Table VIII. Determination o f Tin in Presence of Extraneous Organic Matter
Method Organic matter destroyed Xithpermanganate WithHk30, "03 Organic matter not destroyed
+
Tin Found, % 5 80 5 i9
5 80 5 80
5 01
4 64
manganate can also be used for traces of organic, if preferred.
ORGANICMATTERPRESENT.Add 20 ml. of sulfuric acid, place on a hot plate, evaporate until strong fumes of sulfur trioxide appear and continue heating on the plate or over an open Meker flame until the organic matter is thoroughly charred. Cool, add 10 to 25 ml. (or more, if the sample contains much organic matter) of potassium permanganate solution (4%) and heat again until fumes are evident. It is not necessary to continue fuming once the solution has been brought to that point. Cool, dilute with 80 ml. of water, add 10 ml. of hydrochloric acid, and bring to a boil to dissolve any manganese dioxide and to remove chlorine. Adjust the volume after boiling, if necessary. Then add 90 ml. of hydrochloric acid and 100 ml. of water, and reduce and titrate as described above.
Procedure. TRACEOF ORGANIC. Weigh or measure accurately a sample of suitable size, add 20 ml. of sulfuric acid, place i t on a hot plate, and evaporate until strong fumes of sulfur trioxide appear. If the solution darkens slightly, indicating the presence of a small amount of organic matter, Extraneous organic matter can be carefully add 4 drops of perchloric acid destroyed with sulfuric and nitric acids (70 to 72%) in 1-drop portions with an as well as with potassium permanganate interval of about 15 seconds between nithout loss of tin (Table VIII). Poeach addition. Cool, add 80 ml. of tassium permanganate is to be prewater and 100 ml. of hydrochloric acid ferred, however, because it is less teand then 100 ml. of additional water. dious, especially in the presence of Reduce and titrate as described under certain types of organic matter. standardization.
LITERATURE CITED
(1) Belcher, R., Gibbons, D., Sykes, A,
Mikrochemie ver. Mikrochim. Acta 4 0 ,
85 (1952). (2) Evans, B. S., (3) Farnsaorth, CHEW26, 735 (4) Gilman, H.,
Analyst 56, 171 (1931).
M., Pekola, J., ANAL. (1954).
King, W. B , J . Am. Chem. Soc. 51, 1213 (1929). (5) Gilman, H., Rosenberg, S. D., Ibid., 75, 3592 (1953). (6) Goldberg, C., Iron Age 171, 130 (1953). (7) Hallett, L. T., Ax.4~.CHEK 14, 981 (1942). (8) Holtje, R., 2.anorg. Chem. 198, 287 (1931). (9) Kinnunen, J., Merikanto, B., Chemist Analyst 4 1 , 4 (1952). (10) Xocheshkov, I. A,, Ber. deut. chem. Ges. 61, 1659 (1928). (11) Krause, E., Becker, R., Zbid., 53B, 178 (1920). (12) Pfeiffer, P., 2. anorg. 11 allgem. Chem. 68. 102 (1910). (13) Rappdrt, R.; F o u h r y 8 1 , 115 (1953). (14) Strafford, X., Mikrochim. Acta 2 , 306 (1937).
RECEIVEDfor review May 21, 1958. Accepted August 26, 1958.
Eriochrome Black T and its Calcium and Magnesium Derivatives HARVEY DlEHL and FREDERICK LINDSTROM' Department o f Chemistry, Iowa State College, Ames, Iowa ,In agreement with the findings of Schwarzenbach and contrary to those of two American groups, Eriochrome Black T forms only 1 to 1 compounds with calcium and magnesium at pH 8 to 10. The apparent stability constants for the compounds and the acid dissociation constants found agree with the values given b y Schwarzenbach. These measurements were made a t constant ionic strength using a crystalline dimethylammonium salt of Eriochrome Black T. Commercial preparations of Eriochrome Black T are impure, their water content varies with the condition of storage, and they may not be used directly in studies involving the method of continuous variations. The highly purified dye i s no more stable in solution than commercial preparations but a solution of the magnesium compound may be stored for considerably longer periods.
