V O L U M E 25, N O . 6, J U N E 1 9 5 3 Table 11.
Spectrophotometric Data of Various PhenolTitanium Complexes
Name of Phenol m-Aniinophenol a-.4minophenola p-Aminophenol p-Bromophenol Catechol p-Chlorophenol a-Cresol 2,4-Dichlorophenol p-Ethylphenol Hydroquinone p-Hydroxybenzaldehyde p-Hydroxybeneoic acid 5-Hydroxy-l,3-dimethylpheno 1-Naphthol
Wave Length of Max. Absorption,
14p 417
...
2-Iiaphthol o-Nitrophenol" p-Nitrophenol Phenol o-Phenylphenol p-Phenylphenol Phenyl salicylate Phloronlucinol
Specific E x t . , Liter/(Gram Cm.) 12.6
...
418 473 460 465 455 490 473 503 420 390 453 440 655 435
17.6 20.6 27.4 18.4 16.2 16.8 34.4 63.2
451 455 450 482 435 415 460 405 469 438
5.0 15.6 12.2 28.8 15,7 4.7 22.4
...
...
a
983
1.5
4.3 17.7 33.6 35.2 28.4
...
6.8
16.8 20.4
No visible absorption spectrum. Failed t o dissolve in titanium sulfate reagent.
nip obtained with the earlier method when reacting the reagent with the solid phenol. There was no indication of secondary absorption maxima. &4color complex with a 1 to 1 molar ratio of o-phenylphenol to titanium is indicated by Figure 2. A study of catechol-titanium and hydroquinone-titanium complexes Pholved that they also formed in a 1 to 1 molar ratio. Griel and Robinson ( 1 ) reported the thymol-titanium complex formed with a 1 to 1 molar ratio. Appreciable dissociation is indicated with all four of these complexes. Testing the Method of Analysis. The following example illus-
trates the accuracy of the procedure. Samples of vegetabletanned sheepskin were prepared containing between 1.0 and 2.0% of o-phenylphenol by weight. These samples were leached by ether and reacted with titanium reagent as described in the procedure. The experimental results, presented in Table I, indicate an error of about 1.5%. Sublimation of o-Phenylphenol. B sample of 0.3144 grams of o-phenylphenol with a surface area of 2.46 sq. cm. lost about 0.2% by weight when heated for 12 hours a t 37' C. This emphapizes the importance of reacting the solid o-phenylphenol with the titanium reagent immediately after evaporation of the volatile solvent. Reaction of the Titanium Reagent with Other Phenols. The color-forming characteristics of the complexes formed in the reaction of the titanium sulfate reagent with 27 phenols have been recorded in Table 11. Included are the wave lengths of maximum absorption and the specific extinction coefficients, which have been calculated on the basis of 100% association of the phenol. These data indicate both the relative interference of the various phenols with the estimation of o-phenylphenol and the utility of the titanium sulfate reagent in the estimation of the various phenols. 4ChNOWLEDGMENT
Part of the spectrophotometric measurements in this investigation were made by the first author on the Cary spectrophotometer of the United States Air Force, Materials Laboratory, Kright .4ir Development Center, Dayton, Ohio. LITER4TURE CITED
(1) Griel, J. V., and Robinson, R. J., h . 4 ~ CHEW, . 23, 1871 (1951). (2) Hall, J., and Smith, J., Proc. Phil. Soc., 44, 196 (1905). (3) Lenher, V.,and Crawford, W.G., J . Am. Chem. Soc., 35, 138 (1913). (4) T-oshurgh, I T , C., and Cooper, G. R., Ibid., 63,437 (1941). R E C E I ~ for E Dreview Soyember 24, 1953. Accepted March 2, 1953.
