Molecular formula. C₃H₈OS₂

Relative molecular mass. 124.2

Graphic formula.

Chemical name. 2,3-Dimercapto-1-propanol; CAS Reg. No. 59-52-9.

Description. A clear, colourless or slightly yellow liquid, with an unpleasant, mercaptan-like odour.

Miscibility. Miscible with 20 parts of water; miscible with ethanol (~750 g/l) TS and methanol R.

Category. Antidote for arsenic, gold, and mercury poisoning.

Storage. Dimercaprol should be kept in a small, well-filled and tightly closed container, protected from light, and stored at a temperature not exceeding 5°C.

Requirements

Definition. Dimercaprol contains not less than 98.5% w/w and not more than 101.5% w/w of C₃H₈OS₂.

Identity tests

A. Mix 0.05 mL of cobalt(II) chloride (30 g/l) TS with 5 mL of water and add 0.05 mL of the test liquid; a yellow-brown colour is produced.

B. Dissolve 0.1 mL in 4 mL of water and add a few drops of lead acetate (80 g/l) TS; a yellow precipitate is formed.

Refractive index. = 1.568 - 1.574.

Relative density. = 1.239 - 1.259.

Halides. Dissolve 2.0 g in 25 mL of potassium hydroxide/ethanol TS1 and heat under a reflux condenser for 2 hours. Evaporate the ethanol in a current of warm air, add 20 mL of water, and cool. Add a mixture of 10 mL of hydrogen peroxide (~330 g/l) TS and 40 mL of water, boil gently for 10 minutes, cool, and filter rapidly. Add 10 mL of nitric acid (~130 g/l) TS and 5 mL of silver nitrate (0.1 mol/l) VS and titrate with ammonium thiocyanate (0.1 mol/l) VS, using ferric ammonium sulfate (45 g/l) TS as indicator. Repeat the operation without the test liquid being examined. The difference between the titrations does not exceed 1.0 mL.

pH value. pH of a 0.5 g/mL solution in carbon-dioxide-free water R, 4.6-6.8.

Assay. Dissolve about 0.12 g, accurately weighed, in 20 mL of hydrochloric acid (0.1 mol/l) VS and titrate rapidly with iodine (0.05 mol/l) VS, using starch TS as indicator. Repeat the operation without the test liquid being examined and make any necessary corrections. Each mL of iodine (0.05 mol/l) VS is equivalent to 6.211 mg of C₃H₈OS₂.

Additional requirement for Dimercaprol for parenteral use

Complies with the monograph for "Parenteral preparations".