1125
V O L U M E 25, NO. 7, J U L Y 1 9 5 3 iodosobenzene wave was proportional to concentration up to 0.002 31 whether 4 X l O - 3 0 / 0 methyl cellulose was present or not. Anodic wave heights in the region 0.001 t o 0.002 M were approximately equal to cathodic wave I for iodosobenzene when measured a t the same concentration. On this basis it appears likely that the anodic wave involves two electrons. Slope analysis (plot of E ' / ? VR. log I/Id - I) showed a linear relationship for the anodic wave and yielded a slope of 0.13 a t either 0.001 or 0.002 M iodosobenzene. indicating an irreversible reaction between iodosobenzene and mercury. Iodosobenzene can be identified in the presence of iodoxybenzene by virtue of its different anodic behavior.
Table 11. Half-Ware Potentials, Diffusion CurrentConcentration Ratios, and Slope .4nalysis of Iodoso- and Iodoxj-benzene Waves Kave I Id
~~
Coinpound
--El/?
0.004 .VI iodo;oben0.88 zene 0.004J l i o ~ l o z y b ~ n - 0 . 8 8
W a i f . I1 Id px-
&.4
C'mh
Slope
3.84
0 04RU
7.92
0 04.jC
4CKNOW LEDG.M ENT
??'$&
Slopr
1.65
3 96
0.0clOb
1 65
4.02
0 09lb
-E1/2
tron addition a t a dropping-mercury surface takes place under considerably different conditions. The two types of reduction need not be comparable. The kinetics involved would he expected to be different due to the nature of the reducing agents, namely. iodide ions and electrons a t a mercury boundary. The polarographic reduction is an irreversible phenomenon occurring a t the mercury interface. Under these conditions, it is not too surprising that a certain threshold-applied potential is necessary before electron addition to either iodine compound is effected. This fact was considered in the polarographic reduction mechanism proposed. Preparation of fresh samples of iodoso- and iodoxybenzene and corresponding iodometric determinations assured the purity of the samples. The substantially double I d / C values for wave I obtained for iodoxybenzene as compared to iodosobenzene and the different anodic behavior observed for these two compounds further substantiate the authenticity of the materials investigated. The support of this investigation by the Research Corp. is acknodedged with gratitude.
mni.
LITERATURE CITED
Slope increases t o 0.14 at 0.001 AI.
b I n agreement with prpvio:isIy reported s l o i x s for C
Slor~ri n c r r a v s to 0.27 at 0.001 .\I.
iodohenzene ( 2 , 3 )
Comparison with Chemical Behavior. That both iodoso- and iodoxybenzene show the same half-wave potentials might a t first seem unusual. In ordinary chemical reactions the oxidation-reduction tendencies exhibited by these t\yo compounds are different. Iodosobenzene r d l oxidize iodide ions in a saturated b0ra.c solution, whereas iodosybenzene rvill not (8). The oxida2 0 H - = CsHJ02 tion potential of the couple CsHJO H20 2e. has been measured, and the electrode has been suggested for pH measurements (6). Reduction, however. by elec-
+
+
+
Colichman, E. L., J . Am. Chem. Soc., 74, i 2 2 (1952). Colichman, E. L., and hlaffei, H. P., Ibid., 74, 2744 (1952). Gergely, E., and Iredale, T., J . Chem. Soc., 1951, 3502. Gilman, H., "Organic Chemistry, -4n Advanced Treatise," Vol. 11, 2nd ed., p. 1840, Kew York. John Wiley & Sons, Inc. 1938. Grossman, F., Roczniki Chem., 7, 567 (1927); Bzill. SOC. chim., 43, IO63 (1928).
Lucas, H. J., and Kennedy, E. R., Org. Syntheses, 22, i 2 (1942). Lucas, H. J., Kennedy, E. R., and Formo, AI. I\-.,Ibid.. 22, 50 (1942). Masson, I., Race, E., and Pounder, F. E., J . Chem. Soc., 1935, 1669. Stackelbcrg, 11. V.,and Stracke, W.,Z. Elektrochem., 53, 118 (1949). R E C E I V Ef oDr review Aiigl.ist 2 6 , 1952.