S
CHWARZENBACH and
Biedermann (9), in the first paper on the use of azo dyes as indicators in complexometric titrations, investigated four dyes, Erio-
414
ANALYTICAL CHEMISTRY
chrome Blue Black B. Eriochrome Blue Black R, Eriochrome Black T, and Eriochrome Black A. These dyes are designated 239, 240, 241, and 242, respectively,in the Schultz-Lehmann Farbstofftabellen and 201, 202, 203, and 204 in the Colour Index. Each of these o,o'dihydroxyazo dyes had the property of forming calcium and magnesium derivatives with colors different from those of the dyes themselves. All of the dyes nere useful as indicators in complexometric titrations with (ethylenedinitri1o)tetraacetic acid (EDTA). Schwarzenbach and Biedermann found in all cases that the ratio of dye to calcium or magnesium was 1 to 1. They further measured the acid dissociation constants of the dyes and the formation constants of the metal derivatives. From these constants, they showed that Eriochrome Black T was the most sensitive of the four dyes for the detection of small amounts of magnesium and therefore, presumably, best as a n indicator for complexometric titrations. Contrary to these findings, two American groups using the method of continuous variations have reported that Erio-
chrome Black T and magnesium coinbine in the ratio 2 to 1 a t p H 10.1 (4, and with calcium and magnesium in the ratio of 1 to 1, 2 to 1, and 3 to 1, tlepending on p H ( l a ) . A series of o-hydroxyazo and 0.0'-dihydroxyazo dyes was investigated by Diehl and Ellingboe ( S ) , who found that two hydroxy groups ortho to the azo group are necessary for the union of calcium and magnesium with the dyestuff, and that with all of the dyes studied the combining ratio was 1 to 1, irrespective of pH. The work reported deals with the purification and properties of Eriochrome Black T and the nature of its alkaline earth derivatives. EXPERIMENTAL
Apparatus and Materials. All pH measurements rvere made using a Beckman Model G p H meter with a Type E glass electrode. Prior t o all measurements, the meter was 1 Present address, Clemson College, Clemson, S. C.
solve in this concentration of acid standardized against an appropriate and did not swell or assume the propSational Bureau of Standards reference erties of a colloid as it did when treated buffer ( I ) , phthalate (4.01 at 25'), with water. The slurry was stirred and borax Dhosohate (6.86 a t 25"), ,, for several minutes and filtered on a &LISat 250j. Certain individual absorption measfritted-glass funnel. This process was urements were made using a Beckrepeated with another 500 ml. of 1 to man D C spectrophotometer. Absorp5 hydrochloric acid, a t which point 48 tion spectra were obtained on a Cary grams of salt had been removed. The Rlodel 12 recording spectrophotometer. material was then air-dried. All solutions were prepared in boroThe acid-washed dye was extracted silicate glassware using distilled and with benzene for 12 hours in a Soxhlet deionized water and were stored in extractor. The benzene was evapplastic containers. All inorganic chemorated, yielding a yellowish, crystalline icals used were of reagent grade quality. material of indefinite melting point, and The organic chemicals were purified as the residual dye was air-dried. needed by recrystallization or redisThe dye was desalted again with tillation. The magnesium standard so1 liter of 1 to 5 hydrochloric acid, bringing the total amount of salt relutions were prepared using reagent grade magnesium acetate (% calcium = moved to 54.5 grams. All of the acid 0.001) and their concentration was extracts contained appreciable amounts checked by EDTA titrations. The of iron. EDTA solution was in turn standardized The desalted dye was recrystallized from dimethylformamide. The dye was against calcium carbonate and metallic zinc. The calcium carbonate was a very soluble in dimethylformamide and product of