active species has no charge and oxidation of mercury is clearly not involved. A possible explanation of the current decrease may be based on the desorption of the tin-pyrogallol complex, assuming adsorption of the complex is necessary for its reduction and the rate of adsorption is large compared to the rate of diffusion of the species to the electrode surface. At negative potentials, the complex is desorbed, probably being replaced by pyrogallol or water molecules, and the current decreases. I n the presence of Triton X-100 at concentrations higher than O.OOl%, the current decrease is more pronounced and begins a t more positive potentials (Figure 1). The extent of decrease becomes smaller with increasing concentration of sodium perchlorate (Figure 3). For the reduction of an uncharged molecule Frumkin gives the equation (3): i
= kCb
exp [-
CY(+
- $q)F/RT]
(where k is a constant, Ca is the bulk concentration of the electroactire species, .$ is the potential difference between the electrode itself and the solution, and is the potential of the inner Helmholtz layer). Adsorption of cations makes more positive, making the e-xponential term more positive and increasing the current at a given potential (4). The increase of current a t the minimum with increasing NaC104 concentrations may be this effect, and implies that the adsorbed film of Triton X-100 interferes with the electron-transfer step in the reaction rather than with the penetration-step of the complex through the adsorbed film [as was found by Loshkarev and Kryukova for the reduction of neutral species (12)1. Current-time curves during a single mercury drop are useful in examining
adsorption effects (6, 18). Currenttime curves in this case indicate the difference of inhibition behavior in the absence and the presence of Triton X100 (Figure 4). I n the absence of maxima suppressor (Figure 4,A) curves are characteristic of processes where surface coverage is controlled by the adsorption equilibrium, in this case the desorption of the complex [compare with (18) Figure 41. I n the presence of Triton X-100 (Figure 4,B and c), the current-time curves go through a maximum, indicative of surface coverage controlled by the rate of diffusion of the inhibiting species [compare (181, Figure 21. I n this case the concentration of the adsorbing species (Triton X-100) is low, and the relative rate of coverage to rate of growth of the drop increases during the drop life. The mechanism for the current decrease in the absence of maxima suppressor (desorption of the electroactive species) may be the same for the decreases found for molybdenum(V1) in tartrate media (IC), and for vanadium (V) in oxalate (11) and EDTA (15) media. The current decrease in the presence of maxima supressor is similar to that found for tin(1V) in a chloride medium upon addition of camphor ( 7 ) . The decrease of id/C a t tin concentrations greater than I m M may be caused by the inability of a n equilibrium amount of complex to be adsorbed during the drop life. A similar decrease of id/C was observed during the reduction of cadmium(I1) in a n alkaline tartrate medium (9). Since this wave was affected by addition of gelatin, an adsorption effect for the decrease seems likely. Interference by other metals depends upon their polarography in a pyrogallol medium, a study of which is currently being made in this laboratory. I n
practical analysis, use may be made of the passage of the electroactire complex through both anion and cation exchange resins, and the nonreduction of the complex a t pH’s greater than 5 or 6. LITERATURE CITED
( 1 ) Abichandani, C. T.. Jatker, S.K. K., J . Indian Inst. Sci. 21 A, 417 (1938). (2) Delahay, P., Trachtenberg, I., J . Am. Chem. Soc. 79, 2355 (1957). (3) Frumkin, A. N., Trans. Faraday Soc. 55, 156 (1959). (4) Kivalo, P., Laitinen, H. A , , J . Am. Chem. Soc. 77, 5205 (1955). ( 5 ) Kolthoff, I. M., Lingane, J. J.,
“Polarography,” Interscience, Sew York, 1952. ( 6 ) Laitinen, H. A,, Onstott, E. I., J.
