94
INDUSTRIAL AND ENGINEERING CHEMISTRY
only is used, but if photography is employed, a setting period must be provided, long enough for the particles to come to rest. Moreover, with extremely fine particles, the movement, resulting partially from Brownian motion and partially from flow, may result in some degree of reflocculation. Although no segregation of particles normally occurs, some segregation can result in the first step of the operation if the entire mass is not gathered into one spot several times during the kneading or rubbing. Whether or not a n excess of the larger particles has been swept to the side can be determined by removing 0.5-mm. pieces from different localities (Figure 2) , diluting, and examining them. The mounts prepared according to this method are permanent if care is exercised t o ensure a thin layer of cement in the
Vol. 14, No. 1
final preparation. It is not always possible to arrive at this condition, however, particularly with coarse pigments. Where the largest particles are 40 to 50 microns in size, the cement layer also will be of that thickness and sometimes sufficient shrinkage will occur eventually to spoil the preparation. No other difficulties have been discovered in the use of this method in preparing some t,housands of specimens for microscopic examination.
Literature Cited (1) Green, J. Franklin Imt., 192,654 (1921). (2) Haslam and Hall, Ibdd., 209, 777 (1930). PRESENTED before the Division of Microchemistry at the 97th Meeting of the AMEEICAN CHEMICAL SOCIETY, Baltimore, Md.
Microtechnique of Organic Qualitative Analysis Identification of Compounds Containing Nitrogen CELSO R. G A R C ~ AAND FRANK SCHNEIDER Department of Chemistry, Queens College, Flushing, N. Y.
A
C C O R D I S G t o the scheme of Mulliken and Huntress (11) for the analysis of organic compounds, the second order of compounds consists of substances which contain nitrogen in addition to carbon, hydrogen, and possibly oxygen. These authors divide this second order into two subgroups, the colored and the colorless compounds. Inasmuch as the former group is small, generic tests are unnecessary. The second group, however, is divided into three genera, based upon the results of titrations which place the substance in one of the following: (1) acidic species, (2) basic species, and (3) neutral species. I n developing a microtechnique for the analysis of such compounds, the authors of the present paper have endeavored to use a technique which would not require the use of special or unusual apparatus. For the concentrations given by Mulliken and Huntress (11) it is necessary to work with and measure with reasonable accuracy volumes of 0.012 to 0.06 ml. The possibility of using more dilute solutions was therefore studied. It is realized, of course, that using 1 ml. of a 0.1 N solution is not the same as using 0.1 ml. of a 0.01 N solution. However, since the division of these organic compounds into the three genera is more or less arbitrary, the theoretical considerations are not important. This becomes evident when one observes that many of the so-called acids do not have sufficiently high ionization constants to give clean-cut end points and that so-called pseudoacids are found in the acid genus, and amines such as diphenylamine are placed in the neutral genus. Since the division is an arbitrary one, it was decided that the best procedure would be actually to try out the titrations on a variety of compounds of all three genera to determine whether the use of more dilute solutions and a microsample would give the same results as the macroprocedure. Therefore, for example, anthranilic acid, nitrobenzene, 3-nitrophthalic anhydride, acetamide, aniline, diphenylamine, phthalimide, sulfanilic acid, and benzamide were used. The results obtained were in complete accord with the classification according to the tables of Mulliken.
Procedure The titration setup is the same as that used in the microtitration of organic acids (12). Care must be taken to regulate
the stream of air bubbles, so that very volatile substances will not be carried out by the air. Some difficulty was experienced with substances which were insoluble prior to their reaction with acid or base. The color of the indicator changed and then faded again as more of the substance went into solution and reacted with the excess of acid or base. I n such cases the titration must be carried out slowly. The constantly changing cushion of purified air makes sure that the fading of the color is not due to absorption of carbon dioxide or ammonia from the atmosphere of the laboratory. The only precaution necessary is to avoid too great an excess of base which may destroy the indicator.
