General Qualitative Test for Epoxides RICHARD FUCHS, RUSSELL C. WATERS, AND CALVIN A. VANDERWERF Unioersity of Kansas, Lawrence, Kan. importance of epoxides, both in industrial use THandE groning in research, underscores the need for a quick, general
qualitative test for the epoxide linkage. This paper reports such a test, using acidified periodic acid. This reagent effects hydrolysis of the epoxide to the corresponding glycol, which is then oxidized by the periodic acid, and the resulting iodic acid is detected by precipitation of silver iodate upon addition of silver nitrate. Periodic acid has been used successfully for some years in this laboratory for proof of structure of unknown epoxides (3)and, rather recently, in the quantitative estimation of ethylene oxide (1). The periodic acid test is negative for simple aldehydes and ketones, and therefore serves to distinguish these compounds sharply from epoxides, a differentiation which cannot be made by analysis and which is not clear cut from physical constants nor by use of the familiar carbonyl reagents. Styrene oxide, for example, gives a positive test with 2,4-dinitrophenylhydrazine reagent and with fuchsin-aldehyde reagent, probably because of an acid-catalyzed isomerization to phenylacetaldehyde. Other compounds that are oxidized b y periodic acid give positive tests; thus 1,2-gIycols, a-hydroxyaldehydes and ketones, l,a-diketones, and or-hydroxy acids may interfere. I n practice, however, these may be differentiated from the corresponding epoxides by use of other chemical tests and by the relatively sharp differences in physical properties. The test was positive for the following representative epoxides
tested: ethylene oxide, propylene oxide, epichlorohydrin, 1,2epoxybutane, 2,3-epoxybutane, l-bromo-2,3-epoxybutane, butadiene monoxide, cyclopentene oxide, cyclohexene oxide, styrene oxide, p-chlorostyrene oxide, and safrole oxide. Very slightly water-soluble epoxides, such as safrole oxide, give the test rather slowly in water solution, but rapidly in 50% aqueous dioxane. PROCEDURE
The procedure is a modification of the qualitative glycol test of Shriner and Fuson (2). Exactly 2 drops of roncentrated nitric acid is added to 2 ml. of a 0.5% solution of periodic acid, and 1 or 2 drops of the unknown is added. Water-insoluble unknowns should first be dissolved in 2 ml. of dioxane or acetic acid, The mixture is shaken and I or 2 drops of 5% silver nitrate is added a t room temperature. A positive test is the appearance of a 1vhit.e precipitate of silver iodate which usually forms immediately, but may require up to 5 minutes for complete precipitation. I n all cases a blank should be run for comparison. The test is negative for simple aldchydes, ket,ones, and alcohols. LITERATURE CITED
(1) Eastham, A. ?VI.,and Latremouille, G. A., Can. J. Research, B28, 264 (1962). (2) Shriner, R. L., and Fuson, R. C., “Identification of Organic Compounds,” 3rd ed., pp. 115-16, New York, John Wley & Sons, 1948. (3) Waters, R. C., Ph.D. thesis, University of Kansas, 1962. R E ~ E I v E Dfor
review March 14, 1952. Accepted J u n e 26, 1952.
Flame Photometric Determination of Sodium in Salts of Organic Acids SAMUEL B. KNIGHT AND M. H. PETERSON‘ Venable Chemical Laboratory, University of North Carolina, Chapel Hill,N . C . organic acids may often be characterized by analysis BECAUSE of their sodium salts, an accurate and rapid method for the
determination of sodium in salts of organic acids is of considerable interest. A number of surface active sodium salts were available in this laboratory from the studies of Bost and coworkers (4). It was felt that these surface active salts of high molecular weight, would represent extreme cases of the applicability of a flame photometric procedure for the determination of sodium in salts of organic acids. The results from the flame photometric procedure developed for the analysis of the sodium salts reported in this paper are compared with the thcorctical amount of sodium, assuming the salts to be pure, and v i t h the generally used metal residue method of Xiederl and Xederl (6) for the determination of sodium. hIetal residue determinations were available from the work of Bost and coworkers on some of the sodium salts and enough eample was available on most of the remaining salts to complete both a flame determination and a metal residue determination. On some few samples, however, not enough material -ms available for both flame and metal residue determinations. Therefore, a few metal residue comparisons are unavailable. FLAME PHOTOMETRIC MEASUREMENTS
The instrument used for this study is a Perkin-Elmer Model 52.4 flame photometer, which may be used for readings by eithcr the direct (or absolute) method or the internal standard method. Both methods are well knon-n. 1 Present address, U. S. Naval Ordnance Laboratory, White Oak, Silver Spring, Md.
I n the direct method, the sample is introduced into the flame, and the amount of emitted light is measured relative to concentration through the use of standards. The direct method assumes that the delivery of mist from the atomizer is constant, that the rate a t which the sample is atomized is constant, and that the flame characteristics do not vary from sample to sample. This is not strictly true and may introduce considerable error in some instruments. It is also knon-n that considerable error may be introduced through the presence of salts, acids, ions, and organic materials ( 2 , 3, ‘7). Considerable effort was made to determine sodium in these salts by direct comparison with curves prepared from known concentrations of pure sodium chloridc. The direct method gave percentages n-hich were of the order of 50% of the known value. It was to bc expected that the direct method would give erroneous results on the instrument available, as the work of Dunker and Passaw ( 5 )indicated that emission is affected by a change in the surface tension of a solution. Because the salts under examination produce a marked lowering of surface tension, the authors expected to find high sodium values instead of the low values actually recorded. They have no eqlanation whatever for this phenomenon. Further work showed that if 0.1% of a nonionic surface active agcnt were added to both standard and unknown solution, the results were improved somen-hat but still unacceptable. Efforts a t determining sodium by the direct method on the instrument available were therefore abandoned. Thc internal standard method (1, 2) employing lithium a t the same concentration in known and unknown samples n-as used exclusively in the analyses reported in this paper. 1514
