Molecular formula. C19H12O6
Relative molecular mass. 336.3
Chemical name. 3,3'-Methylenebis[4-hydroxycoumarin]; 3,3'-methylenebis[4-hydroxy-2H-1-benzopyran-2-one]; CAS Reg. No. 66-76-2.
Description. A white or creamy white, crystalline powder; odour, characteristic, faint.
Solubility. Practically insoluble in water, ethanol (~750 g/l) TS and ether R.
Storage. Dicoumarol should be kept in a well-closed container, protected from light.
Definition. Dicoumarol contains not less than 98.5% and not more than 101.0% of C19H12O6, calculated with reference to the dried substance.
• Either test A alone or tests B and C may be applied.
A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from dicoumarol RS or with the reference spectrum of dicoumarol.
B. Fuse 0.2 g with 0.2 g of potassium hydroxide R, cool, stir with 5 ml of water, filter and acidify the filtrate with hydrochloric acid (~250 g/l) TS; a white, crystalline precipitate is obtained (salicylic acid). Retain the filtrate for test C.
C. To 1 ml of the filtrate from test B add 5 ml of water and a mixture of 1 drop of ferric chloride (25 g/l) TS and 2 drops of hydrochloric acid (~70 g/l) TS; a violet colour is produced.
Sulfated ash. Not more than 2.5 mg/g.
Loss on drying. Dry to constant weight at 105°C; it loses not more than 5.0 mg/g.
Acidity. Shake 0.5 g with 10 ml of carbon-dioxide-free water R for 1 minute and filter; titrate the filtrate with sodium hydroxide (0.1 mol/l) VS, methyl red/ethanol TS being used as indicator; not more than 0.1 ml is required to obtain the midpoint of the indicator (orange).
Assay. Dissolve about 0.35 g, accurately weighed, in 40 ml of 1-butylamine R, add 5 drops of azo violet TS and titrate with lithium methoxide (0.1 mol/l) VS to a deep-blue end-point, as described under 2.6 Non-aqueous titration, Method B. Each ml of lithium methoxide (0.1 mol/l) VS is equivalent to 16.82 mg of C19H12O6.