I
I
I
/ I
n
amount of the isomer present in the range below about 35 or 40 (50% a t the largest) mole % of methylnaphthalene (Figure 5 ) . Using the calibration curve of Figure 4, several commercial amethyl compounds were analyzed, with the resulk shown in Table 111. Agreement with the results of infrared absorption measurcrnents, where available, scems satisfactory.
n"
ACKNOWLEDGMENT
Oi
;v hh c e n3 0t r a t'libo n 5bof
0 Re; J ' I
i o '10 80 90 100 a - Methvlnaohthalene
(mole%
The authors are grateful to Ryo Kato, Kanto-Kagaku-Kogyo Co., Ltd., who supplied samples. LITERATURE CITED
Figure 4. Calibration curve for NMR determination of 1-methylnaphthalene Concentration of total amount of methylnaphthalene (a 4- 8 ) kept as 30 mole % in CCI,
nonlinearity in Figure 2 is due to the nonlinear responsibility of the detector system. In Figures 3 nnd 4 for 30 mole % solutions of 1- and Zmethylnaphthalene in CCl,, the relative concentration of CY(= U / C Y 8) can be determincd from measurements of the rclative intensities of the NMR signals, I(cY).In other solvents, such as benzene or n-heptanc, also, the relative intensity i q relatcd linearly to the
+
ConccntratLon of a -Mt-thyLnaphthatew (
)
(1) Bernstein, H. J., Schneider, W. Q., Pople J. A., Proc. Roy. SOC.A236, 615 (1956). (2).Fujiwara, S.,"Relaxation and Saturation in Nuclear Magnetic Resonance," Symposium, Chemical Society of Japan, Tokvo. 8eDtember 1959. (3) Fijiwara, S., Shimieu, H., J. Chem. Ph 8.32, 1636 (1960). (4) utowsky, H. S., Me er, L. G., McClure, R. E., Rev. Sci. fmtt. 24, 044 (1953). ' (5) K a m a t , H.,Tanaka, N., "Analysis of Tar Products by Infrared Spectroacopy," Annual Meeting, Japan Society of Analytical Chemistry, Tokyo, May 1953. (6) Pople, J. A.,Schneider, W. G., Bernstein, H. J., Can. J. Chem. 35, 1060 (1957).
mole 5 )
Figure 5. Relative intensity of NMR signal of a-methyl proton resonance as a function o f relative concentration of the a isomer
-In benzene
--- In n-heptane (7) +eves, L. W., Schneider, W. G., Zbtd., 35,251 (1957). (8) Reilly, C.A., ANAL.CHBM.32, 221R (1960). (9) Shimbu. H..Fujiwara. S.. J . Chem. ' Phys., in press: (10)Williams, R. B., Ann. N. Y . A d . Sa.70,890 (1958). I
.
RECEIVED for review September 8, 1960. Accepted April 10,1961.
Triphenyl Phosphite, a Selective Extractant for Cop per(I) HaIides THOMAS H. HANDLEY Analytical chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn. JOHN A. DEAN Department o f Chemistry, University of Tennessee, Knoxville, Tenn.
b Triphenyl phosphite dissolved in CCld selectively extracts copper(1) from various halide systems. The influence of a wide range o f halide ion, reagent, and copper concentrations, and the effect of temperature and diverse anions and cations have been investigated. In the range 0.07 t o 0.15M halide ion and with a 10% reagent concentration, distribution coefficients exceed 500 for KBr, KCI, and NHdCI systems, and 100 for NaCl and HCI systems. Reduction i s accomplished b y heating with ascorbic acid a t 60" C.; after cooling to 25" C., the extraction i s accomplished in a single, 10-minute equilibration. The copper i s easily stripped from the organic phase. From 0.003 pg. to 30 mg. of copper p e r 5 ml. can b e handled with 5 ml. of 10% reagent.
