of tellurium in the range of 5 to 100 ppm. A series of nickel-base alloys has been analyzed by activation analysis in the range of 0.5 to 5 ppm (4). Table IV presents a comparison of the values. Five milliliters of sulfuric acid were added in the dissolution process to prevent the separation of molybdenum ; however, some precipitation occurred. The prefiltration for the removal of molybdenum may also have removed some tellurium and caused the tendency toward low results. Table V shows the values obtained in the analysis of two certified NBS white cast irons, and certified copper-base alloys. The values for the copper-base standards agree very well with the NBS values as well as with the polarographic and activation methods (3). The x-ray values for the white cast irons (NBS 1174 and 1175) fall within the limits measured by the butyl acetate-hexone extraction method (3); however, they are low compared with the polarographic and activation methods (3). Any loss of tellurium in the preflltration of silica and graphite was small; thus the lack of agreement is probably due to the nature of these spectrographic standardsLe., only the top 6 / ~ einch is certified. The x-ray sample was not taken from this portion of the standard.
The method has been applied to the analysis of highpurity material such as 99.8x nickel and 99.999xselenium. This type of nickel had been analyzed by the solid mass spectrograph and found to contain 0.3 ppm of tellurium. Using the x-ray method 0.6 ppm was found. A semiquantitative determination of tellurium in selenium showed the presence of between 1 and 3 ppm; the x-ray method found 1 ppm. Most of the selenium was volatilized before the method was applied (14). ACKNOWLEDGMENT
The authors are indebted to Ute Moehring and Thomas Ruppert for obtaining many of the analytical data. RECEIVED for review May 26, 1966. Accepted October 17, 1966. Seventeenth Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, February 1966.
(14) N. Etten and J . Muschaweck, 2.Anal. Chem., 206, 17 (1964); Anal. Abstr., 13, 37 (1966).
Arsenazo 111 as a Sensitive and Selective Reagent for the Spectrophotometric Determination of Palladium in Iron and Stony Meteorites J. G.Sen Gupta Geological Survey of Canada, Ottawa, Ontario, Canada Arsenazo Ill is a very sensitive and selective reagent for the spectrophotometric determination of palladium in mixtures of palladium, platinum, rhodium, and iridium isolated from iron and stony meteorites and copper-nickel matte by perchloric acid decomposition and ion exchange separation. Palladium forms a 1:l complex with Arsenazo 111, with a dissociation constant of 5.04 X 10-6 at 24O C. The optimum concentration range for the determination of palladium is from 1.16 to 3.00 ppm. Also, a combination of ion-exchange separation and the sensitive thorium-arsenazo 111 reaction has been used in the determination of microgram amounts of thorium in some stony and iron meteorites. Palladium concentrations were found to be in the range of 2.4-13.4 ppm in three iron meteorites, 0.4-0.8 ppm in five stony meteorites; the thorium concentrations were in the range of 0.10-0.15 ppm in the iron meteorites and 0.05-0.09 ppm in the stony meteorites.
THEREAGENT ARSENAZO I11 (1,8-dihydroxynaphthalene-3,6disulfonic acid-2,7-bis[(azo-2)-phenylarsonic acid)], as represented in Figure 1, has been used for the colorimetric determination of a number of elements as summarized in recent reviews by Savvin (1-3). A search of the literature indicated that this reagent had never been proposed nor used as a colorimet(1) S. B. Savvin, Tuluntu, 8,673 (1961). (2) Zbid., 11,l (1964). (3) Ibid., p. 7.
