Aug., 1918
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
filtered, while hot, through a coarse I j cm. filter paper into another Kjeldahl flask. The aeration flasks are washed with hot water and the washings poured into the other flasks without filtration, since practically all the residue has been transferred t o the filter paper. The residue is washed 4 or j times with small quantities of boiling water. A small piece of paraffin and a n ebullition tube are placed in the flask t o prevent frothing and bumping, 4 cc. of a 50 per cent sodium hydroxide solution added, and the solution boiled for 30 min. The solution is diluted back t o 250 cc., and 0 . 9 cc. of concentrated sulfuric acid added t o reduce the alkalinity of the solution t o about N / I o . The nitric nitrogen is then determined by reducing with I g. of Qevarda’s alloy and boiling the solution for 40 min. after bringing it t o boiling in minimum time. When the solution reaches the boiling point it is advisable t o reduce the flame. The reaction is quite vigorous and may result in foaming over if this precaution is not taken. As soon as the vigorous action ceases, the flames are turned up and boiling continued. S U M MARY
The work reported in this paper justifies the following conclusions: I-Organic and ammonia nitrogen can be separated by aerating the solutions in the cold over magnesium oxide or sodium carbonate. 11-Ammonia determinations obtained by boiling soil suspensions or soil extracts rich in organic matter with magnesium oxide are unreliable. 111--Ammonia and nitric nitrogen can be accurately determined upon the same sample by the method reported in this paper. The author takes this opportunity t o thank Dr. E. R. Allen for his helpful criticisms in this investigation. LABORATORY OF S O I L BIOLOGY OHIOAGRICULTURAL EXPERIMENT STATION WOOSTER. OHIO
STUDIES IN SYNTHETIC DRUG ANALYSIS’ V-ESTIMTION OF THEOBROMINE B y W. 0.EMERY A N D G. C. SPENCER Received April 25, 1918 INTRODUCTION
Questions having quite recently arisen relative t o the actual therapeutic strength of certain diuretic combinations of theobromine and theophylline, notably with sodium acetate and sodium salicylate, a n investigation of such products seemed desirable. In the present paper, however, consideration will be given only t o experiments involving theobromine and looking t o the utilization of its periodide as a basis for evaluation. A description of very similar work on theophylline and its combinations is reserved for a future communication. The quantitative estimation of theobromine in admixture with other agents of medicinal value, or with materials of a more or less inert nature, is complicated by the great insolubility of this compound in the more 1
THIS JOURNAL, 6 (1914), 665.
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common organic reagents. A somewhat similar difficulty, encountered in developing a procedure for the estimation of acetanilide and phenacetin (acetphenetidine) in admixture, was met by the employment of glacial acetic acid. A number of preliminary trials soon demonstrated the adaptability of this solvent also for theobromine when applied t o periodide formation. It was further found t h a t the solubility is favorably affected by the presence of sodium acetate. While it is by no means difficult t o prepare several periodides of theobromine, its quantitative separation in the form of a n iodine addition-product of unvarying composition, suited t o the purposes of titrimetric control, is manifestly beset with difficulties naturally inherent in operations of this character, such as I;lomogeneity, freedom from other periodides and salts, losses by decomposition, evaporation, etc. I n the method presently t o be described, advantage is taken of,the fact t h a t , when a n acetous solution of theobromine containing sufficient iodized potassium iodide is treated with a mineral acid, a grayish black crystalline precipitate separates, which, judged by its iodine content, has the composition C7HsN402.HI.14. The separation of this hydriodo-tetriodide becomes quantitative if the iodine solution is reenforced with a small quantity of sodium chloride. If, therefore, the precipitation is effected in a measured volume of standard iodine and the insoluble additionproduct removed by filtration, the volumetric determination of the unconsumed iodine is readgy accomplished, and therefrom the quantity of theobromine involved as readily calculated by means of t h e appropriate factor. EXPERIMEKTAL
For purposes of identification, the above-mentioned periodide was prepared by dissolving theobromine in a feN cubic centimeters of hot glacial acetic acid, transferring the clear liquid to a flask containing sufficient iodized potassium iodide, adding a little concentrated hydrochloric acid with constant agit?tion, and then shaking the mixture vigorously. After standing some hours, the periodide was isolated by pouring the product onto a small suction plate provided with a suitable filter, washing the mass several times with a saturated aqueous iodine solution, a n d exposing the crystals in the open air until apparently dry. Protracted exposure of the substance t o atmospheric influences, however, is inadvisable, such treatment inducing a n appreciable lightening in the color of the crystals with consequent loss of chemically combined iodine. The “exterior” iodine was determined by titration with sodium thiosulfate in alcoholic solution, and in t h e presence of sodium bicarbonate. Total iodine, on the other hand, was estimated by first treating the substance in acetic a c i d . with a saturated solution of sulfur dioxide in water, followed by precipitation with silver nitrate. Calcd. for C7HsN40e.HI.L: 14, 62.2; Is, 77.8. Found: IP,59.9, 61.7, 62.2; Is, 76.5, 7 7 . 0 , 77.2.
