MERCURIMETRIC METHOD FOR THE DETERMINATION OF HALOGENS IN ORGANIC COMPOUNDS

R. D. GLUKHOVSKAYA, N. A. UGOLNIKOV, and Z. M. MURAV’EVA

(Presented by Prof. B. V. Tronov, Doctor of Chemical Sciences)

Previously we proposed a bomb for the decomposition of organic substances [1] and developed a mercurimetric method for the determination of halogens using diphenylcarbazone [2, 3], as well as β-nitroso-α-naphthol [4, 5] as indicators. The shortcomings inherent in these indicators prompted us to carry out certain investigations, as a result of which a new mixed indicator [6] was proposed for the mercurimetric determination of chlorides, bromides, and iodides; it is a mixture of diphenylcarbazone with β-nitroso-α-naphthol.

In the present work a method is described for determining halogens with the use of the mixed indicator in various organic compounds, including halogen derivatives of lignin.

Principle of the method. An organic substance containing a halogen is decomposed by heating with metallic sodium in a steel bomb [1], followed by mercurimetric determination of the halide with the mixed indicator [6].

Reagents

Metallic sodium, chemically pure.

Mercuric nitrate, 0.025 N.

Sodium chloride, chemically pure, 0.02 N.

Nitric acid, 6 N and 1 N, free of halides.

Ethyl alcohol (rectified spirit).

Phenolphthalein, 1-percent alcoholic solution.

Diphenylcarbazone, 1-percent alcoholic solution [7].

β-Nitroso-α-naphthol, 3-percent alcoholic solution.¹

Carrying out the analysis. A sample of the substance, 10–20 mg, is taken in a small test tube; in the case of liquid substances, in sealed ampoules [8], it is placed at the bottom of the test tube (bomb), and 50–70 mg of metallic sodium is added. The bomb is closed and heated with the flame of a gas burner (with an air blast) for 2–3 minutes to red heat. The bomb is then cooled by immersion in a beaker of cold water, the test tube is freed from the stopper, and the sodium that has not entered into the reaction is dissolved with ethyl alcohol.² The cont—

¹ β-Nitroso-α-naphthol, prepared according to Henrichs and Il’inskii [7], must be recrystallized from dilute alcohol.

² All the operations described above, beginning with the addition of metallic sodium, are carried out wearing goggles.

the contents of the test tube are filtered into a conical flask with a capacity of 50 ml; the bomb is washed several times with water, each time rubbing its walls with a glass rod with a rubber tip until all the halide has been quantitatively transferred into the flask (test with AgNO$_3$ or Hg(NO$_3$)$_2$).

To the alkaline solution of the halide add 1 drop of phenolphthalein and, dropwise, 6 N nitric acid until the crimson color of the solution disappears. Then add one more drop of nitric acid and boil the solution until its volume decreases to 1.5–2 ml. The flask is cooled; to the colorless solution add 1–2 drops of 1 N nitric acid, 2–3 ml of alcohol (in the case of analysis of iodine-containing substances: 2 ml of alcohol for each mg of iodine), 1 drop of diphenylcarbazone, 1 drop of $\beta$-nitroso-$\alpha$-naphthol, and titrate from a microburette with a solution of mercuric nitrate until the color changes from yellow-green to red.

\[ \% \text{ halogen } = \frac{a \cdot T \cdot 100}{b}, \]

where

$b$ — consumption of mercuric nitrate, ml,

$T$ — titer of the mercuric nitrate solution with respect to the halide,

$a$ — weight of the substance in g.

Preparation and standardization of the titer of the mercuric nitrate solution. 4–5 g of mercuric nitrate are weighed on technical balances, several ml of distilled water are added, and then, dropwise, 6 N nitric acid (about 0.5 ml) until the salt has completely dissolved. Distilled water is added to 1 l and the solution is left to stand until the next day. If a precipitate forms, the solution is filtered and its titer is established against sodium chloride. For this purpose, a standardized sodium chloride solution (approximately 0.02 N) is prepared; 5 ml of it are transferred to a conical flask, 1 drop of 6 N nitric acid is added, and the contents of the flask are boiled until the volume of the solution decreases to 1.5–2 ml. The solution is cooled; 1 drop of 1 N nitric acid, 2–3 ml of alcohol, 1 drop of diphenylcarbazone, and 1 drop of $\beta$-nitroso-$\alpha$-naphthol are added, and the solution is titrated from a microburette until the color changes from yellow-green to red.

Some results of the determination of halogens in chloro-, bromo-, and iodo-derivatives of organic compounds and in halogen derivatives of lignin containing, in addition to halogen, nitrogen, phosphorus, and sulfur are given in Tables 1 and 2.

As the data in the tables show, the mercurimetric method using a mixed indicator makes it possible to determine halogens in organic compounds with sufficient accuracy. The method is distinguished by its simplicity and the short duration of the analysis.

Conclusions

A mercurimetric method for the determination of halogens with a mixed indicator has been described. The method makes it possible to determine chlorine, bromine, and iodine in various classes of organic compounds, including halogen derivatives of lignin containing, in addition to halogen, nitrogen, phosphorus, and sulfur, with sufficient accuracy and speed.

Table 1

Determination of halogens in certain organic halogen derivatives

Table 2

Determination of chlorine in certain halogen derivatives of lignin

References

1. Glukhovskaya R. D.; Ugolnikov N. A. Proceedings of TGU, 145, 173, 1957.
2. Ugolnikov N. A.; Glukhovskaya R. D. Scientific Notes of TGU, 26, 173, 1955.
3. Glukhovskaya R. D. Proceedings of TGU, 145, 77, 1957.
4. Glukhovskaya R. D.; Ugolnikov N. A. Scientific Notes of TGU, 29, 130, 1959.
5. Glukhovskaya R. D.; Ugolnikov N. A. Scientific Notes of TGU, 29, 134, 1959.
6. Glukhovskaya R. D.; Ugolnikov N. A. Proceedings of Higher Educational Institutions, series “Chemistry and Chemical Technology,” 3, No. 1, 49, 1960.
7. Kulberg A. M. Syntheses of Organic Reagents. Goskhimizdat, 1947.
8. Korshun M. O.; Gelman N. E. New Methods of Elemental Microanalysis. Goskhimizdat, pp. 84 and 111, 1949.