B
of the unshared pair of electrons on the phosphorus, tertiary phosphite esters, (RO)aP, form a number of addition compounds with such inorganic substances as CuCl, PdCl,, PtCI2, PtCL, AuCl, and HgClt (1, 2). In this investigation the extraction possibilities of the addition compounds formed by the reaction of triphenyl phosphite (also named triphenoxyphosphine) with copper(1) halides have been explored and an extraction method has been devised. ECAUSE
EQUILIBRIUM DISTRIBUTION STUDIES
Materials. Triphenyl phosphite, Eastman reagent grade, 3.78M,was used without further purification. Its infrared spectrum showed on1 a faint band which might be ascribeBto a P d group present in the diary1
ester. Known dilutions of the triester were prepared by dissolving the appropriate weight of ester in ACS grade carbon tetrachloride. A 10% (w:/v.) solution is recommended. The triester is inexpensive. Ascorbic acid, 10% solution, 1.1M, waa prepared by dissolving 10 grams in distilled water and diluting t o 100 ml. The solution is stable about one week. Method. T o a given amount of carrier (stock) solution, the radiotracer, the reductant, and enough alkali halide or hydrohalic acid were added t o make a solution X M in halide ions and yM in copper. T h e solution was immersed for 10 minutes in a water bath maintained at 50" to 70° C., and then was cooled to room temperature before proceeding. T h e aqueous solution, which varied in volume from 6.00 to 7.25ml., was shaken with exactly 5.00 ml. of the triphenyl VOL. 33, NO. 8, JULY 1961
1087
phosphite solution for 10 minutes. After scparation of the phases, which is hastened by centrifugation for 2 minutes a t 2000 r.p.m., an aliquot of each phase was measured for copper-64 by counting in a gamma scintillation counter. While the extractability of other elements was being surveyed, flamephotometric methods were employed for elements for which suitable radioisotopes were not readily available. The influence of the various factors affecting the reduction of copper(I1) by ascorbic acid was studied by observing the change in absorbance of the copper (11) halide complexes a t 825 mp with a Bausch and Lomb Spectronic 20 and 1-em. test tubes. Reductants. Inasmuch as the copper(1) halidrs are the extractable species, i t was necessary to survey the several reducing agents which have been suggested for the reduction of copper(I1) salts to coppcr(1) salts. In a chloride medium, the standard reduction potential of the system, CU+* C1- = CuCl(s), is 0.538 volt; and for the further reduction to copper, CuCl(s) = CuO C1-, is 0.14 volt. The corresponding values in a bromide medium are 0.64 and 0.03 volt, respectively. Obviously the reduction potential of the reducing agent must lie within these limits. Sulfite salts added to an acid solution, or sulfur dioxide added directly as the gas or as a solution saturated with the gas, acted erratic a t times. Furthermore, it proved difficult to control the amount of sulfite in excess and the concentration of acid, especially if the solutions were heated. Hydrazine hydrochloride and hydroxylamine hydrochloride proved ineffective on trial runs and were not investigated further. Ascorbic acid (4, 10) and stannous chloride were suitable reductants. The former was preferred because i t did not introduce extraneous metal ions or additional hydrohalic acid into the
+
+
,
E
,
, ,
,
1 I
,.,
1
,
I
I
I
,
I
Y
0.00.01 4 ~ l ~ U ~0.tU I I I ~ 1.0 . L , I I L 1~0 L L PER CENT iw/v) TRIPHENYL M S P H I T E IN'CCI,
Figure 1. Distribution coefficient of copper as a function of reagent concentration lnitlal copper
concentratlon, 0.01bM
test solution. To ensure complete reduction, 1 ml. of 10% ascorbic acid solution should be added, for each 20 mg. of copper present in t h e test solution. Upon addition of the ascorbic acid to a neutral halide system, the reduction of copper(I1) is almost instantaneous. However, in dilute acid solutions the rate is slower and increasing the hydro-
gen ion Concentration decrcases thc rate even more. Davis (4) suggestcd that the dissociated form of ascorbic acid is the specks that actually reduces the cupric ion and, if so, increasing thc hydrogen ion concentration would decrease thc concentration of dissociation species. Rctardation of the reduction process is climinated in acid systems when the trmperature is raised to 50" C. or higher. Actually, a t elevated tcmperatures and in acid solutions the rate of reduction is more rapid the higher the acid concentration. However, since the extraction is less complete under these conditions, the solution should be diluted prior to the extraction Rtep. In general, immersion of the aqueous phase in a water bath a t 60" C. for 10 minutes is recommended. The solution L is then cooled to room temperature before equilibration with the organic phase. Reagent Concentration, The effect of thc Concentration of triphenyl phosphite in carbon tetrachloride on the extraction of copper from NaCl and HCl solutions is shown in Figure 1, in which the logarithm of the distribution coefficient is plotted against the logarithm of the rragent concentration. For reagent concentrations in excess of 0.4% (0.013M), significantly different distribution curves were obtained. A reagent conccntration of 10% (0.3811-1) provided a distribution coefficient of 100 or largcr for all halide syfitems investigated. Actually a rcogent concentration of 5%
,1.0
AWECUS PHASE EQUILIBRIUM COPPER CONCENTRATION (moles per lfter I
Figure 2. Distribution of copper between an organic phase containing 5% triphenyl phosphite in CCl4 and an aqueous phase 0.375M in KCI Equal volume of bo* phases
1088
ANALYTICAL
CHEMISTRY
to 001 /
-
u
.
