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Химия Ethanol
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Absolute Alcohol; Dehydrated Alcohol

H3C CH2OH

C2H6O 46.07

DEFINITION

Anhydrous ethanol contains not less than 99.5 per cent V/V of C2H6O (99.2 per cent m/m), at 20°C.

CHARACTERS

A colourless, clear, volatile, flammable liquid, hygroscopic, miscible with water and with methylene chloride. It burns with a blue, smokeless flame.

It boils at about 78°C.

IDENTIFICATION

First identification: A, B.

Second identification: A, C, D.

A. It complies with the test for relative density (see Tests).

B. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the Ph. Eur. referencespectrum of anhydrous ethanol.

C. Mix 0.1 ml with 1 ml of a 10 g/l solution of potassium permanganate R and 0.2 ml of dilute sulphuricacid R in a test-tube. Cover immediately with a filter paper moistened with a freshly prepared solution containing 0.1 g of sodium nitroprusside R and 0.5 g of piperazine hydrate R in 5 ml of water R. After a few minutes, an intense blue colour appears on the paper and becomes paler after 10 min to 15 min.

D. To 0.5 ml add 5 ml of water R, 2 ml of dilute sodium hydroxide solution R, then slowly add 2 ml of 0.05M iodine. A yellow precipitate is formed within 30 min.

TESTS

AppearanceIt is clear (2.2.1) and colourless (Method II, 2.2.2) when compared with water R. Dilute 1.0 ml to 20 ml with water R. After standing for 5 min, the dilution remains clear when compared with water R (2.2.1).

Acidity or alkalinityTo 20 ml add 20 ml of carbon dioxide-free water R and 0.1 ml of phenolphthalein solution R. The solution is colourless. Add 1.0 ml of 0.01M sodium hydroxide. The solution is pink (30 ppm, expressed as acetic acid).

Relative density(2.2.5). 0.7907 to 0.7932.

AbsorbanceExamined between 235 nm and 340 nm, the absorbance (2.2.25) measured in a 5 cm

cell using water R as the compensation liquid is not greater than 0.40 at 240 nm, 0.30 between

250 nm and 260 nm, and 0.10 between 270 nm and 340 nm. The absorption curve is smooth.

Volatile impuritiesExamine by gas chromatography (2.2.28).

Test solution (a). The substance to be examined.

Test solution (b). Add 150 μl of 4-methylpentan-2-ol R to 500.0 ml of the substance to be examined.

Reference solution (a). Dilute 100 μl of anhydrous methanol R to 50.0 ml with the substance to be

examined. Dilute 5.0 ml of the solution to 50.0 ml with the substance to be examined.

Reference solution (b). Dilute 50 μl of anhydrous methanol R and 50 μl of acetaldehyde R to 50.0 ml with the substance to be examined. Dilute 100 μl of the solution to 10.0 ml with the substance to be examined.

Reference solution (c). Dilute 150 μl of acetal R to 50.0 ml with the substance to be examined. Dilute 100 μl of the solution to 10.0 ml with the substance to be examined.

Reference solution (d). Dilute 100 μl of benzene R to 100.0 ml with the substance to be examined.

Dilute 100 μl of the solution to 50.0 ml with the substance to be examined.

The chromatographic procedure may be carried out using:

— a fused-silica capillary column 30 m long and 0.32 mm in internal diameter coated with

poly[(cyanopropyl)(phenyl)][dimethyl]siloxane R (film thickness 1.8 μm),

helium for chromatography R as the carrier gas at a column flow rate of 1.5 ml/min,

— a flame-ionisation detector,

Inject 1 μl of reference solution (b). Adjust the sensitivity of the system so that the heights of the

two peaks eluting before the principal peak, are at least 50 per cent of the full-scale of the recorder.

The test is not valid unless in the chromatogram obtained, the resolution between the first peak

(acetaldehyde) and the second peak (methanol) is at least 2.0. If necessary, decrease the initial

column temperature.

Inject 1 μl of each solution. The area of any peak corresponding to methanol in the chromatogram

obtained with test solution (a) is not greater than half the area of the corresponding peak in the

chromatogram obtained with reference solution (a) (200 ppm V/V).

Calculate the sum of the contents (ppm) of acetaldehyde and acetal from the areas of the corresponding peaks in the chromatogram obtained with test solution (a) using the following expression:

AE=area of the acetaldehyde peak in the chromatogram obtained with test solution (a),

AT=area of the acetaldehyde peak in the chromatogram obtained with reference solution (b),

CE=area of the acetal peak in the chromatogram obtained with test solution (a),

CT=area of the acetal peak in the chromatogram obtained with reference solution (c).

The sum of the contents of acetaldehyde and acetal is not greater than 10 ppm (V/V), expressed as

acetaldehyde.

Calculate the content of benzene (ppm) from the area of the corresponding peak in the chromatogram

obtained with test solution (a) using the following expression:

BE=area of the benzene peak in the chromatogram obtained with test solution (a),

BT=area of the benzene peak in the chromatogram obtained with reference solution (d).

If necessary, the identity of benzene can be confirmed using another suitable chromatographic

system (stationary phase with a different polarity).

It contains not more than 2 ppm (V/V) of benzene.

In the chromatogram obtained with test solution (b), the sum of the areas of any peaks, apart from

the principal peak and any peak due to methanol, acetaldehyde, acetal or benzene, is not greater than the area of the peak corresponding to 4-methylpentan-2-ol (300 ppm). Disregard any peak with an area less than 0.03 times that of the peak corresponding to 4-methylpentan-2-ol in the chromatogram obtained with test solution (b).

Residue on evaporationEvaporate 100 ml to dryness on a water-bath and dry at 100°C to 105°C

for 1 h. The residue weighs not more than 2.5 mg (25 ppm m/V).

STORAGE

Store in a well-closed container, protected from light.


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