Am. Chem. Soc. 72, 4565 (1950). (7) Laitinen, H. A,, Subcasky, IT, J., Ibid., 80, 2623 (1958). (S).La$mer, W. M.,“Oxidation Potentials, Prentice-Hall, Xew York, 1952. (9) Lingane, J. J., IYD. ENG. CHEM., ANAL.ED. 15, 587 (1943). (10) Lingane, J. J., J . Am. Chem. Soc. 67,
919 (1945). ( 1 1 ) Lingane, J. J., Meites, L., Zbzd., 69, 1021 (1947). (12) Loshkarev, M.A,, Kryukova, A. A., J . Phys. Cheni. (L‘.S.SR.) 31, 542 (1957). (13) Meites, L., J . .4m. Chem. Soc. 72, 2293 (1950). (14) Parry, E. P., Yakubik, M. G., ANAL.CHEM.26. 1294 (1954). (15) Pecsok, R. L.’, Juvet, R. S., J . Am. Chem. Soc 75, 1202 (1953). (16) Phillips, S. L., Morgan, E., AKAL. CHEM.33, 1192 (1961 ). (17) Schaap, K. B., Davk. J. .4., Xebergall, K. H.. J . A m . Chem. Soc. 76. 5226 11954) (18) Schmid, R. IT.,Reille), C . S.,Ibid., 80, 2087 (1958). (19) Sheppard, S. E., Trans. .4m. Electrochem. Soc. 39,429 (1921). (20) Takagi, S.,Sagase, Y.,J Pharm. Soc. Japan 56, 170 (1936) (21) Welcher, F., “Organic AnalyticaI Reagents,” p. 161, Van Yostrand, Xew York, 1947. RECEIVEDfor revieF August 17, 1961. Accepted November 30, 1961.
Polarographic Behavior of Indium in Presence of Chloride EDWARD D. MOORHEAD’ and WILLIAM M. MocNEVlNa McPherson Chemical Laboratory, The Ohio State Universify, Columbus
b A study of indium reduction a t the dropping electrode in noncomplexing perchlorate supporting electrolytes and in the presence of varying concentrations of chloride yielded results which cast considerable doubt on previously reported, polarographically obtained dissociation constants for the chloride complexes of In(III).
T
IO, Ohio
chemically similar to gallium in many respects, indium differs from that element curiously in its pronounced ease of reduction in the presence of, e.g., chloride or thiocyanate (3, 7, 10, 11). The reduction of indium at the dropping mercury electrode (d.m.e.), unlike that of gallium, exhibits a minimum on the diffusion HOUGH
current plateau in the presence of polarizable supporting electrolytes. This paper discusses several aspects of indium polarography in the light of 1 Present address, Coolidge Laboratory, Department of Chemistry, Harvard University, Cambridge 38: Mass. 2 Deceased.
VOL 34, NO. 2, FEBRUARY 1962
0
269
2.0
L
0.0
I
-0.40
-0.80 E
VI
-1.20
, - 1.60
S.C. E. (volts)
Figure 1. Corrected cathodic wave for 5 X 10-4M In(lll) in equivalent chloride, 0.1M KNOa and 0.01% gelatin experimental data obtained for the indium system in the course of two recently reported, comparative studies of the electrochemical behavior of gallium in solutions of thiocyanate (9, 11). Our examination of the reduction behavior of In(II1) in the presence of chloride yielded results which cast considerable doubt on the significance of accepted, polarographically obtained dissociation constants of InCl,(3-.) reported by Schufle, Stubbs, and Witman (19). Further, the results of our study of indium reduction in perchlorate medium are in serious disagreement with those reported by Schufle et al. (19) but are consistent with those reported earlier by Lingane (8).
-1.00 volt us. S.C.E.) for the droming In(Hg) electrode (0.0005 weight % In7 in O.1N KNOa. Reagents and Chemicals. Indium chloridY, indium oxide, and indium metal were of Specpure grade obtained from Johnson-Matthey, Ltd. Stock indium solutions were prepared by dissolving the metal, or oxide. in a calculated excess of the appropriate mineral acid. All other chemicals, including mercury, were of reagent grade. All solutions were prepared with demineralized, double-distilled water and outgassed, when necessary, with Linde high purity nitrogen.
