Thursday, 23 July 2009

Monographs: Pharmaceutical substances: Chlorali hydras - Chloral hydrate


Relative molecular mass. 165.4

Chemical name. 2,2,2-Trichloroethane-1,1-diol; CAS Reg. No. 302-17-0.

Description. Colourless, transparent or white crystals; odour, aromatic, pungent and characteristic.

Solubility. Very soluble in water; freely soluble in ethanol (~750 g/l) TS and ether R.

Category. Premedication.

Storage. Chloral hydrate should be kept in a tightly closed container.

Additional information. Melting temperature, about 55 °C; when exposed to air it slowly volatilizes.


Chloral hydrate contains not less than 98.5% and not more than 101.0% of C2H3Cl3O2.

Note: Prepare the following test solution for use in "Identity tests A and B", and for "Clarity and colour". Dissolve 2.5 g in sufficient carbon-dioxide-free water R to produce 25 ml.

Identity tests

A. To 1.0 ml of the test solution add 2.0 ml of sodium sulfide TS; a yellow colour develops which quickly becomes reddish brown. On standing, a red precipitate may be produced.

B. Transfer 10 ml of the test solution to a conical flask and add 10 ml of 1- ethylquinaldinium iodide (15 g/l) TS that has previously been filtered through a 0.45-μm filter. Then add 60ml of 2-propanol R, 5ml of monoethanolamine (0.1 mol/l) VS, and 15 ml of water. Mix, and heat in a water-bath at 60 °C for 15 minutes; a blue colour develops.

Chlorides. Dissolve 2.5 g in a mixture of 2 ml of nitric acid (~130 g/l) TS and 20 ml of water, and proceed as described under 2.2.1 Limit test for chlorides; the chloride content is not more than 0.1 mg/g.

Chloral alcoholate. Warm 1.0 g with 10 ml of sodium hydroxide (~80 g/l) TS. Filter the upper layer and add iodine (0.05 mol/l) VS a drop at a time until a yellow colour is obtained; no precipitate is produced within 1 hour.

Clarity and colour of solution. The test solution is clear and colourless.

Sulfated ash. Not more than 1.0 mg/g.

pH value. pH of a 0.10 g/ml solution in carbon-dioxide-free water R, 3.5-5.5.

Assay. Dissolve about 4 g, accurately weighed, in 10 ml of carbon-dioxide-free water R and add 30.0ml of carbonate-free sodium hydroxide (1 mol/l) VS. Allow the mixture to stand for 2 minutes and titrate with sulfuric acid (0.5 mol/l) VS, using phenolphthalein/ethanol TS as indicator. Repeat the procedure without the Chloral hydrate being examined and make any necessary corrections.

Each ml of carbonate-free sodium hydroxide (1 mol/l) VS is equivalent to 0.1654 g of C2H3Cl3O2.

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