THE USE OF CRELATES IN THE CONFIRMATION OF ORGANIC COMPOUNDS ALPRED 1. MOSES Iowa State College, Ames, Iowa
IN QUALITATIVE organic analysis the problem of dif- sis (3). These are, according to Welcher (3) and ferentiating an ortho-substituted compound from its Sheintis (4): Cu++, Hg,++, Pd++,Zn++, and Ag+. This meta- or para-isomer often arises. A method is demon- author used a spot-paper technique instead of the strated here in which a comparison of colored chelates microchemical methods previously described. Spot of a known isomer with those of the unknown isomer paper was prepared by treating 6lter paper, or preferquickly identifies the unknown. ably spot paper, with an aqueous solution of anthranilic The problem illustrated here involves an amino- acid and allowing the paper to dry. Drops of various henaoic acid which was characterized as such using the solutions containing the anion of interest were applied methods described in the literature (1). The com- to the paper and after drying the following colors were Ag+-purple, Ce++++pound's physical properties suggested the ortho isomer, observed: Cu++-green, anthranilic acid. If we are dealing with this ortho brown, and Fe+++-yellow. A similar procedure involving the unknown isomer isomer, six-membered chelates should be possible; this hypothesis was confirmed by Feigl (2), who gives the fol- yielded colors identical to those mentioned, while the meta and para isomers gave either none or different lowing structure for these chelates. colors. It is hoped that the application of chelates mentioned here will stimulate work in a field in which small-scale work can be done a t practically no expense because samples are readily obtainable from manufacturers. This should make research along these lines ideally suited for undergraduate research a t small liberal-arts colleges. According to Welcher (3) anthranilic acid reacts with the LITERATURE CITED following ions to form insoluble colored chelate com- (1) MCELWAIN, S. M., "The Characterization of Organic Compounds: Zn++, 1Mn++, Pb++, Hg++, Go++, Ni++, pounds," The Macmillan Company, New York, 1947. Cd++, and Cu++. He recommends the use of sodium (2) FEIOL,F., "Specifio, Selective, Sensitive Rertctions," Academy Press, Inc., New York, 1949, p. 219. anthranilate as the reagent and gives the proper p H ' F. J.. "Organic Analytical Reagents," Van Nosconditions for quantitative precipitation. Where an- (3) WELCHER, trand Company, New York, Vol. 11, 1948, p. 192. thranilic acid is used only a few of these metals will give (4) S m m ~ r s0. , G., Zhur. ObshcheZ. Khim., 8,596 (1938); C. A., Crystals suitable for quantitative microchemical analy33,1234 (1939).