01 .
-
l
I
-10.
AOUEOUS S A L T OR ACID CONCENTRATION
iJ
..4L 0
, M
Figure 3. Distribution coefficient of copper as a function of halide ion or hydrohalic acid concentration 5% triphenyl phosphite In CCI, and ,0.031M copper initially in aqueous phase
is often sufficient, especially when one is working at the optimum halide ion ronceritration (Figure 3). Copper Concentration. Thc data i n Tahlc I illustrate the effect on the distribution coefficient whcn the amount of copper initially prcsent in the aqueous phasc is incrcascd from 0.0027 g. to 50 mg. pcr 5 ml. aqueous volume. In Figure 2 the equilibrium concentration of the copper in the organic phasc is plotted against its rquilibrium concentration in the aqueous phase for a series of extractions in which the total triphenyl phosphite concentration and chloride concentration are constant. The lower portion of the curve shows a limiting slope of 1 011 the log-log plot, indicating that the distribution coefficient is constant. The ncgative deviation of the curve from thie limiting slope is a saturation effect which rrsulk from the decrease in free reagent conccntration as the copper roncentration in the organic phase increascs. The saturation effect becomes apprrciable a t copper-reagent ratios greater than 0.2 whrn the con-
Table 1.
Effect of Copper Concentration on Extraction Aqueous phase w a ~0.376M in KCl and 0.28M in ascorbic acid. Orgmic phase
was 5% triphenyl phosphite in CCI,. Each phase wad 5 ml. in volume Copper Initially in Aqueous Distribution Phase, Mg. Coefficient 2 . 7 X 10-4 . 175 2 . 7 x 10-4 420 1 420 .5
10
20
30 40 50
Table II.
30.5
260
176 107 30.3 8.1
Effect of Equilibration Time
Aqueous phase was 0.0314M in copper, 0.142cf in ascorbic acid. Organic phase was 6% triphenyl phosphite A iieous Distribution Coefficient PtCl Concn., M 10 min. 3 hr. 0.044 262 336 0.062 265 288 0.089 49.5 560 -. --0 . ioS 461 1048 0.124 547 1067 0.140 367 728 1.78 41 52 3.3 13 13 Equilibration Distribution Time, Min. Coefficient HCI 0.375M 2 6
10 20 30
12
46 54 65
96
centration of reagent is 0.173M (6% solution). Halide Systems. To ascertain the optimum concentration of halide ion for the extraction of copper(1) halides, several aqueous halide salt systems and one hydrohalic acid system were examined. Thc rrsults arc shown in Figure 3, in which tho logarithm of the distribution cocfficicnt for copper is plotted against the logarithm of the conccntration of the particular halide ion prcsrnt in the aqueous phase. The largest values of distribution coefficients arc restricted to a narrow concentration range of halide ion, 0.07 to 0.15M. However, exrrpt for NaCl and HCI, adequatc distribution coefficients prevail over the conccntration range 0.05 to 0.7M. Gcncrally thc presence of hydrogen ions lowercd the distribution cocfficient from its valuc in the absence of any acid (Tablc 111). No explanation is offered for thc apparently anomalous dip in the HCl curve. Although thcra might be some justification for drawing a fairly smooth curve through the same points with no dip, the minimum WRR obtained on repetitive studies with several different reagent concentrations. Bixllander and Stsrbeck (3) have shown that copper(1) halides are present in halide solution substantially in the form of thc dihalocuprate(1) anion, CuXZ-, so long as thc halide solution is of moderate strength-namely, from about 0.05 to 0.30M. In more concentrated halide solutions a large portion of CuXa-* anion exists and probably it is the formation of this anion which interferes with thc extraction. In more dilute halide solutions a considerable proportion of cupric ion may be formed through disproportionation of soluble but uncomplcxcd CuCl, and this would lower the distribution corfficient. Noyes and Chow (8) have determined the equilibrium ronstant for the rcaction, CuCl(s) C1- = CuC12-, a t several temperaturcs; i t incrcascs from 0.0661 a t 25" C. to 0.153 a t 50' C. The foregoing obscrvntions provide an explanation for the increase in the distribution cocfficicnt upon prolonged contact of thc two phasrs (Table 'I1 and thc dnshcd lines on Figure 4). The incrcase was particularly noticeable for halidc ion concrntrations which fell within thr range 0.07 to 0.3021f. Upon addition of the ascorbic acid to a cupric salt solution whose halide ion concentration was less than about 0.3M, a precipitate of CuX consistently appcarcd and pcrsisted until the aqueous phase was contactcd with the organic reagent. No emulsion troubles were encountered and the prccipitatc quickly reacted a t thc interface and partitioned into the organic phasc. The solubility of CuCl is 0.111 gram per liter and is said to dccrcnsc in the presence of
+
chloride salta in the order: KCl > N&C1 > NaCl > HCl (9),which is in agreement with the extraction pattern shown in Figure 3. Effect of Other Anions. The extraction of,copper in the presence of a variety of anions and combination of anions was explored. The results are shown in Table 111. Strong oxidants would naturally interfere, but small amounts of free nitric acid and large amounts of nitrate ion can be tolerated. Nitrous acid interfered seriously, b u t i t can be removed by addition of urea to the mmple solution prior to the addition of the ascorbic acid. Cyanide and thiosulfate ions com-
Table 111.