special primary standard produced heat on dissolving. The dipurity supplied by the Mallinckrodt methylformamide solution, saturated Chemical Works on special order. The with the dye a t the boiling point, was zinc used as a primary standard was allowed to cool slowly. Three crystalreagcnt grade material, assay 100.O~o. line fractions were collected successively The standard calcium solutions were and each was washed with benzene. A prepared by dissolving weighed total of 85.5 grams of fine red needles amounts of the pure calcium carbonate was obtained. The mother liquor was in dilute hydrochloric acid, evaporating treated with benzene and the remainto dryness, and diluting to volume. ing dye precipitated. This yielded a All dye solutions were prepared using further 50 grams of amorphous dye. the crystalline dimethylammonium salt The crystalline material so obtained prepared as described below and the was found to be the dimethylammonium measurements made within 2 hours of salt. Found (Huffman Rlicroanalytical their preparation. Laboratories): C, 53.37; H , 4.28; So that all absorption and pH measN', 10.99; S, 6.30; 0 (by difference), urements could be made on solutions 24.73. Calculated for CZOHI207?J3S of constant ionic strength ( p = 0.100), (CH3)zKHz*1/2Hz0: C, 53.54; H, 4.29; the procedure described by Bates was N, 11.35; S,6.50; 0,24.32. Dimethylemployed in designing buffers for each amine was determined by distillation p H range for the absorption measurewith sodium hydroxide, collection of ments (1). For an ionic strength of the amine, and titration with acid: p = 0.100, a stock solution, A , was found, 9.36, 9.10, 9.04, 9.14, average prepared containing 0.05M of a salt 9.16y0 dimethvlamine ; calculated 9.14. of a monobasic weak acid or of a salt The amine was identified as a secondary of a monoacidic weak base and 0.05M amine by the Hinsberg test and as of potassium chloride. The p H was dimethvlamine as the Dhenvlthiourea varied by adding various amounts of a derivat'ive; melting p o h t 1'34-7' restock solution, B, which contained either aorted (10). 135'. 0.2M sodium hydroxide or hydrochloric About 2 grams of the crystalline acid and 0.1M potassium chloride. material was dissolved in 100 ml. of For p H values near 7.5, sodium p20y0 dimethylformamide and the solunitrophenolate and hydrochloric acid tion was titrated potentiometrically were used. This buffer does not abvvith 0.1N sodium hydroxide using a sorb light in the wave length region Beckman Model H 2 pH meter. After investigated. For values near p H 8.0, the first few drops, the solution changed trishydroxymethylmethylammonium to a bright blue, indicating that the chloride and sodium hydroxide were proton of the sulfonic acid group had used; near pH 10.0, ethanolammonium already been neutralized. A sharp end chloride and sodium hydroxide; near point was obtained, which indicated pH 11.0, piperidinium chloride and the neutralization of the more acidic of sodium hydroxide. Potassium chloride the two hydroxyl groups. The neutralwas added to the metal and dye stock ization equivalent was found to be solutions so that all resulting mixtures 494.9; calculated, 493.5. were at constant ionic strength ( p = A sample of the crystals was dried in 0.100). a vacuum desiccator over anhydrous Eriochrome Black T Dimethylammagnesium perchlorate. The loss in monium Salt. Two hundred grams weight corresponded to 1.75% water; of practical grade Eastman Kodak calculated for 0.5 molecule of water, Co. 1- (l-hydroxy-2-naphthylazo)-61.83%. nitro-2-naphthol-4-sulfonic acid soAn attempt to obtain a melting point dium salt was desalted by dissolving n.as unsuccessful. When heated in the it away from the dye by stirring the thermobalance, the material showed mixture with 500 ml. of 1 to 5 hydrolittle or no change in weight until an chloric acid. The dye did not disexplosive loss occurred near 280'.