EXPERIMENTAL
Indium in Presence of Nitrate and Perchlorate. Repeated careful efforts to obtain a cathodic reduction wave for 1 X and 5 X 10-4M In(II1) in acidified (with boiled HNOJ O.1M KNOa adjusted to a pH of 1.35 and in 2M KNOa adjusted to a pH of 1.20 yielded residual current curves which showed no reduction of indium prior to the final reduction of the supporting electrolyte. The experiment was repeated, again without success, using the dilute (0.0005 weight % In) d.In(Hg).e. In this instance, however, a well-defined anodic wave was obtained a t -0.47 volt us. S.C.E., but, on crossing the abscissa, the cathodic current remained essentially flat, until the final current rise attributed to hydrogen ion reduction. The slope of the anodic wave, which proved to be slightly less than that for either the reversible, anodic wave for gallium [obtained with the dropping gallium amalgam electrode ( 9 ) ] or the reversible, 3-electron reduction of indium in the presence of chloride, indicated that the oxidation of indium from the amalgam was proceeding with some degree of irreversibility. A current-voltage study of the reduction of 1 x 10-3M In(C104)s in 0.1V NaC1O4 (prepared from reagent grade HC104 and NaOH to minimize the inclusion of chloride as an impurity)
Current-voltage (c-v) data were obtained with both the Leeds & Northrup Electrochemograph and a precision, manual instrument especially constructed for the purpose. The latter instrument, polarographic procedures used in this investigation, cells, capillaries, and method of preparing the dropping amalgam electrodes have been described (9). Half-wave potentials determined in this investigation are reported us. the saturated calomel electrode with liquid junction. The reference potential was calibrated experimentally by comparing the observed Ell2 of a Tl(1) reduction wave (-0.460 0.003 volt) with the accepted Ell2 (-0.459 =t 0.003 volt) of the TlII) reduction wave in 0.1111 KNOa (S).‘’ Dropping Indium Amalgam Electrode. The amalgam electrode was used and stored- in an all-glass apparatus modified (9, 10) after the designs of Cooper and Wright (2) and Furman and Cooper (6). Between runs the nitrogen gas above the amalgam in the reservoir was restored to atmospheric pressure and the amalgam allowed to drop continuously into either ethyl alcohol or acidified distilled water to prevent clogging of the capillary orifice. Capillary Characteristics. mz’3t1’6 = 2.403 mg.2/s t-1’2 (Esppld= -1.20 volts us. S.C.E.) for the d.m.e. in 7.5M KSCN; 2.125 mg.*’a t-1’2 ( E a p p i d . =
*
270
ANALYTICAL CHEMISTRY
RESULTS AND DISCUSSION
acidified to a pH of 1 with HClO4 fully substantiated Lingane’s original observation (8) that no reduction wave occurs for indium prior to the drawnout, irreversible In(II1) wave a t -0.95 volt us. S.C.E. The polarographic data were taken with a newly prepared, saturated calomel electrode which utilized a freshly prepared, saturated NaN03-4a/, agar salt bridge. The dropwise introduction of 0.1M NaCl to the perchlorate test solution resulted in a new, small wave forming a t about -0.53 volt us. S.C.E. which increased in height as more chloride was added. Indium in Presence of Chloride. A study of indium reduction in the presence of 1.0 and 0.1M KC1 yielded c-v waves which confirmed the very unusual minimum (pronounced in 1M KC1 but much shallower in 0.1M) on the diffusion current plateau first reported by Lingane (8). [A theory has been proposed by Frumkin and Frumkin and Florianovitch (4, 5 ) to explain the existence and behavior of similar minima noted on the reduction waves of Sz08-2, PtC14-2, and Fe( C S ) B - ~ ] . Lingane observed -0.595 and -0.561 volt us. S.C.E. for EIl2lnin 1.0 and 0.1M KC1, respectively. Our measurements are in agreement, and, in addition, we also find -1.4 volts us. S.C.E. for