Complexes of Eriochrome Black T with Calcium and Magnesium ALLEN YOUNG and THOMAS R. SWEET McPherson Chemical Laboratory, The O h i o State University, Columbus 70, O h i o
ml. with 95% grain alcohol. After mixing, the solution was transferred to a 500-ml. Florence flask, which was fitted with a rubber stopper and a constricted glass tube that served as a vent. This was placed on a reciprocal motor-driven shaker for 0.5 hour. The solution was stored in the dark until it was used.
The complexes of the d>-eEriochrome Black T with the alkaline earth metals calcium and magnesium were studied by the method of continuous variations. Evidence is presented which indicates that l to l, 2 to l, and 3 to 1 complexes exist for both calcium and rnagnesium. Previous literature on the subject has described only a l to l complex for calcium and a l to l and a 2 to 1 complex for magnesium.
OH
EXPERIMENTAL
All p H measurements were made with a Beckman Model G p H meter equipped with a Beckman Type E micro glass electrode and a micro saturated calomel electrode. The absorption measurements were made with a Beckman Model DU quartz spectrophotometer equipped with 5-mm. Corex cells. All measurements were made against water as the blank solution. The slit width was adjusted so that the sensitivity knob was maintained a t or very near its counterclockwise limit-Le., a minimum slit width was used for each reading.
HO
T
HE dye Eriochrome Black T, has been used to a large extent as a metal ion indicator in analytical chemistry (f-8). Perhaps its most widely known application as a metal ion indicator is in the determination of the total calcium and magnesium content of water, where ethylenediaminetetraacetic acid is used as the titrant. Schwarzenbach and Biederniann (9) described the indicator action of the dye with variation of p H and have determined the following ionization constants; K2 = [H+][HF--]/[HZF-] = and K , = [H+][F--3]/[HF-z] = 10-11J5. The form H2F- is red, the form HF-2 is blue, and the form F-3 has been described as orange. Schwarzenbach and Biedermann (9) have shown that both calcium and magnesium form 1 to 1 complexes with the F-3 anion and Harvey, Komarmy, and Wyatt (6) reported a 2 to 1 complex for magnesium a t p H 10.1. Some preliminary work on a spectrophotometric determination of calcium and magnesium led the present authors to believe that other complexes in addition to those mentioned existed in solutions containing the dye and calcium or magnesium. In the present paper, the method of continuous variations has been used in order to determine the various calrium and magnesium complexes that are formed with the dye, E~iochromeBlack T.
W A V E LENGTH. m y
Figure 1. -4bsorption curves 1. 2. 3. 4. 5. 0.
REAGENTS
Water. Triple-distilled water was used in all the experiments. I t s conductance was less than 1 micromho. Buffers. Buffers in the region p H 8.4 to 10 were prepared by mixing 25 ml. of concentrated ammonium hydroxide and the required volume of concentrated hydrochloric acid with sufficient water to make a final volume of approximately 500 ml. Buffers in the region pH 10 to 12 were prepared by mixing 75 ml. of piperidine and the required volume of concentrated hydrochloric acid with sufficient water to make a final volume of approximately 500 ml. -411 buffer solutions were stored in polyethylene bottles. Calcium Solution, 0.001M. A 0.1000-gram sample of calcium carbonate (Hach Chemical Co., 99.97yo pure) was dissolved in 0.3 ml. of concentrated hydrochloric acid and the solution was . diluted with water to 1 liter. Magnesium Solution, 0.001M. A 0.0913-gram sample of 3MgC03.Mg(OH)2.3H20 (Baker and Adamson, 99.96% pure) was dissolved in 0.3 ml. of concentrated hydrochloric acid and this was diluted with water to 1 liter. Dye Solution, 8.66 X 10-4M. A 0.100-gram sample of Eriochrome Black T (W. H. and L. D. Betz) was transferred to a 250ml. volumetric flask by means of small portions of water. The total volume of water used was about 15 ml. One milliliter of pH 11.70 buffer was added and the solution was diluted to 250