The absorbancy of each of the three crystalline fractions was measured using the Beckman DU spectrophotometer a t 620 mp and pH 10 and the values of E::. of 656.6, 654.4, and 653.0 were found. In a similar manner, the absorbancy for the fraction precipitated by benzene was E:: = 424.6 indicating serious contamination. Purity of Commercial Preparations of Eriochrome Black T. The absorbancy of sereral commercial samples of Eriochrome Black T Jyas measured and compared to the purified material described above (E::: = 656 a t 620 mp, pH 10). The values obtained for E:,", and the indicated purity m r e , 392 (59.8%), 383 (58.4%) , 404 (61.5%) , 371 (56.5%) , 403 (61.4%), and 443 (67.5%). Among these samples were the materials supplied by the following concerns: Hach Chemical Co., K&K Laboratories, Mathieson Co., W. D. & L. D. Betz, Hartman-Leddon Co., Inc., and Eastman Kodak Co. Dyestuffs are often precipitated from solution by the addition of salts and are notoriously contaminated with starting materials and salts; Eriochrome Black T is no exception. (Eriochrome Black T, purified by a process similar to the procedure described above, is available from the G. Frederick Smith Chemical Co.) Under a microscope commercial samples of the dye show many regular, transparent crystals among the dye particles. These impurities are not harmful when the material is used as a dye or indicator. The absorption spectra of the pure dye were obtained a t different dye concentrations a t pH 10, and ionic strength of p = 0.100, mith a cell length of 1 cm. The spectra were the same as reported by Schwarzenbach ( 8 ) , except for a higher level of absorption. A plot of absorbancy vs. concentration was made from the spectra for 650, 615, 546, and 470 mp. The plots were strictly linear except for 650 mp, which starts to fall off a little above a concentration of 2 X M. Using the plot for 615 mp, the maximum, the molar extinction coefficient (absorptivity) was 32,300. Eriochrome Black T, Acid Form. The crystalline diniethylammonium salt was repeatedly treated with dilute hydrochloric acid to form the insoluble free acid and the material air-dried. It was then dissolved in alcohol, and the solution was filtered and evaporated. The remaining semicrystalline mass \vas air-dried. A sample of this material was dried to constant weight in a vacuum desiccator over anhydrous magnesium perchlorate. The loss in weight was 8.6670. The sample was then stored in a 31% relative humidity hygrostat. The gain in weight was 6.9670. After storing to constant weight in a 56% hygrostat, the gain in weight relative to the anhydrous VOL. 31,
NO. 3, MARCH 1959
415
T
PH
Figure 1. Spectrophotometric determination of acid (phenolic) dissociation constants of Eriochrome Black T A, 61 5 mp; p, 0.1 00
material was 13.60%. None of these percentages could be compared with the calculated percentage of water present in an integral or half integral hydrate, 14.09% water being the value for a four hydrate. When heated in the thermobalance, the air-dried material started to lose weight a t 70". It continued to lose weight until it exploded a t 223". Acid Dissociation Constants of Eriochrome Black T. As pointed out by Schwarxenbach, the sulfonic acid group on Eriochrome Black T is a strong acid and is not of direct interest in the functioning of the dye as a metal ion indicator. Rather, the phenolic hydrogen atoms are important in the basic solutions in which the metal-dye interaction occurs. A new measurement of the acid dissociation constants of the two phenolic hydrogen atoms was made on the purified dimethylammonium salt of the dye using the spectrophotometer. A series of solutions of Eriochrome Black T of varying pH and constant ionic strength was prepared in the following manner: A solution of the dye was prepared by dissolving 0.1226 gram of the crystalline dimethylammonium salt in 500.0 ml. of 0.100M potassium chloride. Ten milliliters