(9) Kolthoff, I. M., Elving, P. f.,“Treatise on Analytical Chemistry,” Part 11, Vol. 2, Sect. A., Interscience, New York, 1962. (I?) Kolthoff, I. M., Stenger, V. A., Volumetric Analysis,” Vol. 11, p. 181 et seq. Interscience, Kew York, 1947. (11) MacNevin, W. M., Moorhead, E. D., J . Am. Chem. SOC.82, 6283 (1959). (12) Pvlilligan, IT.O., Weiser, H. B., Ibid., 59, 1670 (1937).
(13) Moeller, T., Ibid., 63, 1206 (1941). RECEIVEDfor review May 29, 1963. (14) Ibid., p. 2625. Accepted August 7, 1963. One of the (15) Ibid., 64, 953 (1942). authors (G. M. F.) expresses special (16) Moorhead, E. D., Ph.D. dissertagratitude to the National Science Foundation, Ohio State University, 1959. tion for support he received in the form of (17) Moorhead, E. D., unpublished rean Undergraduate Summer Training Grant sults, Harvard University, 1961. while engaged in a portion of this study. (18) Moorhead, E. D., Furman, K . H., Gratitude is expressed also to the Harvard ANAL.CHEM.32, 1507 (1960). University Research Foundation for a (19) Moorhead, E. D., MacNevin, W. >I., grant of research funds part of which Ibid., 34, 269 (1962). supported the present work.
Polarimetric Investigation of d-Tartrate-Ort hotel Iurate Complex JOHN G. LANESEI and BRUNO JASELSKIS2 Department of Chemistry, The University o f Michigan, Ann Arbor, Mich.
b Orthotellurate and d-tartrate in aqueous solution at 22” C. form a one to one complex of moderate stability. The nature of the complex was established by Job’s continuous variation method and the apparent stability 2.5 a t pH 9.5 and constants of 45 62.0 f 3.0 at p H 1 2 were determined b y the Benesi-Hildebrand method using optical rotation measurements at 31 2 mF. Stoichiometry of the complex was confirmed b y preparing the crystalline salt, lithium
*
d-tartrate-orthotellurate.
T
forms chelates not only with cations but also with oxyanions such as borate and tellurate. Oxyanion chelates with polyhydroxy alcohols have been extensively studied by Edwards and eo-workers (4-6, 11). Reactions of arsenate n-ith sorbitol and mannitol have been investigated by Englund (‘7, 8 ) . Recently, optical rotatory measurements of borate chelates with mannitol and d-tartrate have been used in the quantitative determination of borate (3, 9). Optical rotation as a technique for determination of stability constants and stoichiometry in reactions involving optically active compounds has been reviewed by Rossotti and Rossotti (10). Since the orthotelluratetartrate complex has no characteristic absorption peaks in the ultraviolet region, except a continuous absorption below 260 m l , optical rotatory measurements are very suitable for the study of this reaction. In this htudy a n attempt is niade to (,lucidate the naturc of thc orthotellurate rcltctioii with d-tartmte ant1 to estimttc ARTARIC ACID
Present adtlrcss, Union College, Schenectndy, N. Y. Present address, Department of Chemistry, Loyola University, Chicago 26, 111. 1878
ANALYTICAL CHEMISTRY
the potential possibility in applying optical rotatory measurements to the determination of orthotellurate. EXPERIMENTAL
Apparatus. Optical rotation mas measured with a Rudolph Photoelectric Polarimeter using a mercury arc source and a 10-cm. cell with quartz windows. Solutions were adjusted t o approximate p H by means of a Beckman Model H pH meter. Final p H measurements were made with a Beckman G p H meter using a blue tip glass electrode. Materials. White label grade dtartaric and orthotelluric acids were obtained from the Eastman Kodak and Amend Drug Co. Other materials m r e reagent grade. Preparation of Lithium &TartrateOrthotellurate Salt. Orthotelluric and d-tartaric acids were weighed in a 1:2 mole ratio and were dissolved in a small amount of water. The resulting solution was adjusted to pH 9.5 with lithium hydroxide. Most of the solution was evaporated a t room teinperature under reduced pressure. illethanol \\as then added until a slight turbidity appeared. The mixture was transferred to a glass-stoppered Erlenmeyer flask. The flask was sealed and heated a t 70” C. for 4 days. White crystals were formed on standing. After filtration, they were washed with methanol-water mixture and were dried by air suction. The amount of tartrate and orthotellurate u as determined titrimetrically after passing the sample through an ion exchange column in hydrogen ion form. Tellurium was determined gravimetrically by sulfur dioxide and hydrazine reduction. In all preparations cryqtals contained from 3 to 10% of lithiiim tartratc as an impurity. Atteinpti to purii“> the I)rc>cipit:ttc by recry~tallizntionwcre ut~~iicccs~ful. Study of &Tartrate Reactions with Orthotellurate. Optimum conditions for thc orthotellurate ant1 d-tartratc reactions mcre detcrniined by nicasur-
