1356
ANALYTICAL CHEMISTRY
expressed in granis par liter instead of the grams per 100 cc. used In the formula for specific rotation. If the value he gives were grams per 100 cc., the solution would be so highly colored that i t would be impossible to pass enough light to operate a polarimeter. If his concentrations are interpreted to be grams per liter, they would be approximately the same as for the solutions in this work. No difficulties were encountered in following the synthesis of uaphthazarin reported by Zahn and Ochmat, although it was necessary to modify the method of purification. Practical heptane, a high-boiling petroleum ether, was found t o be an excellent solvent for recrystallizing naphthazsrin. Naphthazarin may be synthesized in the necessary quantities much more readily than an equivalent amount of alkannin may be extracted from the root. Inasmuch as Underwood and Neuman (8) have shown the two reagents to be equivalent, it is recommended that naphtha7arin he iiqerl in the microdetermination of beryllium.
IEND
LITERATURE CITED
Betrabet, M. V., and Chakravarti, G. C., J . Indian Inst. 8ci.. 16A,41 (1933).
Brockmann, H., Ann., 521,l (1935). Dieterle, H.,Salomon, A,, and Nosseck, E., Ber., 64, 208n (1931).
Dubsky, J. V., and Kramets, E., Mikrochemie, 20,57 (1936). Ellis, G.H., Olpin, H. C., and Kirk, E. W., U. 9. Patent 1,911.945 (1933).
Formanek, J., 2.anal. Chem.,39,417 (1900). Rraudnics, H., Redlich, L., and Fiedler, F., Ber., 64,1835 (1931, Underwood, A. L.,and Neumsn, W. F., ANAL.CHEM.,21, 134h (1949).
Underwood, A.L.,and Neuman, W. F., University of Rochester Atomic Energy Project, Rept. UR-19 (1947). Zahn, K.,and Ochwat, P., Ann. 462,81 (1928). RECEIVED August 3, 1949. Based on work performed under contraoi with t h e United States Atomic Energy Commission a t t h e University of Rochester Atomic Energy Projert, Rochester, N. Y.
OF SYMPOSIUM]
Chloroform Extraction of Ferric Cupferrate E. B. SANDELI,
AND
PIIYLI,TS F. CI:XIRIINGS, University of Minnesota, fifinneapolis, Minn.
The distribution of ferric iron between chloroform and an aqueous phase containing much chloride in the presence of nitrosophenylhydroxylamine is governed by the relation
The value of K f depends upon the chloride concentration and also upon the indifferent electrolyte concentration. Values of K' for various chloride concentrations are reported.
T
HERE are a considerable number of scattered references in
the analytical literature on the extraction of metal cupferrates from aqueous medium by various immiscible organic solvents such as chloroform, carbon tetrachloride, and ether. The metals extracted are those forming cupferrates slightly soluble in mineral acid medium-e.g., ferric iron, vanadium, and molybdenum. Particularly, the extraction separation of ferric iron from such metals as aluminum and beryllium has been applied by H number of workers. I t seemed worth while t o determine the value of the extraction coefficient of ferric cupferrate as an aid to the evaluation of the wparation. The instability of cupferron in acid solutions prevents accurate quantitative data from being obtained, but even approximate results should have some analytical utility. DISTRIBUTION OF A METAL BETWEEN AQUEOUS AND IMMISCIBLE SOLVENT PHASES IN PRESENCE OF CUPFERRON
The following equilibria exist in this system:
H+
HCf (HCf), A ueous &as,
MCf,
+ Cf-
(hICf,), Aqueous phase
+ m Cf-
(MCfl), Organic solvent
[ H + l [Cf-I = fic,
[HCflu -[HCflo = [HCf],
(partition coefficient of nitrosophenylhydrox 1. pcf amine between organic solvent and watery [ l I + m ] [Cf-lm
[1VICfmll.
= kM
[-= LlCfmlo
[llCf,lW
!JM
The combination of these expressions gives:
The value of the equilibrium constant, K , may be found by direct experiment. It may also be obtained by calculation if certain data are known:
(aqueous phase). (HCf = nitrosophenylhydroxylamine) (1)
(HCf), Organic solvent
T=51 +m
The respective equilibrium constants are:
(aqueous phase).