of this solution was placed in each flask, followed by 20.0 ml. of constant ionic strength buffer stock solution A (Apparatus and Materials). Stock solution B was added to adjust the pH to the desired value and then sufficient 0.100M potassium chloride to bring the volume to 100.0 ml. The absorbancy was measured using the Gary spectrophotometer, 1-cm. cells. For the solution above p H 13,5.6 grams of potassium hydroxide was added to the solution of the dye and the mixture diluted t o 100.0 ml. with water; solutions of such high p H cannot have an ionic strength of 0.100. The absorbancy a t 615 mp is plotted as a function of pH in Figure 1. This absorbancy represents the concentration of the species HD- (Eriochrome Black 416
ANALYTICAL CHEMISTRY
= HaD); the mid-point of the low pH portion of the curve represents pK1, and the mid-point of the high p H portion, pK2. (Strictly pKl should refer to the hydrogen of the sulfonic acid but the Schwarzenbach notation is followed here, K1 and K z referring to the phenolic hydrogen atoms.) Combining Ratio and Stability Constants of Eriochrome Black T Compounds with Calcium and Magnesium, Log-Ratio Method (9, 3, 8, 7). For nMg = Mg,D the reaction H D H in which H D represents the uncomplexed dye in solution between p H 8 and 10 and in which the charges are neglected, the equilibrium expression
+
4 L O G K,
:
(E
+
is
u -4
-3 LOG [Mg'q
Figure 2. Black T
-2
-I
0-'
Log-ratio plot of Eriochrome
Magnesium at p H 81 p, 0.1 00; A, 6 1 5 mp
The apparent stability constant, Kn
=
4
K/[Hl
may be introduced giving the expression used by Schwarxenbach (8)
Casting the latter equation into logarithmic form and rearranging gives the linear equation
-
log [MgnD]/[HD] =
- 0
-
n log [L\Ig] f log Kh.
The first term in this equation can be obtained from the absorption spectra of a series of solutions which have the same total dye concentration but different concentrations of magnesium. The second term contains the concentration of free magnesium in solution. The success of this method depends on the complexes having such a low Stability that the concentration of free magnesium in solution is essentially the same as the total amount of magnesium added. The plot of log [Mg,D]/ [HD]us. log [Mg] is thus linear with slope n and intercept Kh (Figures 2 and 3). The experimental work was carried out as follows: I n each 100-ml. volumetric flask in a series were placed 10.0 ml. of a solution containing 0.2422 gram of the dimethylammonium salt in 1000 ml. of 0.100M potassium chloride solution, and 10.0 ml. of the pH 8 buffer, p = 0.100. The first flask was then diluted to the mark with 0.100M potassium chloride. The remaining flasks were treated with varying amounts of magnesium acetate solution, p = 0.100, the last solution containing a large excess of magnesium to provide the spectrum of the magnesium complex. The solutions were diluted to the mark with 0.100M potassium chloride, the p H checked, and all found to be 8.0. The absorption spectra of the solutions were then obtained. The ratio [MgnD]/[HD] was obtained from the
-4
-3
-2
-I
0
L O G [Go*]
Figure 3. Black T
Log-ratio plot of Eriochrome
Calcium at p H 10, p, 0.1001 A, 615 mp
absorption data using the relationship developed as follows: By the law of additive absorbancies the absorbancy of each of the solutions, A = €HD[HD] €M~,D[M~,D], where t represents the molar extinction coefficient. For the solution containing no magnesium, AHD = [D]; for the solution with excess magnesium, A M ~ , D = E M ~ , , D [D]. The total dye concentration is given by [D] = [Mg,D] [HD]. Substitution and rearrangement give : A=.-----AHD[HDI + A M ~ "[MgtDI. D [Dl ID1 ' AID1 = AHD[HD]f AME,D[M~~DI ; A[HD] f A[Mg,D] = AHD[HD]f A Y g n D [MgnDI ;
+
+
[MgnD]( A - AY,,D)=[HDI (AHD - A i ; AHD - A -[MgnDl = [HD] A There are no concentration terms on the right. The data and method of calculation are given in Table I. The combining
Table 1.
