V O L U M E 2 6 , NO. 10, O C T O B E R 1 9 5 4 of cobalt from the elements rvith which it is frequently associated. There is no need to restrict the organic reagents to those that give good weighing forms. LITERATURE CITED
(1) Rarbieri, G. 4 . , Atti accad. nazl. Lincei, 8 , 405 (1928). (2) Biedermann, W., and Schwarzenbach, G., Chimia (Switz.), 2, 56 (1948). (3) Dickens, P., and Maassen, G., Arch. Eisenhutcenw., 9,487 (1936). (4) Dobbins, J. T.. and Sander, J. P., IXD.ESG. CHEM.,ANAL.ED., 6, 469 (1934). (5) Engle, K.D., and Gustavson, R. G., J . Ind. E p g . Chem., 8, 901 (1916). (6) Evans, B. S..Analysc, 62,363 (1937).
1651 (7) Faleev, F. V., Gorno-Obagatitel. D e b , 10, 53 (1932). (8) Flaschka, H., Chemist Snalyst, 42,56 (1953), (9) Flaschka, H., Mikrochim. A c t a , 39,38 (1952). (10) Job, A,, Ann. chim. phys., 20, 214 (1900). (11) Laitinen, H. A., and Burdett, L. W., ANAL. CHEW. 23, 1268 (1951). (12) K'ikolow, C., Przemyd. Chem., 17, 46 (1933). (13) Prible, R., and Malicky, V., Collection Czechoslot. Chem. Commum.. 14,413 (1949). (14) Vance. J. E.. and Boruu. R. E.. ANAL.CHEM..25. 610 (1953). (15) Willard, H. H., and Diehl, H., "bdvanced Quantitative Analysis,'' p. 382, Xew York, D. Van Nostrand Co., 1943. (16) Willard, H. H., and Hall, D., J . Am. Chem. Soc., 44, 2237 (1922). ,
RECEIVED for review April 10, 1054. Accepted July
I
14, 1954
Determination of Pyridinium Nitrogen FRANCIS E. CRANE, JR., and RAYMOND M. FUOSS Chemical Laboratory, N e w Jersey College for W o m e n , N e w Brunswick, Y a l e University, N e w Haven, Conn.
Treatment of pyridinium salts with alkaline peroxide liberates about '75% of the nitrogen in titratable form and renders the balance accessible to standard Kjeldah1 determination. A n analytical procedure based on these facts is described : using methylpicolinium iodide 0.13% nitrogen (14 analyses) as a test compound, 5.84 =I= was found, compared to 5.969'0 theoretical. -4t least 2 grams of sodium peroxide per millimole of nitrogen must be used.
N. J.,
and Sterling Chemistry Laboratory,
1.2 grams of red phosphorus (0.038 mole), and 13 ml. of 57% hydriodic acid (0.10 mole) \vas heated for 10 hours at 95' to 100" C. The hot reaction mixture was filtered through an asbestos mat to remove phosphorus and was then washed with 35 ml. of water. Filtrate and washings were allowed to stand overnight; 3.0 grams of white crystals melting a t 172-6" C. separated. Two recrystallizations from water (20 ml. per gram) gave a product melting a t 177-8" C. Potentiometric iodide, 34.5, 34.9%, us. 35.16% Lheoretical; total iodine (after alkaline hydrolysis), 70.3% u8. (0.27% theoretical. PROCEDURE
H
ETEROCYCLIC nitrogen frequently is difficult to determine quantitatively, especially when it is present in the quaternized state. Even the Dumas method gives erratic results when the salt is a halide such as methylpicolinium iodide. A variety of modifications of the conventional Kjeldahl procedure have been suggested (1-15). This note describes another procedure for the quantitative determination of pyridinium nitrogen which is simple and reasonably rapid. illkaline peroxide (from sodium peroxide and water) converts pyridinium salts (via the pyridone) to aliphatic cleavage products, the nitrogen of which is then accessible to quantitative determination. The method is based on this sequence of reactions. MATERIALS
Methyl-4-picolinium iodide was prepared from methyl iodide and 4-picoline in ethyl alcohol, and was twice recrystallized from 50:50 ethvl alcohol-ether and once from 90 to 10 ethvl alcoholether; melting point, 157-8 '. Potentiometric iodide, 53.9, 53.9%, os. 54.0% theoretical. p-Iodoethylpyridinium Iodide. -4mixture of 21 grams (0.27 mole) of pyridine and 34 grams (0.27 mole) of ethylene bromohvdrin was daced in a flask under a reflux condenser and, after b&ng heated gently to start the reaction, the mixture was kept from overheating by immersion in cold water. Too vigorous reaction gives vinylpyridinium bromide and other by-products. The mixture set 'to a white solid which was remelted and heated for 15 minutes more t o ensure completion of the reaction. The crude product (8-hydroxyethylpyridinium bromide) was washed with three 60-ml. portions of dry ethyl ether to remove unreacted reagents and was stored under vacuum over phosphorus pentoxide; it is extremely hygroscopic. Yield, 39 grams = 71%; melting point 108-10' C.; potentiometric bromide, 39.0, 39.1, 39.2, 39.2y0 us. 39.16% theoretical. The iodide was then prepared by the following reaction:
A mixture of 5.0 grams of the above bromide (0.025 mole),
