Copper(II) Cornplex of 2-Quino1inealdehyde 2-Quinolylhydrazone Richard E. Jensen,' Norman C.Bergman,* and Richard J. Helvig Department of Chemistry, Gustauus Adolphus College, St. Peter, Minn. 56082 As A PART of our continuing investigation of chelating ligands containing a modified terroin linkage (-N=C-NHN=C-C=N-), it was found that 2-quinolinealdehyde 2-quinolylhydrazone, QAQH (Figure l), undergoes a parU
1.05
r-----I
U
a m
0.45 0.30 0.15
Figure 1. 2-Quinolinealdehyde 2-quinolylhydrazone
425
475
525
575
625
WAVELENGTH (nm)
ticularly sensitive reaction with copper(I1) ion. A closely related ligand, picolinealdehyde 2-quinolylhydrazone9has been employed in the analysis of palladium ( I , 2) and iron and cobalt (3). These ligands are capable of functioning as tridentate chelating ligands with transition metal ions. The complexes are unique in that they are capable of deprotonation to form neutral, water-insoluble species. It will be shown in this work that this new ligand fulfills every expectation as a chelating ligand for copper. EXPERIMENTAL
Apparatus. All absorbance measurements were made with a Beckman D U or Beckman DB-G Ratio Recording spectrophotometer. Matched silica cells, 1.OO-cm, were used for all measurements. All pH measurements were made with a Beckman Zeromatic pH meter equipped with a saturated calomel electrode and a glass electrode. Reagents. PREPARATION OF QAQH. 2-Quinolinealdehyde 2-quinolylhydrazone was prepared in this laboratory. The starting material, 2-quinolylhydrazine, was prepared by the method of Perkin and Robinson (4). QAQH was prepared by mixing 3.18 grams (0.02 mole) of 2-quinolylhydrazine with 3.14 grams (0.02 mole) of quinoline-2-carboxaldehyde in 75 ml of ethyl alcohol. The solution was heated at reflux temperature for 10 minutes and allowed to cool to room temperature. The solid product, QAQH, was then filtered and recrystallized from pyridine. The purified QAQH was recovered light yellow in color, yield 4.34 grams (68 %), mp 268 "-70" C. Calculated for CI9HlaN4: C, 76.49%; H, 4 . 7 3 x ; N, 18.78%. Found: C, 76.58%; H, 4.91%; N, 18.65x. A 5.23 X 10-4M aqueous solution of QAQH was prepared by dissolving 0.0780 gram of the reagent in a minimum of concentrated hydrochloric acid and diluting to 500 ml with deionized water. A standard copper solution was prepared by dissolving 1
To whom correspondence should be directed.
2
Present address, Mapleton High School, Mapleton, Minn.
(1) M. L. Heit and D. E. Ryan, Anal. Chim. Acta, 34,407 (1966). (2) R. E. Jensen and R. T. PRaurn, Zbid.,37, 397 (1966). (3) R. W. Frei and D. E. Ryan, Zbid., 37, 187 (1967). (4) W. H. Perkin and R. J. Robinson, J. Chem. SOC.Trans., 103, 1973 (1913).
624
ANALYTICAL CHEMISTRY
Figure 2. Absorbance of copper(II)-2-quinolinealdehyde 2-quinolylhydrazone complex Concd Cu A.
= 20.00 X 1O*M, pH = 10.2 Copper(lIk2-quinolinealdehyde 2-quinolylhydrazone
complex B. 2-Quinolinealdehyde 2-quinolylhydrazone 0.6347 gram of copper wire in a minimum of concentrated nitric acid and diluting to 1 liter with deionized water. The solution was standardized by electrodeposition and the concentration was found to be 9.913 X 10-3M copper ion. All water used in the investigations was purified by passing distilled water through a Barnstead Bantam demineralizer, cartridge Type 0802. A sodium borate buffer was prepared at pH 10.2. All other reagents were analytical grade and were used as received.