(M+" = metal ion) (3) (4)
The value of p ~ / isk obtained ~ by dividing the molar solubility of the metal cupferrate in the organic solvent by the solubility product in water saturated with the organic solvent; the value of kcr/pcr is found similarly. The values of the solubility products of the cupferrates of ferric iron, copper(II), aluminum, bismuth, and tin(1V) have been reported(1). The solubility of the cup-
V O L U M E 2 1 , NO. 11, NOVEMBER 1 9 4 9
1357
ferrates in organic solvents does not appear to have been determined. The solubility of nitroTable 11. Extraction of Ferric Cupferrate by Chloroform frnm Hydrochloric Acid Solutions sophenylhydroxylamine in organic solvents and in water has not been reported. The dissociation constant, kci, of nitrosophenylhydroxylamine is approximately 5 X 10-5 (1). The 1.00 .... .... .... .... 6 X iU*" value of the partition coefficient, pct, for nitro3.8 0 67 1.13 2.00 1.80 7.2 2 . 4 x 108 3.9 2 1 x 108, 1.07 2.00 1.80 7.2 0.73 sophenylhydroxylamine between chloroform and 14.4 1.70 9.3 2.00 1.80 0.095 1 . 8 x 100, water has not been determined exactly, but it Av. 2 . 1 x 10' is known to be greater than 100. This means 3.00 7.1 1.25 0.55 5.4 7 . 4 x 107 1.80 3.00 1.80 10.6 0.80 1.00 7.6 7 . 6 X 107) that the amount of nitrosophenylhydroxylamine .4v. 7 . 5 x 10' remaining in the aqueous phase, acidifled with 4.00 1.80 10 8 1.29 0.51 9.3 3 . 2 x 107 107) a mineral acid, after shaking with chloroform, is Z 00 1.80 14.4 0.97 0.83 11 . 9 Av. 3 . 2 X 10' iisually negligibly small. The amount of undisAverage of 15 values ranging from 1.4 X 10' t o 1 5 , X 108. Variability probably due ti +ociated metal cupferrate in water solution is exexperimentally unfavorable distribution ratio (most of iron goes into chloroform phase). tremely small and need not be considered. The analvst is interested in the distribution (Jf a metal in all its forms between the two [ h l +m]u = Z[ M Iw X constant phases. This means that account must be taken of metal ~pecies other than the simple ion-i.e., complex ions and alightly dissociated molecules. If the equilibrium constants of d l the reactions involved and the concentration of the complexforming agents are known, [M+"] in the equation can be reK' is a constant for a specified concentration of CI- at constant placed by an expression involving these and the total metal conionic strength and in the absence of other complex-forming subcentration in the aqueous phase. If the concentration of the stances. complex-forming substance is large compared to that of the As long as there is no real or virtual association of the metal in either phase-i.e., if the species in the aqueous phase contain metal, it can be taken to remain approximately constant as the only one atom of M-the fraction of total 11 in the organic phase total concentration of metal varies, and a simple expression is will be independent of the total amount of metal present obtained for the ratio of the metal forms in the two phases under specified c-onditions, provided the compleaing substance is uniK ' FOR FERRIC CUPFERRATE valent. The preceding expression was tested for ferric iron in a mixture As an example, suppose that 11 +m forms a series of complexes of hydrochloric acid and sodium chloride in which the chloride with chloride ion. The aqueous solution will contain the species concentration was maintained constant a t 4 M . The values of t v + m , MCI+"-', MC12+"-2 . blCInm-". A4ta sufficiently high acidity, the hydrolysis of L1+m can be neglected. The sum constant K' are shown in Table I. In thpse and other euperiof concentrations of the metal in all its forms in the aqueoug ments the procedure waq a$ follrin?: phase is given by: .
.
.
