Banks and Richard ( I ) found that monoximes of oic-diketones interfered with the iodometric determination of vic-dioximes. The acetylation of LYbenzil dioxime in the presence of 20 mole % of a-benzil monosime gives a recovery of 101% diosime, indicating that small amounts of monoximes do not interfere seriously. The same acetylation in the presence of 40 and 66 mole yo monoxime gives recoveries of 115 and 134% dioxime, respectively. The monoxime acetylates partially and gives a color a t the end point which masks the indicator color change. ACKNOWLEDGMENT
The author expresses his appreciation to James Fritz for his interest and
encouragement throughout this research, and to Charles Banks for supplying many of the vic-dioximes used as acetylation samples,
v.
LITERATURE CITED
(1) Ranks, C. V , Richard, J. J., Talanta 2, 235 (1958).
(2) Diaper, D. G. M., Richardson, F. R., Can., J . Chem. 34, r835 (1956). (3) Fritz, J. S., "hcid-Base Titrations in Xonaqueous Solvents," p. 28, G. F. Smith Chemical Co., Columbus, Ohm, ,,,E"
LJdLi.
(4) Fritz, J. S., Hammond, G. S., "Quan-
titative Organic Analysis," p. 261, Wiley, XeF York, 1957. (5) Fritz, J. S., Schenk, G. H., ANAL. CHEM.31,1808 (1959). ( 6 ) Hall, X. F., J . Am. Chem. SOC.52, 5115 (1930).
17) Hall, S. F., Werner, T. H., J . Am. Chem. SOC.50, 2367 (1928). (8) Higuchi, T., Barnstein, C. H., AXAL. CHEM.28,1022 (1956). (9) Milone, M., Gazz. chim. ital. 61, 584 (1931); 62, 863 (1932). (10) Prochazka, J., Czcrcpko, K., Jansa, J.. Chem. Anal. 2. 926 (1957). ( 1 1)' Schenk, G. H'., Fritz> J: S.,AXAL. CHEM.32,987 (1960). (12) Senebaugh, .4.J., Cundiff, R. H., Markunas, P. C., Zbid., 30, 1-1.15 (1958). (13) Snyder, H. R., Levin. R. H., Wilev, P. F:. J.' Am. Chem. 'SOC.60. 2025 (i938j. (14) Trusell, F.: Diehl, 31, 1979 (1959).
H.:AXAI,. CHEM.
RECEIVEDfor review May 6, 19Sp. Accepted October 20, 1960. Presented in part at the Division of Analytical Chemietry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
Homogeneous Precipitation of Aluminum 8-QuinoIate LESTER C. HOWICK and WILLIAM W. TRIGGl Department of Chemistry, University o f Arkansas, Fayefteville, Ark.
b A method has been devised for the homogeneous precipitation of aluminum 8-quinolate from buffered solutions. The hydrolysis of 8-acetoxyquinoline at pH 5 and a temperature of 60" C. results in the quantitative precipitation of aluminum 8-quinolate in a dense, pure, crystalline form. The method of synthesis of 8-acetoxyquinoline has been modified to permit the rapid, convenient preparation of this material in a stable mixture suitable for direct use in this analysis.
