with iodine t o form a stable compound. The purpose of this investigation was to ascertain if diisobutylene could be used in place of 2-naphthol in the indirect Kurt Meyer titration.
These titrat'ions were compared with others which were performed according to the indirect Kurt hleyer method, with the exception that after the potassium iodide solution had been added the titration was carried out as above. The results of these and the first titrations are giren in Table I. The sodium thiosulfate solution was st'andardized according to the method of Treadwell and Hall (4)using iodine as the primary standard. The mean of these titrations was 0.1003 N , and the average deyiation 1 part per 1000.
Discussion Solutions of bromine in et'hyl alcohol are not very stable, but a solution in methyl alcohol retains its strength for a longer time. Therefore absolute methyl alcohol was employed in preparing all the alcoholic solutions used. The proposed method gives better agreement Of than the original indirect Kurt lleyer method. Some experiments, not included in the table, which were performed by using the indirect Kurt ?\leyer method, gave variations of the same magnitude. The end point in the authors' titration is sharper and a blue color is al\\-ays produced with starch, while gray-blue colors are often obtained when Kurt Meyer titrations which employ 2-naphthol are performed under the same conditions. The amount of precipitate formed upon dilution in the original Kurt Illeyer titration is greater than that formed when the proposed method is employed. The authors have found it possible to titrate the liberated iodine without dilution and addition of starch if their procedure is used. The end point is sharp and the brown color due to excess 2-naphthol is not present to cause an error in the results. The excess of diisobutglene does not form a precipitate, but floats on the surface as an oil and gradually evaporates. The mean of the authors' titrations is 95.66 per cent. This represents the approximate percentage of enol under the conditions of the experiment. The authors believe that they have improved the Kurt Meyer titration because their titrations agree within 1 per cent, while the indirect Kurt Meyer titration gives variations as high as 7 per cent.
Preparation of Reagents The dibenzoylmethane was prepared according t o the method given by Pond, York, and Moore (s),and was further purified by repeated recrystallizations from methyl alcohol, yielding a practically colorless substance. The iodine was sublimed twice. An approximately 0.1 itsolution of sodium thiosulfate n-as prepared and allowed to stand for several months, protected from the atmosphere by a tube filled with soda lime. The diisobutylene \vas the practical grade obtained from the Eastman Kodak Company. -411 the other reagents were c . P . products.
Titrations A sample of dibenzoylmethane Ivas weighed, placed in a widenecked Erlenmexer flask, and dissolved 111 25 nil. of absolute
TABLE
I. TITRATIOS OF DIBEXZOYLI\IETHASE m-11" S O D I ~ . > I THIOSCLFATE SOLUTIOX
0.1 N Bromine Thiosulfate
CnHn02 Gram
Solution
0.2421 0,2407 0.2114 0.2651 0.1799 0.3489 0 2665 0 4505 0.2795 0 2257 0,2774 0.2035 0.1964 0 2206 0 2076 0 1991 0.2382 0 2551 0 2403 0.2486 0,2128 0.1797
25 25 25 25 25 40 35 52 30 25 30 25 25 25 25 25 30 30 35 30 30 30
M1,
Solution M1. 20.65 20.45 18.00 22.45 15.40 29.50 22.70 38 50 23.72 19,30 23 52 17 35 16.70 18 75 17.62 16 95 19.90 20.60 I9 85 21.00 18 00 15.75
Decolorizing Agent
Enol CibHi202
CaHis CsHis C6H16 CSHl6 C~HIE CsHis csH16 CaHis CsH16 C~H~E CBHX CeHis CaHi6 CsHia CsHi6 C8H16 CioH;OH CioHiOH CioH;OH CuH;OH CioH;OH Ci,HiOH
95.88 95.52 95,79 95.25 96.15 95.16 95.70 96 07 95.43 96.07 95.34 95.88 95.70 95.52 95.43 95 i o 93.74 90.85 92.86 94.97 95 07 9s 52
%
Literature Cited (1) Meyer, K . H . , Ann., 380, 212 (1911). ( 2 ) Meyer, K. H., and Kappelmeier, Paul, Ber., 44, 2718 (1911). (3) Pond, F. J., Tork, H. J., and Moore, B. L., J . Am. Chem. Soc., 23, 789 (1901). (4) Treadwell, F. P., and Hall, T. T., "Analytical Chemistry," 7th ed., Vol. 11, p. 552, New Tork, John Wiley K- Sons. 1930.