The sample (enough to give 2 to 6 mg. of nitrogen) is weighed from a long-handled weighing bottle into a 100-ml. Kjeldahl flask. A borosilicate glass tube (3 X 1 cm.) containing 2 to 3 grams of sodium peroxide (Mallinckrodt's reagent grade or Baker's C.P. analyzed) is then dropped into the flask, care being taken not to spill peroxide on the sample. The conventional Kjeldahl apparatus is then assembled, with the outlet condenser dipping under 0.025N sulfuric acid in a 250-ml. Erlenmeyer flask. The connection to the steam generator is closed a t this stage of the procedure. rlbout 10 ml. of water are run into the Kjeldahl flask through the addition funnel. By gentle swirling, the sample can be dissolved (or be thoroughly w d ) without peroxide coming in contact with sample or water. Then 20 ml. more of water are admitted (taking care to keep a water seal above the entrance stopcock), and the peroxide tube is tipped so that water and peroxide mix. The mixture is allowed to stand with occasional swirling for 20 minutes; then the contents of the Kjeldahl flask are slowly heated to about 80" C. Too rapid heating here produces serious foaming. Steam distillation is then started (taking care that a positive pressure of steam exists in the generator before the stopcock to the Kjeldahl flask is opened) and is continued until the volume in the Erlenmeyer flask reaches about 150 ml. The Kjeldahl flask is also heated to prevent undue condensation of steam. The Kjeldahl flask is allowed to cool and, after a drop of phenolphthalein solution is added, the contents are cautiouslv neutralized with concentrated sulfuric acid. An excess of 7" to 12 ml. of acid is added. &lost of the water is evaporated over a microburner and then the residual solution is heated in a fume chamber below the boiling point until frothing ceases. Next, the temperature is raised so that the solution boils gently. After the iodine is evaporated, 5 to 10 mg. of catalyst (1 part of red mercuric oxide and 3 parts of selenium) are added and the solution is digested a t 300" t o 350" C. for at least 1 hour (some samples required 2 to 3 hours for complete digestion). Evaporated acid is replaced to maintain approximately constant volume during the digestion. During this operation, the first distillate in the Erlenmeyer flask is evaporated to 40 to 50 ml. -4fter the digestion, the Kjeldahl flask is cooled to 50" C. or below, and 25 ml. of water are cautiously added to dissolve the sodium sulfate. One drop of phenolphthalein solution is added and the Kjeldahl apparatus is reassembled with the Erlenmeyer flask, containing the concentrated distillate, a t the condenser tip
ANALYTICAL CHEMISTRY
1652 again. Steam for agitation is started through the solution in the Kjeldahl flask, and 30% sodium hydroxide solution is carefully and s l o ~ - l yrun in to neutralize the acid; then 10 ml. in excess are added and steam distillation is started again. After 100 ml. have distilled, the contents of the Erlenmeyer flask are concentrated by evaporation, and titrated with 0.025S potassium hydroxide solution (mixed indicator, 5 parts of 0.2% bromocresol green and 1 part of 0.2% methyl red in ethyl alcohol), with the usual precautions ( 2 ) . Sitrogen content of the unknown is then calculated from the titer after correction for the blank (nitrogen in the reagents).
sulfate (blank by difference). These and other control data average to 0.009 weight % of nitrogen in the lot of sodium peroxide used. This figure is higher than the label analysis (0.002 to 0.003%) but undoubtedly is the proper figure to use, because the data of Figure 1 would show a systematic increase in apparent nitrogen with increasing R if the low figure were used. The 0.009 includes extraneous nitrogen from all sources (sulfuric acid, sodium hydroxide, and water, in addition to the peroxide).
RESULTS AYD DISCUSSION
hlost of the test analyses were made on methylpicolinium iodide which contains 5.96% of nitrogen. By the conventional Kjeldahl procedure, only 1.04% of nitrogen TTas obtained. This result is typical of the behavior of pyridinium salts: According to the authors' experience, nitrogen analyses are erratic and invariably loiv when made by the unmodified Kjeldahl method. I n Figure 1 are shown the results of a series of analyses made by the peroxide method described in the preceding section. The ratio, R, of peroxide to sample (units = grams of sodium peroxide per millimole of nitrogen in sample) was varied from zero to a large excess. The figure clearly shows that the analyses are loiv until about 2.2 grams of sodium peroxide per millimole are used. This amount corresponds to a twentyfold excess over the minimum theoretical amount required to oxidize the pyridol to the pyridone. Possibly less peroxide could be used, but a high concentration is needed to obtain reasonable reaction speed and, furthermore, some , peroxide is wasted in oxygen evolution. Beyond R ~ 2 . 5 the nitrogen found was 5.84 & 0.13% (average of 14 analyses), with no systematic dependence on R. The cycles in Figure 1 are drawn with a radius equal to 0.13%; the theoretical composition (5.96%) is indicated by the horizontal arrow.