Log-Ratio Method for Magnesium and Dye
pH, 8.00;
p
0.100; and A, 615 mp
AED - A log A - AM*,,D IMgl X 10’ 0 I
1.78 3.16 5.62
10.00
17.80 31.60 56.20 Excess Slope or n
=
log [Mg] -4.00
-3.75 -3.50 -3.25 -3.00 -2.75 -2.50 -2.25
1.09. Log Kh
=
A 1.60 1.40 1.28 1.12 0.92 0.69 0.51 0.38 0.32 0.225 3.60.
...
0.20 0.32 0.48 0.68 0.91
1.09 1.22 1.28
...
1.37 1.17 1.05 0.89 0.69 0.46 0.28 0.15 0.09
...
-01767 -0.516 -0.268 -0.007 0.296 0.590 0.910 1.152 ...
M O L E % MAGNESIUM
Figure 4. Continuous variations plot of Eriochrome Black T Magnesium at pH 10; p, 0.100
ratio and apparent stability constant are given in Figure 2. In a similar manner the combining ratio of the calcium-dye complex a t p H 10 was measured (Figure 3). The magnesium-dye complex a t pH 10 is too stable to measure by the above method, so the continuous variations method was employed. Method of Continuous Variations ( 5 , l l ) . A 1 X 10-4M magnesium solution was prepared by quantitatively diluting a standard magnesium solution. A 3tandard dye solution of the same concentration was prepared by dissolving 0.2422 gram of the crystalline dimethylammonium salt in 500 ml. of water and diluting to volume. This solution was 0.982 X lO-*M, for a t the time this solution was prepared, it was not known that the crystalline dimethylammonium salt contained about 0.5 mole of water. Both solutions were adjusted to p = 0.100 with potassium chloride. To each of a series of ten 100-ml. volumetric flasks, 10 ml. of pH 10 buffer was added. Then to each flask, in order, 0, 5, 10, 15, 20, 25, 30, 35, 40, and 45 ml. of magnesium solution and 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5 ml. of the dye solution were added. The solutions were diluted to volume with 0.1OOiM potassium chloride. All of the solutions were of p H 10.0. The absorption spectra were obtained and continuous variations plots were made a t wave lengths 650, 615, 546, and 470 mp (Figure 4). The apparent stability constant was calculated after obtaining the fraction of the complex which was dissociated obtained in the following manner from the continuous variations plots: The straight-line portion of the plots n as extended until the lines intersected. This nould be the plot obtained if the reaction were quantitative. The fraction dissociated was obtained by dividing the
Table
II.
Summary of Results on Combining Ratios and Formation Constants of Eriochrome Black T with Magnesium and Calcium
Schwarzenbach and Biedermann (8, 9) This Work Complex combining ratio M :dye Mg pH 8 1:l 1:1.09 Mg pH 10 1:1 1: 1 Ca pH 10 1:1.04 1:l pK,a*b 6 . 3 (p = 0.008) 6.91 (p’= 0.100) 6.9 ( p = 0.08)c 11.55 (p = 0.08) 11.50 ( p = 0.100) P K ~rbQ 3.60 ( p = 0.100) log Ks for Mg 3.45 (p = 0.10) 5.44 (p = 0.10) 5.75 ( p = 0.100) log Kiofor Mg 3.72 ( p = 0.100) log Klofor Ca 3.84 (p = 0.10) 0 . b Second and third replaceable hydrogen atoms of molecule. c Value obtained from inspection of graph in (8). Item Studied
distance from the maximum of the plot to the intersection of the straight lines by the distance from the intersection to the horizontal axis. The values of the fraction dissociated were 0.245 (615 mp), 0.233 (650 mp), 0.219 (546 mp), and 0.233 (470 mg); average 0.233. When the fraction dissociated is designated as d, the apparent stability constant Kh = where Cois the concentration of the complex in solution assuming no The dissociation; Cb = 2.5 X value obtained was Kh = 5.64 X IO6 and thelog K h = 5.75 =k 0.10.
