Trialkyl- and Hexaalkylphosphorothioic Triamides as Extractants for Metal ions Selective Extraction of Mercury(lI), Silver(l), and Copper(1) THOMAS H. HANDLEY Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b N, N', N" - Trihexylphosphorothioic triamide (thio-THPA) and N,N',N"hexabutylphosphorothioic triamide (thio-HBPA), which are nitrogen analogs of the neutral esters of phosphorothioic acid, were evaluated as reagents for extracting metal ions from solutions of aqueous mineral acids. Of 33 metal ions studied, only Cu+, Hg+2, Ag+, Pd+*, and A u + ~extract in significant amounts. The extracted species are formed rapidly. From aqueous solutions 0.1 to 6M in acid and far a 2.62mM solution of thioTHPA or thio-HBPA in CHC13, the metal ions Hg+2, Ag", and Cu+ are extracted quantitatively. The distribution ratio, DHp, is independent of the concentration of " 0 3 or HzS04 of the aqueous phase. The DAg depends on [NOa-]. Hg-2 combines with thioTHPA in a mole ratio of 2 to l . The metal ion concentration, type of organic solvent, and substituent group of the trialkyl phosphorothioic triamides are significant variables. Structures are postulated for the complex species formed between the extractant and the metal ions.
T
alkyl esters of phosphorothioic acid selectively extract Ag+ and H g f 2 from H x O 3 media (4). The semipolar sulfur atom has very little electron-donating ability and apparently will bond only to ions of high field strength. A high mole ratio of triisooctyl phosphorothioate (TOTP) t,o metal ion and a high concentration of H?;03 in the aqueous phase are required for quantitative extrac,tion. The low electrondonating ability of trialkyl thiophosphates has been observed by others (IO). An increase in bonding strength of P=S while maintaining selectivity would improve extracting properties and usefulness of compounds containing the P=S group. .kcording to theories regarding the electronic structure of organic compounds, replacement of oxygen by nitrogen should improve the electron-donating ability of the semipolar sulfur. The present study was made to determine whether the nitrogen analogs of HE
phosphorothioic acid show improved extraction characteristics for metal ions as compared to the trialkyl phosphorothioates. The S-alkyl- and A'-arylsubstituted derivatives of (NHz)JS ' may be considered as the nitrogen analogs of the esters of phosphorothioic acid. Theoretically, these analogs should serve as good extractants because of the presence of both sulfur and nitrogen atoms, which may act as electron donors. Xudrieth and Toy ( I ) report that X-trialkyl phosphorothioic triamides are strong hydrogen-bonding agents. Tolkmith (9) studied the reaction of Y-trialkyl phosphorothioic triamides with other organics and has shown that the reaction depends strongly on the number of hydrogen atoms replaced in (?;H2)3PS by aliphatic groups. The extraction characteristics of the N-alkyl- and Aiarylphosphorothioic triamides will probably be affected by the number of hydrogen atoms replaced in (XH2)3PS. EXPERIMENTAL
Instrumentation
and
Apparatus.
Geiger-Muller (G-M) counter, for measuring beta-emitting radioisotopes. Gamma-scintillation counter, welltype, for measuring gamma-emitting radioisotopes. Centrifuge tube (50-ml.) and mechanical stirrer, for equilibrating the aqueous and organic phases. Reagents. S ,'N,N"-TRIHLxYLPHOSPHOROTHIOIC TRIAMIDE, (C6HI3XH)J'S (thio-THPA), is a white needle-like crystalline solid (m.p., 5051" C.; molecular weight 363). It is insoluble in water and in dilute solutions of mineral acids but soluble in many organic solvents, especially those that contain a labile hydrogen-e.g., CHC13 (1).
