ANALYTICAL EDITION
January 15, 1942
ends of the capillary are sealed and it is heated 0.5 hour in the water bath. If a solid a pears on cooling, it is centrifuged to one end of the capillary ancfthis end is cut off just above the solid layer. The solid is recrystallized from water. Should no solid appear, the tube is cut open at both ends and the liquid is blown out on a slide, evaporated to dryness, and taken up in 5 cu. mm. of 10 per cent sodium hydroxide. The solution is taken up in a capillary pipet. The end of the pipet is sealed and the contents are centrifuged. If the liquid does not separate into two layers, it is extracted with ether or distilled in an Emich distillation tube. B. With Sulfuric Acid. The sample is heated with 1 to 1 sulfuric acid as in A. After the heating, the solution is diluted with 5 to 10 cu. mm. of water. If a precipitate forms, the solution is cooled and filtered. I n the case of anilides, the precipitate is aniliie sulfate. C. With Potassium Hydroxide. The same procedure as above is used but with 36 per cent alcoholic potassium hydroxide in place of the acids. The tube is centrifuged occasionally during the heating. After heating, the capillary is cut a t both ends and the contents are blown out on a slide. The alcohol is allowed to eva orate. The capillary is washed out with 6 N hydrochloric acifonto the residue on the slide. The solution is diluted with water and the precipitate is washed and recrystallized. ALKALIDECOMPOSITION. A capillary of the size and shape shown in Figure 3 is used. The substance (0.1 mg. or less) is introduced into end A of the tube which has been previously fitted with a cotton plug and a piece of moist litmus as shown. The sample can be introduced easily by placing it on the end of a microscope slide, holding the end of the capillary horizontally against the end of the slide, and pushing the solid into the tube with a needle or glass rod. One milligram of powdered potassium hydroxide is introduced in the same way, 3.5 cu. mm. of alcohol are drawn in the same end, and the droplet of the resulting solution is allowed to slide down the tube for a distance of 2 to 3 mm. The end of the tube is sealed cautiously in the microflame. The litmus paper is observed during the sealing. If no change of color occurs, the sealed end of the tube is dipped into hot water, then cut off, and the contents of the tube are blown out onto a slide. The tube is rinsed out with dilute nitric acid onto the residue on the slide. If a clear solution does not result, the liquid is drawn up into a capillary, heated, and centrifuged, and the portion of the tube containing the precipitate is cut off and discarded. Silver nitrate solution is added to the clear solution. SILVER NITRATETREATMENT OF ORIGINALSUBSTANCE.A few micrograms of the sample are introduced into a capillary.
97
About 5 mm. of water or alcohol are added plus a few drops of 6 N nitric acid and a few drops of silver nitrate (in water or alcohol solution). If a precipitate forms, either in the cold or when warmed, the contents are blown out onto a slide and the drop is held over a bottle of ammonia.
Conclusion A11 the melting points determined in this work were taken on a Johns melting point block. They were, in conformance with the experience of others, usually about 1O below the value given in the literature. Spot tests for some nitrogen compounds and classes of compounds can be found in the literature but have not been considered in the present work.
Literature Cited (1) Alexander, J. W., and McElvain, S. M., J . Am. Chcm. SOC.,60, 2285 (1938’1. Behrens; H., 2. anal. Chem., 41,268 (1902). Bost and Nicholson, IND. ENO.CEEM.,ANAL.ED., 7,90 (1935). DenigBs, G.,Bull. SOC. phurm. Bordeaux, 64,3 (1936). Emich-Schneider, “Microchemical Laboratory Manual”, p. 92, New York, John Wiley & Sons, 1932. (6)Ibid.,p. 119. (7’1Ibid.. D. 124. (Si Hearon, W. E., and Gustavson, R. G., IND. ENQ.CHEM.,ANAL. ED., 9,352 (1937). (9) Kirchhof, F., Chem.-Ztg., 57,425 (1933). (10) Kulikov, I. V.,and Panova, S. V., J . Gen. Chem. (U.S. S. R.),2 (64),736 (1932). (11) Mulliken and Huntress, “Method for Identification of Pure Organic Compounds”, 2nd ed., New York, John Wiley & Sons (in preparation). (12) Schneider, F.,and Foulke, D. G., IND.ENG.CHEM.,ANAL.ED., 11, 111 (1939). (13) Turpin, G.S.,J . Chem. SOC.(London), 1891,I , 714. (14) Wacek, A,. and Loffler, H., Mikrochemie, 18, 277 (1935). I
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PREBENTED before the Division of Analytical and Micro Chemistry at the CHEMICAL SOCIETY, Atlantic City, N. J. 102nd Meeting of the AMERICAN
Improved Semimicrodetermination of Sulfur in Organic Materials Peroxide-Carbon Fusion Followed by a Titration Using Tetrahydroxyquinone Indicator JOHN F. MAHONEY’ AND JOHN H. MICHELL*, Massachusetts Institute of Technology, Cambridge, Mass.