l F - 3
I / iI
I
L
i
I
‘II, i
FIGURE I A. Two t o 3 mg. of the substance (weighed on an analytical balance) are dissolved in 1 ml. of alcohol In a microbeaker and 0.05 ml. of 0.02 N sodium hydroxide is added drop by drop. If a color develop^, the compound is in the acidic series, Genus 1. If no color develops, two drops of thymol blue indicator solution are added (from a capillary pipet). The addition of alkali is continued until a clear blue solution is obtained in which the color persists for 60 seconds. B. If more than 0.1 ml. of 0.02 N sodium hydroxide is used in A, another 2 to 3-mg. sample IS titrated, using water as the solvent in dace of alcohol and phenolphthalein instead of thymol blue. If more than 0.1 ml. of 0.02 N sodium hydroxide is used to bring about a permanent color change, the compound is placed in the acidic series, Genus 1. 0
January 15, 1942
ANALYTICAL EDITION
If less than 0.1 ml. of 0.02 N sodium hydroxide is used, the compound is laced in the neutral series Genus 3. C. If pess than 0.5 ml. of 0.02 N' sodium hydroxide is used in A, another 2- to 3-mg. sample is titrated aa in A but with 0.02 N hydrochloric acid in place of the sodium hydroxide until the solution remains pink for 1 minute. If more than 0.1 ml. of 0.02 N hydrochloric acid is required, the compound is placed in the basic series, Genus 2. If less than 0.1 ml. of 0.02 N hydrochloric acid is used, the compound is placed in the neutral series, Genus 3.
Tests for Genus 1 MILLON'STEST. A tiny particle (a few micrograms) of the substance is added to a small drop (2 mrn. in diameter) of the rea ent (4) on a inicroscope slide, and any color which develo s is otserved against a white background. The test drop may {e warmed if necessary. MULDER'SREACTION. A tiny crystal (a few micro rams) of the substance is added to a small drop of concentTatecf nitfic acid on a microscope slide. The color is observed against a white background, if necessary, warming the slide on a water bath. Then the slide is inverted over the mouth of a bottle of concentrated ammonia, and the color is again observed against a white background. MUREXIDEREACTION.One to 2 micrograms (or less) of the protein are added to a very small drop (2 to 3 mm. in diameter) of 6 N hydrochloric acid on a thin crucible cover and then a very small crystal (just visible) of potassium chlorate is added. The cover is heated on the water bath. If no color develops after evaporation, heating is continued cautiously over a free flame. Charring is to be avoided. A pink or brown color which turns purple-red on addition of a drop of ammonium hydroxide is positive. ADAMKIEWICZ-HOPKINS-COLE REACTION.Three to 4 cu. mm. of the reagent are placed in a centrifuge cone and a few micrograms of the protein are added. Five to 6 cu. mm. of concentrated sulfuric acid are added by means of a capillary pipet to the bottom of the cone under the reagent. After standing for a few minutes, the two layers are mixed. If no color is visible after mixing, the liquid is drawn up into a coloriscopic capillary (6) and examined under the microscope or lens.
Tests for Genus 2 SPECIFICTESTFOR AMMONIA.This test is carried out in a gas chamber consisting of a microscope slide, preferably one with a concave depression, as a base, a glass ring, and a 2.5-cm. (1 inch) watch glass as a cover. A small drop of water is placed on the under side of the watch glass, a large drop of acetone or ether on the upper side. The evaporation of the latter keeps the watch glass cool. The drop of test solution is placqd on the .slide and the yatch glass on the chamber. After warming the slide for a few minutes, the watch glass is taken off and the under side is touched to a clean slide, so that the dro of distillate is taken off on the slide. This drop is then tested f% ammonia by means of the formation of the tetraiodide of hexamethylenetetramine. Wacek and Loffler (14) use a gas chamber for the identification of volatile amines in the presence of ammonia. They use bases of varying strength to liberate ammonia and some of the amines: 5 per cent sodium carbonate solution for methyl amine, and 2 and 8 per cent sodium hydroxide for other amines. TESTFOR SALTSOF AMMONIUM TYPE. This test should be carried out before the eneric tests, since ammonium salts are not listed in the tables. T f e same procedure and apparatus as above are used, except that 15 cu. mm. of water and 0.15 mg. of finely r d e r e d magnesium oxide are added to 0.1 mg. of the substance. he complete as chamber is set on a metal block, which is heated until the drop%eing distilled begins to decrease in size. The drop of distillate is tested as described in the test for ammonia. If ammonia is