Polarographic Characteristics of Metallic Cations in Acetate Media MICHAEL A. DESESA AND D.47lD Y. HUME Massachusetts Institute of Technology, Cambridge 39, AMass. ARTHUR C. GLAJIM, JR., AND DONALD D . DEFORD .Vorthu.estern University, Ecanston, I l l . XCIDEPZTAL to
a study of complex formation in acetate medium
I ( 2 ) and the development of a polarographic method for the
determination of indium ( 1 ), observations have been made of the polarographic characteristics of 29 metal ions in various acetatecontaining supporting electrolytes. The measurements were made with Model X X I Sargent visible recording polarographs. The initial and final span voltages were measured to 1 0 . 1 mv. with an auxiliary potentiometer when very precise determinations of half-wave potentials were required. All measurements were made a t 25 + 0.1" C., and corrections were applied for zR drop in the cell unless negligible. Potentials were measured directly against the saturated calomel electrode. In the 1I.I.T. aork, the supporting electrolyte was always a mixture 2 -l4in ammonium acetate and 2 *If in acetic acid with 0.01% of gelatin added as a maximum suppressor. The workers at Sorthwestern University employed a mixture 1 -11each in sodium acetate and acetic acid, unless otherwise indicated, with 0.001%gelatin added. All reagents were made up from c.P., or better, grade chemicals. Most of the metallic constituents were used as solutions of the nitrates in dilute nitric acid. Reagent grade disodium acid arsenite, sodium molybdate, thallous acetate, stannous chloride, gallium sesquioxide, ferrous sulfate, tungstic acid, vanadium
pentoxide, gold chloride, and indium metal were used in the preparation of the corresponding stock solutions. The palladium stock solution was obtained by dissolving the metal in aqua regia. Where complex-forming anions such as chloride could not be excluded in the preparation of the stock solution, care was taken to keep their concentration low enough in the final acetate mixture so that they exerted no appreciable influence. Polarograms were taken with the various metallic constituents present a t a concentration of 0.001 M. The data are summarized in Table I. The half-wave potentials in the two media were found to be similar but not identical, values in the more concentrated buffer invariably being slightly more negative. Experiments with a number of the elements showed the half-wave potentials to be quite dependent on acetate ion concentration, as would be expected in view of the fact that most of the elements form moderately stable acetate complexes. Copper, although showing a single wave in acetate buffers of moderate concentration, developed a clearly defined double wave in 4 -21ammonium acetate, indicating stabilization of the cuprous state. The double wave obtained with antimony was not inveatigated further but is probably attributable to sluggish equilibrium between different complex formfi. Uranyl ion in 1M am-
ANALYTICAL CHEMISTRY
984 Table I. Polarographic Characteristics of Metal Ions i n Acetate Media, pH 4.8 Ei/a CharE'/¶ 1 M NaOAc aoter- 2 M NHdOAc CharacElement + I M HOAc istics + 2 M HOAc teristics
... ... ...
...
-0:ioo ...
WN
-1.2 -0.9 -0.051 -0.004 -1.4
+0:i 3 6 ... K.W.
FB ...
... ...
WR
-0 4
P7K
... P
-0.599
-0.2
WRa W-Ka,e
-0:458
6R
. . I
...
...
X.W. -1.2 -0 072 10.0
K.W.
WN" ' b
-1.0 -0,476 .
>o.o
-0,250 -0,653
P WN PN PN
...
.
-0.92 K.W.
... ...
... I
> +o. 2
...
... ...
... ... m-N
U' P ,
..
w
TV WR B P
w
P" B
h*.W.
...
-0.708
\V R
>o.o
N.W.
-0.6: -1.1: -1 2 -1.1 -0,499 -0.6
w
...
PB
wR P
h-d
-0.624 -0.156
WR, W
-1.1 -0,467 -0.448 >o. 0
WR
-1.2
P
m-R
P PB I WNB
+1+0 + 3 + 0 (?)
-----. --...
+3-?
+3 0 (?) +2-0" +2 0 +3 +2 (1) +2 0 +3 ---c + 2 $2 0
+2 f3
... 0 0
7
+2-0 +2 0 +2 0
?
f2 +2
0 +4
+4+1-0 +6+ +5 +4
IC
3.2 6.J
3.1 3.7 2.9 2.7 ... 4.2; 2.6 ... 2.4 2.3 l.5C 1.71 1.5 1.8 ( d / ( C m 2 / 3 t l / 9 in 1 .VI NaOAc, 1 M H 0 . 4 ~with 0.001% gelatin. td/(Cmz/atl16)i,n 2 i M NHaOAc, 2 'VI HOAc with 0.01% gelatin. id/iCm2/atI/') in 1 M NHaOAc. d For the sum of both waves. e Sn(I1) 'Sn. f U(V1j C(V).
...
;
-
"
f 2
+5
f4 +3 (1)
...