h research sample of thio-THPA, with which this study was initiated, was obtained from the Shell Oil Co., Wood River, Ill. The compound IS not available commercially. ;in additional quantity of thioTHP.\ was synthesized for this work according to the method first used by Michaelis and Steinkopf (6) and more recently by others ( I ) . The phosphorothioic triamides have also been
synthesized by reaction of phosphorus pentasulfide with the selected amine (2, I I ) in a mole ratio of 1 to 6, respectively. N , X', N" - HEXABCTYLPHOSPHOKOTHIOIC TRIANIDE [ (C4H9)J]3€~S,thioHBPA, is a viscous oil a t room temperature (m.p., 19-20' C.; I P O , 1.4869; molecular weight', 447.5) (8). It has a slight odor and is insoluble in water and in dilute solutions of mineral acids. Thio-HBPX is not available commercially. A research sample was donated by H. P. Lankelma, Western Reserve University, Cleveland, Ohio; with it, this study was begun. An additional amount of thio-HBP.1 was synthesized according to the method reported by Stuebe and Lankelma (8). The degree of toxicity of the 'Vsubstituted phosphorothioic triamides is not known. Thio-THPh and thioHBPA are stable towmd hydrolysis ( 2 , 8). The extractive properties of a CHC13 solution of these compounds are unaffected by dilute solutions of mineral acids during a 10-minute equilibration period. RADIOACTIVE TRACERS. The radioisotopes were obtained from the Isotopes Division, Oak Ridge h'ational Laboratory. S T O C K CARRIER SOLUTIOKS. Stock carrier solutions of the metal ions tested were prepared by weighing out appropriate inorganic salts and standardizing the solutions, when necessary. Procedure. 5-ml. aqueous phase was prepared t h a t contained a mineral acid in known concentration, the radioactive tracer of the metal ion to be tested, and the metal ion in concentration of 0.02 to 0.1 mg. 1)er ml. Special precautions were taken, when necessary, to ensure that the tracer and the carrier were in the same chemical and oxidation st,ate. The aqueous phase was equilibrated with 5 ml. of 2.62m-11 thio-THP-4 or thioHBP.1 in CHC13. Each extraction was made a t room temperature (27' C.) for 10 minutes; however, experiments indicated t'hat equilibration was attained in considerably lese than 10 minutes. The D values shown in tables and figures are the result of a single equilibration. The D is a measure of the extraction and is defined as t'he ratio of total metal mnccntr:ition in t'he organic phase to that in the VOL. 36, NO. 13, DECEMBER 1964
2467
dependent of [HKOs] or [H2S04]. The decrease of DH, as [HCI] increases shows the effect of complexation of Hgf2 by C1-. For a given [HCI], DE, increases as [thio-THPX], increases, and Hg+2 is quantitatively extracted from 1N HCl. However, under the conditions of this study (Figure l), Hg+2 is quantitatively extracted at [HClJ < 0.6-V. Tests wherein inorganic salts that contain NO3- or SO4+ were substituted for most of the acid prove that D,, does not depend on [NO3-] or [SOa-]. The effect of the acidity ( H N 0 3 or H2S04)of the aqueous phase on DH, a t high loading is shown by Figure 1, line A . High loading is defined as that condition wherein the M + n exceeds the n [thio-THPA],. As a re-
t
1__-__
LINE A
1.o
___/__
2-,-,-,. +
. _f _ - - - r - ._ r - \ . F_ ,
INITIAL [ H X ] ,
,,/ 40
LO
0.1
N
I
Figure 1. D H , as a function of initia [ H X ] a t fixed initial [Hg+'] and [ thio-TH PA lo Aqueous phose.
5.0 ml. [HX], as shown
__ 0.25mM Hg - - -2.5mM H g c 2
+*
Organic phase.
5.0 ml. CHCl 2.62mM thio-THPA
aqueous phase a t equilibrium. Centrifugation was used to hasten phase separation. The concentration of total metal in each phase was determined by counting a suitable aliquot in either a gamma scintillation or G-RI counter, as required. The total count rate indicated a material balance within +2Oj, of the tracer added initially. RESULTS AND DiSCUSSlON
-
lYJ LVJJS" - Tri n - hexylphosphorothioic Triamide, (C6HI3NH)3PS, Thio-THPA, a s Extractant. A 2.62m M solution of thio-THPA in CHCI, extracted significant amounts of Hgt2, Ag+, C u i , Pd+2,and from solutions of mineral acids. For this extraction system, the D of each of the following metal iotis is (6M in H S 0 3 are necessary for quantitative extraction of Hgt2 (4). With thioT H P A as extractant, He+*is quantitatively extracted by a mole ratio of THPh to Hg+2 of 2.1 and from an aqueous phase 0.1 to 9JI in "03. Hg+2 is also quantitatively extracted by thio-THPX from H&O, and HCl solutions in the absence of the nitrate anion. Thus, the trialkyl phosphorothioic triamides are more effective and Cu+ extractants for H R + ~Ag+, , than the trialkyl phosphorothioates and have a much wider range of practical usefulness.
ACKNOWLEDGMENT
The contributions from Dow Chemical Co, Midland, Mich., and H. P. Lankelma, Western Reserve University, of certain of the compounds (Table V) are gratefully acknowledged. The assistance of W. H . Baldwin, Oak Ridge Kational Laboratory, in the synthesis of other compounds is also gratefully acknowledged.
(3) Danis, D. G., ANAL.CHEM.32, 1321 il960'r. ( 4 j Handley, T. H., Dean, J. A., Ibid., 32, 1878 (1960). (5) Ibid., 33, 1087 (1961). (6) Michaelis, A,, Steinkopf, K., Ann. 326, 218 (1903). ( 7 ) Stathis, E. C., Anal. Chim. ilcta 16, 21 119571. (8) St'uebe,'C., Lankelma, H. P., J . Am. Chem. SOC.78, 976 (1956). (9) Tolkmith, H., Ibzd., 85, 3246 (1963). (10) Wendlandt, W. R.. Bryant. " _ J. M., gcience 123, 1121 (1956). (11) Wise, G., Lankelma, H. P.. J . Am. Chem. SOC.74, 529 (1952).
