used t o obtain quantitative data for mixtures which contain isocyanates. ACKNOWLEDGMENT
The author thanks J. H. Saunders, S. Steingiser, and R. L. Moore, Mobay Chemical Co., for their assistance in this project. LITERATURE CITED
(1) Bellamy, L. J., “Infrared Spectra of Complex Molecules,” 2nd ed., Methuen, London, 1958. (2) Bellamy, L. J., J . Chem. SOC.1955, 2818. (3) Clark, L., “Encyclopedia of Spectroscopy, Reinhold, New York, 1960.
F.
(4) Eyster, E. H., Gillette, R. H., J . Chem. Phys. 8, 369 (1940). (5) Friedel, R. A., Orchin, M., “Ultraviolet Spectra of Aromatic Compounds,” Wiley, New York, 1951. (6) Goddu, R. F., ANAL.CHEM.29, 1790 (1957). ( 7 ) Goddu, R. F., Delker, D. A., Zbid., 32, 140 (1960). (8) Gould, E. S., “Mechanism and Struc-
ture in Organic Chemistry,” Henry Holt, New York, 1959. (9) Hammett, L. P., J. Am. Chem. SOC. 59.76 (1937). (10) ‘Holman, R. T., Edmonson, P. R., AXAL.CHEW28, 1533 (1956). (11) Ingold, C. K., Chem. Rev. 15, 225 (1934).
(12) Jaffe, H. H., Ibid., 53, 191 (1953). (13) Kaplan, M. J., J. Chem. Eng. Data
-, -.-
6. 371 /lac1 ,-“.,A \
(14) Kaye, W.: Spectrochim. Acta 6, 257 (1954). (15) Reilley, C. N., “Advances in Analyti-
cal Chemistry and Instrumentation,”
Vol. 1, p. 347, Interscience, New York, 1 wn -””-.
(16) Taft, R. W., Jr., J. Phys. Chem. 64, 1805 (1960). (17) Wheeler, 0. H., Chem. Rev. 59, 629 (19SS’r.
(18) Wheland, G. W., Pauling, L., J . Am. Chem. SOC.57, 2086 (1935). RECEIVEDfor review bray 7 , 1962. Accepted October 23, 1962.
S pectro photome tric Dete rminatio n of PaI ladium with 8-Aminoquinoline VAUGHN K. GUSTIN and THOMAS R. SWEET McPherson Chemical laboratory, The Ohio State University, Columbus 7 0, Ohio
b The spectrophotometric determination of bivalent palladium with 8aminoquinoline is described. The method involves the formation of an insoluble dichloride salt of palladium and 8-aminoquinoline in dilute HCI solutions and the conversion of this salt to the Pd(8-aminoquinoline)2 derivative by the extraction of 2 moles of HCI with N a O H . The latter complex is extracted into chloroform and .the absorbance is measured a t 590 smp, The sensitivity of the method is 9.04 p.p.m. of palladium.
B
and quinolinethiol are useful reagents in analysis and there exist in the chemical literature many publications concerning each of them. However. the 8amino derivative of quinoline has received very little attention. I n the one paper where 8-aminoquinoline was used as a n analytical reagent, copper was determined gravimetrically by precipitation in dilute hydrobromic acid solutions ( 1 ) . OTH
QUINOLIKOL
EXPERIMENTAL
Data for t h e absorption curves shown in Figure 1 were taken on a Cary Model 14 recording spectrophotometer. All other absorbance measurements were made with a Beckman DU s ectrophotometer equipped with a p otomultiplier attachment. The absorbance of all solutions was measured in Beckman 1-cm. quartz window absorption cells. All pH measurements were made with a Beckman Model G p H meter standardApparatus.
ized a t p H 4 and 9 with Beckman standard pH buffers. Reagents. 8 - AMINOQUINOLINE REAGENT SOLUTION. T h e acidic solution of 8-aminoquinoline was prepared b y dissolving 50 mg. of 8-aminoquinoline (Eastman Organic Chemicals No. 4033) in 2 ml. of concentrated hydrochloric acid and diluting to the mark in a 100-ml. volumetric flask with distilled water. STANDARDPALLADIUM SOLUTIONS. The standard bivalent palladium solutions were prepared by dissolving weighed amounts of spectrographic pure palladium sponge (Johnson Matthey and Co.. Ltd., Hatton Garden, London, E. C. I.) in aqua regia. The solutions were boiled to remove oxides of nitrogen and diluted with distilled water. They were standardized by titration with E D T A (9). All solutions used in the interference studies were prepared b y dissolving the chloride salts of the metals in distilled water. HC1 was added to prevent hydrolysis. Procedure. To a 100-ml. beaker add 3 ml. of 8-aminoquinoline reagent solution and 10 ml. of 0.01N E D T A solution. Add a 50-ml. sample containing 2 to 150 pg. of bivalent palladium. Adjust the p H to 2.5 or less, mix well, and adjust the p H to 10.2 or greater with 1M NaOH. Quantitatively transfer the mixture to a 125-ml. separatory funnel and add 10 ml. of
PI
44
ANALYTICAL CHEMISTRY
Table 1.
