A Permanganate Test for Unsaturated Fats Using Phase Transfer Catalysis J o h n W. Hill a n d Thomas C. Boyd University of Wisconsin River Falls. W I 54022
Significant Digits: Numbers and their Logarithms
The Baeyer test, using aqueous potassium permanganate, has long been used to detect unsaturated hydrocarbons. Solubility problems, however, limit the applicability to lower molecular weight alkenes and alkvnes. Indeed, even with these compounds, students sometimes-get false negative tests. The Baever test does not work well, if a t all, for unsaturated fats or the higher unsaturated fatty acids. We have found that the use of a phase-transfer catalyst virtually eliminates false negatives and also enables us to extend the utility of the test to unsaturated fats and fatty acids. For simple alkenes and alkynes, the usual p r o ~ e d u r e ' .is~ followed exceot that a droo or two of catalvst . .(Adoeen'464 or Aliquata 3'36)" is added along with the compound to be tested. For semi-quantitative determinations, dissolve about 1 g of fat or oil in 50 ml heptane. Add a few drops of the phasetranstrr c.itillyit and a catalytic amount (.fa manpane~e1111 salt. then titrare with a~proximatrlyU . 1 9 auueous KhlnO,. The test works quiteiell on a qualitative basis. Quantitatively, results on natural fats and oils parallel the iodine numbers on those products. Corn oil gave the highest "per-
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'Wawzonek. S., Buckles, R. E., Coleman, G. H., "Laboratory Manual of Organic Chemistry," 3rd Ed., Kendall-Hunt, Dubuque,
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Iowa., o. 27.
"dams, R., Johnson, J. R., and Wilcox, C. F., Jr., "Lahoratory Experiments in Organic Chemistry," 7th Ed., Macmillan, New York, 1979. p. 166. :'Adagen" is a trademark of Ashland Chemical Company. Aliquatb is a trademark of General Mills Chemicals. The catalyst is essentially a methyltrialkylammonium chloride, where the alkyls are C8-ClO.
824 / Journal of Chemical Education
manganate numbers," followed by peanut oil, olive uil, and lard. We are indebted to Dr. Charlie Kolpin for a helpful suggestion.
H. Lawrence Clever Emory University Atlanta, GA 30322 Tht; number of digit.. tu report i n n rommcrn (ha;? 101 h g ;irithm o i a numher, to reproduce wriifactwilv the s~an~ticant digits of the number, is an unresolved problem fur many students. The rule I have used for many years is tu report one more dieit in the loearithm mantissa than thereare sienificant digits i n t h e numb&. The additional digit in the mantissa is reauired to obtain Drooer . . roundine when takine" the antilogarithm. The logarithm characteristic, which locates the decimal ooidt. is not counted as a sienificant dieit. 'l'hui a nun~heruf three significant f~gure;,.uch a