present, the acid must be identified in the residue or by preparation of the sodium salt. DETECTIONOF PRIMARY AMINESWITH NITROUSACID. The presence of primary amines is established by collecting the gas evolved when the sample is treated with nitrous acid. A small distilling flask is set up as shown in Figure 1. The flask is stoppered with a small cork, the side arm is placed in the Petri dish, and the latter is filled with alkaline permanganate solution. A 5cm. (2-inch) watch glass is then inverted over the opening of the side arm in such a way that a small bubble (approximately 10 rum. in diameter) of air is entrapped under the glass and is brought over the mouth of the side arm. The presence of the bubble is necessary later to prevent sucking back of the permanganate
95
solution due to the contraction of the gases in the distilling flask because of the initial absor tion of the oxides of nitrogen. The circumference of this as bugble is marked on the watch glass with a glass-marking pencfi The cork is removed from the flask and the bulb and part of the neck of the flask are immersed in a beaker of ice water. The sample (0.5 m .) and 0.1 ml. of ice-cold 6 N hydrochloric acid are placed in theqbulb, and 0.02 ml. of ice-cold 3 N sodium nitrite solution is added. The flask is quickly stop ered and allowed to stand for 1 or 2 minutes. The water in the &eaker is then slowly heated to boiling. The boiling must not be continued too long. The flask and contents are allowed to cool, keeping the outlet of the distilling flask open to the gas bubble at all times to prevent the sucking-back of the permanganate solution. The diameter of the final bubble of gas is measured and compared with the original and with that of a gas bubble obtained in a blank experiment run in the same way but without the sample. CARBYLAMINE REACTION FOR PRIMARY AMINES. This test has been described in detail by Emich (6).
FIGURE 2 RIMINI TESTFOR PRIMARY ALIPHATIC AMINES. One drop (1 mm. in a capillary) of the amine is placed in the depression of a spot plate. Twenty times as much water (20 mm. in the capil-
lary) is added from an adjacent depression. Then 1 drop of pure acetone and 1 drop of 1 per cent sodium nitroprusside solution are added, both from a capillary pipet. A violet color is a positive test. SIMONTESTFOR SECONDARY ALIPHATICAMINES. One drop (from a capillary) of the substance to be tested in a depression of a spot plate is treated with 12 times as much water and 1 drop of 1 per cent sodium nitroprusside solution. In an adjacent depression 1 to 2 drops of 50 per cent ethyl alcohol are placed. The end of a piece of copper wire is heated red hot and then immediately dipped into the alcohol. The heating and immersion are repeated. One drop of this solution is added to the test drop. A blue color fading to green and yellow is a positive test. ACYLATION OF AMINESAND HYDROXYL COMPOUNDS.Direct A n Iatim. To 3 to 6 mg. of the substance in a centrifuge cone is added twice as much acetic anhydride, and the mixture is heated in a metal block or on a water bath for 1 minute. After cooling, the product is dissolved in a hot solvent (water, dilute alcohol, or 95 per cent alcohol). The tube is cooled with ice and the sides are scratched until precipitation occurs. After centrifuging and decanting the supernatant liquid, the precipitate is rinsed sparingly with the solvent. A melting point is taken and, if necessary, the material is recrystallized. Schotten-Baumann Reaction. Three to 6 mg. of substance are placed in a refluxing tube (Figure 2). A slight excess of 3 N sodium hydroxide is added (Mulliken and Huntress recommend potassium hydroxide for a better yield) followed by 4 to 7 cu. mm. of benzoyl chloride. The tube is sealed and allowed to stand for 0.5 hour with occasional centrifuging of the contents back and forth. The tube is then opened and if the odor of chloride is noticed, the tube is resealed and again allowed to stand for another half hour with centrifuging as before. If a precipitate appears when the reaction is complete, it is centrifuged out. If there is no precipitate, the reaction mixture is acidified with hydrochloric acid. The precipitate in either case is washed with water and extracted with cold ether, the extract being discarded. The chief difficulty in this preparation lies in the purification of the roduct. The principal impurity is benzoic acid which should Rave been removed by the cold ether. However, since the derivative in some cases is also soluble in ether, this separation is not very efficient. The authors found that the benzoic acid can readily be removed by sublimation. A Johns melting point block, used in determining the melting points, made an excellent sublimator. The residue from the cold ether treatment is placed on a cover slip on the block and heated to 90" to 100' C. A microscope slide is laid over the block. The shape of the block keeps the slide about 2 mm. above the cover slip and sample. When no more sublimate forms on a clean ortion of the slide, another cover slip is placed on the sample a n i the temperature is raised to the melting oint. An interesting observation was made in the case of the genzoyl derivative of diphenylamine. The melting point given in the literature is 178" C. I n the authorsbexperiments the derivative obtained melted sharply at 107-9 , but on heating fur-