DISCUSSION AND RESULTS
An insoluble yellow complex with the composition
1
is formed by 8-aminoquinoline and bivalent palladium in hydrochloric acid solutions. If the solution is made basic, a violet precipitate is formed. This precipitate has the following composition
I1
The analysis of these compounds is shown in Table I. The reagent, &aminoquinoline, is insoluble in basic solution. If t h e
Analysis of Palladium Complexes with 8-Aminoquinoline
c, % Complex Theoretical Found I I1
chloroform. Shake the solution for 2 minutes and fill a 1-em. absorption cell with the organic phase. Measure the absorbance at 590 mp against a chloroform blank.
46.6 55.0
46.12 54.65
H, % Theoretical Found 3.44 3.56
3.60 3.52
N, % Theoretical Found’ 12.04 14.25
11.94 14.00
0.3
0.1
/--\
I
i
1
,
L
0.0 1
,
400
450
550
500
Wavelength
700
650
600 (rnp)
Figure 1 . Absorption curves of chloroform extract of complex and 8-aminoquinoline
Pd(ll)-aminoquinoline
Weight of palladium, 81.6 fig. O4
00
r
0
i
2
3
4
5
6
7
8
9
I011
1 2 I 3 1 4 I 5 1 6 1 7
I1 Mores of B-Aminoqulnolln*
Figure 2.
IO’
Effect of concentration of reagent on absorbance 5.07 X 1 O-’ moles of Pd(ll) present
hivalent palladium is mixed with the reagent in basic solution, Pd(OH)* precipitates. The complex I must first he formed in acid solution. Then, upon addition of base, two protons are removed from I t o produce the neutral form 11. T h e chloride salt, I, is insoluble in organic solvents while the neutral species I1 extracts readily in chloroform t o give a violet colored O4
1
solution. The absorption curve of the chloroform extract of I1 and the absorption curve of the reagent are shown in Figure 1. The curve given in Figure 2 shows the molar ratio of reagent t o palladium needed t o form the complex. The solutions were prepared by mixing 52.9 pg. of palladium and various volumes of the reagent. The pH was
r 020
adjusted as stated in the procedure, the solutions were extracted with 10 ml. of chloroform and t h e absorbance was measured at 590 mp. If the two straight lines in Figure 2 are extrapolated until they meet, i t can be seen that the ratio of reagent to palladium in t h e complex is 2. Figure 2 also shows that a large excess of reagent mill not affect the absorbance. The chloride salt of the complex must be formed in acid solution. A study was made t o determine the mayimum p H at which this complex would be completely formed. The solutions were prepared by mixing 52.9 fig. of bivalent palladium with 3 ml. of the reagent solution and adjusting the pH with 1X HCl or 1 M NaOH solution. After the desired p H had been obtained the solutions were made basic to a p H of 11.0 with 1Jf NaOH and were extracted with chloroform. The results of this study are shown in Figure 3. From the results obtained in the above study i t can be seen that in order to form completely the chloride salt of the palladium complex, the p H of the solution must be adjusted to a value of 2.25 or below. A t higher p H values the complex is not completely formed. I n order t o obtain the neutral form of the complex 11, the solutions containing the insoluble chloride salt must be made basic. The p H for this conversion was studied and the results are shown in Figure 4. The solutions ITere prepared in t h e following manner. Bivalent palladium (26.4 pg.) in 50 ml. of solution were added to 3 ml. of the reagent. The p H was adjusted t o 2.25 with 1M HCl t o precipitate the chloride salt of the complex. The debired p H was obtained by adding 1Jf S a O H and the solutions were extracted with 10 ml. of chloroform. A pH of 10.2 is necessary t o remove completely two protons from the chloride salt of the complex 1 and convert i t to the neutral extractable species I1 (Figure 4). Higher con-
-
3.
7-
h
5:
-
015
c
-
2a 010 -
2
O00
I
3
2
4
I
I
I
ow 10
PH
Figure 3. Effect of p H on initial reaction of Pd(ll) with 8-aminoquinoline in acid solution Weight of Pd(ll), 52.9 fig. Final pH odjusled to 11 .O
I/
13
12
PH
Figure 4. Effect of pH on formation and extraction of Pd(ll) complex (PdR2) Solutions contain 26.4 fig. Pd(ll). p H originally adiusted to 2.25
VOL. 3 5 , NO. 1, JANUARY 1 9 6 3
e
45
Table II. Interferences 52.9 pg, Pd( 11) added
Ion added Cu(I1) Co(I1) Ni(I1) Cr(II1) Cd(11) Al(II1) Zn(I1) Ca(I1) Mg(II) V(V) Fe( 111) Fe(II1)
Rh(II1) Pt(I1) Pt(1V) Os( IV) Ir( IV) Ir( IV) Ir( IV) Ru( 111)
Wt. mg.