W
HILE investigating the ptoluenesulfonic acid esters of
certain carbohydrates, i t became desirable t o develop a simple rapid method for the determination of 0.5 to 5 mg. of combined sulfur. The titration of sulfate ion with tetrahydroxyquinone indicator has acquired considerable prominence because of its rapidity (1, 2, 6-8, IO); b u t has been used in conjunction with oxidation procedures which were often lengthy, usually required special equipment, or were unsuited t o all types of compounds. T h e authors have found that the oxidation of sulfur in organic compounds t o sulfate by sodium peroxide-carbon fusion, originally developed for
* Present address, Merck & Co., Rahway, N. J.
*
Present address, Canadian Industries, Ltd., Beloeil, Quebec, Canada.
the analysis of coal (3), may be satisfactorily combined with the titration of sulfate ion with standard barium chloride solution, using tetrahydroxyquinone as an internal indicator. The improved technique of Marvin and Schumb ( 4 ) was followed closely in the oxidation, and time W&B saved by using concentrated reagents in decomposing the fusion cake and in adjusting the pH of the resultant solution. The addition of a small amount of silver nitrate to the solution before titration was suggested by W. H. & L. D. Beta, Philadelphia, Penna., and has greatly increased the sensitivity of the indicator, making it unnecessary to subtract a titration blank. Common laboratory equipment was employed throughout and du licate estimations were within the accepted accuracy of the anafytical balance and the 10-ml. buret used in the titration. Four analyses were ordinarily begun and completed in less than an hour’s time.
Vol. 14, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
98
TABLE I. DETERMINATION OF SULFUR wt. of Sample p-Toluenesulfonyl chloride Sulfanilamide
Wt. of Sample Me. 22.5 13.8 23.5
26.9
2,6Dichloroaulfanilamide Sulfonal
17.8 16.0 10.0
10.1
Thiourea Sulfur
C~HIIOIIS (p-toluenesulfonic acid Fter of erythrose derivative) Wool (air-dried) Rubber (laboratory tubing, contained no rinc) Rubber (laboratory tubing, contained einc) Mineral oil
12.9 12.2 2.71 2.54 9.1 17.7
Sulfur (Calcd.) Me. 3.84 2.32 4.37 5.00 2.37 2.12 2.81 2.84 5.41 5.14
2.71 2.54 0.61 1.19
20.3 30.3
1.22 1.82
46.5 49.2
0.981
Sulfur Calcd.
Sulfur Found
%
%
16.8
16.8 16.8 18.6 18.6 13.3 13.5 28.1 28.2 42.2 42.3 99.8 99.9 6.8
18.6
13.3 28.1 42.2 100.0 6.73 5.915 6.13 2.115b 2.11 1.976s 1.977 l.09C
1.05 35.7 0.705 39.6 0.783 45.3 0.49 48.4 0.53 0.701b 89.4 0.627 Mineral oil 87.3 0.610 0.699 Determined by Carius analysis. b Determined by method of Waters ( 8 ) . e Determined by A. 9. T. M. method D-129-39. 4 Zino removed by method of Sheen, Kahler, and Cline (8).
6.8
6.00 6.00 2.11 2.11
1.98d
2.00 1.10 1.13
0.71 0.71
Materials and Reagents A mixture of 15 parts by weight of granular sodium peroxide and 1 part of 30- to 60-mesh sugar carbon, kept in a well-stoppered bottle. Hydrochloric acid, 12 N , reagent grade. Ammonium hydroxide, 16 N , reagent rade. Barium chloride solution, 0.01 N , stanjardized gravimetrically by precipitation as barium sulfate; 1 ml. = approximately 0.0003 gram of sulfur. Silver nitrate solution, approximately 0.1 N . Ethyl alcohol, 95 per cent, denatured with 5 per cent methyl alcohol. Phenolphthalein indicator, 1 per cent solution. Tetrahydroxyquinone indicator, as obtained from W. H. & L. D. Betz, Philadelphia, Penna. Measuring dipper, capacity 0.15 gram of indicator.