18
ANALYTICAL CHEMISTRY
ric reagent for the platinum metals, nor had it been used for the determination of traces of thorium in meteorites, The complex formed between Arsenazo I11 and palladium(I1) in a buffered aqueous medium of pH 3.4to 5.9 has an intense purple color and is suitable for the spectrophotometric determination of palladium. The reaction is highly selective because no other noble metals react with the reagent under similar conditions. Osmium and ruthenium are usually separated from a mineral, ore, or meteorite containing the platinum metals by distillation with perchloric acid; the base metals are then separated from palladium, platinum, rhodium, and iridium by first adjusting the pH of the solution to 1.5 and then passing it through a Dowex 50W-X8cation exchange resin which retains the base metals, including the thorium, but not the platinum metals (4, 5). It is then possible to determine the palladium directly with Arsenazo I11 in the effluentin the presence of the other platinum metals. The reagent Arsenazo I11 has, therefore, an advantage over other reagents which can be used only after partial or complete separation of palladium from the associated noble metals (6, 7). (4) J. G. Sen Gupta and F. E. Beamish, Am. Mineralogist, 48, 379 (1963). (5) J. G. Sen Gupta and F. E. Beamish, ANAL.CHEM.,34, 1761 (1962). (6) J. G. Sen Gupta, Tuluntu, 8, 729 (1961). (7) J. H. Yoe and J. J. Kirkland, ANAL.CHEM., 26,1335 (1954).
0.20
Figure 1. Arsenazo I11
It is the purpose of this paper to introduce Arsenazo I11 as a useful and convenient colorimetric reagent for palladium and to apply it to some iron and stony meteorites to determine their palladium and thoriulri contents. A detailed study has been made of the wavelength required for maximum absorption of the palladium-arsenazo I11 color complex in solution, the optimum range of concentration, the effects of varying pH, reagent concentration and time, and the influence of the other noble metals. The composition and dissociation constant of the palladium-arsenazo I11 complex have also been studied. Thorium can be easily isolated from the ion-exchange column by first eluting the column with 3N hydrochloric acid, which separates the base metals and the rare earths, and then eluting with 3.6N sulfuric acid which elutes the thorium (8). From this separated fraction, final determination of thorium is made by using its color reaction with Arsenazo I11 in perchlorate medium (9). EXPERIMENTAL Apparatus. All absorption measurements were made with a Beckman Model B spectrophotometer using matched, 1-cm, borosilicate glass, rectangular cells. A Radiometer Universal (No. 22) pH meter was used for all pH measurements. The distillation apparatus consisted of a 1-liter roundbottom flask connected to a 300-ml flask, a water condenser, and two 60-ml borosilicate glass receivers, designed for distillation and separation of osmium and ruthenium (IO). For separating the base metals and thorium from the platinum metals, two ion-exchange columns were used. The first column was 42 cm in length and 5 cm in internal diameter and contained 20-50 mesh Dowex 50W-X8 cation exchange resin supported on a plug of borosilicate glass wool; this was used for separating most of the base metals and all of the thorium from the platinum metals. A second, smaller column, 22 cm in length and 1.7 cm in internal diameter and containing 5C-100 mesh Dowex 50W-X8 ion-exchange resin, was used for the final reparation of the remaining traces of base metals from the platinum metals. Before use, the columns were washed *ith 3N hydrochloric acid to free them from iron and finally with deionized water until the washings were neutral to litmus paper. Reagents. STANDARD PALLADIUM SOLUTION.An accurately weighed quantity of Johnson, Matthey and Mallory Co., Inc., Specpure palladium sponge was dissolved by heating with aqua regia. It was converted to chloride by repeated evaporation with concentrated hydrochloric acid on a steam bath and finally diluted to 100 ml in a volumetric flask with 0.12N hydrochloric ac d to give a final concentration of 1.0502 mg Pdlml. Solutions containing microgram quanti-
(8) M. R. Hughson and J. G. Sen Gupta, Am. Mineralogist, 49,937 (1964). (9) S . Abbey, Anal. Chiin. Acta, 30, 176 (1964). (10)A. D. Westland and F. E. Beamish, ANAL.CHEM.,26, 739 (1954).
\
005t
0.001 600
!
I
620
640
1
660
!