T
HE MANY ADVANTAGES of homogeneous precipitation methodsgreater purity of precipitates, larger crystals, etc.-are well known and have been carefully reviewed by Gordon, Salutsky, and Willard (2). Stumpf (4) has shown that the homogeneous precipitation of aluminum 8-quinolate may be effected by urea hydrolysis in an initially acidic solution. Although this procedure results in a precipitate of greatly improved characteristics, the use of any procedure involving changing pH presents certain inherent difficulties. Chief among these is the loss of the ability to separate one cation from another which may be achieved by precipitation from carefully buffered solutions ( 5 ) . The purpose of this work w m to effect a homogeneous precipitation in
Present address, Department of ChemArkansas Polytechnic College, Russellville, Ark. istry,
302
ANALYTICAL CHEMISTRY
buffered solutions. 8-quinoline was generated by the hydrolysis of an appropriate ester. Several esters were investigated and 8-acetoxyquinoline was found to meet the requirements. APPARATUS A N D REAGENTS
All chemicals used were reagent grade. Standard aluminum(II1) solutions were prepared by dissolving 7.0 grams of aluminum potassium sulfate in sufficient 0.1N sulfuric acid to make 1 liter of solution. The resulting solution, containing approximately 20 mg. of aluminum(II1) per 50 ml. of solution, was analyzed by the direct precipitation of aluminum quinolate according to Kolthoff and Sandell (3). A Beckman Model DK-1 spectrophotometer was used to measure absorption spectra in 1.00 0.02 cm. matched cells. Preparation of 8-Acetoxyquinoline. The method of Dimroth (1) was modified in that, after 16 grams of 8-quinoliiol had been heated with 96 grams of acetic anhydride for 30 minutes and 14.9 grams of water had been added to the cooled mixture, there were elowly added 94 .grams of anhydrous sodium carbonate in place of the sodium carbonate solution called for in Dimroth's method. This resulted in the formation of a white, free-flowing mixture of 8acetoxyquinoline and sodium acetate. This ester-salt mixture, calculated to be 11.1% ester, was used directly in this work. A &gram portion of the ester-salt mixture was extracted with three 20-ml. portions of dry ether. Dry hydrogen chloride was passed through the result-
*
ing ether solution and the white material thus obtained was twice recrystallized from acetone. This material had a melting range of 1634" C. and was 15.74% chloride by gravimetric silver chloride determination (8-acetoxyquinolinium ChlOrid~C~iH~~ClNOr 15.86% chloride). A weighed sample of the ester hydrochloride was warmed for 2 hours in a sodium hydroxide solution. The resulting solution was made 0.1N in hydrochloric acid and the ultraviolet absorption curve recorded. The absorption spectrum obtained agreed quantitatively with the amount of 8-quinolinol predicted by the formula. RECOMMENDED PROCEDURE
Add 7 grams of the ester-salt mixture dissolved in 35 ml. of 4iV acetic acid to approximately 50 ml. of a slightly acidic solution containing between 5 and 22 mg. of aluminum(II1). Following the addition of 25 ml. of 2N ammonium acetate, heat the solution in a water bath a t 60" C. for 5 hours. Transfer the precipitate which formsto a weighed, medium-porosity glass filtering crucible, wash twice with water, dry for 3 hours a t 125" C., cool, and weigh. The theoretical gravimetric factor for the resulting duminum 8-quinolate is 0.05872. DISCUSSION
8-Acetoxyquinoline w m prepared as described (1) and a material with the same physical characteristics m those reported was obtained. This proeedure
was time-consuming and inconvenient. Inasmuch as the only requirement for the use of the product as a homogeneous precipitant is the absence of unreacted 8-quinolinol and any other interfering substances, the preparation was modified as described above. The presence of the ester was proved by the preparation of its hydrochloride from the mixture, and the absence of unreacted 8-quinolinol by the lack of an immediate precipitate when added to an aluminum(II1) solution of p H 5 . The stability of the ester in this estersalt mixture was demonstrated by the fact that after a sample of this mixture had been exposed to the air for 23 days, its reactions were not detectably different from those of a freshly prepared sample. The modified preparation is a simple, rapid procedure requiring very little apparatus. It results in the complete esterification of the 8-quinolinol in a form that is stable, easily handled, and niay be used without further purification. Factors such as the temperature and time of hydrolysis, the amount of estersalt mixture present, and the amount of acetic acid had qualitative and/or quantitative effects upon the precipitate produced. Each of these factors was investigated in arriving a t the optimum conditions as described. At temperatures above 70” C. the reaction proceeded so rapidly as to result in the formation of a visible precipitate in less than 1 minute. Reduction in the hydrolysis temperature below this level resulted in an increase in