Semimicro-Kjel da hl Procedure for Pyrid inium Halide and Oxyhalide Salts VELMER B. FISH and PHILLIP R. COLLIER Wm.
H. Chandler
Chemistry Laboratory, Lehigh University, Bethlehem, Pa.
,This work was done to demonstrate the use of the semimicro-Kjeldahl method for the analysis of a variety of pyridinium halide and oxyhalide salts. Tin or stannous chloride in the digestion mixture increased the percentage of ammoniacal nitrogen recovered. The method is applicable to both refractory and nonrefractory halide compounds.
T
success of the Kjeldah! method of analysis depends in part on the position of nitrogen in the organic compound. Nitrogen present in a chain, as in amides and amines, is considered easier to determine than t h a t present in ring structures, nitrogen-nitrogen linkages, and nitrogenoxygen linkages. However, with various modifications of the digestion procedures or a predigestion treatment of the organic nitrogen, this method of analysis is applicable to a wide variety of compounds ( 1 - 7 ) . Some heterocyclic nitrogen conipounds are very resistant to the usual method of acid digestion; hence, many modifications have been suggested (4, 5 , 7-9, 11-13). The analysis of halide salts of heterocyclic nitrogen has been reported as erratic with the unmodified Kjeldahl method ( 5 ) . Many of the suggested modifications are tinie-consuming and require additional manipulations. This article presents a simple and reasonably rapid method for the analysis of pyridinium salts. HE
APPARATUS A N D REAGENTS
An Ainsworth microbalance, Type FDJ, was used. The samples were weighed in tin-foil cups (unless otherwise stated) made by cutting circles of 0.05-mm. pure tin foil with a No. 15 cork borer. The circles were made into cups by shaping them over the end of a 0.16-inch plastic rod. The average weight of the cups was about 140 mg. The samples were digested in a 30ml. Kjeldahl flask, using electric heaters. Distillations were made in the improved Pregl-Parnas-Wagner apparatus. The reagents were prepared, without modification, according to the directions of Cole and Parks (4).
PROCEDURE
Weigh a sample, containing approximately 1.5 mg. of nitrogen, in a tinfoil cup and place in the digestion flask. Add 1.5 grams of catalyst mixture and 4 ml. of concentrated sulfuric acid. Digest the material until colorless or clear and then for 2 hours. If the material is not a refractory nitrogen compound, the afterboil may be shortened t o 30 or 45 minutes. Allow the digestion mixture to cool and then proceed with the conventional distillation and titration (6). RESULTS A N D DISCUSSION
I n Table I are shonn the results obtained b y Kjeldahl and Dumas methods of analysis. The Kjeldahl nitrogen values are the average of six determinations. They are in good agreement with theoretical percentages and Dumas values. I n Table I1 are shown the results obtained when cigarette paper instead of tin foil was used as the sample cup. The values reported are the average of five or six determinations. Significantly low nitrogen values for
Table I.
2 hours 5.94
Theory 5 94
After Digestion 3 4 5 hours hours hours 5.59 5.48 5 40
Table I11 s h o w the results obtained when cigarette paper was used as the
Determination of Nitrogen in Tin-Foil Cup
Compound 1,2,4,6-Tetramethylpyridinium iodide 3-Carbomethoxy-1-methyl pyridinium iodide 1,2-Dimethylpyridinium iodide lJ2,4,6-Tetramethylpyridiniumperchlorate 3-Carbamido-1-benzylpyridiniuni chloride 3-Carbamido-1-methylpyridinium iodide 1-Methylpyridinium iodide Phenyltrimethylammonium iodide Table 11.
the iodide salts were obtained in the absence of tin, except for l-methylpyridinium iodide, which gave good results by both methods. Apparently tin, or some oxidation state of tin, had a beneficial effect. The type of compound analyzed did not influence the results obtained for iodide derivatives; phenyltrimethylammonium iodide gave low nitrogen values in the absence of tin. Hence, lon- nitrogen values were obtained for both refractory and nonrefractory iodide salts in the absence of tin. As reported ( I S ) , an extended afterboil of 5 hours resulted in a notable loss of ammoniacal nitrogen. When a n extended afterboil was applied to 1,2-dimethyl pyridinium iodide in the absence of tin, the percentage of nitrogen found was:
Percentage of Nitrogen Kjeldahl Av. Standard Dumas Theory method deviation deviation method 5.32
5.23
10.03
0,032
5.22
5.01 5.94
5.00 5.94
h0.02 10.03
0.032 0.034
4.94 5.88
5.94
5.93
hO.01
0.002
5.94
11.26
11.26
10.04
0.044
10.92
10.62 6.34 5.32
10.57 6.25 5.26
10.01 hO.01
0.014 0.014 0.033
10.57 6.25 5.28
1 0 .03
Determination of Nitrogen in Cigarette Paper Cup
Compound 1,2,4,6-Tetramethylpyridinium iodide 1,2-Dimethylpyridinium iodide 1,2,4,6-Tetramethyl pyridinium perchlorate 3-Carbamido-1-benzylpyridinium chloride 3-Carbamido-1-methylpyridiniumiodide 1-Methylpyridinium iodide Phenyltrimethylammonium iodide
Theory 5.32 5.94 5.94 11.26 10.62 6.34 5.32
Percentage of Nitrogen Av. Standard Found deviation deviation 5.06 AO.05 0.056 5.69 10.06 0.074 5.93 1 0 .02 0.024 11.24 10.02 0.027 10.28 f0.06 0.076 6.25 10.03 0.026 5.17 10.04 0.050
VOL. 30,
NO. 1, JANUARY 1958
151
Table 111.