Thus i t appears t h a t , even with the greatest care, the operations of washing and drying are likely t o be
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attended with some loss in iodine, which is reflected in the above analytical findings obtained on different samples. I n order t o determine experimentally the conditions best’ suited t o the iodometric estimation of theobromine in commercial samples, it was necessary to carry through several hundred analyses on controls involving this substance, both a l m e and in various combinations. As typical of thess experiments, t h e following tabulated results show the percentage recovery from precipitates prepared with varying amounts of hydrochloric acid, as also with and without t h e addition of brine. No. l... 2... 3.. 4 5 6... 7... 8.. . . . . 9.. . . . . 10.. . . . . 11.. , , , . 12.. . . . . 13.. 14.. ....
...
... ..... ...... ...... ... ... ....
Tbeo- Glacial bromine AcOH G. cc. 0.1000 2 2 0.1000 2 0.1000 0.1000 2 2 0.1000 2 0.1000 2 0.1000 2 0.1000 0.1000 2 2 0.1000 0.1000 2 2 0.1000 2 0.1000 2 0.1000
0.1 N Iodine cc. 50
50 50 50 50 50 50 50 50 50 50 50 50
Concd. Satd. NaCl HCl Soh. cc. cc.
Theobromine Found Per G. cent
1
1 3 3 5 5 2
2 2 2
50
2 2
2
2
The influence of other factors like sodium acetate, sodium salicylate, sodium benzoate, and sodium formate on the estimation of theobromine is shown in the following series, this substance and the component salt being applied in molecular proportions : Satd. Theo- Glacial 0.1 N Concd. NaCl bromine AcOH Iodine HCl Soh. No. G. Cc. Cc. Cc. Cc. 20 2 2 50 l..... 20 2 50 2 2.. 20 2 2 50 3. 20 2 50 2 4.. 20 2 2 50 5.. 20 2 2 50 6.. 20 50 2 2 7..... 20 50 2 2 8.. ... 2 20 2 50 g..... 4 2 2 50 10. 8 2 2 50 11 2 15 2 50 12.. 20 2 50 2 13.. 20 2 2 50 14.. 20 2 2 50 15.. * 20 2 2 50 16.. 2 5 2 50 17.. 5 50 2 2 18.. 20 2 50 2 19 2 20 50 2 20.. 20 50 2 2 21..
. ._. .... ... ... ...
*. .. .... .... .. ... ..
... ... ... ....; ... ...
Org. Salt
NaAc NaAc N a Sal. N a Sal. N a Sal. N a Sal. N a Sal. Na Sal. N a Sal. N a Sal. N a Sal. N a Form. N a Form. N a Form. N a Form, N a Benz. N a Benz. N a Benz.