44,87 15.38 0.00 0.00 0.00
1.78 2.64 2.09 2.74 2 28
40 40 40 50 45
50 0 50 40
45
9.74 3.526 0.309 0.226 0.179
9.52 3.260 0.00 0.00 0.00
0.0127 0,0101 0.0148 0.0083 0.0078
Several samples of urea, alone and with picolinium methiodide viere also analyzed by the peroxide method: 15.36 mg. of urea 1.89 grams of sodium peroxide, found 46.74% of nitrogen, theoretical 46.65%; 25.34 mg. of urea, 39.36 mg. of methylpicolinium iodide, 3.07 grams of sodium peroxide, found 14.07 mg. of nitrogen us. 14.15 mg. present; 12.25 mg. of urea, 81.65 mg. of methylpicolinium iodide, 1.83 grams of sodium peroxide, found 10.43 mg. of nitrogen us. 10.58 mg. present (all after correcting on the basis of 0.009% of nitrogen in the peroxide). Based on the results of various control analyses, it may be concluded that sodium peroxide does not interfere with the determination of nitrogen normally accessible to the Kjeldahl treatment, and that it renders pyridinium nitrogen accessible. One experimental precaution needs emphasis: Approximately three quarters of the nitrogen is carried over as amine and/or ammonia during the first distillation following the sodium peroxide treatment. Adequate acid must therefore be available in the Erlenmeyer flask used as the receiver; as a safeguard, a drop of mixed indicator is added to the acid. I n three analyses, the contents of the Erlenmeyer flask were titrated after the first distillation instead of being concentrated and batched with the second distillate: 75.9, 74.4, and 75.5% of the total nitrogen was in the first distillate, the remainder being in the second. This observation suggests that further development of the technique could lead to a method of determining pyridinium nitrogen in which the time consuming treatment with concentrated sulfuric acid could be eliminated entirely. LITERATURE CITED
Belcher, R., and Godbert, A. L., J . SOC. Chem. I n d . , 60, 196 (1941).
Cole, J. O., and Parks, C. R., I N D .ENG.CHEW, ANAL.ED., 18, 61 (1946).
Figure 1. Dependence of Apparent Nitrogen Content on Amount of Sodium Peroxide Used
Analysis of 8-iodoethylpyridinium iodide gave the following results: per cent nitrogen found, 3.60, 3.49, 3.61, 3.69, 3.63, 3.74; average, 3.63 & 0.08 us. 3.88% theoretical. The peroxide ratio R was varied from 3.3 to 12.1; no correlation was observed between R and per cent nitrogen found. This salt is only slightly soluble in water, and the somewhat low analysis may have been due t o exhaustion of the peroxide before all the salt was decomposed. All of the above analyses required a correction for nitrogen in the sodium peroxide. This was determined by control analyses, examples of which are given in Table I. Agreement is satisfactory between mixtures with no deliberately added nitrogen and those where known amounts of nitrogen were added as ammonium
Dupuy, P., Compt. rend., 232, 836 (1951). Fish, V. B., AKAL. CHEM., 24, 760 (1952). Friedrich, A , , Kiihaas, E., and Schnurch, R., Z . phusiol. Chem., 216,68 (1933).
Gautier, J. A., and Renault, J., Ann. chim. anal., 28, 85 (1946). Levi, T. G., and Gimianani, L., G a m chim. ital., 59, 757 (1929). hlaraadro, 1I.,Mikrochemie per. Mikrochim. A c t a , 36/37, 671 (1951); 38,372 (1952); 40,359 (1953).
hIeulen, H. ter, Chem. Weekblad, 23, 348 (1926). Meulen, H. ter, Rec. trav. chzm., 43, 643 (1924). RIeulen, H., ter, and Ravensway, H. J., Chem. Weekblad, 33, 248 (1936).
LIoreau, c.,Compt. rend., 233, 1616 (1951). Ogg, C. L., Brand, R. W., and Willits, C. O., J . Assoc. Ofic. Agr. Chemists, 31,663 (1948).
Rosenthaler, L., and Bulat, H., Ret. jac. sci. uniu. Istanbul, 9A, 124 (1944).
Shirley, R. L., and Becker, W.W., IKD.EKG.CHEM.,ANAL.ED., 17,437 (1945). RECEIVEDfor review January 25, 1954. Accepted June 8, 1954. Contribution S o . 1208, Sterling Chemistry Laboratory, Yale University, S e w Haven, Conn.