ing the optical rotation as a function of the wavelength, pH, and concentration. Concentration effects were studied by mixing appropriate aliquots of standard stock solutions of dtartrate and orthotelluric acid. Hydrogen ion concentration was varied by the addition of 1.0M sodium hydroxide until the p H reached 9.5; beyond this pH, 0.1M sodium hydroxide was used. Final p H of the solution was determined after dilution and measurement of optical rotation. Optical rotation of d-tartrate-orthotellurate solutions as a function of dtartrate was studied at p H 9.5 and 12 by keeping the concentration of orthotellurate constant at 1.74 X 10-2M, and varying the amount of d-tartrate. Blank solutions, containing the same d-tartrate concentrations as the solutions of the complex, were measured. The difference in optical rotation between the blank and d-tartrate-orthotellurate complex was determined. Effect of time upon the optical rotation of d-tartrate and of d-tartrateorthotellurate complex at p H 12 was checked at various time intervale in a 24-hour period. The combining ratio of d-tartrate to orthotellurate was determined by the Job’s continuous variation method. RESULTS AND DISCUSSION
The optical rotation of d-tartrate alone increases when going to shorter wavelengths, while that of the dtartrate-orthotellurate complex remains relatively constant, as shown in Figure 1. The greatest separation between the optical rotation of d-tartrate alone and the complex occurs at 300 m l or below. However, orthotellurate, when present in high concentration, starts to a h o r b apprcci:rhly a t 300 i n l , ant1 thus the mercury liiie at 312 tnp may be used when orthotellurate concentration is less than 1.60 X 10 -zM. The effect of p H on the optical rotation of the d-tartrate-orthotellurate
may be derived. A plot of ( P e l t X [Tal A / A a
us.
([Talt
+ Pel
t)
Figure 1. Optical rotation as function of wavelength for &tartrate and dtartrate-orthotellurate solutions at pH
gives a slope of 1/AaAW,the reciprocal of the change in optical rotation caused by one mole of the complex. The intercept , K , is the apparent is ~ / K , A ~ , where formation constant for the d-tartrateorthotellurate complex. Treatment of the data for p H 12 is summarized in Table I. The logarithm ratio method for the d-tartrate reaction with orthotellurate yields an expression
9.5
log [ A a / ( A a ,
A.
d-Tarirate, 0.26M d-Tarlrale, 0.26M
B.
d-Tartrate,
0.26M
orihotellurate,
and
orlhotellurate,
0.035M
vomplex and d-tartiate is shown in Figure 2. Optical rotation changes rapidly as pH increases. The difference in optical rotation hetween d-tartrate alone and the coml lex becomes pronounred above pH 3.5, and it increases i o pH 9.5. Above pH 9.5 the change in optical rotation remains essentially negligible, and precise pH control of the solutions is not necess:iry. Treatment of the &TartrateOrthotellurate Data, A logarithmic type curve is obtained by plotting the difference in optical rotation, A a , as a function of d-tartrate concentration. The ACYis defined as the difference between d-tartrate blank and d-tartrate in the presence of orthotellurate. At high d-tartrate concentr:ttions, A a approached the finite Jalue of Aa,, as shoan in Figure 3. 1 t is apparent that the complex is of a inoderate stability and that the stability constant can be determined either by the BenesiHildebrand or logarithm ratio methods. The Benesi-Hildekaand method has been successfully used in the study of charge transfer complexes of iodine and hromine with some organic bases (1, 2 ) . -1pplicability of this method to the study of complexes has been critically reviewed by Tanires (12). This method is based on t n o assumptions: a one to one complex is formed, and tEe apparent formalion constant, K,, is such that the square of the concentration of d-tartrate and orthotellurate [TeTa12