RESULTS AND DISCUSSION Characteristics of the Reagent. The hydrochloride salt of QAQH required two equivalents of base for each mole of salt. The equh alent weight calculated from potentiometric data on three samples of the salt were: 182.0, 183.6, and 181.0 (average: 182.2). The theoretical equivalent weight for the dihydrochloride salt is 185.5. It is assumed, therefore, that the dihydrochloride salt has been formed. Because of the precipitation of the free ligand during the titration, which coated the electrodes and caused erroneous pH readings, it was impossible to calculate accurate dissociation constants. However, it was noted that the salt loses both of the protons simultaneously. The ultraviolet spectrum of the reagent in methyl alcohol shows maximum absorbance at 370 nm, e = 33,400, with diminished peaks at 232 nm, e = 25,400, and 255 nm, e = 18,400. The reagent, 2-quinolinealdehyde 2-quinolylhydrazone, is slightly soluble in common organic solvents, insoluble in water, but soluble in dilute acidic solution. The reagent is nonselective and forms insoluble colored complexes with Cd(II), Cr(III), Cu(II), Fe(III), Mn(II), Co(II), Ni(II), and Zn( I I). Characteristics of the Copper Complex. Copper(I1) ion
forms a water-insoluble complex which is an intense purple in color. The colored complex occurs over a pH range of 2.95 to 12.45. The complex had been found to be extractable from aqueous solution into isoamyl alcohol, chloroform, and nitrobenzene. The species of interest has a wavelength of maximum absorption at 536 nm in nitrobenzene (Figure 2). At this wavelength there is no interference from excess ligand. The colored copper complex can be 100% extracted from aqueous solution with one 10-ml portion of nitrobenzene at a pH of 10.2 over the concentration range studied. Effects of pH and Excess Reagent. A pH study was carried out over a pH range of 2.95 to 12.45. The data indicate that full color development does not occur at pH values of less than 9.45, apparently because of incomplete complex formation. At pH values of greater than 11-02, the aqueous and nonaqueous phases do not achieve a clear-cut separation. At a pH of 10.2, a mole ratio study demonstrates that in order to get complete and reproducible color development, a t least a fourfold excess of QAQH in the aqueous phase is necessary. An excess of the reagent of up to 50-fold does not interfere with color development. Conformance to Beer’s Law. The analytical species of interest obeys Beer’s law over the concentration range studied of 3.332 X 10-6 to 22.21 x 10-6M copper(l1) ion (Table I). The sensitivity of the reaction as defined by Sandell (5) is 0.0013 pg/cm*. The best value for the molar absorptivity at 536 nm, as determined by least squares, was 47,300. The color intensity of the complex was constant over the measured 1.5-hour period. Effect of Diverse Ions. The reagent is nonselective and forms colored reaction products with Cd(II), Co(II), Fe(III), Mn(II), Ni(II), and Zn(I1) as well as Cu(I1). These complexes are also water-insoluble and interfere with the determination of copper(I1) ion because of their extraction and high color intensity in nitrobenzene. Common anions do not interfere with the formation or extraction of the copper(I1) complex. However, the following anions, because of the formation of strong copper(I1) complexes, have been shown to interfere: thiosulfate, EDTA, cyanide, and thiocyanate. SAMPLE ANALYSES
The results of the analysis of several synthetic samples according to the recommended procedure are presented in Table 11. Comparison of the QAQH method for copper in municipal water supplies with the neocuproine method, Table 111, indicate its possibility of practical application. The high results in the QAQH analysis were caused by the presence of iron in the untreated sample. It is of interest to note the smaller volume of sample used and the high sensitivity of the QAQH method. RECOMMENDED PROCEDURE
Dissolve the sample to be analyzed by appropriate means. Separate copper from the interfering ions by common ionexchange procedures (6, 7). Aliquots of the sample should be taken to contain between 0.2 and 1.4 ppm copper(I1) ion. Add at least a fourfold excess of QAQH to the copper sample in a 125-ml separatory funnel. Make the solution basic (approximately pH 10) with sodium hydroxide solution and (5) E. B. Sandell, “Colorimetric Determination of Traces of Metals,” 2nd ed., Interscience, New York, 1950, p. 50. (6) C. K. Mann and C. L. Swanson, ANAL.CHEM.,33,459 (1961). (7) J. S. Fritz and J. E. Abbink, Ibid.,37, 1274 (1965).
Table I. Data for Beer’s Law Study Copper(II)-2quinolinealdehyde 2quinolylhydrazone system (Concd QAQH = 1.569 X 10-4M, pH = 10.2) Concentration of copper(I1) present ( M x 1V) Aass n m 3.332 0.166 6.663 0.304 9.994 0.462 13.33 0.638 16.66 0.785 19.99 0.970 22.21 1.102 Table 11. Summary of Copper Determinations
Copper, ppm Sample s1
52 Sa s4 s5
Present 0.212 0.635 0.847 1.059 1.411
Found 0.223 0.621 0.857 1.055 1.479
Table 111. Analysis of Municipal Water Supply Copper QAQH present, A53s nm ppm sample Volume ml 1.280 4.30 1 4 2 6 1.984 4.43 3 7 2.170 4.07 Average 4.27 Copper Neocuproine present, A454 urn ppm sample Volume ml 1 20 0.387 4.01 2 50 1.013 4.04 3 70 1.408 3.97 Average 4.01
add 20 ml of 0.035M sodium borate-sodium hydroxide buffer solution, Dilute to approximately 40 ml with deionized water, and extract the aqueous solution with exactly 10 ml of nitrobenzene. Transfer an aliquot of the nitrobenzene extract to a 1.00-cm cell and measure the absorbance of the solution at 536 nm us. a nitrobenzene blank. Determine the concentration of copper(I1) in the sample from a previously prepared calibration curve. ISOLATION AND STRUCTURE OF THE COMPLEX
