EQUIPMENT
Table 1.
A 1-liter round-bottomed flask, with a fractionating column 50 em. long and 2.5 em. in diameter, is filled with ceramic beads 7 mm. in diameter. The column is connected to a water condenser 50 em. long and is mounted in a slanting position (ea. 40' with the vertical). This condenser is connected to another vertical one, 25 em. long, with insulation, which is cooled with a urea-water solution to -5' C. The distillate is collected in a 50-ml. flask, cooled to -15' C. with a mixture of ice and ammonium chloride. The apparatus has ground-glass joints, because methylal dissolves rubber. Silicone Dow Corning stopcock grease was used as a lubricant. PROCEDURE
Transfer to the round-bottomed flask 100 ml. of the sample, then add 50 grams of powdered sodium sulfite and 100 ml. of methanol. Heat the contents of the flask to boiling and hold the distillation rate a t 20 to 40 drops per minute. Count the drops after they pass the first condenser After 20 minutes draw o f f the cooling water from the first condenser and distill for 10 minutes, to wash down the walls of the condenser with methanol vapor. If the content of methylal in the sample is about a%, 30 minutes of distillation time is sufficient. If the content is higher, up to S%, it is necessary to distill for 60 minutes. The distillate contains all the methylal and much methanol, but not more than 0.1% water and 0.05% formaldehyde. It is impossible to obtain a distillate without water. The graph for the refractive index of methylal-methanol mixtures was therefore made so that it corresponds to a mater content of 1.00%. The distillate is rreighed exactly, and the water content determined in a sample of about 1 gram with Karl Fischer reagent. The water content in the distillate is then adjusted by use of a microburet to 1.00%. After mixing, the refractive index is measured a t 18' C. The per cent of methylal in the adjusted distillate is determined from the calibration curve and the per cent of methylal in the original 100-ml. sample is calculated. The following points can be used for construction of the calibration curve in the graph (Table I).
+++ ++
0.0% methylal 8.0% methylal 20 .O% methylal 28.0% methylal 40.0% methylal
Data for Construction of Calibration Curve
99.0% methanol 91.0% methanol 79.0% methanol 71 .O% methanol 59.0% methanol
reproducibility of the method are illustrated in Table 111. DISCUSSION
If small amounts of methylal are to be determined, it is advantageous to use a 200-mi. sample, 100 grams of sodium sulfite, and 200 ml. of methanol. If a sample with more than 50% methanol content is to be examined, no more methanol should be added. The above amount of sodium sulfite was found suitable for formalin with 3575 formaldehyde content. The amount of sodium sulfite should be increased or decreased according to formaldehyde content of the sample. It was found that a formaldehyde content of 0.10% in the distillate increased the refractive index by 0.00015. This error of analysis decreases with increasing methylal content in the sample. In the presence of exceedingly small amounts of methylal, the refractive index measurements should be corrected, according to the content of formaldehyde in the distillate. The remaining distillate, after the refractive index measurement, is then analyzed for formaldehyde, using the sulfite method. A value of about 0.03 to 0.04% formaldehyde was normally obtained by these determinations, and the correction was calculated by interpolation.
Table
II.
Physical Properties of Methylal (7)
iluthors' Marsden Product Density, 20°/4" C. 0.8601 0.8610 Boiling point, 760 mm. HE. C. 42.3 42.3 -, n'," 1.3534 1 ,35335 Water content, % 0 0.15 Formaldehyde content, % 0 0 A z e o t r o p e me t h y la 1-methanol. B.p. 41.82' C. with 92.15% methvlal Azeotrope methylal-watir. B.i_42.05"C. with 98.60% methylal
RESULTS
Methylal produced in the laboratory according to Fischer and Giebe (10) was used. The obtained methylal was distilled three times through a fractionation column. The first portions were discarded. A product with the properties shown in Table I1 was obtained. The methanol used contained 0.007% water and had a refractive index of 1.3295 at 20' C. The accuracy and
Table Ill. Accuracy and Reproducibility of Method
Weighed Oit Methylal, G.
0.172 1.03 1.82 5.26 8.70
-
I 0.19 0.98 1.88 5.22 8.53
Found I1 0.13 0.99
i.83
5.39 8.55
I11 0.15 I ni 1.84 5.18 8.58
++ + ++
1.00% water shows nL8 1.00% water shows n1,8 1.OO% water shows n1,8 1.OO% water shows n1,8
1.00% water shows n y
1.3299 1.3317 1.33455 1.3365 1.33945
LITERATURE CITED
( I ) Bourgom, A., Bull. SOC. chim. Belg. 33, 101-15 (1924). (2) Furter, M., Helv. Chim. Acta 21, 1144
(1938). (3) Hoffman, D. O., Wolfrom, M. L., ANAL.CHEM.19, 225 (1947). (4) Johnson, P. R., Barnes, H. M., McElvain, S. M., J . Am. Chem. Soc. 62, 969 (1940). (5) Langer, A., Fox, R. E., ANAL.CHEM. 21, 1032 (1949). (6) Long, F. A., McIntyre, D., J . Am. Chem. Soc. 76, 32$3 (1954). (7) Marsden, C., Solvents and Allied Substances Manual," p. 246, CleaverHume Press, London, 1954. (8) Skrabal, A,, Eger, H. H., 2. physik. Chem. 122, 349 (1926). (9) Smith D. M., Mitchell, J., Jr., ANAL. &HEM. 22, 750 (1950). (IO) Walker, F. I., "Formaldehyde," 2nd ed., p. 203, Reinhold, Kew Pork, 1953. (11) Zbid., p. 400. RECEIVED for review May 2, 1958. Accepted September 2, 1958.
Determination of Reducing Sugars and Reducing End Groups in Polysaccharides by Reaction with Carbon14-Labeled Cyanide -Correction In the article on "Determination of Reducing Sugars and Reducing End Groups in Polysaccharides by Reaction with Carbon-14-Labeled Cyanide" [J. D. Moyer and H. S. Isbell, ANAL.CHEM. 30, 1975 (1958)] the abstract a t the beginning should have read : ,A method is presented for the determination of reducing sugars in quantities of less than 0.2 mg. and for the estimation of carbonyl groups in polysaccharides. The material is allowed to react with carbon-14-labeled cyanide, excess cyanide is volatilized as hydrogen cyanide, and the nonvolatile residue is assayed for radioactivity. Monosaccharides and some disaccharides fix one mole of cyanide per mole of sugar. Alkali-labile polysaccharides and some sugars fix more than one equivalent of cyanide per reducing end group. Mechanisms are presented to account for the high cyanide combining power of the alkali-labile substances. VOL. 31, NO. 1, JANUARY 1959
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