A N A L Y T I C A L CHEMISTRY
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rotating the rack several tiniea. After heating, each tube was dropped into a 50-ml. Erlenmeyer flask containing 10 to 15 ml. of alcohol and 3 drops of the indicafor. The solution was neutralized with 0.01 N base. While under the alcohol solution, the tube was crushed with a stirring rod and the stirring rod was removed after it waa washed free of any base with a few milliliters of carbon dioxide-free water. In the case of tubes with a capillary in the center, the capillary w&s broken near b (Figure 1) while it stood upright in the flask. This allowed the two main bodies of the tube t o fall into the alcohol solution, where they were crushed below the alcohol as in the case of the straight tube. Excess alkali was titrated with 0.01 N acid under an atmosphere of carbon dioxide-free nitrogen or air. Blanks were pre ared and run with each series of analyses. In casea where a d i g r e n t solvent or different heating time was employed, a blank was run under exactly the same conditions.
Table 11.. Saponification Numbers Obtained on Fats and Oils Micromethod 1-hour heating (av. of two or Lhour heating Same more detas.) (single detns.) 183.9 Castor oil 183.2 190.3 Soybean oil 192 0 Linseed oil 189.0 187 8 Beef fat 198,4O 2 0 0 . 0a 199.2 Lard 194 0 0 0.2 to 0.3 ml. of 1-propanol uiecl.
ASThl Macromethod 182.1 189.3 191.2 197.7 196.6
Only 92.7% of the ester was saponified. The methoxyl content of the sample indicated it was pure.
Table I. Saponification Equivalents of Various Esters so. of Found Compound Ethyl acetatea Ethyl formate” b Glucosan triacehteb Sorbitol hexaacetateb Ethyl ester of dimethylene gluconic acidb Methyl hydroxystearateb, Methyl ricinoleateb Ethylene dilaurateo Ethylene dimyristateC Tristearine Triacetin
Deterruinations 12 3 I
4 4
3 4 3 3
il
12
4 3
3 3 4 2 5
Theory 88.1 74.0 96.0 74.5
(Mean f Mean Deviation) 88.2 f1 . 0 73.8 f2 . 0 96.7 f 1 . 4 73.2 f1 . 0
218.2 314 3 312.3 213.2 241.2 297,3 72.7 80.0 87.0 139.1 97.0 73.0 92.3 134.0 108.1 125.1 129.3 144.1 172,2 131.1 316.1
248.0 i5 . 2 311.2 i 2 . 1 3 0 7 . 0 zt 5 . 0 209.4 r 1 . 1 234.6 i0 . 3 290.9 i 2 . 6 74.5 A 0 . 3 80.5 f0 . 5 84.4 A 0 . 8 140.4 f 0 . 7 98.0 f 1.2 7 3 . 2 i. 0 1 94.4 0.6 134.0 f 1 . 4 110.6 i 0 . 6 126.3 i 1 . 0 133.3 f 1 . 2 149 7 i 2 . 3 179.6 i2 . 6 128.5 i0 . 0 341.0 & 1 6
* Ethyl citrate Phtbalide (lactone) Ethyl n-butyl malonate 3 Ethyl benzyl malonate 3 Ethyl isoamyl ethyl malonate 5 Methyl amyl acetatea 2 Octyl acetatea 2 n-Butyl tartrateb R Methyl abietatee a Run in capillary tubes. b Prepared at this laboratory, All other compounds were Eazttiian White Label products. C 0.2 to 0.3 ml. of 1-propanol used. d Saponified 12 hours at 160’ C. in ethylene glycol. Saponified 15 hours at 130’ C. in cyclohexanol and ethylene glyrol. Milligrams of reagent neutralized per milliliter of standard acid were calculated from each blank. The average value from the blanks was used in the calculation according to the following equation :
where S. E. = saponification equivalent W = sample weight z = mg. of reagent 21 = mg. of reagent neutralized per ml. of standard acid (obtained from the blank) z = ml. of standard acid used in titration N = normality of standard acid
Table I1 gives the saponification number obtained on five different fats and oils. In one case the method was found to be of value in determining the saponification equivalent of a highly colored material because the sample was diluted to such an extent in the ethanol solution that the color did not interfere with the indicator end point a? it did in the conventional macroprocedure. PRECISION AND ACCURACY
In order to gain information concerning the precision and accuracy attainable, a sample of ethyl malonate [found: carbon 52.4%, hydrogen 7.3%, ethoxyl (Zeisel method) 56.1%; theory: carbon 52.45%, hydrogen 7.56%, ethoxyl 56.2%] w a s analyzed by the method 12 consecutive times. Results calculated as per cent of theory were as follows: arithmetical mean 99.5%, standard deviation 0.79%, extremes - l.i% and +1.2%. An examination of Table I indicates that, as might be expected, this precision is not always obtained in the routine use of the method with a wide variety of esters. ACKNOWLEDGMENT
The author thanks E. H. Giehl for the macro saponification numbers on the oils. LITERATURE CITED
(1) B r y a n t , \V. 11. D . , and Smith, D. M. J . Am. Cicem. SOC..58, 1014 (1936). (2) Chargoff,E., Z.physiol. Chem., 199,221(1931). 13) Foulke. D.G.. and Schneider, F., IND.ENQ.CHDM., 4 x 4 ~ED., . 12,554 (1940). (4) Fuitei, M., Hela. Chim. Acta, 21,601 (1938). (5) Gorhach, G.,Fette u. Seifen, 47,499 (1940). (6) Jlaicali, K., and Rieman, W., 111,IND ENG.CHEM.,. ~ N A L . ED., 18,144 (1946). (7) Natthes, E., and Ziegenspeck, H., Botan. Arch., 15, 187 (1926). (8) . , Mitchell. J.. Jr.. Smith. D. M., and bfoney, F. S., IND. ENQ. CHEM.,ANAL.’ED.. 16;410 (1944). (9) Redeniann, C.E., and Lucas, H.J., Zbid.,9,521 (1937). (10) Shaefer, W.E., and Piccard. J . , I b i d 10,515 (1938). RECEIVED February 24, 1951.
APPLICATIONS
Table I gives the results obtained on 25 different esters including those that are volatile and alkali-resistant. Bryant and Smith ( 1 ) experienced trouble in saponifying mono- and disubstituted malonic esters. With the procedure given here, no trouble was encountered in saponifying the two monosubstituted malonic esters determined. The disubstituted ethyl isoamyl ethyl malonate, however, required 12 hours’ heating a t 160” C. in ethylene glycol to give an average of 97% saponification. The ethoxyl content (Zeisel method 35.1 %, theory 34.970) indicated the compound was pure. Methyl abietate is very difficult to saponify ( 1 , IO). The present method failed for this compound even after heating a t 130”C. for 15 hours with cyclohexanol and ethylene glycol as solvents.
Corrections In the article on “Determination of Rotenone by the Use of lMercuric Acetate” [.\YAL. C m x , 23, 1329 (1951)], the second sentence of the procedure should read: “Dissolve the precipitated carbon tetrachloride-rotenone solvate without drying and weighing into a 500-ml. flask, using approximately 50 ml. of ethylene dichloride.” IRWIN HORNSTEIN In the article by Frederick R. D u b and Robert F. Bremer 23,1516 (1951)], the title should have been: “Formal Potential of Cerium (1V)-Cerium (111) Couple in Perchloric Acid.” [;\VAL. C H m f . ,
