CS242288B1 - The method of simultaneous determination of free hydrogen cyanide and acetone in acetone cyanohydrin - Google Patents

Abstract

The solution deals with the procedure for the simultaneous determination of free hydrogen cyanide and acetone in acetone cyanohydrin by the polarographic method. As a basic electrolyte, a solution consisting of 90 g of ammonium acetate, 180 cm3 of glacial acetic acid, 65 g of hydrazine sulfate and 90 g of sodium dihydrogen phosphate in 1 liter of solution is used. The pH of the solution is 3.5 + 0.1.

Description

in acetone cyanohydrin

2

The solution deals with the procedure for the simultaneous determination of free hydrogen cyanide and acetone in acetone cyanohydrin by the polarographic method. A solution consisting of 90 g of ammonium acetate, 180 cm ³ of glacial acetic acid, 65 g of hydrazine sulfate and 90 g of sodium dihydrogen phosphate in 1 liter of solution is used as the basic electrolyte. The pH of the solution is 3.5 + 0.1.

The invention relates to a method for the simultaneous cyanation of free hydrogen cyanide and an atom in acetone cyanohydrin by the polarographic method.

Acetone cyanohydrin is an unstable substance and readily decomposes into acetone and hydrogen cyanide. To monitor the degree of decomposition, it is necessary to determine both decomposition products side by side. Titration, chromatography and polarography methods are used for determination [Hoffmann E.: Zeit. anal. chem. 169, 258 (1957). Hetman J.: J. Appl. Chem. 10, 16 (1968). Kramer 0. N.: Anal. Chem. 38, 834 (1966)] and spectrometric methods [Bark L. S., Higgson H. G: Talanta 1, 471 (1964)]. In all these methods, hydrogen cyanide is usually blown out of the acidic medium with nitrogen into a sodium hydroxide solution and then determined by one of the methods mentioned.

The simultaneous determination of hydrogen cyanide and acetone is not described.

In the polarographic determination of hydrogen cyanide, the reduction of mercuric cyanide is involved. It has been found [Tomeš J.: Coll. Czechoslov. Chem. Communn. 9, 81 (1937)) that the following relationship holds for the change in the half-wave potential of the reduction:

E(1/2) = E° (Hg2+) -|-----^-ln [H ⁺ ] + K h

(D

A change in pH by one unit shifts the half-wave potential by 0.058 V to more positive values. Other authors [Newman L., Cabral J. O., Hume O. N.: J. Am. Chem. Soc. 80, 1814 (1958); Canterford D. K.: Anal. Chem. 47, 88 (1975)] confirmed the validity of this equation, but found that it is valid only for the pH range from 5.5 to 9.5. At pH lower than 5.5, a larger shift of the half-wave potential occurs than would be determined by equation (1).

The essence of this invention is a method for the simultaneous determination of free hydrogen cyanide and acetone in acetone cyanohydrin by polarography, which is carried out by using as the basic electrolyte a solution consisting of 90 g of ammonium acetate, 180 cm ³ of glacial acetic acid, 65 g of hydrazine sulfate and 90 g of sodium dihydrogen phosphate in 1 liter of solution and whose pH is 3.5 ± 0.1.

It was found that at pH values below 5, the value of the half-wave potential is also influenced by the concentration of hydrogen cyanide.

If hydrogen cyanide and acetone are to be determined simultaneously, they must be determined at a pH below 5. Hydrogen cyanide by anodic oxidation, acetone by cathodic reduction of its hydrazone, after adding a sufficient excess of hydrazine [Turjan J. I., Tolstikova V. A., Střelková N. A.: Závod. lab. 35, 1320 (1969)].

Since hydrogen cyanide is in an undissociated form in an acidic environment, it can easily escape from the environment. Therefore, the solution must not be purged with nitrogen to remove the first and second waves of oxygen.

At pH 3.5 and a hydrogen cyanide concentration of 10 ^-4 M, the difference between the half-wave potential of the first oxygen wave and the anodic hydrogen cyanide wave is 0.2 V, which is sufficient to distinguish them. Similarly, at this pH, the difference in half-wave potentials between the second acetone hydrazone wave is also large enough to distinguish them in the derivative connection of the current recording.