w,
RESULTS AND DISCUSSION
Having prepared a crystalline form of Eriochrome Black T, it was possible to determine with some certainty the combining ratio with magnesium and calcium (Table 11). As seen from Figure 2, a t p H 8, magnesium and Eriochrome Black T combine in the ratio of 1 to 1, the slope of the log-log plot being 1.09 and the value of log K h being 3.60. That the Eriochrome Black T-magnesium compound a t p H 10.0 is also a 1 to 1 compound is evident from the continuous variations study, the results of which are shown in Figure 4. The data obtained from the continuous variations study yield by the procedure outlined
above, a value for K A5.64 X 1 0 - 6 (log Kh = 5.75 =!= 0.10).
Calcium and Eriochrome Black T also combine in the ratio of 1:1, log Kh = 3.84, as shown by the log-ratio method a t pH 10 (Figure 3). The formation constant for the calcium-dye compound is so low that a satisfactory determination of the combining ratio and formation constant cannot be obtained a t values much below 9 by this method. There is no reason to suppose, however, that the compound a t pH 8 is other than 1:1. The various values obtained and those of Schwarzenbach are summarized. The method employed by Schwarzenbach is essentially the log-ratio method given here; this method is successful even with a reagent of unknown purity. In the paper in which Paul Job outlined the method of continuous variations, the following passage is set in italics (5): La condition nbcessaire e t suffisante pour que la composition maximum ne varie pas, si l’on change les concentrations des deux solutions simples, est que ces deux solutions soient BquimolBcuhires. Dans ce cas, et dans ce cas seulement, la composition maximum correspond 3, la proportion des deux constituents qui rkagissent pour former le complexe. Job states further that where the VOL. 31, NO. 3, MARCH 1959
417
original concentrations are not equimolecular, the position of the maximum depends on the ratio of the concentrations and the equilibrium constant. It would Seem that those choosing the hethod of continuous variations as a method of attack in this work would do well to examine the purity of the reagents. LITERATURE CITED
(1) Bates, R. G , “Electrometric pH
Determination,” p 117, Wiley, New 1954* (2) Diehl, Harvey, Sealock, R. R.,
Record Chem. Progr. (Kresge-Hooker Sci. Lib.) 13, 10 (1952). (3) Ellingboe, J. L., Ph.D. thesis, Iowa State Ames, Iowa, lg5‘. (4) Harvey, A. E., Komarmy, J. M., Wyatt, G,, A ~ cHEM. ~ ~ 25, . 498
(1953). (5) Job, Paul, Ann. ehim. (Paris) (IO) 9 , 113 (1928). (6) Ibid., (11) 6, 97 (1936). (7) Kinger , W. D., Hume, D. N., J . Am. &em. SOC.71, 2393 (1949). (8) Schwarzenbach, Gerold, “Die kom-
plexometrische Titration,” 2nd ed., p. 30, Ferdinand Enke Verlag, Stuttgart, 1956. (9) Schwarzenbach, Gerold, Biedermann, W., Helv. Chim. Acta 31, 678 (1948). (10) Shriner R. L.,Fuson, R..C., Curtin, D. Y. “gystematic Identification of Organic Compounds,” p. 288, 4th ed., Wiley, New York, 1956. (11) Vosburg, W. C., Cooper, G. R., J . Am. Chem. Soe. 63, 437 (1941) (12) Young, Allen, Sweet, T. R., ANAL. CHEM.27, 418 11955). RECEIVED for review July 11, 1958. Accepted October 14, 1958.
Determination of 2,2-Dichloropropionic Acid, 2-Chloropropionic Acid, and 2,2,3-Trichloropropionic Acid in Chlorinated Propionic Acid by Use of Mercuric Salts ROLAND
P.