4.33 x 10-5M 4.33 X 10-6M 4.33 X 10-5-W 0 4.33 X 10-5.W 0
hlg, 12.99 Ca, 12.99 M g , 12.99 , 12.99 Ca, 12.99 , 12.99
X lO-5M dye, pH 11.50 X 10-6-W dye, pH 11.50 X lO-6M dye, pH 9.32 x lO-6.W dye, pH 1 l . d X lo-3.W dye, pH 9.32 X 10-aM dye, pH 9.32
The solutions for Figure 1 were prepared by mixing 5.0 ml. of water or 5.0 ml. of 4.33 X 10-4 metal solution (prepared by diluting 43.3 ml. of the 0.00lM metal to 100 ml.) with 7.5 ml. of the 8.66 X lO-'M dye and 12.5 ml. of 95% grain alcohol. The appropriate volume of buffer solution (5.0 ml. of p H 9.32 buffer or 2.5 ml. of pH 11.50 buffer) was added and the solution was diluted to 50 ml. with water. For the continuous variations experiments (see Figures 2 through 4), solution A is 8.66 X 10-4,U dye and solution B is 8.66 X 10-4N calcium or magnesium (86.6 ml. of the 0.001M metal solution diluted to 100 ml. with water). Volumes of A and B totaling 10 ml. were pipetted into 50-ml. volumetric flasks. Five milliliters of one of the ammonium hydroxideammonium chloride buffers (for pH values between 8.4 and lo), 2.5 ml. of one of the piperidinepiperidine hydrochloride buff ers 418
V O L U M E 27, NO. 3, M A R C H 1 9 5 5
419 In the continuous variations experiments, the value of n, the number of ligands per cation, is obtained from the relation
0.0
0.2
0.4 0.6 Fraction of Dye, X
0.8
1.0
Figure 2. Continuous variation for magnesiiini at pH 9.52 h = 540
nip, CIIg
+
Cdke =
1.732
n = 2.08
x iw4.v, sma,.
=
0.675,
X,,X.
, where X,,,. represents the fraction of solution 1- x m a x , B present a t the point where the difference curve Y isamaxinium. The value obtained for n corresponds to t'hat complex which predominates a t the pH of measurement. It was found that n varied with the pH and that a t certain p H values no one complex predominates. For magnesium the following values of n were obtained by the method of continuous variations: 1.08 a t pH 8.41, 2.08 a t p H 9.52, 2.33 a t pH 10.11, 2.84 a t p H 10.61, and 3.00 a t p H 11.70. These values indicate a 1 to 1 complex a t p H 8.41, a 2 to 1 complex a t pH 9.52, solutions that are composed of rnixhres of the 2 to 1 and 3 to 1 complexes a t pH 10.11 and 10.61, and a 3 to 1 complexat pH 11.70. The formation of higher complexes increases as the pH increases. This is to be cxpected ifitisassumed that the metal ion coordinates with the F--- anion, since the proportion of F--- ion in the solution is controlled by the pH and increases as the pH becomes higher. n=-
07
0.200
n
Y
02
0.0
F r a c t i o n of Dye, X
Figure 3. Continuous variation for magnesium at pH 11.70 h = 540 l l l p , CIIE + Cdie = 1732 x 10-4.\f, X m a x = .07i, ! 1 = 3.00
(for p H values between 10 and 12), or 1 ml. of pure piperidine (for a pH of 12.4) were then added and the solutions were diluted to 50 ml. with water. These solutions were stored in the dark for 1 hour. Following this period of standing, their absorbance (defined as the function loglo __
I
Z.oln. blank>
0.6
0.4
0.8
1.0
Fraction o f Dye, X
Figure 4. h = j40
Continuous variation for calcium at pII 12.4
11111, CCa
+
Cdxe
=
1.732 x io-4.\1, zYrn,x
= 0.76,7i = 3.00
o m-
was measured a t 520, 530,
540, 550, and 560 mp. The curves marked Y represent the differences between the measured absorbance and the absorbance that would be obtained if complex formation had not taken place -i.e., the straight line of no reaction that can be drawn between the ends of the measured values. I n Figure 5, solution A is 4.33 X lO-4M with respect to the dye and 2.165 X 10-4Alfwith respect to magnesium ion-i.e., dye and cation are present in a 2 to 1 ratio in solution A. Solution B is 2.165 X lO-*M dye. Volumes of A and B totaling 20 ml. were pipetted into 50-ml. volumetric flasks. Two and one half milliliters of buffer were added and the solutions were diluted to 50 ml. with water. These were stored in the dark for 1 hour and then measured a t 630,640, and 650 mp. DISCUSSION
Figure 1is a series of absorption curves for the dye Eriochrome Black T with and without calcium and magnesium ions and illustrates the effect of changes of p H and the presence of metal ions.
