Determination of Boiling Points of Pure Organic Liquids A Micromethod for Use with Reduced Pressures CELSO R. GARCiA, Biochemical Laboratories, Long Island College of Medicine, Brooklyn, N. Y.
A
MONG the methods available for determining the boiling point of a pure organic liquid, Emich’s method (2, 3,6) is the most desirable in that it requires only 2 to 3 cu. mm. of material, but it can be used only a t the pressure existing in the laboratory. Methods for determining the boiling point of an organic liquid under reduced pressures have been described by Smith and Mensies (7) and by Rosenblum (6),but both methods require the use of a t least 50 to 100 cu. mm. of fluid. The author has
bulb. The bath is slowly heated; within close range of the boiling oint condensation of material takes lace in the cooler part of tge capillary above the liquid level o r t h e bath. When this occurs, the bath is heated very cautiously until a droplet which completely fills the cross section of the capillary tube starts to form ( A , Figure 2). If the bath is heated too rapidly or heated too far above the boiling point of the liquid in the capillary tube, more than one droplet will probably form, and an incorrect result will be iven. If this happens, the boiling point capillary tube should %e removed and recentrifuged to bring all the fluid to the bottom of the capillary tube and the rest of the rocedure repeated, heatin the bath with more caution. Now t i e bath is allowed to cool sfowly. The droplet will descend with the cooling of the bath and the boiling point is recorded as that temperature at which the droplet reaches and starts to descend below the level of the liquid in the bath.
TABLE 11.
FIGURE 1
Material
observed that in organic qualitative analysis, an analyst working with small quantities prefers to use as little as possible in the determination of his physical constants, so as to have more material available for the preparation of derivatives. With this in mind, the author considered the possibility of adapting Emich’s method for use under reduced pressures, and found that it could be adapted by use of a boiling point tube such as that shown in Figure 1,and using 2 to 5 cu. mm. of a pure organic liquid.
Procedure A boiling point tube of the dimensions shown in Figure 1is prepared from 5- or 7-mm. bore glass tubing simply by drawin out the tube into a capillary of 1-mm. bore and sealing the caphary at the end. Two to 5 cu. mm. of fluid are placed at the opening of the capillary of the boiling point tube by means of a capillary. The droplet of material is forced down to the bottom of the capillary tube by centrifu ing. The boiling point tube is then connected to suction and &e pressure is lowered to the desired value and determined by means of a manometer. At this point, the boiling point tube is inserted into the liquid bath (sulfuric acid waa used by the author) in a Thiele meltin point tube arrangement, 8s shown in Figure 2, and submerge$ 26 to 30 mm. below the surface of the liquid. The thermometer bulb should be placed as near the capillary as possible and just below the surface of the bath, but the bath liquid should cover the entire
TABLE I. Material
BOILINQ POINTS OF ORQANIC
Hg Mm.
Boiling Point
c.
LIQUIDS Values in Literature ( 1 , 4 )
oc
47 46.6 20 125.9 126 24 81.5 81.8 22.5 84 84 24 73 21.5 72.8 Hexalino 75 24 110) 1146 110 22.5 Terpineol” 120) 125b 120.3 36 97 22.5 97 TetralinQ 4 Courtes of E. I. du Pont de Nemours L Co.. Inq. b The au&or’s attention W M attracted by the dmcrepancy between the reaultd obtuned and those glven by Gardner and Brewer 4) in their graph of Y P o i . T. drawn on logarithmic graph paper. Since this waa the only c u e where such a discrepancy occurred a close investigation of the raphe w u made. The atraight line of the curie did not go through three of b e experimental values but when a straight line was drawn through all points, the value8 given above in parentheses were obtained. Amyl acetate Butyl Carbitol Decalin’
Aniline Benaene Decalin Hexalin Tetralin
BOILINQ
POINTS OF ORQANIC LIQUIDS
Boiling Point at 700 Mm. of Hg
Values in Literature
184.4 80.0 193.0 161.0 206
184.4 80.1 193.3 161.0 206-207.5
c.
c.
Discussion The values obtained for the boiling points of several organic liquids were checked several times by the method described above and compared with those given in the literature. Typical results are tabulated in Table I. The striking ditrerence between the above procedure and that of Emich is that no air bubble is left at the bottom of the capillary below the sample; the space which exists below the condensed droplet is completely filled with the vapors of the pure organic liquid. Theoretically this gives a more accurate relation between changes in pressure of the pure vapors and corresponding changes in temperature, such as occur when the droplet descends as the temperature of the bath is lowered. Since the boiling point is related to these effects and Emich’s method does not have pure vapors below the droplet, it might be adviable to follow this procedure even in the determination of t h e boiling FIOUB~ 2 point at ordinary
ANALYTICAL EDITION
October 15, 1943
conditions. Determinations by the above method a t normal atmospheric conditions are reported in Table I1
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Medicine, for the laboratory facilities and encouragement which made this work poasible.
Conclusions The boiling point of a pure organic liquid using but 2 to 5 cu. mm. of makrial can be obtained by use of the above procedure at both reduced and normal pressures. The melting point of crystals can conveniently be determined by this method; by continuing to apply heat and at the pressure desired, the purity may be verified by determination of the boiling point.