-i:039 -1.1 +2 0 X.W. ... ... W = well defined wave and diffusion current p = poorly defined wave and diffusion current. R = reversible K = not ;eversible B = breakdown of supporting electrolyte interferes with the ware, and X'.W. = no wave. Hydrolysis resulting in precipitate formation gives difficulty. Half-wave 'potential p H dependent. Potenhal given is zero current potential for a solution 1.0 X 10-3 .M in mercuric ion and 1.0 .M in ammonium acetate ( p H = 7.0). Three ill-defined waves. d T n o vell-defined waves of about equal height. Anodic wave. f Very small wave, even after standing 24 hours. Does not correspond t o a normal polarographic reduction. . . I
IC0 4.1 3.1c 2.9
Electrode Process
P C
-0,400 -0.593
(-0.70)
.
Table 11. Diffusion Current Constants i n Acetate Supporting Electrolytes a t 25" C.
The polarograms obtained for bismuth(II1) cadmium, copper, indium, lead, antimony(III), tin( 11), thallium(I), uranium(V1) and zinc showed diffusion currents which were well enough defined to suggest that the waves could be used for analytical purposes. Some of the diffusion current constants have been estimated and are given in Table 11. The diffusion current constants of several of the metals are greatly dependent on medium, and the values given should not be used as a substitute for a calibration curve. The values given were obtained using capillaries with droD times in the range - of 3 to 5 seconds and delivering between 2 and 3 mg. of mercury per second, and solutions 0.001 llf in reducible constituent. ACKNOWLEDGMENT
The authors are indebted to the U. S.Atomic Energy Commission for partial support through the agency of the XI.1.T. Laboratory for Suclear Science and Engineering. LITERATURE ClTED
monium acetate showed two waves, the first well-defined and reversible a t -0.434 V. corresponding to reduction to the +5 oxidation state. The second, a t about - 1.2 v., was poorly defined and probably involved reduction to the +3 state.
(1) DeSesa, 31. A , Ph.D. thesis, Massachusetts Institute of Technology, 1953. (2) Glamm, -4.c., M . S . thesis, Xorthwestern University, 1949. RECEIVEDfor review January 15, 1953.
Accepted March 3. lQ53.
Stable, Sensitive linear Starch Indicator Solution for Iodimetry JACK L. LAMBERT Kansas State College, Manhattan, Kan. STABLE
solution of linear starch fraction in 10% acetic acid is
A described here as an extremely sensitive end point indicator
for volumetric iodimetry. As it contains the pure linear fraction, the end point is sharp, and the intense blue color of the linear starch-triiodide (Is-) ion complex is without the purplish tint noticeable with starch solutions containing the branched starch fraction or partially degraded starches. Members of an undergraduate quantitative analysis class who used this indicator found that 1 to 2 ml. were sufficient for titrations in which the total volume a t the end point was 150 to 250 ml., in place of the 3 to 5 ml. of the usual starch solution. PREPARATION
The indicator solution is prepared by dissolving 2.5 grams of linear potato starch fraction, twice-recrystallized from 1-butanol by the method of Schoch and coworkers (3, 7, 8 ) , in less than 600 ml. of boiling distilled water and filtering while hot through lowspeed (barium sulfate retention grade) filter paper. After cooling, 100 ml. of concentrated (glacial) acetic acid, which has been diluted to approximately 200 ml., is added with stirring and the volume is brought up to 1 liter. Concentrated acetic acid causes temporary flocculation of the linear starch when added without prior dilution. Any slight turbidity remaining in the solution
usually settles out after 1 or 2 weeks but does no harm if present. The amount of turbidity is related to the uality of the crystalline linear starch used, as demonstrated by a jightly greater turbidity in one batch of solution prepared with an inferior sample of oncerecrystallized linear potato starch. DISCUSSION
This indicator is an outgrowth of the development of a linear starch-iodate colorimetric reagent ( 2 ) , in which it was observed that a solution of twice-recrystallized linear potato starch fraction and a small amount of potassium iodate in 10% acetic acid showed no precipitation or increase in turbidity after shelf storage for 1 year in clear glass bottles. Berause of retrogradation and growth of microorganisms, ordinary starch indicator solutions must be prepared as needed for use within a few days or weeks. Experiment proved that the 10% acetic acid alone kept the solution free of microorganisms and prevented retrogradation of the linear starch, as did cadmium iodide in the cadmium iodide-linear starch colorimetric reagent ( 1 ) . The latter reagent itself could be used as an end point indicator in reactions where cadmium ion would not interfere, although there is evidence (6) that cadmium iodide solutions react slower with oxidizing agents than do other iodide