Y
0.OOOvI
I
QO
0.2
Figure 5 .
I
I
I
I
I
I
0.4 Q6 0.8 Fraction of Solution E, X
i k,000
1.0
*Modified continuous variation for magnesium at pH 11.70
= 640 Illp, C l l g F P
+ Cd,e = 2.165 x w4,
xmax,
= 0.54,?Z = 3.18
For calcium, the following values of n m-ere obtained by the method of continuous variations: 2.1 a t p H 10.61,2.33atpH11.70, and 3.00 a t p H 12.4. A 2 to 1 complex is indicated for calcium a t pH 10.61. At p H 11.70 it appears that the calcium solution is composed mainly of both the 2 to 1 and 3 to 1 complexes. Since the calcium complexes are less stable than those of magnesium, it is necessary to use higher p H values in order to obtain values of TZ that are comparable to those found for magnesiumfor example, for magnesium, n = 2.33 a t p H 10.11, whereas for
420
ANALYTICAL CHEMISTRY
calcium n = 2.33 a t p H 11.70. By increasing the pH to 12.4
it was possible to obtain a solution that was composed primarily of the 3 to 1 calcium complex. The values given were all obtained from curves that were drawn a t 540 mp. Curves drawn a t 520, 530, 550, and 560 mfi are very similar and indicate the same values of n. A modified method of continuous variations that was used by Watters and Aaron (IO)in their study of copper pyrophosphate complexes was utilized in the present work in order to provide additional evidence for the presence of the 3 to 1 complex for magnesium. This is shown in Figure 5. The value of n, the number of ligands per cation, is obtained from the relation n = (2 - Xmax,)/(l- Xmx) where Xmx, represents the fraction of solution B present a t the point where the difference curve Y is a maximum. Since X,,, = 0.54, n = 3.18. This is reasonable since a maximum in the difference curve Y a t 0.50 would indicate that a 1 to 1 complex is formed between the 2 to 1 complex and the dye. This is the same as a 3 to 1 complex of dye with metal. A wave length of 640 m r was used because data a t 640 m r showed greater deviation from the straight line of no reartion than did data that was obtained when using wave lengths between 520 and 560 mu. Data obtained a t 630 and 650 mu resulted in curves that were very similar to those in Figure 5. This modified method of continuous variations was also used with calcium a t p H 11.7 and pH 12.4. The refiults were not so well defined as those for magnesium. Nevertheless, they indicate reaction between the 2 to l complex and the dye. CONCLUSIONS
T h e dye Eriochrome Black T forms 1 to 1, 2 to 1, and 3 to 1 complexes with magnesium and also with calcium.
Schwarzenbach and Biedermann (9) suggested that calcium and magnesium have a coordination number of 6 when they form 1 to 1 complexes with the dye. Their proposed formula for these complexes showed one bond with each of the phenolic oxygens, one with each of the azo nitrogens, and one with each of two water molecules. A possible explanation of the 3 to 1 complexes that are indicated in the present work is that the dye anion acts as a bidentate through the two phenolic oxygens or through one azo nitrogen and an adjacent phenolic oxygen, and that the alkaline earth metal ion has a coordination number of 6, thus forming an octahedral complex in whirh the spadl orbitals of the metal are involved in bond formation. LITERATURE CITED
(1) Beta, J. D., and Noll, C. A . , J . Am. Water W o r k s Assoc., 42, 49 (1950).
(2) Biedermann, W., and Schwarzenbach. G., Chimia (Switz.), 2, 56 (1948). (3) Cheng, K . L., Kurtz, T.. and Bray, R. H., ANAL.CHEY., 24, 1640 (1952). (4) . , Debnev. E. W.. Nature. 169. 1104 (1952). ( 5 ) Diehl, H., Goetz, C. -4., Hach, C. C.:J. Water W o r k s Assoc., 42. 40 - - (iwn.