Effect of Anions on Copper Extraction
the
Aqueous phase waa 0.14M in ascorbic acid and contained 5 or 10 mg. copper as CuCI, in a volume of 5 to 7 ml.; organic phaae w a ~5 ml. of 5% triphenyl phosphite DistribuAnion Concentration, tion Teated M Cmfficient Acetatc, aa Each 0.7 234 NaOrCZH: plus HCI Bromide AB KBr 0.7 290 As KBr plus Each 0.7 290 HCl
CtJoride As HCI As KC1 As NaCl As NaCl plus HCI AE NHiCl AS NHtCl DIU8 HCl Cyaiidc, as NaCN Fluoride, aa NaF plus HCI Iodide AB NaI As NaI plus HCl Nitrate As NaNO, As NaNO: plus HCl As "01 plus HCI
0.7
0.7 0.7
Each0.7
71 202 180
80
0.7 Each 0.7 Each 0.1 0.7
le0 64 167
Each 0.7
206
0.7 Each 0 . 7
83 67
0.0006
0.7 172 0 . 7 a n d 151 0.1
Each 0.1 0.3and
123
Perchlorate, as Each0.7 KCIO, ~ l uHCl s Ph'osphate, as Each 0.7 NanHPOi 0 . 7 and 1.4 SUYf%Hcl AE HI SO^ 4.3 As H 8 0 1 4.3 and
20
83 73
6.5and
17
0.1
1.o
As NaZSO,
plus HCI
1.o
89
0.025 16
Each 0.7 139 1 . 4 a n d 99 1.o
Thiocyanate, Each 0 . 7 as KNCS plus NaCl Thiosulfate, aa Each 0 . 7 Nan&Oaplus NaCl
VOL. 33, NO. 8, JULY 1961
29
O.OOO3
1089
pletely inhibited the extraction. A precipitate of copper(1) thiocyanate formed but it failed to extract completely upon equilibration with the triphenyl phosphite. Back-extraction Studies. Less than 0.1% copper was lost from the organic phase when the organic extract was washed three times with distilled water. A slight loss occurred when the extract was washed with an 1.OM hydrochloric acid solution, as would be expectrd from Figure 3. Thus it is possible to back-wash the extract, if necessary, to remove any other metal ion which exhibits a tendency to coextract with the copper. Effective reagents for quickly stripping copper from the organic phase include those which complex with the copper(1) ion or which oxidize copper(1)
and the value of the distribution coefficient is lessened a t 25" and a t 0" C., whereas, by comparison, the values of 60" C. are virtually identical for the two systems. DISCUSSION
IV. Back-extraction Studies Equal volumes of the two phases used. Contact time 2 minutes
Table
Halide Anion Bromide
Chloride
Stripping Solution Distilled water 0 . 6 M NHa 1 .OM NHa 6.OM NHa 1.OM HCl plus 5% HzOz 1.OM "01 1.OM NaCN 1 . OM NatSnOs Distilled water 1.OM NHI 1 .OM HCl 1.OM HCl plus 5% H201 1.OM HNOs
6 . OM
%
(=oPW
Removed < 0.1 98.5 99.1 >99.99 99.9 < 1
>99.99 99.9
