Molecular formula. C₂₂H₃₀Cl₂N₁₀,2HCl

Relative molecular mass. 578.4

Graphic formula.

Chemical name. 1,1'-Hexamethylenebis[5-(p-chlorophenyl)biguanide] dihydrochloride; N,N''-bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecanediimidamide dihydrochloride; CAS Reg. No. 3697-42-5.

Description. A white or almost white, crystalline powder; odourless.

Solubility. Sparingly soluble in water; soluble in 450 parts of ethanol (~750 g/l) TS.

Category. Disinfectant.

Storage. Chlorhexidine dihydrochloride should be kept in a well-closed container, protected from light.

Requirements

Definition. Chlorhexidine dihydrochloride contains not less than 98.0% and not more than 101.0% of C₂₂H₃₀Cl₂N₁₀,2HCl, calculated with reference to the dried substance.

Identity tests

A. Dissolve 20 mg in 10 mL of methanol R by warming, and add a mixture of 2 mL of sodium hydroxide (~150 g/l) TS and 2 mL of bromine TS1; a deep red colour is produced.

B. Dissolve 0.1 g in 10 mL of water and add, with shaking, 0.15 mL of copper(II) chloride/ammonia TS; a purple precipitate is produced immediately. Continue to add 0.5 mL of copper(II) chloride/ammonia TS; the colour of the precipitate changes to blue.

C. Dissolve 0.1 g in 50 mL of nitric acid (~130 g/l) TS; the solution yields reaction A described under 2.1 General identification tests as characteristic of chlorides.

Sulfated ash. Not more than 1.0 mg/g.

Loss on drying. Dry to constant weight at 130°C; it loses not more than 20 mg/g.

Chloraniline. Dissolve 0.20 g in 30 mL of water. Add with mixing 5 mL of hydrochloric acid (1 mol/L) VS, 1 mL of sodium nitrite (35 g/L) TS, 2 mL of ammonium sulfamate (50 g/L) TS and shake. Then add 5 mL of freshly prepared N-(1-naphthyl)ethylenediamine hydrochloride(1 g/L)TS, 1 mL of ethanol (~750 g/L) TS, and sufficient water to produce 50 mL. Allow to stand for 30 minutes. Treat similarly 30 mL of a solution containing 0.10 mg of chloraniline R that has been slightly acidified with hydrochloric acid (~70 g/L) TS. The colour produced in the test solution is not more intense than that of the reference solution when compared as described in 1.11.1 Colour of liquids (0.5 mg/g).

Related substances. Carry out the test as described under 1.14.1 Chromatography, Thin-layer chromatography, using silica gel R4 as the coating substance and preparing a slurry as follows: To 8 g of silica gel R4 add 16 mL of water containing 1 g of sodium formate R and coat the plates with a layer, 0.5 mm thick. Use a mixture of 50 volumes of chloroform R, 50 volumes of ethanol (~750 g/l) TS, and 7 volumes of formic acid (~1080 g/l) TS as the mobile phase. Prepare solution A by dissolving 1.1 g of the test substance in 35 mL of hydrochloric acid (~330 g/l) TS, add 100 mL of 2-propanol R, cool in ice, make alkaline with sodium hydroxide (~200 g/l) TS, cool in ice, add 200 mL of ice-cooled water, and extract with 100 mL of chloroform R. Dry the chloroform extract over anhydrous potassium carbonate R, filter, evaporate the chloroform almost to dryness under a stream of nitrogen R, add 50 mL of methanol R, evaporate to dryness under a stream of nitrogen R, and dry the residue at 65 °C for 30 minutes; dissolve 0.56 g of the dried residue in sufficient acetic acid (~90 g/l) TS to produce 100 mL. Apply to the plate in the form of a band, 4 cm wide, 20 μl of solution A. After removing the plate from the chromatographic chamber, allow it to dry in air and examine the chromatogram in ultraviolet light (254 nm). Score a rectangular area around each group of bands above and below the principal band, quantitatively transfer the enclosed areas of silica gel to a glass-stoppered test-tube, add 5 mL of methanol R, shake for 15 minutes, centrifuge, and measure the absorbance of the clear supernatant liquid in a 1-cm layer at the maximum at about 256 nm. For the blank solution treat in a similar manner equivalent-sized areas of silica gel removed from the coating adjacent to the areas previously removed. Prepare solution B in the following manner: Dissolve 0.11 g of the dried residue in sufficient acetic acid (~90 g/l) TS to produce 100 mL and dilute 200 μl of this solution to 50 mL with methanol R. The absorbance obtained from the eluted solution A is not greater than the absorbance obtained from solution B.

Assay. In order to avoid overheating in the reaction medium, mix thoroughly throughout the titration and stop the titration immediately after the end-point has been reached.

Dissolve 0.100 g in 5 mL of anhydrous formic acid R and add 70 mL of acetic anhydride R. Carry out a potentiometric titration using perchloric acid (0.1 mol/L) VS, as described under 2.6 Non-aqueous titration, Method A.

1 mL of perchloric acid (0.1 mol/L) VS is equivalent to 14.46 mg of C₂₂H₃₀Cl₂N₁₀,2HCl.