680
700
WAVE LENGTH (rn,u)
Figure 2. Wavelength-absorbance curves of arsenazo I11 and its palladium(I1) complex (1) 3 ml of 1.2 X 10-4M arsenazo I11 diluted to 25 ml with sodium acetateacetic acid buffer solution of pH 3.42 5 ml of 1.3 X 10-4M arsenazo I11 diluted (2) 25 p g of palladium to 25 ml with sodium acetate-acetic acid buffer solution of pH 3.42. After 1 hour’s standing the absorbance of the reagent was measured against water and that of the color complex against the reagent blank
+
ties of palladium per milliliter were prepared fresh by diluting an aliquot of this stock solution with 0.12N hydrochloric acid. STANDARD THORIUMSOLUTION.This was prepared by dissolving an accurately weighed quantity of Specpure Tho2 in a platinum crucible by heating with 2 ml of concentrated nitric acid and 1 drop of 1:40 hydrofluoric acid. It was converted to sulfate by heating with sulfuric acid and dissolved in ice-cold water. REAGENT SOLUTION.A 1.3 X 10-4M reagent solution was prepared by dissolving 10.30 mg of Arsenazo I11 in 100 ml of deionized water. BUFFERSOLUTION.A buffer solution of pH 3.42, used most frequently in this study, was prepared by mixing 95 ml of 0.2N acetic acid with 5 ml of 0.2N sodium acetate. Other buffer solutions of pH range 3.72 to 5.89 were obtained by mixing 0.2N acetic acid with 0.2N sodium acetate in different proportions ( I I ) . Solutions of other platinum metals were prepared by procedures previously described ( 4 ) . SPECTROPHOTOMETRIC STUDY OF THE REACTION OF ARSENAZO I11 WITH PALLADIUM(I1) Spectral Curve. The wavelength-absorption curves of Arsenazo 111 and its palladium complex (Figure 2 ) show that the maximum absorption of the complex at pH 3.42 occurs at 630 mp, where the absorbance of the reagent is very small. The absorbance of the color complex remains constant between the pH range 3.42 to 5.89 in the presence of sodium acetate-acetic acid buffer. At pH values lower than 3.42 and in the presence of free hydrochloric acid, the absorbance of the color complex is diminished; hence, any free hydrochloric acid should be removed by evaporation before developing the color. For amounts of palladium up to 3 ppm, 3 ml of 1.3 X lO-4M reagent solution are required for maximum color
(11) A. I. Vogel, “A Text Book of Quantitative Inorganic Analysis,” Longmans, Green, New York, 1953. VOL. 39, NO. 1, JANUARY 1967
19
0.251
0.001
0
I
I
I
I
I
0.5
1.0
1.5
2.0
2.5
3.0
MOLES OF REAGENT/ MOLE OF PALLADIUM
1
2
3 4 5 CONCENTRATION OF PALLADIUM, P.P.M.
Figure 3. Calibration curve for palladium(I1)-arsenam complex at 630 mp; pH 3.42
Figure 4. Determination of ratio of palladium to arsenazo 111 by the molar ratio method
6
I11
Palladium(II) concentration = 9.28 X 104M; reagent concentration varied ion-exchange column would contain a mixture of palladium, platinum, rhodium, and iridium as their anionic chlorocomplexes. If only the determination of palladium is necessary, it is obviously an advantage to determine the palladium directly without having to separate it from these other metals and to this end the effects of platinum(IV), rhodium (111), iridium(IV), as well as osmium(IV), ruthenium(III), and gold(III), on the spectrophotometric determination of palladium by Arsenazo I11 were investigated. Synthetic mixtures of palladium(I1) with each noble metal, and with mixtures of the other metals approximating the concentrations known to occur in meteorites, were evaporated to dryness in 20-ml beakers on the steam bath after the addition to each solution of 2 ml of 2 sodium chloride solution. The residue was then dissolved and the color developed as described in the Recommended Procedure. An increase or decrease of more than 0.005 unit in the absorbance value was considered to be an interference. Table I shows that palladium(I1) can be determined in the presence of as much as 4 times its concentration of platinum(IV), 3 times its concentration of each of rhodium(III),g old(III), ruthenium(III), and osmium(IV), and twice its concentration of iridium(1V).