I
The ferric chloride solution, contairiirig the requisite Liniuuui of hydrochloric acid and sodium chloride, was treated with a freshly prepared cupferron solution (prepared from a 99.8% pure product) in a separatory funnel. The volume of the solution after the addition of cupferron was 10.0 ml. After mixing, 10.0 Therefore, for a constant milcentration (actually activity) of Cl-, we have the relation: ml. of chloroform were added immediately and the mixture was shaken for 2 minutes. Special experiments showed that this Deriod of shaking sufficed for attainme'nt of distribution e uilibrium. The chloroform was Table I. Extraction of Ferric Cupferrate by Chloroform from Aqueoic?i allowe3 to settle and an aliquot portion Solution of Constant Chloride Ion Concentration (4 M ) of the clear aqueous phase was evaporated almost to dryness ~ i t nitric h acid and a.little sulfuric acid to destroy any organic matter present. The iesidue nas taken up in water and iron was 4.00 0 1.80 10.8 1.29 0.51 9.3 3.2"\ determined colorinietrically by the o4.00 0 1.80 14.4 0.97 0.83 11.9 3.2 plienan t h r o l i n e method, R ith hydro. Av. 3.2 quinone as reducing agent. A blank 3.00 1.00 1.80 7.2 1.37 5,9 4.2 0.43 nas always run on the acids. The dis3.00 1.00 1.80 10.7 1.22 0.67 8.7 2.5 3.00 1.00 1.80 10.6 1.14 tribution experiments were carried nut 0.66 8.6 2.5 3.00 1.00 1.80 14.2 0.81 0.99 11.2 2.3 1 a t 23 * 1 ° C . 3.00 1.00 3.60 21.4 1.00 2.60 13.5 2.9 ,
,
1
3.00
1.00
3.60
28.4
0.44
3.16
18.9
2.9 I
Av. 2 . 9 2.00 2.00 2.00 2.00 2.00
2.00
2.00 2.00 2.00 2.00 2.00 2.00
1.80 1.80 1.80 1.80 2.70 2.70
7.2 7.2 10.8 14.4 14.4 21.5
1.17 1.07 0.72 0.38 0.75 0.19
0.63 0.73 1.08 1.42 1.95 2.51
7.2 5.0 7.5
10.1 8.5 13.9
3.5 4.2
Av. 3 . 5 1.00 1.00 1.00
3.00 3.00 3.00
1.80 1.80 1.80
7.2 7.2 14.4
0.65 0.65 0.07
1.15 1.15 1.73
3.7 3.7 9.1
\.slues of K' for various hydrochloric acid concentrations (no other chloride present) are given in Table 11. A4t constant chloride concentration K' in the equation
3.4 3.3 Av. 3 . 4
a When ferric cupferrate precipitate was allowed to stand 5 minutes before extraction with chloroform under conditions similar to above, apparent value of K' was found t o be 1.5 X 107, thus ahowing effect of deoomposition of nitrosophenylhydroxylamine. b When ferric cupferrate was allowed t o stand 5 minutes before extraction, apparent value of K' was 1.8 X 107.
is seen to remain constant, within the limits of experimental error in this unstable system, as [FeCf,],/B [Fc], i p
1358
ANALYTICAL CHEMISTRY
varied from about 0.3 to 25 and [H+] is varied from 1 tu 4. With increasing chloride concentration the value of K ' decreases in accordance with the greater transformation of F e + + + into FeCl++, FeC12+, FeC13, and possibly other species (2). A plot of log K' versus hydrochloric acid concentration appears to give a straight line in the range 1 to 4 AI (Figure 1). No great accuracy is claimed for the values of K' reported, and the clow conformity to linearity may be fortuitous.
