1697
V O L U M E 23, N O . 11, N O V E M B E R 1 9 5 1 available, samples were taken for analysis which has been previously analyzed for sulfur by the gravimetric barium sulfate method of the American Society for Testing Materials (4). The results are shown in Table 111. The average deviation was found to be 0.03%. DISCUSSION
Yery erratic sulfur values were found using the original Lindberg high frequency unit. These poor results were traced to the aluminum alloy dome cap and the metal spring of the dispersion plug, and were probably due to the attack of the metallic parts by the sulfur dioxide liberated during the combustion. On substitution of a borosilicate glass dome cap, accurate sulfur values were once more obtained. A plug of glass wool was found to be very efficient in removing the metallic oxides from the gas stream. If the amount of Alundum placed on top of the charge is too light, large amounts of metallic oxides will be volatilized, if it is too heavy, the molten oxides will spatter. The correct amount was found to be that which just covered the charge so that the underlying metals did not show through. The sulfur values for the coal and coke samples are in good
agreement IThen the errors ( 8 ) i n thc determination of sulfur as barium sulfate are considered. LITERATURE CITED
Aites, \V. K., Steel, 125, 92 (Dec. 12, 1949). Am. Soc. Testing Materials, “A.S.T.M. Methods for Chemical Analysis of Metals,” pp. 20, 129 (1950). Ibid., p. 286. Am. SOC. Testing Materials, “A.S.T.M. Standards 1949,’’ Part 6 , p. 595. Bondarenko, M. M., Krolouets, S. hl., and Belyaeva, A. P., Zavodskaya Lab., 14, 991 (1948). Holler, A. C., and Yeager, J. P., F o u d r u , 72, 83 (1944). Holler, A. C., and Yeager, J. P., 1x0. ENG.CHEM.,ANAL.b;i>.. 16,349 (1944). Kolthoff, I. M., and Sandell. E. R . , “Textbook of Quantitative Inorganic Analysis,” p. 329, Ken l o r k , Macmillan Co.. 1947. Lindberg Engineering Co., Chicago, “Instructions for Installation and Operation of Lindbei g High Frequency Combustion Furnace, LI-500-,4,” 1950. Lundell, 0. E. F., Hoffman, J. I., and Bright, H. A , , “Chemical Analysis of Iron and Steel,” p. 249, New York, John Wiley &- Sons, 1931. U. S. Steel Corp., “Sampling and Analysis of Carbon and Alloy Steels,” p. 309, New York, Reinhold Publishing Corp., 1938. RECEIVED hlay 2, 1951.
Microdetermination of Saponification Equivalent CECIL H. VANETTEN, Northern Regional Research Laboratory, Peoria, 111. of the micromethods for determination of saponification M OST equivalent described in the literature consist of essentially a
reduction in the size of sample and apparatus of conventional macromethods for determination of saponification number of fats and oils (2-5, 7 ) . The ingenious method of Marcali and Rieman ( 6 ) , in which the blank is eliminated, is limited to materials in which the organic acid derived from the ester is soluble in benzene. Mitchell et al. ( 8 ) reported a semimicroprocedure using 1 to 2 me. of sample and its application to a variety of synthetic esters. The present paper describes a micro saponification technique which is different from the techniques described in the above references. I t is applicable to a wide range of esters, including volatile esters and some requiring drastic treatment in order to bring about complete reaction. APPARATUS AND SUPPLIES
Reaction Tubes. For solids and high-boiling liquids, thinwalled soft glass tubes, from 50 to 60 mm. long and from 5 to 8 mm. in diameter, were sealed a t one end. For volatile liquids, similar tubes (Figure 1) with a capillary in the center were used. The diameter of these tubes was not critical. For low-boiling esters, the capillary must be small enough to prevent loss of sample. Reagent-Dispensing Tube. A convenient dispenser for the alkali solution was an ordinary 10-ml. glass stopcock microburet, protected a t the top with an Ascarite tube. The tip of the buret was drawn out, so that the reagent could be easily delivered to the bottom of the reaction tube without touching the side walls. Support Rack. During saponification, the tubes were attached t o a metal rack by means of rubber bands. This rack consisted of a notched metal strip about 3 cm. wide and 20 em. long with numbered positions to accommodate eight tubes. With the use of this rack the tubes could not become interchanged, and a series of tubes could be agitated simultaneously by rotating the rack. REAGENTS
Potassium hydroxide solution, 1.0 to 1.3 N in technical grade ethylene glycol. Diethylene glycol (Q),water, and ethanol were equally satisfactory for those esters soluble in them, Standard hydrochloric acid, 0.01 A‘ aqueous. Mixed indicator. One part of 0.04% aqueous cresol red and 3 parts of 0.04y0 aqueous thymol blue. 1-Propanol. Ethanol, %yoor absolute. Sodium hydroxide, approximately 0.01 N .
PROCEDURE
For solids or high-boiling liquids, about 0.05 me. of the ester was weighed to the nearest 0.005 mg. in the reaction tube. In the case of viscous liquids the material was forced from a transfer capillary (inside diameter about 2 mm.) by using a small rubber Q I
\\
v
Figure 1. Reaction Tuhe for Volatile Esters tube as a pressure bulb. Potassium hydroxide solution (I00 to 175 mg.) was delivered on the sample from the tip of the reagentdispensing tube. The final weighing to determine the weight of potassium hydroxide solution was made to the nearest 0.1 mg. About 0.1 ml. (0.2 to 0.3 ml. with less soluble esters) of 1-propanol was delivered into the tube from a medicine dropper or micropipet, and the tube was centrifuged for about 30 seconds. The open end of the tube was sealed in a micro flame. I n the case of volatile liquids, the tube in Figure 1 was used. The sample was inserted by means of a capillary about 0.8 mm. in inside diameter into the weighed tube a t point b. After a suitable weight of sample had been delivered, the tube was centrifuged to force the sample through the capillary to position c, and its weight was accurately determined. Reagent was introduced a t point b and centrifuged into c, and the final weight was taken. 1-Propanol was introduced and centrifuged into c, and the open end of the tube was sealed a t a. The solution wae mixed from one end of the tube to the other through the capillary by centrifugation. The sealed reaction tubes, mounted on the support rack, were heated in an oven a t 100” to 105” C. for 1 hour. After 15 to 30 minutes in the oven, the eamples were thoroughly mixed by
A N A L Y T I C A L CHEMISTRY
1698 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 . ,