development; however, excess reagent up to 5 ml has no adverse effect on the absorbance as long as the measurements are made against the reagent blank. The color develops at once when the reagent is added at room temperature to the palladium solution buffered at pH range 3.42-5.89, but the maximum color development is not attained until the solution has stood for 1 hour, after which it remains constant for 24 hours. Standard Curve, Optimum Range, and Accuracy. When the absorbance of the palladium-arsenazo I11 complex is plotted against the concentration of palladium, a linearity is obtained from 0 to 3.0 ppm of palladium; above this the absorbance is not proportional to concentration. On plotting 100 minus per cent transmittance against log concentration (Figure 3), the optimum concentration range is found to lie between 1.16 and 3.00 ppm of palladium, where the relative analysis error per 1 absolute photometric error (12) is 3.5. Sensitivity. The spectrophotometric sensitivity of the color complex, as given by Sandell (13), is 0.007 pg/cm*, and the molar absorptivity is 1.26 x 105. Recommended Procedure for Palladium. Add 2 ml of 2 z sodium chloride solution to the chloride solution of palladium(II), present alone or in a mixture with other noble metals, in a 20-ml beaker, and evaporate to dryness on the steam bath. Dissolve the residue in 5 ml of the buffer solution (pH 3.42) and add 5 ml of the reagent solution. Transfer the solution to a 25-ml volumetric flask, rinse the beaker into the flask with the buffer solution (pH 3.42) and dilute to volume with the same buffer solution. Allow to stand at room temperature for one hour and then measure the absorbance at 630 mp against the reagent blank. Effect of Other Noble Metals. Arsenazo I11 usually reacts with ions having ionic radii greater than 0.7-0.8d; (3). Because palladium and other noble metals can be easily separated from the base metals as anionic complexes by Dowex 50W-X8 cation exchange resin (4, 3,no attempt was made to determine the effects of these base metals on the determination of palladium by Arsenazo 111. The effluent from such an
The composition of the complex in solution was studied by the molar ratio method (14). Solutions were prepared at pH 4.1 (buffer) in such a way that the palladium(I1) concentration remained constant but the ratio of the moles of reagent to the moles of palladium varied from 0.25 to 3.00. After allowing to stand for 1.5 hours, the absorbances of these solutions were measured at 630 mF against a water blank. The results as plotted in Figure 4 indicate that palladium(I1) forms a 1 :1 complex with Arsenazo 111. This is in agreement with Savvin’s observation (3) that, with elements forming doubly charged cations, Arsenazo I11 forms only complexes with a 1 : 1 composition. Arsenazo I11 contains two functional groups, but because of steric considerations only one can take part in complex formation. The structure of 1 :1
(12) G. H. Ayres, ANAL.CHEM., 21,652 (1949). (13) E. B. Sandell, “Colorimetric Determination of Traces of Metals,” Third ed., Interscience, New York, 1959.
(14) J. H. Yoe and A. L. Jones, IND. ENG. CHEM.,ANAL.ED., 16, 111 (1944).
