2,4-Dichlorobenzyl alcohol, with the chemical formula C₇H₆Cl₂O and a molecular weight of 177.0, is also known as (2,4-Dichlorophenyl)methanol. According to the European Pharmacopoeia, it should contain 98.0 to 102.0 percent of anhydrous 2,4-Dichlorobenzyl alcohol.

Appearance: White or almost white, crystalline powder.

Solubility: Very slightly soluble in water, very soluble in 96 percent ethanol.

Melting Point: About 59 °C.

• Method: Infrared absorption spectrophotometry (2.2.24)
• Comparison: 2,4-dichlorobenzyl alcohol CRS

• Related Substances: Carried out by Liquid Chromatography (LC).
• Solvent Mixture: 50 percent acetonitrile R1 and 50 percent water R.
• Buffer Solution: Dissolve 0.68 g of potassium dihydrogen phosphate R in 900 mL of water R, adjust the pH to 3.0 with phosphoric acid R, and dilute to 1000.0 mL with water R.
• Test Solutions:
  • Test Solution (a): Dissolve 0.100 g of the substance to be examined in 10.0 mL of acetonitrile R1 and dilute to 50.0 mL with the solvent mixture.
  • Test Solution (b): Dilute 5.0 mL of test solution (a) to 50.0 mL with the solvent mixture.
  • Reference Solution (a): Dilute 1.0 mL of test solution (a) to 100.0 mL with the solvent mixture. Take 1.0 mL of this solution and dilute to 10.0 mL with the solvent mixture.
  • Reference Solution (b): Dissolve 20.0 mg each of 2,4-dichlorobenzyl alcohol impurity A CRS and 2,4-dichlorobenzyl alcohol impurity C CRS in 100.0 mL of acetonitrile R1. Dilute 1.0 mL of this solution to 100.0 mL with the solvent mixture.
  • Reference Solution (c): Dissolve 0.100 g of 2,4-dichlorobenzyl alcohol CRS in 10.0 mL of acetonitrile R1 and dilute to 50.0 mL with the solvent mixture. Dilute 5.0 mL of this solution to 50.0 mL with the solvent mixture.
• Column
• Size: l = 0.15 m, Ø = 4.6 mm.
• Stationary Phase: End-capped octadecylsilyl silica gel for chromatography R (5 μm).
• Temperature: 30 °C.
• Mobile Phase
• Mobile Phase A: Methanol R2, acetonitrile R1, buffer solution (20:30:50 V/V/V).
• Mobile Phase B: Acetonitrile R1.
• Time Schedule:

• Flow Rate: 1.2 mL/min
• Detection: Spectrophotometer at 214 nm
• Injection: 10 μL of test solution (a) and reference solutions (a) and (b)
• Relative Retention Time: Relative to 2,4-dichlorobenzyl alcohol (approx. 7 minutes):
• Impurity C: about 0.87
• Impurity A: about 0.91
• System Suitability: Reference solution (b)
• Peak-to-Baseline Ratio: Minimum 4 (Hp: height of peak due to impurity C, Hv: baseline height of the lowest point between impurity C and impurity A).
• Percentage Content Calculation: For each impurity, use the concentration of 2,4-dichlorobenzyl alcohol in reference solution (a).
• Limits:
• Unspecified Impurities: For each impurity, maximum 0.10 percent.
• Total: Maximum 0.3 percent.
• Reporting Threshold: 0.05 percent.
• Water Content: Maximum 0.2 percent, determined using the evaporation technique on 0.500 g sample at 120 °C.
• Sulfated Ash: Maximum 0.1 percent, determined on a 1.0 g sample.

The content of 2,4-dichlorobenzyl alcohol is measured using liquid chromatography (2.2.29) as described in the test for related substances with specific modifications. Test solution (b) and reference solution (c) are used for the calculations.

Other detectable impurities:

• A: (2,5-dichlorophenyl)methanol
• B: (2,6-dichlorophenyl)methanol
• C: (3,4-dichlorophenyl)methanol
• D: 2,4-dichlorobenzyl acetate
• E: 2,4-dichlorobenzoic acid
• F: 2,4-dichlorobenzaldehyde
• G:1,1′-(oxydimethylene)bis(2,4-dichlorobenzene)