the time required for the appearance of precipitate up to 25 to 30 minutes a t room temperature. The longer induction periods resulted in a more crystalline precipitate but this improvement falls off rapidly for periods beyond 5 minutes. Induction periods are also dependent upon the amount of ester present and, under the conditions given above, are 12, 8, 5, and 4 minutes for 4.7, 5.9, 7.0, and 9.4 grams of the ester-salt mixture, respectively. The use of increased amounts of ester caused a desired reduction in the reaction time necessary for complete precipitation but an undesired reduction in the crystallinity of the precipitate. The conditions suggested thus represent a compromise in these opposing effects. The effects of reaction time are shown in Table I. Whereas the slight decrease in weight for periods longer than 4 hours does not appear to be significant, such a decrease was consistently observed and was aggrevated by hydrolysis a t higher temperatures, for longer periods, or in the presence of increased amounts of acetic acid. At 85” C. the maximum amount of aluminum precipitated was 80% of the theoretical and decreased to 70% upon further heating. Such observations im-
ply a slow reaction that reduced the amount of quinolate ion in equilibrium with the the precipitate. Table I1 reports data collected in a typical series of determinations performed by the recommended procedure. In every case the particle size was much larger than that obtained by the direct precipitation and the particles were actually crystalline in appearance. Tendency for the precipitate to creep was greatly reduced, resulting in easier handling of the precipitate. Filtration and washing were also facilitated by the increased particle size which eliminated the tendency encountered in the standard procedure to plug the filter. A test of the ability of the homogeneous precipitation to yield a more pure precipitate in the presence of diverse ions mas performed. The effect of diverse cations upon the homogeneous production of aluminum 8-quinolate should be similar to that in the direct precipitation techniques for those c a b ions which precipitate a t a lower pH. However, the technique of homogeneous production should yield purer precipitates when the interfering cation is one whose 8-quinolate is supposedly soluble but which was brought into the solid phase by coprecipitation. Cadmium(I1) was chosen to test the situation and the results of both direct and homogeneous precipitation of aluminum(II1) 8-quinolate in the presence of various amounts of cadmium(I1) are shown in Table 111. By the homogeneous method an aluminum sample containing as much as 30% cadmium may be analyzed without prior separations. The data presented in Table I1 prove the feasibility of the homogeneous precipitation of aluminum 8-quinolate by the hydrolysis of S-acetoxyquinoline in a buffered solution. The increased particle size results in easier handling of the precipitate and the modified procedure for the preparation of the ester is convenient, rapid, and inexpensive. While this paper was in preparation, E. D. Salesin and L. Gordon [Talanta 4 , 7 5 (1960)l reported a different method for the preparation of 8-acetoxyquinoline and noted its ability to precipitate the quinolates of several ions. Private communication with Professor Gordon has indicated that his group independently arrived a t a procedure for the quantitative precipitation of aluminum with this reagent.
ACKNOWLEDGMENT
The authors express their sincere gratitude to the Research Corp. under whose support this work was performed.
Table 1. Effect of Time on Quantity of Precipitate Obtained under Recommended Conditions
Lenath of ReLCtion Time (Hr.)
Weight Aluminum, Mg. Present Found
1 2 3 4 5 6
28.09 28.09 28.09 28.09 28.09 28.09 28.09
10
Table II.
21.04 26.76 27.77 28.04 28.02 28.00 28.01
Quantitative Determination
of Aluminum(lll) by Hydrolysis of 8Acetoxyquinoline
Weight Aluminum, Mg. Sample Present Found
Parts/ 1000
22.09 21.37 21.37 21.37 21.37 17.60 13.48 11.44 5.479
-4.5 +0.5 -1.4 -2.3 -2.8 -2.3 -1.6 -5.3 +1.1
9
21.99 21.38 21.34 21.32 21,31 17.56 13.46 11.38 5.485
Mean
Table
Error
2.4
111. Cadmium(ll) Precipitated per 10 Mg. Aluminum(lll)
Cadmium (11) Added (Mg.1
Cadmium(11) Precipitated (Mg.) Direct Homoaeneous method meThod
LITERATURE CITED
(1) Dimroth, O., Ann. 446,119 (1926). (2) Gordon, L., Salutyky, M. L., Willard, H. H., “Precipitation from Homogeneous Solution,” Wiley, New York, 1959. (3) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” 2nd Ed., p. 327-8, MacMillan, New York, 1958. (4) Stumpf, K. E., 2. anal. Chem. 138, 30 . ‘(1953): (5) Walton, H. F., “Principles and Methods of Chemical Analysis,” p. 96, Prentice-Hall, New York, 1952.
RECEIVED for review September 14, 1959. Resubmitted October 31, 1960, ACcepted October 31, 1960. Division of Analytical Chemistry, 138th Meeting, ACS, New York, N. Y., September 1960. Abstracted from the thesis of William .W. Trigg in partial fulfillment of the requirements for the degree of Master of Science. VOL 33, NO. 2, FEBRUARY 1961
303
