QUANTITATIVE DETERMINATION OF NITROGEN IN ORGANIC COMPOUNDS CONTAINING NO OXYGEN

E. E. SIROTKINA, R. G. TOROPOVA

(Presented by the scientific seminar of the Section of Organic Chemistry)

In practical work with organic substances, the method of detecting nitrogen by fusing a weighed portion of the substance with metallic sodium or potassium (Lassaigne’s test) is widely used. This method is one of the most general and is practically suitable for any compounds containing nitrogen, but it has usually not been used for obtaining quantitative results [1]. Replacement of the alkali metals by magnesium does not increase the accuracy of the method, and all modifications (Fedorseev’s test, etc.) remain qualitative [1].

In the present work an attempt has been made to modify the technique of quantitative determination of nitrogen by fusing a sample of the substance with metallic sodium in a closed bomb. We were familiar with the experience of analytical determinations of halogens [2—7] and nitrogen in bombs; however, quantitative analysis for nitrogen is carried out over several hours [8], i.e., it does little to reduce the time required for determination of nitrogen by the Dumas or Kjeldahl methods.

Our investigations have shown that quantitative results for the determination of nitrogen can readily be obtained when organic substances containing no oxygen are fused with metallic sodium. We introduced certain design changes into the bomb proposed by R. D. Glukhovskaya and N. A. Ugolnikova [7]. By equipping the bomb with a well-ground stopper, we eliminated the use of a copper gasket, which becomes unusable after 5—6 determinations.

Fusion takes only 4—5 minutes, after which the reaction products, containing sodium cyanide, are titrated with a solution of silver nitrate [9]. The end of the titration is determined by the formation of the first stable turbidity. The substances analyzed were mainly derivatives of carbazole, diphenylamine, certain technical products, for example, crude or enriched anthracene, and also polymers. Comparative results of the analysis of several substances by different methods are given in the table.

The titration described above may be used in determining nitrogen in colorless solutions. In the case of colored solutions it is more convenient to use potentiometric titration [10]. As is evident from the table, oxygen-containing organic compounds by this meth—

Table

cannot be analyzed for nitrogen content by this method, since they do not give well-reproducible results. Fusion of the sample of the substance with metallic sodium was carried out in a bomb with a ground stopper. The bomb was a test tube with a flange made of stainless steel (40 mm long, internal diameter 8 mm, wall thickness 4 mm). The test tube had a steel lid fitted with a cone with a ground surface (cone height 10 mm). A tight connection between the lid and the body of the bomb was achieved by inserting the cone of the lid into the upper conical part of the body, which was also well ground. In the assembled state, a gap of 3–4 mm remained between the flanges of the body and the lid; this was needed to facilitate opening the lid.

The proposed method is convenient in that no more than fifteen minutes are required to perform the analysis, and it gives good agreement between experiments.

In our work, an apparatus was used in which 6 bombs were heated simultaneously, which is convenient for carrying out series analyses. The method can be used in any laboratory, since it does not require complicated equipment. It should be noted that nitrogen and a halogen can be determined simultaneously in one sample if the filtrate is divided into two parts and the halogen is determined by the previously proposed procedure [1].

Experimental Part

A sample of a substance containing 0.009–0.01 g of nitrogen is placed on the bottom of the bomb, and metallic sodium, freed from its oxidized layer, is added in a tenfold amount relative to the presumed nitrogen content. The bomb is closed with the ground stopper, which is pressed tightly in a special apparatus, and heated with the flame of a gas burner (with air blast) for 4–5 minutes at red-heat temperature. After this, the bomb is cooled by immersion in a beaker with cold water or snow, opened, and 1.5–2 ml of ethyl alcohol is added (to bind the sodium). The contents of the bomb are quantitatively transferred, by repeated washing with water, into a beaker containing 25 ml of distilled water, filtered through glass filter No. 2, and the filtrate is drained into a 250 ml beaker; the filter and the Büchner flask are rinsed, the wash waters are added to the filtrate (the total volume should be 100 ml), and titrated with 0.01 N silver nitrate solution until a persistent turbidity appears.

The percentage nitrogen content is determined by the formula:

$$ \% = \frac{N_{\mathrm{AgNO_3}}\cdot V_{\mathrm{AgNO_3}}\cdot 28\cdot 100}{a\cdot 1000}, $$

where \(a\) is the sample of substance, in g.

If analytical determination of nitrogen in colored products is necessary, it is more convenient to use potentiometric titration [10]. In this case, the mean relative error of determining nitrogen in carbazole and its derivatives reaches 0.5%.

Conclusions

A rapid method has been developed for the quantitative determination of nitrogen in organic compounds not containing oxygen.

References

1. C. Weibel. Identification of Organic Compounds. Izdathinlit, 1957.

2. M. O. Korshunov, N. E. Gel’man. New Methods of Elementary Microanalysis. Goskhimizdat, 1949.

3. J. Niederl, V. Niederl. Micromethods of Quantitative Organic Analysis. Goskhimizdat, 1949.

4. R. Kimball, Z. Fufts. Anal Chem. 19, 150, 1947.

5. B. Wurzshmittu. a Forts. chem. Forsch. 1, 485, 1950.

6. B. Wurzschmitt. Mikrochemie. 36/37, 769, 1951.

7. R. D. Glukhovskaya, N. A. Ugol’nikov. Proceedings of Tomsk State University, 145, 173, 1957.

8. R. Banks a. a. Anal. Chem. Acta 13, 442, 1955; RZhKhim. 78512, 1956.

9. F. Treadwell. Course of Analytical Chemistry. Vol. II, GONTI, 1937.

10. R. P. Lastovskii, Yu. I. Weinstein. Technical Analysis in the Production of Intermediates and Dyes, 2nd ed. Goskhimizdat, 1958.

11. R. D. Glukhovskaya, N. A. Ugol’nikov. Proceedings of Tomsk State University, 145, 77, 1957.