96
INDUSTRIAL AND ENGINEERING CHEMISTRY
ther the melt solidified again between 130" and 140", and melted A suggested explanation of this beagain sharply at 176-7 havior is that the benzoyl derivative of diphenylamine exists in two modifications with the melting points @veri and with a transition temperature somewhere between 130 and 140'. Acylation in Pyridine. Procedure A. The reaction is carried out by dissolving 3 to 6 mg. of the substance in 30 to 60 cu. mm. of dry pyridine in a centrifuge cone. An equal quantity or slight excess of reagent is added quickly and with cooling under the tap if necessary. The mixture is diluted with approximately 0.6 ml. of water and stirred until precipitation occurs. If no recipitate appears after a reasonable time, the tube is set aside fpr 10 minutes, and then again stirred. The precipitate is centrifuged off, the supernatant liquid discarded, and the precipitate washed with 0.6 ml. of water, 0.6 ml. of 0.3 N sodium carbonate solution, and finally again with 0.6 ml. of water. The product is recrystallized from a suitable solvent to a constant melting point. Procedure B. The procedure is the same as,in A, except that after the reaction has taken place the mixture is dissolved as far as possible in 500 cu. mm. of ether and the pyridine is extracted by shaking three times with 500 cu. mm. of water. The product is washed twice n-ith 50 cu. mm. of 0.3 N sodium carbonate and twice with 50 cu. mm. of water. The ether is evaporated and the residue allon-ed to stand in an evacuated vacuum desiccator to remove all volatile substances as completely as possible. The residue is then recrystallized from a suitable solvent to a constant melting point. Picramides. Three to 6 mg. of the amine, 50 cu. mm. of ethanol, and 330 cu. mm. of a 2 er cent alcoholic solution of picryl chloride are mixed in a centrigge cone. After standing for a few minutes, the mixture is heated to boiling. If necessary, water is added to produce a slight turbidity to induce crystallization. After a brief centrifuging to concentrate the solid at the lower part of the centrifuge cone (but not enough to pack it down), the larger part of the supernatant liquid is removed. The precipitate is stirred up with the remaining liquid and the slurry transferred to a microscope slide. Here the remaining liquid is drawn off with a iece of filter pa er or a capillary pipet and the precipitate melting point is then taken. washexwith alcohol. As the methyl amine derivative hydrolyzes very readily, the hydrochloride is used in place of the free amine. To 3 to 6 mg. of the hydrochloride, dissolved in 15 to 20 cu. mm. of alcohol, 100 cu. mm. of 2 per cent alcoholic picryl chloride are added. After mixing, 3 to 6 mg. of potassium hydroxide (powdered) are added, and mixed until the color becomes uniform. After centrifuging, the supernatant liquid is decanted to another centrifuge cone and treated with concentrated hydrochloric acid dropwise until the brown liquid turns yellow. The mixture is again centrifuged and the supernatant liquid removed and evaporated to dryness or to the formation of crystals. The solid is washed with alcohol, dried, and the melting point determined. The methyl aniline derivative also gave difficulties by both these procedures, but by modifying Turpin's ( I S ) procedure it is possible to prepare it. Five milligrams of picryl chloride are dissolved in boiling alcohol, then 3 mg. of methyl aniline and 3 mg. of anhydrous sodium acetate are added. The centrifuge cone is placed in the water bath or heating block and heated until half the alcohol has been evaporated. . The cone is then placed in a vacuum desiccator until crystallization takes place.
.
fl
Vol. 14, No. 1
trifuged off and the supernatant liquid discarded. The derivative is extracted from the precipitate with ether and recrystallized from ether or benzene. Alexander and McElvain (1) have suggested the use of 3-, nitrophthalic anhydride for the separation of primary, secondary, and tertiary amines but not on a micro scale.