To verify this possibility, model solutions are prepared. The standard cyanide solution is prepared by dissolving 0.241 g of potassium cyanide in about 60 ml of a 0.1 M potassium hydroxide solution and making up to 100 ml with a solution of the same hydroxide. The standard acetone solution is prepared by dissolving 1.27 ml of acetone of p. a. quality and making up to 1 litre with water.

For polarographic measurements, a basic electrolyte of the following composition is used: 90 g of ammonium acetate, 180 cm ³ of glacial acetic acid, 65 g of hydrazine sulfate and 90 g of sodium dihydrogen phosphate are dissolved in a volumetric flask of 1000 cm ³ containing about 600 ml of redistilled water. After dissolution, the solution is made up to the mark with water.

Creating a calibration curve:

Into a 50 cm ³ volumetric flask, pipette 10 cm ³ of basic electrolyte, successively 0.5 to 8 cm ³ of standard acetone and potassium cyanide solution. To release hydrogen cyanide from cyanide, successively 0.5 to 8 cm ^{3 of} 1 M acetic acid are added. The solution is then made up to the mark with water, the flask is stoppered and after standing for 20 minutes at a temperature of 22 °C, it is poured into a polarographic container, which is stoppered. The solution is immediately polarographed by anodic oxidation at a voltage of -0.6 V and the polarographic wave of hydrogen cyanide is recorded, then by cathodic reduction at the same voltage and the wave of acetone hydrazone is recorded.

By statistical evaluation of the obtained polarographic waves, the values of the linear dependences of the wave height on the amount of hydrogen cyanide and acetone present are obtained. The regression line for hydrogen cyanide is:

χ = 2.8503.10 ⁴ x for acetone χ = 8.2413.10 ⁴ x χ = wave height in mm. x — concentration of the substance being determined in moles per liter.

Determination of handling losses of hydrogen cyanide:

When pouring the sample solution from the volumetric flask into the polarographic vessel, partial leakage of hydrogen cyanide may occur. These losses are determined by polarography of the standard cyanide solution in an open polarographic vessel immediately after pouring and then every 3 minutes. The loss of hydrogen cyanide with time is linear and extrapolation to zero time shows that the losses of hydrogen cyanide are from 1.2 to 2.9% depending on the initial concentration of hydrogen cyanide.

If the measured polarograms are evaluated using a calibration curve, then the error caused by losses will be compensated.

Example 1

Into a 50 ml volumetric flask, pipette 10 cm ³ of basic electrolyte, 1 cm ³ of standard cyanide solution containing 300 mg HCN in 100 cm ³ .1 cm ³ of standard acetone solution containing 300 milligrams of acetone in 100 cm ³ , add 1 cm ^{3 of} 1 M acetic acid, stopper the flask and let stand for 20 minutes. Then the solution is poured into a polarographic vessel, the vessel is closed and polarographed similarly to the measurement of the calibration curve. This procedure is repeated 6 times, the following results are measured:

experiment concentration given [mg/cm ³ ] determined concentration [mg/cm ³ ] HCN í 3H3COCH3 HCN CH3COCH3 1 3.00 3.00 2.86 3.15 2 3.00 3.00 3.12 2.89 3 3.00 3.00 2.90 3.12 4 3.00 3.00 2.89 2.88 5 3.00 3.00 3.01 2.90 6 3.00 3.00 3.03 3.17 7 3.00 3.00 2.88 3.05 Example 2 flow with acetone content and hydrogen cyanide sta- new by the methods used so far. Para- The procedure is the same as in example 1, only places of the world the content of these substances is determined by standard solutions of hydrogen cyanide and ace-porn as in example 1. Results: Acetone cyanohydrin is pipetted into the solution. . In the % given % detected HCN CH3COCH3 HCN CH3COCH3 0.240 0.144 0.233 0.139

Claims (1)

SUBJECT Method for the simultaneous determination of free hydrogen cyanide and acetone in acetone cyanohydrin by polarography, characterized in that the basic electrolyte used is a solution consisting of 90 g of ammonium acetate, 180 cm ^{3 of} glacial acetic acid, 65 g of hydrazine sulphate and 90 g of sodium dihydrogen phosphate in 1 liter of solution and whose pH is 3.5 + 0.1.