Acknowledgment The author is indebted to Matthew Steel, executive chairman of the Department of Biochemistry, The Long Island College of
Literature Cited
‘
Davis, D. S., IND.ENQ.CHEM.,33,401(1941). (2) Emich, F.,Monatsh., 38,219(1917). (3) Emich, F., and Sohneider, F., “Microchemical Laboratory Manual”, p. 32,New York, John Wiley & Sons, 1932. (4) Gardner. G. S.. and Brewer, J. E., IND.ENQ.CHEM.,29, 179 (1937)’. ( 5 ) Gettler, A. O., Niederl, J. B., and Benedetti-Pichler, A. A., Mikrochemie, 11,177-9(1932). (6) Rosenblum, C., IND. ENO.CHEM.,ANAL.ED., 10,449(1938). (7) Smith, A.. and Menaies. A . W. C.. J . Am. Chem. SOC.,32, 907 (1910). (1)
.,
A Dithizone Method for the Rapid Determination of Copper G. H. BENDIX AND DORIS GRABENSTETTER Research Department, Continental Can Company, Inc., Chicago, Ill.
A method is described for the rapid colorimetric estimation of copper with dithizone. Interference from all metallic ions except platinum, palladium, gold, silver, mercury, bismuth, and stannous tin is eliminated by extracting the copper as the dithizonate complex from an aqueous solution at pH 2.3. The reaction products of silver, gold, mercury, bismuth, and stannous tin with dithizone are destroyed by shaking the extract with acidic potassium iodide solution. Recoveries of better than +0.3 microgram were obtained.
E
STIMATING the copper content of canned foods, tin plate, and solders requires a method capable of detecting quantities of copper as low as a few micrograms, yet the determinations must not be subject to interference by many times that quantity of other metallic ions. Various procedures have been recommended for each of these products, but no single method is well suited for all of them. Because no provision is made for the separation of copper from interfering metals in the colorimetric extraction methods of Fischer and Leopoldi (6) and Liebhafsky and Winslow (9) with dithizone, they are unsuitable in general for the analyses of the above-mentioned products. Likewise, the titrimetric extraction of copper with dithiaone, a procedure described by Assaf and Hollibaugh (I),cannot be employed. For a similar reason the use of organic reagents other than dithizone in procedures hitherto published is unsatisfactory. Nickel, cobalt, and bismuth interfere with the determination by means of sodium diethyldithiocarbamate, and with the recently published determination by Benzo Fast Yellow (IS). The Biazzo method ( 2 ) cannot be used in presence of relatively large amounts of iron, and determinations by this method and the carbamate method are frequently complicated by the precipitation of phosphates from which copper cannot be quantitatively recovered. Preliminary Beparations of copper from interfering metals by precipitation as the sulfide or by electrolysis are slow, and, in the former case, incomplete (4). Several methods (11, IS) have been dkcribed in which copper is separated from nickel and cobalt and from part of the bismuth by a quantitative extraction of the copper from acid solution with
a carbon tetrachloride or chloroform solution of dithizone. At the same time, some of the bismuth will form the dithizonate complex and be extracted along with the copper dithiaonate. The dithizonate complexes are destroyed by ashing and copper is determined colorimetrically with sodium diethyldithiocarbamate ; bismuth, if present, contributes to the color and is estimated as copper. Greenleaf (7) eliminated interference from bismuth by extracting the solution containing copper and bismuth dithiaonates with acidified potassium iodide solution, removing bismuth 89 the iodide complex. The remainder of his procedure involves the oxidation of the copper dithizonate with bromine in 5 per cent sulfuric acid, and the extraction of the copper from the carbon tetrachloride layer to the aqueous layer. The aqueous solution is next digested with nitric and perchloric acids. Copper is determined on the resulting solution by the carbamate method. From aqueous solutions having a pH value less than 3, gold, platinum, palladium, silver, mercury, bismuth, stannous tin, and copper are extracted by solutions of dithiaone in chloroform or carbon tetrachloride; other metals do not react with dithizone at this pH (5). The first three metals mentioned may be left out of consideration because of their rarity, and only silver, mercury, bismuth, and stannous tin treated as possible interferences. Fischer and Leopoldi recommended the addition of potassium iodide solution to the weakly acidic aqueous solution containing copper and mercury with the formation of the complex ion (HgL)-- a+? a means of eliminating interference by mercury. However, it was found in this laboratory that the amount of potassium iodide recommended by Fischer was inadequate to shield the mercury from reaction with dithizone. When larger quantities were used, the dithiaone was oxidized by the iodine released in the acidic solution. On the other hand, as the data below show, copper may be extracted by means of dithiaone solution along with the other metals which react at a pH of 2.3, and then separated from these metals by shaking the extract with 2 per cent potassium iodide solution acidified with hydrochloric acid and decolorized with sodium thiosulfate. The copper remains in the carbon tetrachloride layer as the dithiaonate, while the other metals are extracted as iodide complexes. The thiosulfate present in the iodide solution prevents oxidation of the dithizone by free iodine.