. I c c e p t e d April 10, 1953
Trimethylphenylammonium Iodide, Quantitative Precipitant for Bismuth T. S. BURKHALTER' AND JOSEPH F. SOLAREK* North Texas State College, Denton, Tex. RGASIC
precipitants for inorganic ions generally offer the
0 advantage of a favorable gravimetric factor for calculating
weight of inorganic ion from n-eight of precipitate. This is especially true in the case of the inorganic ion, bismuth. where the normal form of t,he completely inorganic precipitate (usually bismuthox)-chloride or bismuth trioxide) exhibits an exceptionally unfavorable gravimetric fact,or. 0.802 for the oxychloride and 0.897 for the oxide. Nany organic reagents have been suggested as precipitants of bismuth. but none have proved to be completely satisfactory. Ethylenediaminecobalt(II1) chloride ( 1 , 10, 1 4 ) and diethylenediaminedithiocyanatocohalt(II1) thiocyanate (10, 1 7 ) quantitativell- pwcipitate the bismuth ion, but the precipitate must be vnruum dried in order to prevent decomposition. 8-Quinolinol ~quinolinol-5-sulfonicacid ( 4 ) ]and dithizone ( l a ) afford ctory precipitates. but none show any selectivity toward bismuth, each precipitating practically all the heavy metals. The use of a-naphthaquinoline (6, 10)requires a very critical control of precipitating conditions to ensure quantitative precipitation wit,hout excess contamination. The use of trimethylphenylammonium iodide as a precipitating agent for bismuth overcomes all these difficulties. The precipita1
Present address, Texas .-i. &- 11.Collrge, College Station, Tex.
- Present addrrss Phillips Chemical Co. Borger.
Tex.
tion is quantitative, the precipitate is readily filterable and can be oven dried at 120" C. Group I1 and the noble metals interfere, but these are easily removed by standard separation practices. Several quaternary ammonium compounds have been suggested for various analytical uses. Remy (15') has described the preparation of several quaternary ammonium bismuth compleies: Girard (3) has reported the use of tetracetylammonium hydroxide for the detection and colorimetric determination of bismuth. Tetraethylammonium chloride has been used by Jones ( 7 ) for the microscopial identification of bismuth. However, none of these compounds has been described as a quantitative precipitant for bismuth. Among these quaternary compounds trimethylphenylammonium iodide has the advantage of being readily available, either commercially (Fisher Scientific Co.) a t a reasonable cost, or by simple synthesis from dimethyl aniline and methyl iodide ( 1 6 ) . Kiba ( 8 ) first reported the use of this salt as a spot test reagent for the detection of cadmium. Pass and Ward ( 1 1 ) have described a volumetric method for the quantitative determination of cadmium using trimethylphenylammonium iodide, but the procedure is long and tedious. The American Zinc Co. of Illinois (4) has refined and greatly simplified this method by conversion to a gravimetric process. The utilization of this reagent depends upon the formation of
ANALYTICAL CHEMISTRY
1126
an insoluble salt of the quaternary entian and a comples inetnl halide anion. I n the ease of bismuth the compound formed is [(CH&(C6H5)N]+ B i V and contains 24.5% bismuth. Under the precipitation conditions employed in this lahoratory the t e t r a hydrate rather than the anhydrous salt is the compound isolated and weighed. For the tetrahydrate thc gravimetric factor is 0.226. The tetrahydrate is a sernigrsnular orange-colored material vhich can he oven dried to constnnt weight at temperatures between 110' and 120' C. It is not practical to attempt to change the precipitate to the anhydrous form as this requires ~ ~150" C., and in this temperature region temperatures in e x c e of decomposition of the salt occurs.
temperature. Failure to digest the precipitate results in incomplete formation of the tetrahydrate and low results. Apparently the anhydrous form is precipitated initially with euhsequent formation of the hydrate. The precipitate is transferred to a tared Gooeh or fritted-glass crucible, washod withdilute reagent ( 1 , S), then with dilute sulfuric acid ( 1 , 16), and finally with 95% ethyl alcohol. The reproducibility and reliability of results are shown in Table I. The results obtained by running 18 checks on aliquot portions of a single sample. each aliquot of whioh contained 0.04450 gram of bismuth, gave an average of 0.04445 gram of bismuth with an average deviation from the mean a l 0.00037 gmm and a relative error of 1.1 parts per thousand. LITERATURE CITED
Table I.
Roproduleihility
w-t. of ~i per *iiquot (sthndara" AT. wt. oi Bi found .4v. deviation from In