9.0
L
8.5
(3
s
8.0
7.5 ~~~
1
P
3
4
HYDROCHLORIC ACID CONCENTRATION, M
Figure 1. Variation of K' for Ferric Cupferrate in Chloroform with Hydrochloric Acid Concentration A few determinations of K' in 1 AI perchloric acid were made The value 7 X 108 was obtained (average of 5 values ranging from 3.6 X 108 to 1 x 10*0), but this figure must be regarded as ver: tentative because of the unfavorable experimental conditions. When the concentration of free nitrosophenylhydroxyIaminein the chloroform phase is 0.1 M the ratio [FeCf3],/Z[Fe], for 1 IM
hjdrochloric acid medium is 6 X lo5, on the basis of the above value of K'. A double extraction under these conditions (final concentration of excess reagent 0.1 AI in the chloroform) should therefore reduce the ferric iron concentration of the aqueous solution to a very small value. The extent of extraction of such metals as aluminum, which do not readily give a cupferrate precipitate in mineral acid medium, cannot be stated at present, although a rough estimate of k" for aluminum can be based on the reported solubility products of ferric and aluminum cupferrates, which are, respectively, 1 X and 2 X according t o PyatnitskiI. If the solubilities of ferric and aluminum cupferrate in chloroform are roughly the same, the value of K' for aluminum rupferrate should be of the order 3 X lo2 in 1 Af hydroehlori( acid. The magnitude of this value indicates that the hydrogen ion and cupferron concentration may have to be controlled with somp care for a satisfactory separation when much iron is present. AP a matter of fact, aluminum cupferrate tends to be extracted from sulfuric acid solutions less acid than 4 Ar (3). If the extraction equilibrium is reversible (the reversibility does not seem to have been tested), a better separation can be achieved by applying the principle of retrograde extraction-i.e., the chloroform solution of ferric cupferrate containing a little aluminum cupferrate and excess cupferron is shaken with a hydrochloric acid solution of suiiable concentration containing added cupferron. By proper choiw of conditions, the major part of the aluminum in the chloroform phasp can be removed without transfer of any significant amniini of iron. LITERATURE CITED
(1) Pyatnitskii, I. V.,Zhur. Anal. Khim., 1, 57 (1946). (2) Rabinowitch, E., a n d Stockmayer, W. H., J . Am. Chem Soc 64 335 (1942).
(3) Strafford, N., a n d Wyatt, P. F., Analyet, 72, 54 (1947). R E C E I V ~June D 13, 1949.
Quantitative Study of Reaction between Beryllium and Quinizarin-2-sulfonic Acid MYRON W. CLCCI, W . F. NEUMAN, AND B. J. RIULRYAIN Department of Radiation Biology, University of Rochester, Rochester,
F
AIRHALL (1) has reported a colorimetric method for the determination of beryllium based on its reaction with an anthraquinone dye, quinizarin-2-sulfonic acid. An attempt to duplicate Fairhall's results led to a critical study of the factors involved in the reaction. The data obtained served as the basis for a revised procedure which permits the analysis of beryllium in quant,ities from 1 to 20 micrograms with a probable error of 3.1 %. EXPERIMENTAL
The procedure described by Fairhall (1) served as a point of departure for these studies. In investigating various anthraquinone derivatives as color reagents for beryllium, 1,4-dihydroxyanthraquinone-2-sulfonir acid (quinizarin-2-sulfonic acid), buffered a t pH 7.0 Kith ammonium acetate, was found to give a red color which is proportional to the amount of beryllium. The color develops rapidlv rprtrhps a maximum in 5 minutes, and does not fade for several
N. Y .
hours. The most satisfactory range for colorimetric comparison in a visual colorimeter is 1 to 20 micrograms of beryllium. KOcolor developed when beryllium and the dye were mixed under the conditions given by Fairhall (1). Heat (100" C. for 10 minutes) was necessary to develop the color. Because ammonium aretate is not an effective buffer in the region of pH 7.0, a search for a more suitable buffer was instituted. Histidine monohydrochloride was found to be a fairly effective buffer a t pH 6.5 and it did not interfere with the color reaction as did phosphate, bisulfite, borate, and maleate. It was also observed that the colored lake formed between beryllium and the dye could be easily salted out, but that this separation was prevented by the addition of gum arabic as a color stabilizer. With these preliminary changes in the Fairhall procedure, the reaction wm studied in more detail
Instruments. Measurements of absorption spectra were madr with a Model DU Beckman quartz spectrophotometer, using the