A copper complex was prepared by dissolving 0.5000 gram of QAQH in 75 ml of hot ethyl alcohol and 1 ml of 2.5M hydrochloric a i d . A copper(I1) chloride solution was prepared by mixing 0.2576 gram of copper(I1) chloride monohydrate in deionized water and made acidic with 1 ml of 2.5M hydrochloric acid solution. The solutions were mixed with stirring and made basic by the slow addition of 6 M sodium hydroxide. The solution was cooled, filtered, and the dark purple precipitate was washed with ethyl alcohol and water and dried in a vacuum desiccator over magnesium perchlorate. Approximately 0.4 gram of the complex was obtained. Calculated for C&IW.N~CU: C, 69.53%; H, 3 . 6 9 z ; N , 17.08%. Found: C,69.82%; H,4.17%;N, 17.28z. VOL. 40, NO. 3, MARCH 1968
e
625
Proposed structure of the isolated, deprotonated
Figure 4. Proposed structure of the analytical species of interest
The above elemental analysis indicates that the complex has the structure shown in Figure 3. This is a deprotonated complex of the general type R2Cu. However, a sample of this isolated species redissolved in nitrobenzene shows maximum absorption at 555 nm and not at 536 nm for that of the extracted species. Obviously, the isolated species is not the analytical species of interest. Geldard and Lions (8) have recently reported the isolation of a series of copper complexes of a closely related ligand (picolinealdehyde 2-pyridylhydrazone) and a variety of anions. They reveal a complex of the general composition, RCuOH, where R indicates the deprotonated ligand. Deprotonation readily occurs at the imine nitrogen in the hydrazone linkage (9). Qualitative tests have shown that when the 555 run species in nitrobenzene is equilibrated with a basic aqueous solution, free ligand is taken into the aqueous phase, and the
absorption maximum of the nitrobenzene phase shifts to 536 nm. Likewise, tests have shown that when the 536 nm species in nitrobenzene is treated with a dehydrating agent, such as anhydrous sodium sulfate, in the presence of excess ligand (QAQH), the absorption maximum of the nitrobenzene phase shifts to 555 nm. As a result of the above observations, the 536-nm species appears to have the structure compatible to that observed by Geldard and Lions (8), and shown in Figure 4. Attempts to isolate and identify positively the 536-nm species have been discouraging; however, work is being continued toward this end.
Figure 3. complex
(8) J. F. Geldard and F. Lions, Znorg. Chem., 4, 414 (1965). (9) J. F. Geldard and F. Lions, J. Chem. SOC.,84, 2262 (1962).
RECEIVED for review October 4, 1967. Accepted December 11, 1967. The authors thank Research Corp. and the Gustavus Research Fund for the financial support of this work. Presented at the Eighteenth Annual Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 6,1967.
Determination of Vanadium and Oxygen in Vanadium Oxides by Differential Spectrophotometry and Inert Gas Fusion-Gas Chromatography Edward W. Lanning and Richard P. Weberling Bayside Laboratory, Research Center, General Telephone & Electronics Laboratories, Inc., Bayside, N . Y.
A RECENT REQUIREMENT in our laboratory for determining the stoichiometry of various oxides of vanadium necessitated precise determination of vanadium and oxygen contents. VANADIUM
Classical titrimetric methods employing either potassium permanganate ( I ) or EDTA (2) are limited by indefinite end points caused by the highly colored vanadium ions. The intense blue color of quadrivalent vanadium ion, however, suggested the possibility of utilizing a differential spectrophotometric method. In addition to eliminating the end point problem, this photometric method permits the use of tartaric acid as the reducing agent and thus eliminates the necessity for expelling excess reagents as well as the need for guarding against autoxidation. Experimental. APPARATUS.A Beckman Model DU was used for all absorption measurements.
(1) "Sutton's Volumetric Analyses," 13th ed., Butterworth Scientific Publications, London, p 457. (2) V. R. M. Kormal and S. C. Shome, Ana(. Chirn. Acta, 27, 594 (1962). 626
ANALYTICAL CHEMISTRY
REAGENTS.Fisher certified reagent grade vanadium pentoxide was used as the standard material for both the vanadium and oxygen methods. PROCEDURE. Samples containing 125 to 162.5 mg of vanadium are dissolved in 15 ml of concentrated sulfuric acid, evaporated to copious fumes of SO3 and diluted to 150 ml with distilled water. Ten milliliters of a 15% tartaric acid solution are added, and the solutions heated just to boiling. The samples are transferred to 250-ml volumetric flasks and diluted to the marks. A standard stock solution is prepared by taking sufficient reagent grade V205to give 2.500 grams of vanadium. The Vz05is dissolved in 150 ml of concentrated sulfuric acid and evaporated to copious fumes. The solution is transferred to a 1-liter volumetric flask and diluted to the mark. The standards are prepared by taking 50.0-, 55.0-, and 60.0ml aliquots of stock solution. The standards are reduced and diluted in the same manner as the samples. The absorbances of the samples and standards are then measured against the 50.0-ml standard at 765 mp using 10-cm cells. A calibration curve is prepared by plotting absorbance against milligrams of vanadium for the standards, and the amount of vanadium in the samples is read from the calibration curve.