Moles interference/ moles Pd(I1)
1.00 1.20 2.24 2.82 3.43 2.71 1.54 3.17 2.83 2.55 2.75 1.03 2.51 1.88 2.03 3.52 0.384 0.960 0.193 2.72
32 41 77 109 133 238 48 160 238 94 100 37 49 20 21 37 4 10 2 54
Table 111.
Ion Added Pd( 11) Cu( 11) Co(11) Ni( 11)
Fe(II1)
Rh(II1) PtlII’,
PtiIV) Ir(1V) Os(1V) Ru(II1)
Pd(I1) found, rg. 52.9 52.3 52.1 53.2 53.0 52.9 52.6 53.3 52.8 52.6 35.5 52.1 52.7 53.1 52.9 52.6 55.0 58.4 53.6 52.6
Analysis of Synthetic Samples Wt. of Pd(I1) found
Wt.
SAMPLE A 52.9 pg. 1.00 mg. 1.20 mg. 2 . 2 4 mg. 0.80 mg. 2.51 mg. 3.76 mg. 2.03 mg. Av. 0.192 mg. 1.76 mg. 2.73 mg.
53.2 52.8 53.4 5 3 . 1 pg.
Error, yo 0 -1.1 -1.5 +0.56 +0.19 0 -0.56 +0.75 -0.19 -0.56 -32.3 -1.5 -0.38 +0.38
0
-0.56 +5.85 +9.44 +1.32 -0.56
Std. dev., pg.
0.3
SAMPLE B
Pd(I1) Ir( IV) Pt(I1) Pt(1V) Os( IV) RhlIII) Ru(111j
10.6 96.0 188 103 88 125 272
10.5 10.8 10.7 Av. 1 0 . 7 pg, pg.
centrations of NaOH do not affect the absorbance of the extracted complex, To check the completeness of the extraction with chloroform the following experiment was performed. A 50-ml. sample containing 105.8 fig. of bivalent palladium was treated according t o the recommended procedure. The first extraction yielded an absorbance of 0.730 a t 590 mp. The solution was then extracted with another 10-ml. portion of chloroform.
46
ANALYTICAL CHEMISTRY
0.2
The measured absorbance of this organic phase was 0.004 at 590 mp. The stability of the color of the extracted organic phase was studied. N o error will be introduced if the absorbance is measured within an hour after the extraction is completed. After four hours, the absorbance had decreased by 11%. Beer’s law was obeyed over the concentration range 2 t o 150 pg. of bivalent palladium in a 50-ml. sample. The
molar absorptivity at 590 mb is 3.65 x IO4 moles-I em.-’ liter. The sensitivity of the method. expressed as the weight of palladium corresponding t o a n absorbance of 0.010 a t 590 mp is 1.44 pg. This is a sensitivity of 0.04 p.p.m. if a 50 ml. sample of unknown palladium solution is used, as suggested in the procedure. Interferences. I n addition t o Pd(II), Cu(II), Co(II), and Ir(1V) also form insoluble complexes with 8-aminoquinoline which will evtract into t h e chloroform phase. T h e interference due t o the copper and cobalt, however, can be eliminated by t h e addition of E D T A which forms stronger complexes with t h e Cu(I1) and Co(I1) t h a n does t h e reagent. T h e addition of t h e E D T A has no effect on t h e formation of t h e palladium complex. The complex formed between the reagent and Ir(1V) has an absorption mayimum at 450 mp and absorbs very little a t the wavelength used for t h e absorbance measurement of Pd(I1). The weight of Ir(1V) needed to cause an error of 0.010 in the ahqorbance of the palladium complex at 590 mp is 261 pg. This weight of Ir(1V) will yield a n error of 1.44 p g . of Pd(I1). If a precipitate such as a metal h-droyidc i q formed in the solution containing the palladium it \Till ad3orh some of the palladium The EDT.4 added will form solublp complexes with many of these ions which would normally precipitate in the basic medin. Large concentrations of iron which precipitate when the solution is made basic interfere by adsorbing palladium. The results of the interference study are given in Table 11. Of the platinum metals, the only interference encountered is that due to Ir(1V). The method was checked by preparing two synthetic samples. The results are given in Table 111. LITERATURE CITED
(1) Bankauskis, J., Latvijas PSR Zinatnu Akad. Vestis, No. 9, 115-19 i1955). (2) Schwartzenbach, G., Complexometric Titrations,” p. 100, Interscience, Kew York, 1957.
RECEIVED for review August 20, 1962. Accepted November 8, 1962.