Determination of Nitrogen (Stannous Chloride Added)
Compound 1,2,4,6-Tetramethylpyridiniumiodide 1,2-Dimethylpyridinium iodide 3-Carbamido-1-methylpyridiniumiodide 1-Methylpyridinium iodide Phenyltrimethylammonium chloride
Theory 5.32 5.94 10.62 6.34 5.32
Percentage of Nitrogen Av. Standard Found deviation deviation 5.23 10.01 0.009 5.84 10.03 0.040 10.57 3~0.03 0,038 6.29 10.03 0.033 5.26 f0.03 0.028
tin-foil sample cup is convenient and the resulting tin salts have a beneficial effect on the reaction. ACKNOWLEDGMENT
The authors are grateful to E. M. Kosower for preparation and purification of the pyridinium salts. LITERATURE CITED
sample cup and stannous chloride solution, equivalent to about 140 mg. of tin, was added prior to digestion. Results are compatible with the original nitrogen values. Measurement of the digestion mixture, using a calibrated iron-constantan thermocouple, showed a temperature of 335’ C., which remained essentially constant, regardless of the presence or absence of tin. A plausible explanation for the difference in nitrogen values obtained in the presence of tin would be the catalytic effect of tin salts in the removal of iodine. Hot concentrated sulfuric acid, an oxidized agent, readily oxidizes iodide to elemental iodine. Any hydriodic acid formed is converted to free iodine. As the reaction proceeds, the iodine formed is gradually distilled out of the digestion flask. However, as the iodine is formed in the digestion mixture, it may react indirectly 1%-ithammoniacal nitrogen being produced, converting it to free nitrogen (10). It is postulated that iodine, and other halogens, may be oxidized to oxyhalogen
acids, which in turn oxidize ammonium compounds (10). The results of these experiments indicate that the presence of tin salts in the digestion mixture prevents the formation of oxyiodine acids. The loss of nitrogen attributed to the action of iodine or its compounds is usually small and may be induced by addition of iodide after the sample has been digested. Thus the reactions involved concern the ammonium salts and/or the mercury-ammonia complex formed when mercury is present in the catalyst. These reactions appear to be absent in the presence of tin salts. The chloride salt was not affected by the presence or absence of tin. For the chloride ion, the reaction of sulfuric acid forms hydrogen chloride, which is readily vaporized from the digestion media. CONCLUSION
The semimicro-Kjeldahl method gives excellent recovery of nitrogen from a wide variety of pyridinium halide and oxyhalide salts (4, 6). The use of the
Bradstreet, R. B., AXAL.CHEM.26, 185 (1954). ,Bradstreet, R. B., Chem. Rets. 27, 331 (1940). Clark, E. P., “Semimicro Quantitative Organic Analysis,” Academic Press, Xew York, 1943. Cole, J. O., Parks, C. R., IND.ENG. CHEST.,API‘AL.ED. 18. 61 (1946). Crane. F. E..Fu O S S . R. M., ANAL. CHEW26, 1651 (1954). ’ Fish, V. B., Ibid., 24, 760 (1952). Friedrich, A., Kuhaas, E., Schnurch, R., 2. physiol. Chem. 216, 68 (1933). Gautier, J. A., Renault, J., Ann. chim. anal. 28. 85 (1946). Marzado, M.,’ Mskrochemie ver. Mikrochim. $eta 36/37,671(1951); 38,372 (1952). Modeer, E., Univ. Wyoming Pub. 7,NO.2,13-26 (1940). Ogg, C. L., Brand, R. W.,Tillits, C. O., J . Assoc. O j i c . Agr. Chemists 31, 663 (1948). Shirley, R. L., Becker, W. W., IXD. EXG. CHEM., ANM.. ED. 17, 437 (1945). Willits, C. O.,Coe, 11.R., Ogg, C. L., J . Assoc. Ofic.Agr. Chemists 32, 118 (1949). RECEIVEDfor revieF March 28, 1957. Accepted August 19,1957.
Determination of Phosphorus in Organic Compounds Rapid Micro and Semimicromethod KENNETH D. FLEISCHER, BURNETT C. SOUTHWORTH, JOHN H. HODECKER, and MURRAY M. TUCKERMAN Sterling- Winthrop Research Institute, Rensselaer, N. Y.
b An
organophosphorus compound may b e burned in an oxygen-filled fiask by the Schoniger method. All phosphorus is converted to the orthophosphate, which may b e determined either titrimetrically or colorimetrically. The colorimetric method is based on the formation of heteropoly blue and is used for a microdetermination. The phosphate may also b e precipitated as magnesium ammonium phosphate hexahydrate. The precipitate is then dissolved in acid and the amount of magnesium determined with (ethylenedinitri1o)tetraaceticacid. The micromethod is accurate to within 270,
152
ANALYTICAL CHEMISTRY
while the semimicromethod is accurate to within 0.5%.
I
rapid method for the microdetermination of halogens and sulfur in organic compounds (6, 7 ) , place the weighed sample in a filter paper envelope, affix to the end of a platinum wire, and burn in an oxygen-filled flask. Absorb the desired element in a suitable liquid absorbent on the bottom of the flask and then titrate. The ease, rapidity, and accuracy of this method recommend that it be extended to other elements. Schoniger ( 5 ) predicted its N A
application to the determination of phosphorus, arsenic, and metals. This paper describes the combustion of organophosphorus compounds by the above procedure followed by either of two methods for the determination of the phosphorus. For semimicroanalysis the authors employed a modification of the method of Flaschka and Holasek ( 2 ) . Precipitate the phosphate as magnesium ammonium phosphate hexahydrate. The salt concentration present affects this precipitation and therefore the lower limit in this case appears to be about 1 mg. of phosphorus. Collect the precipitate on a frit and wash thor-