RECEIVEDApril
379
5, 1938.
Systematic Scheme of Identification TABLEI. IDPSTIFICA9
6
R
1 Ephedrine
2 3 4 5
6 7 8 9 10 11 12 13 14 15 16 17
1s 19
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
10
-
Cocaine Procaine Colchicine Cotarnine Theobromine Arecoline Caffeipe Nicotine Piperine Veratrine Quinidine Quinine Heroine Hyoscyamine Atropine Hashish Codeine Apomorphine
14 -
It br Y It br I’
G Or R
-
R
dk G dk R
Br br R y
-A G br R r Br -
Ro Br
Y
-
L
Y
-
T
P
PkAV dk R
OrR
It Or T 01 GAbr Y
-
-
-
-
YA YA It 1lc Or YAOr Y
v
dk G dk G
Yohimbine Berberine Strychnine Brucine Physostigmine Pilocarpine Dilaudid Hydrastine Papaverine Thebaine
13
dk br Y
L -
I t I A b l I’
PAdk G dty G P
-
O r RAY
R
-
PA01 G
dk R VAOr R
Or
T
Or R P br R dty G dk br R br G
Or R Or R
Or
It Or YA Or Rdbr br R
RABr
-
T
Or R
-
bd R Or R
-
Lupanine Lupinine Monolupine TriluDine Deltiline Narcotine Cinchonidine Emetine Scopolamine
B bd bl Br br ch Cr dk dkng dty
= = = = = = = = = =
Or R R
-
-
br R
blue blood bluish brown brownish cherry crimson dark darkening dirty
ein fl
fd G gr
L
It 01 Or
Or R It Y It Or
Or R
Y
emerald fluorescence fading green greenish lavender light = olive = orange
= = = = = = =
C
Literature Cited
HERIICAL literature abounds with individual tests for alkaloids, but hitherto they have not been applied to all alkaloids and no systematic method for their identification has been available. The author has found that known reactions, modifications of known reactions, and new color reactions with simple reagents will enable one to identify forty-two of the more common alkaloids. The alkaloids in Table I are to be identified in the order given. I n all cases a few milligrams of each are treated a t room temperature, unless otherwise directed, with a fen cubic centimeters of the reagent shown in Table 11, so that effects of all reagents used on these alkaloids are now determined and disclosed. (For various confirmatory tests, see especially Mercks Reagenzien-T’erzeichnis, 1932.)
Acknowledgment The writer is greatly indebted to H. J. Snslinger of the Bureau of Sarcotics, J. F. Couch of the Bureau of Animal Industry, A. W. Ingersoll of Vanderbilt University, E. LaV. Jackson of Emory University, J. C. McManus of the U. S. Food and Drug Administration, and L. F. Small of the University of Virginia for providing some of the samples of alkaloids used in this work. 380
Allen, Merck Rept., 9, 112 (1900). Andr6, Chem. Zentr., 1904, 1180. Archetti, Z . anal. Chem., 40, 415 (1901). Armani and Barboni, Chem.-Ztg., 34, 448 (1910). Arnold, 2. anal. Chem., 23, 228-34 (1884). Biel, Ibid., 25, 452-3 (1886). Eiloart, Ibid., 25, 248-9 (1886). Ekkert, Pharm. ZentraZkalZe, 66, 36 (1925). Goldner, Pharm. Ztg., 34, 471 (1889). Johannson, Merck Rept., 10, 41 (1901). Kippenberger, Nachw. v. Gijtstofen, 1897, 104. Marchand, Chem. Zentr., 1849, 29. Martin, private correspondence. Miranda, Rev.jaarm. chilena, 1904, 317. Peset-Buendia, A n d e s SOC. espail. fis. guim., 14, 257-63 ( 1 9 i h . Richter, Apoth. Ztg., 24, 667 (1909). Robins, Pharm. Zentr., 17, 154 (1876). Schmidt, Arch. Pharm., 247, 141-9 (1909). Sonnenachein, 2. anal. Chem., 11, 440 (1872). Trapp, Canstatt’s Jahresber. (Vandenhoek & Ruprecht. Gottingen), 147 (1864). (21) Vitali, 2. anal. Chem., 20, 563 (1881). ( 2 2 ) Wagenaar, Pharm. lT’eebbZad, 65, 1213-16 (19281. (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20)
RECEIVED March 30. 1938