the potential a t the low point of the minimum in 1.0M KCl. Our studies of 1 X 10-3M In(II1) in 0.1K KSCN show a similar minimum a t -1.08 volts us. S.C.E. More recent work has shown this minimum to become narrower and to occur a t about -1.4 volts us. S.C.E. in 7,531KSCK. The serious inconsistency between the El,2 of In(II1) reduction in perchlorate and the El12 in HCl of concentration less than 0.1M contained in the report by Schufle et al. (12) wag not discussed by these authors. Accordingly, an examination of In(II1) reduction a t lower chloride concentration was undertaken. Figure 1 shows the typical behavior of indium in equivalent chloride-Le., 5 X 10-4M In(II1) in 15 X 10-4i11 KC1-in 0.1M KKOs to which freshly prepared gelatin had been added. The presence of gelatin up to about 0.005 weight yo had no sensible effect on the wave. Unlike gelatin, however, Triton X-100 (Rohm & Haas) added to the solution caused a decrease in the indium diffusion current. A concentration of Triton X-100 greater than about 0.008 weight % caused the wave a t -0.53 volt to disappear completely and a new wave to form a t -1.4 volts us. S.C.E. The two reduction steps shown in Figure 1 correspond, first, to the reversible 3-electron reduction of In(II1) t o the amalgam, while the second, small wave occurring a t about -1.5 volts vs. S.C.E. is evidence for the reduction of hydrogen ion generated by the hy-
drolysis of In(II1) under these conditions. A plot of log [t&i] us. ESppl. for the indium wave of Figure 1 yielded, under these conditions, a straight line with reciprocal slope of 0.020 volt in good agreement with theory (0.0197) for a 3-electron reduction; previous work (8, 12) consistently noted a larger reciprocal slope. The voltage intercept, after careful correction for iR drop and different salt bridge, was 0.003 volt us. found to be -0.531 S.C.E. As might be expected for a complexing cation, the observed El,2 in equivalent chloride is more positive (less reducing) than the potentials reported previously for reduction in 0.1 and 1.OM chloride. Moreover, it is 8 mv. less reducing than the E1,2 reported by Schufle et al. for 0.01M HC1. Significantly, the observed El,* in equivalent chloride is considerably more positive than the value -0.573 volt us. S.C.E. reported by Schufle et al. for the so-called reversible, uncomplexed In(II1) wave in perchlorate supporting electrolyte, notwithstanding the fact that indium in equivalent chloride is most probably complexed to a small extent ( I ) . Thus, on the reasonable assumption that In(II1) in equivalent chloride and 0.1M KN03 is complexed either by hydroxide or chloride (or both) our observed value of -0.531 f 0.003 volt US. S.C.E. would, of course, be more negative us.
S.C.E. than the true
result, a t least in part, of (chloride) Eli2 of the “uncontamination of the test solutions. complexed” aquo In(II1) ion by a term (in the Heyrovskji-IlkoviE equation) involving the indium complexity conACKNOWLEDGMENT stant(s). One of the authors (E.D.M.) is Current-voltage experiments with grateful for the use of facilities provided careful exclusion of chloride have conby Princeton University and for finanfirmed the irreversibility of In(II1) cial support provided by Carter Prodreduction in acidified perchlorate meucts, Inc., for part of this work dium. Measurements of indium re(indium in perchlorate). duction in the presence of equivalent chloride have yielded a corrected E111 of LITERATURE CITED -0.531 f 0.003 volt us. S.C.E., which is 42 mv. more positive (less reducing) (1) Bjerrum, J., ed., “Stability Conthan the value reported by Schufle stants,” Vol. 11, Butterworths, London, 1958. et al. for the “reversible” reduction of ( 2 ) Cooper, W. C., Wright, M. M., indium in noncomplexing perchlorate ANAL.CHEM.22,1213 (1950). medium. On the basis of these