Ah.
- 7
* - - - - I
(6) Harvey, A. E., Jr., Komarmy, J. AI., and Wyatt, G . M., ANAL. CHEM.,25, 498 (1953). (7) Hol, P. J., and Leedertse, G. C. H., Chem. Weekblad, 48, 181 (1952). (8) Kinnunen, J., and hIerikauto, B.. Chemist Analyst, 41, 76-9 (1952). (9) Schwarzenbach, G., and Biedermann, W., H e h . Chim. Acta, 31, 678 (1948). (10) Watters, J. I., andAaron, A, J . Am. C h e m Soc., 75, 611 (1953) REcmvan for review June 15, 1954. Accepted October 4, 1954. From a thesis presented to the Graduate School of The Ohio State University by Allen Young in partial fulfillment of the requirements for the degree of master of science.
New Organic Reagent for Silver and Copper BERNARD GEHAUF and JEROME GOLDENSON Chemical Corps Chemical and Radiological Laboratories, Army Chemical Center,
A red dye prepared from l-phenyl-3-methyl-5-pyrazolone, pyridine, sodium cyanide, and chloramine-T was found to give deep blue compounds with silver and cuprous ions. The sensitivity of a test for metals based on the use of this dye is 1 part in 600,000 for silver and 1 part in 250,000 for copper. As a reagent for silver, the dye can be used as an outside indicator for the titration of chlorides or silver.
I
N T H E course of a search for a satisfactory method of detecting microamounts of cyanides, a blue-green dye was obtained when a mixture of sodium cyanide, pyridine, and l-phenyl3-methyl-5-pyrazolone was treated with chloramine-T. While investigating the stability of this coloring matter under various conditions it was found that a red compound was formed when the blue dye was boiled for a short time in aqueous alkaline solution. Investigation of this new red compound, to which the name Zolon Red has been applied, proved that it is a true dyestuff with interesting properties as such but of even more interest because of its properties of forming deep blue insoluble compounds with silver and cuprous ions. This latter property was of sufficient interest to warrant an investigation of its possible uses as an organic analytical reagent. PREPARATION O F Z O W N R E D
Four grams of pyridine and 18 g r a m of l-phenyl-3-methyl-5pyrazolone were stirred to a uniform paste and diluted with
Md.
250 ml. of water. Two and one half grams of sodium cyanide were then added, and while stirring, 250 ml. of an aqueous solution containing 14 grams of chloramine-?' were added over a period of 10 minutes. A red color formed immediately, rapidly changing through purple to blue. When all of the chloramine-?' had been added, the stirring was continued until tests made by placing a drop of the reaction mixture on filter paper gave a pure blue spot with no trace of a red ring. The mixture was alloTved to stand until a thick paste of dye separated. This was then filtered with suction and the filtrate, which retained a considerable amount of dissolved dye, was treated with 20 grams of sodium chloride, and the salted out dye was added to the original filter cake. After being pressed down well on the filter, the cake was washed once by displacement with an equal volume of water. The blue-black dye paste was then transferred to the original reaction vessel and broken up into a thin paste with a small amount of water. TKOhundred and fifty milliliters of water and 20 grams of sodium carbonate were added, and the niivture mas brought to boiling. This was continued until the conversion to a red dye was complete. The conversion was followed by placing drops of the reaction mixture on filter paper and observing the colors displayed by the spot. When a clear red spot with no blue or purple center was obtained, the heating was terminated and the mixture was allowed to cool to room temperature. The thick deposit of red fibrous crystals n-hich separated was filtered off with suction and washed twice by displacement with a volume of water equal to that of the filter cake. The wet cake, which consisted of the sodium salt of the dye, was broken up in 500 ml. of water and reprecipitated as the free acid of the dvestuff by adding a slight excess of 10% hydrochloric acid. Thebrickred precipitate was filtered with suction, washed thoroughly with water, and dried. The product was very slightly soluble in water, freely soluble in