Theobromine Found Per ‘G. cent 0.0981 98.1 0.0990 99.0 0.0993 99.3 0.0995 99.5 0.0994 99.4 0.1002 100.2 0.1004 100.4 0.0997 99.7 0,0998 99.8 0. .. .0.9. .7 4 97.4 99.0 0.0990 99.8 0.0998 99.4 0.0994 99.6 0.0996 0.1078 107.8 0.1064 106.4 0.1054 105.4 0.1064 106.4 99.7 0.0997 99.5 0.1105 0,0554 99.9
From these experiments i t is evident t h a t t h e periodide method may be safely applied in the quantitative estimation of theobromine, both alone and, in admixture with sodium acetate, sodium salicylate, and sodium benzoate. The abnormal results obtained in the presence of sodium formate, however, for which no satisfactory explanation based upon experimental data is as yet available, clearly indicate t h a t some special treatment would be necessary in combinations of t h a t character. METHOD
In a small (50 cc.) lipped Erlenmeyer flask dissolve 0 . I g. of the sample (with about the molecular equivalent of sodium acetate, in the case of theobromine alone) in z cc. glacial acetic acid by gentle heat on a wire gauze. Dilute with 3 to 5 cc. hot water. Transfer the perfectly clear solution to a 100 cc. graduated glass-stoppered flask containing 50 cc. standard 0 . I N
iodine, using warm water for rinsing. Next add 20 cc. saturated sodium chloride solution, and finally z cc. concentrated hydrochloric acid while rotating the flask. Stopper the latter and
Vol.
IO,
No. 8
allow t o stand at room temperature over night. Make up to the’ mark with water and mix thoroughly. Pass the liquid through a small (5.5 cm.) filter previously fitted to funnel by wetting and drying, reject the first I j cc. and collect 50 cc. in a graduated 5 0 cc. flask. Transfer this aliquot by pouring and rinsing t o an Erlenmeyer flask of about 250 cc. capacity, and titrate the excess of iodine with staridard 0 . 1 N sodium thiosulfate. The quantity of theobromine involved in the sample under examination is thereupon readily calculated from the expression : Theobromine = I (0 0045026 X normality of thiosulfate used), in which I represents the number of cubic centimeters of thiosulfate equivalent to the iodine expended in periodide formation. The foregoing method has been successfully applied to several commercial mixtures or combinations of theobromine, or its sodium salt, with sodium acet a t e and sodium salicylate. Thus, in the case of a well-known brand alleged t o consist of theobromine and sodium acetate, with a calculated theobromine content of 63.9 per cent, t h e following values were obtained: 57.4, 5 8 . 6 , 5 8 . 7 and 59.0 per cent. Another brand of a similar mixture gave 3 2 . 1 9 and 31.87 per cent. A sample alleged t o be the double salt of sodium salicylate and sodium theobromine was found t o contain 49.78 and 49. 73 per cent (calculated 49.73 per cent theobromine). SUMMARY
A method has been developed for estimating the0 bromine, both alone and in combination with sodium acetate and sodium salicylate, based on the formation of its periodide, C , H B N ~ O ~ . H I . I ~ . SYNTHETIC PRODUCTS LABORATORY BUREAUO F CHEMISTRY WASHINGTON. D. C.
STUDIES IN SYNTHETIC DRUG ANALYSIS. VI-EVALUATION OF HEXAMETHYLENETETRAMINETABLETS By W. 0. EMERY AND C. D. WRIGHT Received May 15, 1918 INTRODUCTION
The present study had its inception in certain preliminary experiments connected with codperative work on synthetic drugs, and instituted with a view t o adapt a known or devise a new procedure for the estimation of hexamethylenetetramine as i t ordinarily occurs in tablet preparations. A series of tests looking t o its quantitative isolation by t h e use of immiscible solvents early demonstrated the f u d i t y of attempting a solution of the problem in this way. I n operations with like volumes of water and chloroform, for example, only about 3 t o 4 per cent of the substance are taken up by the latter solvent in one extraction. Attempts t o utilize the condensation product of hexamethylenetetramine with antipyrine as a basis for the quantitative determination met with scarcely better success. After several other equally fruitless trials, recourse was finally had t o a procedure substantially identical with a method proposed by ‘Stuewe,l primarily for formaldehyde and formalin, but quite as applicable t o hexamethylenetetramine. 1
Arch. Pherm., 969 (1914), 430; Pherm. Z l g . , 159 (1914), 215