Procedure The sample, containing 0.5 to 5 mg. of sulfur, was weighed into a 30-ml. nickel crucible and covered with approximately 6 grams of the fusion mixture. The crucible was supported in a vessel so that its lower half was cooled by a current of cold water. A fuse, made by impregnating cotton string with potassium nitrate, was inserted part way into the charge. Combustion was carried out by igniting the fuse and promptly coverin with a nickel lid. Too vigorous an oxidation could be avoided %y increasing the sodium peroxide content of the fusion mixture. Upon cooling, the fusion cake was broken, removed by rap ing the crucible sharply, and placed in a 250-ml. Erlenmeyer lask with 10 ml. of 12 N hydrochloric acid. The flask was covered with a watch glass until the vigorous reaction subsided. Hot aqueous washings of the crucible, its cover, and the watch glass were added, together with a few drops of phenolphthalein. The solution was boiled 5 minutes to destroy peroxides, addin if necessary, more hydrochloric acid to maintain the acidity. %he solution was cooled slightly and made just alkaline with 16 N ammonium hydroxide. Boiling was resumed to remove excess ammonia until the color of the indicator was permanently discharged. The volume of the solution was adjusted to approximately 25 ml. After cooling to room temperature, 25 ml. of alcohol, 0.1 gram of tetrahydroxyquinone indicator (p/8 dipper), and 2 to 3 ml. of 0.1 N silver nitrate were added, and the mixture was shaken until the indicator dissolved. The cloudy yellow solution was titrated very slowly with the standardized barium chloride solution with viaorous shaking throughout. When all the sulfate had been preciGitated, the presence of excess barium ions was denoted by a permanent pink coloration of the solution. The
end point could be readily detected by observing the change in color of the particles of silver chloride under artificial illumination. The presence of precipitated salts, carbon, or large amounts of chloride ion did not affect the end point when determined in this manner. The unpracticed eye may have severe difficulty in accurately detecting the end point of.the titration. False indications of an end point are often given by the color change to pink in the bulk of the solution and on the surface of any sodium chloride precipitates. The true end point is given by the appearance of a pink coloration on the flocculent silver chloride coagulum, which settles more slowly than sodium chloride and is best viewed as a cloud of suspended particles by transmitted artificial light. It is often advantageous to add a few more drops of silver nitrate solution toward the end of the titration. The authors are indebted for these observations to Thomas S. Gardner, whose results entirely support their claims concerning the accuracy and reproducibility of the method. T h e data in Table I show that the estimation of sulfur gave satisfactory results with a variety of pure compounds containing sulfur combined in different ways. and that the figurea for wool, zinc-free rubber, and mineral oil agreed with those obtained by standard procedures. Zinc, 118 i t occurred in rubber, interfered with the titration, but was conveniently removed after the peroxide-carbon fusion by the method of Sheen, Knliler, and Cline (8). T h e method has been applied to the analysis of a large number of p-toluenesulfonic acid esters of partly ethylated carbohydrates. In the following typical series, the per cent of sulfur is first given as directly determined and second as calculated from a single ethoxyl analysis: 2.50, 2.45; 2.84, 2.84; 2.90, 2.90; 3.01, 2.97; 3.10, 3.03; 3.21, 3.13; 3.22, 3.17; 3.25, 3.30; 3.30, 3.30; 3.57, 3.42; 3.70, 3 65; 3.74, 3.80; 3.90, 3.92; 4.04, 3.92; 4.25, 4.15; 4.79, 4.65; 5.22, 5.20; 5.32, 5.30; 5 4 1 , 5.40. An average variation of 1.9 per cent between the two values was obtained.
Summary 8ulfur combined in a variety of nonvolatile organic compounds was oxidized to inorganic sulfate by a sodium peroxide-carbon fusion, and the sulfate ion was estimated b y titration with standard barium chloride solution, using tetrahydroxyquinone as an internal indicator. No special apparatus was required, and 0.5- t o 5-mg. quantities of combined sulfur were determined with speed and accuracy. The method should be especially useful for the routine analysis of materials like oil or rubber, with modification, if neceasary, t o remove interfering ions, and is apparently general for all types of sulfur-containing substances, including sulfonic acid derivatives.
Acknowledgment The authors wish to acknowledge the assistance of W. H. & L. D. Betz in providing unpublished procedures for the determination of suliur with tetrahydroxyquinone, and of C. B. Purves, A. A. Morton, G. G. Marvin, and A. G. Assaf. Literature Cited (1) Brunjes, H. L., and Manning, M. ED.,12, 718 (1940).
J., IND.ENQ.CHEM.,ANAL.
(2) Hallett, L. T.,and Kuipers, J. W., Ibid.,12, 360 (1940). (3) Konek, F. von, Z . angcw. C h m . , 16, 516 (1903). (4) Marvin, G.G.,and Bchumb, W. C., J. Am. Chem. Soe., 52, 674 (1930). (5) Peabody, W. A., and Fisher, R. S., IND.ENQ.CHEM.,ANAL. ED., 10, 651 (1938). (6) Schroeder, W. C.,Ibid., 5, 403 (1933). (7) . , Sheen, R. T..and Kahler, H. L., Ibid., 8,127 (1936); 10, 206 (1938). (8) Sheen, R.T.,Kahler, H. L., and Cline, D. C.,Ibkd.,9,69 (1937). (9) Waters, C. E., IND.ENQ.CHEY., 12, 482 (1920). (10) Wilson, C. W., and Kemper, W. A., IND.ENQ.CHEM.,ANAL. ED., 10, 418 (1938). CONTRIBUTION from the Reaearch Laboratory of Organic C h a d t r y , Mamachusetts Institute of Technology. No. 260.