z
20
ANALYTICAL CHEMISTRY
z
COMPOSITION AND DISSOCIATION CONSTANT OF PALLADIUM(IIkARSENAZ0 I11 COMPLEX
~~
~
Table I. Determination of Palladium by Arsenazo 111 in Presence of Other Noble Metals (Synthetic Mixtures) Other noble metal:; present, Palladium (Pg) (A%) Added Found 25 25 Pt (75) 25 25 Rh (85) 50 49.5 Rh (68)
Pt Pt Pt Pt
Ir (49) Ir (49) Au (75) Au (50) os (75) R u (75) Rh (34) Ir (24.5) Au (25) R h (68) Ir (49) Au (50) R h (34) Ir (24.5) R h (68) Ir (49)
+ + + +
(25) (50) (125) (125)
+ + + +
25 50 25 50 25 25 25 25 30 30
+ +
25 49.5 25 49.5 25 25 25 25 30 29.5
palladium(I1)-arsenazo I11 complex may, therefore, be represented as follows : OH
HO
Distortion of planarity
*4 The dissociation constant K of the complex, as calculated from the absorption data of Figure 4 and from the equations of Harvey and Manning (15),
at 24' C. was found to be 5.04 X Determination of Palladium and Thorium in Iron and Stony Meteorites. The feasibility of the quantitative determination of platinum rnetals from synthetic iron buttons, by distillation with perchloi-ic acid and subsequent separation by ion-exchange technique, was fully demonstrated by Sen Gupta and Beamish ( 4 , 5). Although similar methods for the decomposition and ion-exchange separation steps were used in the present investigatilsn for both iron and stony meteorites, the final determination of palladium was carried out directly in the mixture of platinum metals without the preliminary separation used in the previous study ( 4 ) . Determinationof Palladium. Transfer an accurately weighed amount of the meteorite (4-7 gram of iron or 15-30 gram of powdered stony meteorite) to a 1-liter distillation flask and connect this to a series cf two receivers containing chilled 3 hydrogen peroxide solution to absorb osmium and ruthenium tetroxides, if their determinations are necessary ( 4 ) . Add 60 ml of 70z perchloric acid to the distillation flask and heat it cautiously with a very low flame using a mild suction until the decomposition of the meteorite is nearly complete. Add 40 ml more of perchloric acid and boil for 1 hour. After the decomposition is complete, cool the solution. In the case of iron meteorites, transfer the liquid remaining in the distillation flask to a 600-ml beaker, add 10 ml of concentrated nitric acid, and evaporate to dryness. Convert
(15) A. E. Harvey and D. I,. Manning, J. Am. Chem. Soc., 7 2 , 4488 (1950).
the salts to chlorides with hydrochloric acid ( 4 ) . Dilute with water to a pH 1.5 and pass through a Dowex 50W-X8 cation exchange resin (20-50 mesh) column, 42 cm long and 5 cm in diameter. Wash with 2 liters of dilute hydrochloric acid having a pH of 1.5. Elute the base metals from the column by washing it with 3 liters of 3N hydrochloric acid. Recover any traces of platinum metals from this eluate by evaporating it to dryness, dissolving the residue in dilute hydrochloric acid, adjusting to pH 1.5 (pH meter) by dilution with water and passing it through the column again. Wash with 2 liters of dilute hydrochloric acid (pH 1.5). Mix the two effluents containing palladium, platinum, rhodium, and iridium as the anionic chloro-complexes, add 5 ml of 2 z sodium chloride solution and evaporate it to a small volume on a hot plate and finally to dryness on a steam bath. Adjust the acidity to pH 1.5 with dilute hydrochloric acid (pH meter) and remove any traces of base metals with the small ion-exchange column previously described. In the case of stony meteorites, transfer the perchloric acid pot liquid to a 600-ml beaker by washing with water and allow the residue to settle. Decant the clear supernatent liquid to another 600-ml beaker and transfer the residue to a 100-ml dish made of Teflon (DuPont). Add 10 ml of concentrated nitric acid to the main solution and evaporate it to dryness on the sand bath. Add 30 ml