synthesisofpotassium Tris(oxalato)aluminate(lll) Trihydrate While many different complex metal oxalates and their various types of linkages have been described, the typical chelate complexes are octahedral trisoxalata ions of the trivalent metals.' For example, the tris(oxalato)aluminate(lII) ion, (Al(CzO&]", has been prepared as its potassium salt from aluminum sulfateZor aluminum allay.3The following procedure, using aluminum metal, is suitable for general chemistry students and requires two laboratory per~ods. Experimental ZAl 2KOH 6Hz0 3H2 2KAI(OH)*
+
ZKAI(0HL
+
+ 6HzCzOd + 4KOH
-
+
ZK3AI(C20&.3HzO
Add 0.50 g (0.018 mole) aluminum powder to a 150-mL beaker containing 30 mL water. With adequate ventilation, add 15 mL of 20% (wlv) aqueous KOH (3.0g, 0.054 mole) dropwise to the mixture. When the vigorous reaction has subsided, heat the contents of the beaker t o boiling with a hot plate (avoid an open flame due to the flammability of Hz gas) to effect complete oxidation of aluminum. Add 8.0 g (0.063 mole) malieacid dihydrate in portions, with stirring, to the hot solution. Initially, addition of the acid causes formation of aluminum hydroxide as a gelatinous precipitate. Continue addition of the acid until the solution becomes clear; in almost all cases this will require the total amount of acid. While the solution is still warm, filter it through a Biichner funnel and transfer it to a 150-mL beaker. Allow the solution to cool to room temperature. Add 95% ethanol dropwise until slight turbidity develops (approximately 5 mL); then chill the solution in an ice bath for twenty minutes. Suction filter the large white crystals and wash with 10 mL of a 50% ethanol solution, followed by 20 mL of 95% ethanol. After drying by suction, or air, isolate the product and weigh it. An average yield of 70% (6.0 g) is usual. The purity of K ~ [ A I ( C Z O ~ ) & ~can H ~he O determined by titration with standard potassium permanganate.'
' Cotton, F. A,, and Wilkinson, G., "Advanced Inorganic Chemistry," 4th ed., Wiley-Interscience, New York, 1980, p. 170 .. -.
Bailar, .I. C., Jr., and Jones, E. M., "Inorganic Synthesis," McGraw-Hill Book Co., New York, 1939, Vol. 1, p. 36. Anderson, C. B., and Hawes, J. L., "Basic Experimental Chemistry," W. A. Benjamin, Inc., New York, 1967, p. 213. * Vogel, A,, "Texthook of Quantatitive Inorganic Analysis," 4th ed., Longman, London, 1978, p. 352.
Timothy J. McNeese Derk A. Wierda Loyola College Baltimore, MD 21210
Volume 60
Number 11
November 1983
1001