LITERATURE CITED
(1) Audrieth, L. F., Toy, A. 11. F., J . Am. Chem. SOC.64, 1553 (1942). (2) Buck, A. C., Bortleson, J. D., Lankelma, H. P., Ibid., 70, 744 (1948).
RECEIVEDfor review June 15, 1964. Accepted September 30, 1964. Research sponsored by the U .S. Atomic Energy Commission under contract with the Cnion Carbide Corp.
Simultaneous Colorimetric Determination of Iodate and Bromate M. H. HASHMI, HAMlD AHMAD, ABDUR RASHID,
and FAROOQ AZAM
West Regional laboratories, Pakistan Council of Scientific and Industrial Research, Lahore, West Pakistan
b An equimolar mixture of isonico-
EXPERIMENTAL
tinic acid hydrazide and 2,3,5-triphenyltetrazolium chloride in dilute hydrochloric acid gives a pink color with iodate at room temperature while with bromate the color is produced on heating. The reaction is developed into a colorimetric procedure for the determination of iodate and bromate separately and in presence of each other. Chlorate, halogens, inorganic ions, and organic compounds do not interfere.
Apparatus. All absorbance measurements were made with the Hilger Biochem Absorptiometer using 5 2 filter and 25-ml. cells. Materials. d l 1 reagents were of analytical grade or comparable purity. Iodate and bromate solutions were prepared by Xveight from their potassium salts. Isonicotinic acid hydrazide, 0.270 (by weight) aqueous solution and 2,3,5-triphenyltetrazolium chloride, 0.2y0 (by weight) aqueous solution were prepared. Procedure. IODATE. To a potassium iodate solution cont'aining 16 to 140 p g , of iodate, 1 ml. each of 0.2%, isonicotinic acid hydrazide and 2,3,5triphenyltetrazolium chloride are added. The pH of the solution is adjusted to 1.60-1.70 with 0.1X hydrochloric acid; the volunie is adjusted to 10 ml. and the mixture is let stand for 10 minutes a t room temperature (32-34" C.). The volume of the solution is then made to 50 ml. with ethyl alcohol and is let stand for 5 minutes before absorbance is measured. The experiment is repeated with various amounts of iodate and a plot of absorbance us. concentration of iodate is prepared. The reaction is found to obey Beer's lam. Iodate from the unknown sample may then be directly determined from the curve by measuring the absorbance after the reaction. BROMATE.T o potassium bromate solution containing 60 to 300 pg. of bromate, 1 ml. each of 0.2y0 isonicotinic acid hydrazide and 2,3,5-triphenylt'etrazolium chloride are added in a test tube and p H of the solution is adjusted to
M
have been reported for the spectrophotometric or colorimetric determination of iodate ( 2 , 4 ! 7 , 8) and bromate (3, 5 ) separately, but a method for the determination of the former in the presence of the latter would be desirable. During a systematic study of the action of organic compounds on halates it was found that an equimolar mixture of isonicotinic acid hydrazide and 2,3,5triphengltetrazolium chloride in dilute hydrochloric acid gives a pink color with iodate a t room temperature while bromate gives the color on heating. This reaction has been developed into a colorimetric procedure for the determination of iodate and bromate separately and in presence of each other. The visual limit of identification is 2 pg. and 3 pg. per nil. for iodate and bromate, respectively. Chlorate, Inorganic ions, and organic compounds do not Interfere. A N Y METHODS
0.86 with 0.5'V hydrochloric acid. The r e a d o n is allowed to proceed for 10 minutes at 60" C. in a water bath. The reaction mixture is cooled by tap water and is diluted with alcohol to 50 ml. in a measuring flask and is let stand for 5 minutes before absorbance is measured. The rest of the procedure is the same as for iodate. This reaction also obeys Beer's law. IODATE IS PRESENCE: OF BROMATE. Iodate is determined as above. Hromate in concentrations up to five times that of iodate does not interfere. BROMATEIK PRESESCEOF IODATE. Subsequently, bromate is det,ermined by the procedure given above. Solutions are prepared which contain different amounts of bromate and a constant, predetermined quantity of iodate present in the sample. The reaction is allowed to proceed for 1 minute at 60" C. in a water bath and the pH is adjusted to 0.74 with 0.55 hydrochloric acid. The plot of absorbance zw. concentration of bromate ( I h s constant, amount of predetermined iodate) obeys 13eer'e law. The amount of bromate from the unknown mixture of iodate and bromate may be directly det,ermined from the curve by measuring the absorbance after the reaction of the iodate-bromate mixture with isonicotinic acid hydrazide and 2 3 , s triphenyltetrazolium chloride. RESULTS A N D DISCUSSION
Temperature has a pronounced effect on color development. With iodate. color appears a t room temperature (34" C.) and the intensity iq increayed with temperature, becoming conatant VOL. 36, NO. 13, DECEMBER 1964
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