MARQUARDT and E. N. LUCE
The Dow Chemical Co., Midland, Mich.
b Chemical methods were desired to determine 2,2-dichloropropionic acid, 2-chloropropionic acid, and 2,2,3trichloropropionic acid in the amounts usually found in chlorinated propionic acid. By using mercuric salts in the developed analytical procedures, each acid may be determined in the presence of the other acids with a general accuracy to &0.5% of the absolute value.
to pyruvic acid when refluxed with water.
+
CH3CCIzCOOH HzO + CHsCOCOOH
Pyruvic acid reacts with aqueous mercuric nitrate to produce the anhydride of 3,3-bis(hydroxymercuri)-3nitratomercuripyruvic acid. CHsCOCOOH Hg 0
N THE
CHEMICAL REACTIONS USED IN ANALYSIS OF CHLORINATED PROPIONIC ACID
2,2-Dichloropropionic acid hydrolyzes 418
ANALYTICAL CHEMISTRY
+ 3Hg(NOa)2 + HzO
-+
/ \
I
development of Dalapon (2,2dichloropropionic acid), produced by the chlorination of propionic acid, chemical methods of analysis were required. I n addition to a n assay procedure for Dalapon, the main constituent, analytical methods for the chloroand trichloropropionic acids were also desirable. The constituents in a product of this type are best determined directly. Neither direct acidity titrations nor physical methods such as infrared met all the practical requirements. The chemical methods offer a means of determining directly and independently of the other constituents, the chloro-, dichloro-, and trichloropropionic acids in the amounts in which they occur in this product. These procedures depend upon the reactions of these acids with aqueous mercuric nitrate and mercuric propionate solutions.
+ 2HC1 (1)
\ /I
CCOCOOH +5HNOj
(2)
Hg HgN03
The organic mercury compound reacts with aqueous potassium iodide to produce potassium hydroxide (1).
7YCCOCOOH + 12 KI +
0
h?$lgN03
+
3 HzO
+
CH3COCOOK 3KzHgII KNOs 4KOH (3)
+
+
The base is then titrated with standard hydrochloric acid as a measure of the 2,2-dichloropropionic acid. 2-Chloropropionic acid hydrolyzes to lactic acid when refluxed with water.
+
CHsCHClCOOH HzO CH3CHOHCOOH +
+ HC1
(4)
Lactic acid does not react with aqueous mercuric nitrate.
+
CHsCHOHCOOH 4- Hg(NO3)r H 2 0 -P no reaction
(5)
Acidic aqueous dichromate oxidizes lactic acid to pyruvic acid.
+
+
3CH3CHOHCOOH Na2Cr*0, SHY03 + XCHjCOCOOH
+
2Cr(N03)~ 2NaY01
+ i”z0
+
(6)
Then the anhydride of 3,3-bis(hydroxymercuri)-3-ni t r a t omer c u r i p y r u v i c acid is produced by Reaction 2 and potassium hydroxide is produced by Reaction 3. The base is titrated with standard hydrochloric acid as a measure of the 2chloropropionic acid. 2,2,3-Trichloropropionic acid reduces mercuric propionate in a boiling aqueous solution, precipitating a mixture of mercurous salts.
+
-+
CHzClCC12COOH Hg(0OCCHzCHs)s ? 4 Hg+acid- (7) The mercurous salt mixture reacts with potassium hydroxide to produce mercurous oxide.
+
2Hg+ acid2KOH + Hg,O 2K+ acid-
+
+ H20
(8)
After the mercurous oxide has been dissolved in dilute acid, the mercury is oxidized and titrated with standard ammonium thiocyanate as a measure of the 2,2,3-trichloropropionicacid. DETERMINATION OF 2,2-DICHLOROPROPIONIC ACID IN CHLORINATED PROPIONIC ACID
Analysis of the product of the reaction between 2,2-dichloropropionic acid and aqueous mercuric nitrate shows that the anhydride of 3,3-bis(hydroxy-