of concentrated hydrochloric acid to the residue and evaporate to dryness; repeat this procedure twice more. Dissolve the residue in dilute hydrochloric acid and preserve the solution (solution A). Evaporate the residue in the Teflon dish to dryness on a sand bath to expel all perchloric acid fumes. Cool, add 30 ml of hydrofluoric acid, and evaporate to dryness again. Repeat the addition of hydrofluoric acid and subsequent evaporation to dryness three times. Finally, add 10 ml of concentrated nitric acid and evaporate to dryness; drive off nitrous fumes by repeated evaporation to dryness on a steam bath with hydrochloric acid. Dissolve the residue in dilute hydrochloric acid and after mixing with solution A, filter the whole solution. Ignite the residue, reduce in hydrogen and chlorinate in the presence of sodium chloride for 8 hours at 700" C. Dissolve the product in dilute hydrochloric acid, filter, and mix the filtrate with the main solution. Separate the four platinum metals (Pd+2, Pt+4, Rh+3,Irf4) from this solution by passing it through the large and small ion-exchange columns as described in the procedure for iron meteorites. To the effluent obtained from the small ion-exchange column add 5 ml of 2 sodium chloride solution and evaporate it to a small volume on a hot plate. Transfer it to a 50-ml beaker and evaporate to dryness on a steam bath. Destroy the traces of resin by treatment with fuming nitric acid and hydrogen peroxide and convert the salts to chlorides with hydrochloric acid ( 4 ) . Dissolve the residue in dilute hydrochloric acid and, after transferring it to a 20-ml beaker, again evaporate it to dryness on the steam bath. Dissolve the salts, by swirling, in 5 ml of the buffer solution (pH 3.42) and immediately determine its palladium content spectrophotometrically with Arsenazo 111 according to the Recommended Procedure given previously. Separation and Determination of Thorium. After separation of the platinum metals, the 42-cm ion-exchange column contains all the base metals and any thorium present. The base metals, including the rare earths (if any), may be completely separated from thorium by washing the column with 3 liters of 3N hydrochloric acid (8). Elute the thorium from the column by washing it with 3 liters of 3.6N sulfuric acid and collect the eluate in a 4-liter beaker. Evaporate the eluate to a small volume on a hot plate and finally transfer it quantitatively to a 50-ml beaker, with water. Evaporate to dryness on a sand bath, add 5 ml each of concentrated nitric and 70 perchloric acid, heat to fumes of perchloric acid, cool, rinse the sides with water, and again evaporate to dryness on a sand bath. Continue heating until all perchloric acid fumes have been expelled, convert the residue to chloride by heating to
z
VOL. 39, NO. 1 , JANUARY 1967
21
Table 11. Determination of Palladium and Thorium by Arsenazo I11 in Iron and Stony Meteorites
Sample Iron meteorites Annaheim Madoc Skookum
Found, ppm Pd Th
-
Sample
Found, ppm Pd Th
Stony meteorites 5.2 0.10 Abee 5 . 5 0.08
0.46 0.06 0.44 0.06
2 . 6 0.15 Belly River 2.4
0.71 0.09 0.80 0.10
13.4 0.10 Benton 13.0
Bruderheim Peace River
0.60 0.07
0.50 0.05
ing in a 25-11-11flask. Add 5 mi of oxalic acid and 1 ml of Arsenazo I11 according to the method of Abbey (9) and after making up the volume with water, measure the absorbance against a reagent blank at 660 mp. The palladium and the thorium contents of three iron and five stony meteorites, as determined by the above methods, are given in Table 11. Duplicate values, wherever shown, were obtained by analyzing two fragments of the same piece of iron or stony meteorites. The palladium content of a copper-nickel matte was also determined by this method and the value 6.46 ppm compares well with 6.38 ppm as found by a fire assay method by an independent laboratory.
