696 Table
INDUSTRIAL AND ENGINEERING CHEMISTRY
IV.
Vol. 18, No. 11
method gives results which compare very favorably with those of Method A, and has a marked advantage in simplicity and rapidOlefins ity where only the volume per cent olefin is desired. However, (Distillation Method) Method A should be used where additional work is to be done on 1.8 the unreacted portion of the sample, such as determination of aro15.2 34.2 20 (by bromine 40.) matic content, density, or refractive index. 8 Cooperative results obtained by Sub-committee XXV of 25 4 A.S.T.M. Committee D-2 on a considerable number of synthetic 34.3 27.5 and natural samples, using both Methods A and B, will appear in 27.7 a later paper.
Comparison of Rapid and Distillation Methods
Sample
7 Olefins (Rap?d Method)
Impure heptane-cyclopentane Heptane-2-methylpentadiene Heptane-diisobutylene 100' t o 150' F. gasoline rut Crude benzene
34 20 7
2
15
B-1 ~.
25
B-2 B-3 B-4
34 28 28
were lighter than water, contrary to the behavior of the nitrosate distillate of most olefins. By shaking this light nitrosate distillate with alcoholic potassium sulfide for 3 minutes, it was rendered soluble in 50% alcohol, this minimum time factor being required for complete reaction. I t was also discovered that the nitrosate of decene-1 reacted completely with alcoholic potassium hydroxide to give a compound soluble in 50% alcohol. Therefore, to take care of any type of sample, the rapid method was modified to include treatment with alcoholic potassium hydroxide prior t o the addition of alcoholic potassium sulfide and the shaking time with the latter reagent was increased to 4 minutes as described in Method B. This
ACKNOWLEDGMENT
The author wishes to express his thanks to A. H. A. Heyn of the Sun Oil Co. for the suggested design of adapter, which makes more convenient observation of the point at which the oily diqtillate in Method A becomes heavier than water. LITERATURE CITED
(1) Am. Soc. Testing Materials, Method E3-45, Section 9(a), 1945. (2) Grosse, A. V., and Wackher, R. C., IXD.ENG.CHEM.,ANAL.ED., 11, 614 (1939). (3) Riebsomer, Chem.Revs.,27, 157 (1945). (4) Taylor, T. W., and Baker, W.. "Sidgwick's Organic Chemistry of Nitrogen", p. 225, Oxford, Clarendon Press, 1942.
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Analysis of Furfural W a t e r Solutions JOHN GRISWOLD, M. E. KLECKA,
AND
R. V. 0. WEST,
Rapid and accurate analyses have been developed for determination of water in furfural by a cloud-point method, and for furfural in water by an electtometric titration with bromine.
S
IMPLE, dependable analyses of furfural-water solutions are needed in connection with furfural solvent refining and extractive distillation processes. Current methods for analyzing water in the furfural phase include titration with the Karl Fischer reagent, toluene distillation, and centrifuge, refractive index, and cIoud-point (saturation temperature) determinations. Methods for analyzing furfural in the water phase include ultraviolet absorption (spectrometric), colorimetric determinations with fuchsin-sulfite and with aniline reagents, titration with hydroxylamine hydrochloride, and gravimetric determinations with special reagents such as phloroglucinol. None of the above methods has superseded the others to the extent of being specified for standard or reference analyses. The methods given here are based on calibrations of known quantities of furfural and of r a t e r , and are of sufficient speed and accuracy for general use. Water in furfural is determined by observation of the cloud point of equal volumes of furfural and a cloud-point reagent consisting of a mixture of 1-hexanol and cottonseed oil. Cloud points with cottonseed oil alone occur a t undesirably high temperatures, and are lowered by the presence of the alcohol; by adjusting the ratio of oil to alcohol, the cloud point may be brought t o an optimum temperature level. This procedure and the cloud-point behavior resemble the determination of water in aniline with the cottonseed oil-mineral oil reagent developed by Seaman, Sorton, and Hugonet (6). Using dry furfural, the method should be adaptable to the determination of water in any other organic liquid that does not react with furfural merely by substituting it for 1-hexanol. Hughes and Acree (8, 4) reported that furfural reacts with bromine to equimolar proportions rapidly and with a second mole or more of bromine slowly a t 20" to 30" C. The first mole of bromine (reacted a t 0 " C.) yielded 2 moles of hydrogen bro-
JR., University of Texas, Austin, Texas
mide. The same authors developed a satisfactory bromometric analysis for furfural that consists essentially of providing excess bromine with bromide-bromate reagent, reacting at 0' C. in a 3% hydrochloric acid solution, replacing the excess bromine viith iodine using potassium iodide, and then titrating the free iodine with standard thiosulfate and starch indicator. The method specifies 0.1 N reagents and is not well adapted to samples containing only a few milligrams of furfural. In this laboratory, attempts at direct titration of furfural using bromide-bromate reagent showed that the rate of the first
75
1 EQUAL VOLUMES OF FURFURAL SOLN. AND CLOUDPOINT SOLUTION
0
0.5
3
MI. of Hexanol per M I . of Cottonseed Oil
Figure 1,
Effect of Hexanol-Cottonseed Oil Ratio on Cloud Point
ANALYTICAL EDITION
November, 1946
40.
30.
20. I
I I
Fi ure 2.
Effect of Water Concentration on Cloud Point of 8urfural Solutions with Hexanol-Cottonseed Oil Mixtures
reaction was far too slow to be satisfactory, but that in the presence of hydrochloric acid and mercuric chloride, free bromine in aqueous solution reacts rapidly as far as equimolar proportions. This permits observation of an end point when free bromine persists in the solution. The end point is conveniently observed as e.m.f. (or pH) of a calomel electrode. The e.m.f. rises sharply from about 250 to over 800 millivolts (0.25 to 0.8 volt) and persists for a limited time when the end point is reached. h certain excess of bromine is consumed over the stoichiometric equivalent. Aut with proper precautions and attention to detail, the end point is reproducible. Plots,of stoichiometric bromine against bromine to “potentiometric end points” gave straight lines for any given concentration of bromine water, so the reagent may be standardized by titration against pure furfural in terms of its “potentiometric normality”.
697
commercial Wesson oil. The furfural may be obtained from Quaker Oats Co. and is dried and purified by redistillation under reduced pressure, rejecting the first 25% of distillate. The cloud-point apparatus is a 2.5 X 10 cm. (1 X 4 inch) test tube mounted in a water bath consisting of a 250-ml. beaker warmed by a Bunsen burner. The test tube contains an A.S.T.M. titer test thermometer extending to about 1.25 cm. from the bottom. -4wire bent to form a loop encircling the thermometer is used as the stirrer. The thermometer is mounted in a cork with an off-center hole for the wire stirrer. The A.S.T.M. aniline point apparatus (1) may be used with equal satisfaction. PROCEDURE. The cloud-point reagent is made up of about 0.4 ml. of dry hexanol per ml. of cottonseed oil and is kept in a glass-stoppered flask. The cloud-point apparatus is charged with 10 ml. of furfural and 10 ml. of cloud-point reagent. The mixture is warmed with stirring until i t is perfectly clear and transparent, then cooled slowly with stirring until the cloud point is observed. A haze appears as the cloud point is approached, and the solution becomes suddenly opaque a t about 0.75” C. lower. The ‘