experi(3) Cozzi, D., Vivarelli, S., 2. Elektromental results, and accepting the notion chem. 58,907 (1954). (4) Frumkin, A. N., Trans. Faraday SOC. that a reversibly reduced complexed 55, 156 (1959). metal ion reduces a t a more negative (5) Frumkin, A. N., Florianovitch, G. M., than the reversibly reduced, simple Dokladu Akad. Nauk S.S.S.R. 80, 907 metal ion, it is concluded that the dis(1951).” (6) Furman, N. H., Cooper, W. C., J . Am. sociation constants reported by Schufle Chem. SOC.72, 5667 (1950). et at. for the dichloro (1.5 to 3.3 X (7) Kolthoff, I. M., Lingane, J. J., 10-2) and tetrachloro (6 to 13) indic “Polarography,” Vols. I, 11, Interions cannot be correct. Indeed, as science, New York, 1952. (8)-Ljngane, J. J., Ph.D. dissertation, the indium system is not polarographbnlversitv of Minnesota. 1938:’ J . Am. ically reversible in noncomplexing supChem. So;. 61, 2099 (1939). porting electrolytes-i.e., El,z, Eoamnlrsm (9) MacNevin, W. M., Moorhead, E. D., (uncomplexed) are not obtainableIbid., 81,6382 (1959). (10) Moorhead, E. D., Ph.D. dissertation, the unambiguous determination of these Ohio State University, 1959. constants in a straightforward polaro(11) Moorhead, E. D., Furman, N. H., graphic manner is a t most very unlikely ANAL.CHEM.32, 1507 (1960). (12) Schufle. J. A.. Stubbs. M. F.. ( J J7 ) ’ @itman, K. E., J.‘Am. Chem. Soc. 73; Our observations strongly suggest 1013 (1951). that the reversible In(II1) wave obtained by Schufle et al. a t -0.573 RECEIVEDfor review July 10, 1961. volt in perchlorate medium was the Accepted November 28,1961.
Separation of Isopropyl Alcohol from Aliphatic Sulfides and Thiols by Gas Chromatography VINCENT J. FARRUGIA and CHARLES L. JARREAU Oronite Division, California Chemical Co., Belle Chasse, l a . A method is described for gasliquid partition chromatographic separation of isopropyl alcohol from a series of seven aliphatic thiols and three aliphatic sulfides utilizing a twocolumn technique. The relative retention time and the retention volume per gram of stationary phase are listed for each compound on a system of dual columns as well as for individual columns.
C
odorizing agents for odorless natural gases are composed primarily of low molecular weight mercaptans or sulfides. Isopropyl alcohol is sometimes added to these warning agents as a cloud point suppressant. OMMERCIAL
Previous analytical methods for separation of aliphatic sulfides, mercaptans, and alcohols were time-consuming and required combinations of distillation and spectroscopy to be effective. Gasliquid chromatography has been applied with much success in the separation and identification of sulfur compounds. There are now available many investigational reports for a variety of partitioning agents used as stationary phases for gas-liquid chromatographic separations of thiols, sulfides, and alcohols. Desty and Whyman (4) used a dual stationary phase technique with hexatriacontane and benzyldiphenyl on Celite 545 with nitrogen as carrier gas and reported retention times for seven sulfur compounds. Analysis of C4 to Ca thiols
was reported by Sunner, Karrman, and Sunden (9) and by Liberti and Cartoni ( 6 ) . Ryce and Bryce (7‘) describe optimum conditions for the use of tritolyl phosphate on Celite 545 with helium as eluent gas to separate sulfur compounds from methyl alcohol, ethyl alcohol, and hydrocarbons. Amberg ( I ) reported separation of CSto Ca thiols and sulfides using this stationary phase on firebrick with nitrogen as eluent gas. Coleman et al. (2) employed Dow Corning 550 silicone oil an acidwashed firebrick and helium as the eluent gas to separate C3 to Cg sulfides and thiols. Spencer, Baumann, and Johnson (8) reported separation of C1to Ca thiols and sulfides using dinonyl phthalate on firebrick with helium as VOL. 34, NO, 2, FEBRUARY 1962
271