0.41 0.09 0.44 0.09
dryness with 1 ml of concentrated hydrochloric acid. Add 1 ml of hydrochloric acid and 5 ml of water. Swirl to dissolve and add a few crystals of ascorbic acid. Filter off any silica in the case of stony meteorites through a small glass fiber filter paper. Wash with 10 ml of 4 :1 perchloric acid, collect-
ACKNOWLEDGMENT
Thanks are due to J. A. Maxwell for encouragement, and S . Abbey and K. R. Dawson for kindly supplying Arsenazo I11 and the meteorites, respectively. RECEIVED for review August 15,1966. Accepted November 2, 1966. Presented to the Division of Analytical Chemistry, 152nd Meeting, ACS, New York, N. Y . September 1966.
Acid Dissociation Phenomena of Certain Methyl- and Phenyl-Substituted 8-Mercaptoquinolines Akira Kawasel and Henry Freiser University of Arizona, Tucson, Ariz.
The compounds 4-methy1, 6-methyl-, 7-methyl-, 2,4dimethyl-, 4,6-dimethyl-, and 2-phenyl-8-mercapto. quinolines as well as their S-methyl derivatives have been synthesized and their ultraviolet and infrared spectra determined. All of the methyl derivatives reported here are in the zwitterion form in the pure solids, which, unlike the parent compound and the 2-methyl derivative, are anhydrous. The 2-phenyl compound, a bluish-green liquid, is in the thiol form. The acid dissociation and zwitterion-thiol tautomer equilibrium constants of these compounds have been determined and the results are discussed in terms of structure-behavior relationships. THESIGNIFICANT DIFFERENCES in metal ion selectivity of the analytical reagent 8-mercaptoquinoline from that of its 0analog, 8-quinolinol, as well as its ability to form chelates with many metal ions a t lower p H ranges help explain the growing interest in this compound and its derivatives ( I ) . Study of the behavior and properties of this useful series of compounds until recently has been limited by the absence of a relatively convenient method of synthesis. The recently published method of Kealey and Freiser ( I ) reduces the time required in the Edinger method from several days to several hours, In this study, a series of substituted 8-mercaptoquinolines have been prepared by the new method to learn
On leave from the Metal Chemistry Division, National Research Institute for Metals, Tokyo, Japan
(1) D. Kealey and H. Freiser, ANAL.CHEM., 38, 1577 (1966).
22
a
ANALYTICAL CHEMISTRY
how steric and electronic substituent influences affect the acid strengths of the functional groups, as well as the tendency for zwitterion formation. EXPERIMENTAL Synthesis of 4,4'-Dimethyl-8,8'-diquinolyl Disulfide. 4Methyl-8-nitroquinoline was prepared from 4-methylquinoline (K and K Laboratories, Inc.); yield 42-43z, mp 123 5" C [lit. 126" C (2)]. Reduction with stannous chloride in hydrochloric acid (3, 4 ) gave 4-methyl-8-aminoquinoline; yield 73 79%, mp 83 84" C [lit. 84" C (2)]. This compound required no further purification. 4Methyl-8-aminoquinoline (10 grams) was diazotized with 4.5 grams of sodium nitrite in the mixture of 50 ml of 48 hydro5" C. Excess bromic acid and 150 ml of water at 0 sodium nitrite was destroyed by adding solid sulfamic acid. The cold diazonium salt solution was added slowly to a warm (70" C) solution of thiourea (6 grams) in 200 ml of water, and the mixture was stirred for 40 min. The resulting solution was cooled, made alkaline with sodium hydroxide, and filtered quickly with suction. When a sufficient amount of 30 hydrogen peroxide was added to the yellow filtrate with stirring, a white precipitate of disulfide formed. It was filtered and washed with water. This
-
-
-
-
z
(2) 0. H. Johnson and C. S . Hamilton, J. Am. Cliem. Soc., 63,2864 (1941). (3) R. C. Elderfield, W. J. Gender, T. A. Williamson, J. M. Griffing, S. M. Kupcan, J. T. Maynard, F. J. Kreysa, and J. B. Wright, J . Am. Chem. Soc., 68, 1584 (1946). (4) W. R. Vaughan, J . Am. Chem. Soc., 70, 2294 (1948).