SALTSOF AMIKEB.Picrates. The methods for the preparation of picrates vary according t o the amine. Two examples will show the general technique. Two to 3 mg. of quinoline are dissolved in alcohol and an equal volume of a saturated alcoholic solution of picric acid is added. The precipitate which forms immediately is centrifuged, the supernatant liquid removed, and the residue washed with five times the original volume of liquid, dried at 60°, and the melting point taken. In the case of substances such as urea, 3 to 6 mg. of the sample are dissolved in water and then an equal volume of a saturated aqueous solution of picric acid and a small drop of dilute hydrochloric acid are added. A precipitate will form in about 10 minutes. It is centrifuged out, the supernatant liquid is removed, and the residue is washed with very little water. A
1 I I L 1.5 im.
cotton u¶
Litmus
\ e
,90 . nun
FIGURE3 Salts of 3,iGDinitrobenzoic Acid. Two milligrams of 3,s-dinitrobenzoic acid are dissolved in 25 to 50 cu. mm. of absolute alcohol. This solution is mixed with an equal volume of a solution containing 0.00001 mole of the amine in absolute alcohol. The solution is placed in a stream of dry air until the solution is evaporated. The solid is recrystallized from absolute alcohol or another anhydrous solvent such as benzene. Salts of p-Toluene Sulfonic Acid. Three to 6 mg. of the monoamine or 2 to 4 mg. of a diamine are added to 20 cu. mm. of 2.5 N p-toluene sulfonic acid. The mixture is heated to gentle boiling on the heating block until the solution clears up. One to 2 mg. of decolorizing carbon are added and the solution is again boiled gently for a few minutes. While the solution is still hot, it is centrifuged and the hot liquid transferred to another centrifuge cone. The filtrate is cooled in ice water to crystallize out the salt. If no solid separates, the solution must be evaporated to some extent. The solid is recrystallized from hot water and dried in air at 110' C.
Tests for Genus 3
TESTFOR KITROGROUP. The compound (0.1 to 0.2 mg. or less in 10 cu. mm. of 50 per cent hot ethyl alFohol) is treated w.ith ARYLSULFOXYL DERIVATIVES OF PRIMARY AND SECOKDART 5 to 6 drops (from a capillary) of 1 N calcium chloride solution and a pinch of zinc dust in a centrifuge cone. The mixture is AMINES. Behrens ( 2 ) suggested the use of the Hinsberg heated in a water bath until a reaction takes place, kept hot until reagent for the separation of primary, secondary, and tertiary the reaction ceases, and then brought to a boil. After standing amines on a micro scale, but gave no experimental details. for 2 or 3 minutes, it is centrifuged. The supernatant liquid is siphoned off through a capillary into a second cone which conThe following procedure as developed by the present authors tains 10 per cent silver nitrate solution. The appearance of a gives good results. silver mirror or a gray or black precipitate indicates a nitro compound. A blank must be run on the reagents. To 3 mg. of the amine 5 t o 9 cu. mm. of benzene sulfonyl chloHearon and Gustavson (8) describe a test for the nitro group ride are added, and stirred until reaction takes place. The mixture carried out on a semimicro scale. Other color reactions for nitro is cooled under the tap or in ice water if necessary. Then 12 to 24 compounds are given by Bost and Nicholson (S), Kulikov and cu. mm. of 4 N potassium hydroxide solution are added and the Panova (IO),and Kirchhof (9). mixture is heated slo~vlyto slight boiling in a heating block to reDIPHENYLAMINE REACTIONS FOR NITRATES, KITRITES,ALImove the excess reagent, stirring while heating. I t is then cenPHATIC NITROCOMPOONDS, AND NITROSOAVINES. The extreme trifuged. sensitivity of this test even when carried out on the ordinary A . If the material dissolves completely in the potassium hyscale is sufficient to make a microprocedure unnecessary. droxide, the substance is a primary amine. Any slight insoluble BIURETREACTIOK.This reaction has been described by Emich material is centrifuged off and the clear liquid is acidified rvith ( 7 ) . It can be carried out on a white porcelain spot plate or in a concentrated hydrochloric acid. The resulting precipitate is cencentrifuge cone. trifuged out, the supernatant liquid discarded, and the derivative HYDROLYSIS OF SPECIES OF ORDER2. A . With Hydrochloric extracted from the residue with ether and recrystallized from A d . The sample, 0.5 to 1 mg., of the substance is introduced ether or benzene. If no precipitate appears on the addition of the into a capillary either by pushing the tube into the solid powder hydrochloric acid, the derivative must be extracted from the and then wiping off the outside or by dipping into the liquid. solution with benzene or ether. The same end is then dipped into 6 N hydrochloric acid (in a B. If the derivative does not dissolve in the .potassium hyFatch glass) until a 10-mm. column has men in the tube. Both droxide, the original substance is a secondary amine. It is cen-
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.
